Cement Embolism

Between 2% and 25% of patients who undergo vertebroplasty develop cement (polymethylmethacrylate) pulmonary emboli. These are usually asymptomatic and go undetected by operator at the time of imaging. Cement leakage into the paravertebral veins and/or inferior vena cava may be associated with development of pulmonary cement embolism. There may also a correlation between the total number of treated levels and the number of emboli.

While most patients are asymptomatic, rare but serious complications can occur. Emboli can be lethal if they lodge in the right atrium or ventricle, leading to cardiac perforation and tamponade. In addition, pulmonary infarction, hypercapnia, and even cardiac arrest have been reported in association with cement emboli.

In addition, patients with already low cardiopulmonary reserve may not tolerate the burden of small peripheral emboli.

Radiographs reveal multiple dense tubular and branching opacities scattered throughout the lungs. CT can show branching or punctate high-attenuation along the expected course of a pulmonary artery. Long cement fragments can also be seen a paravertebral vein with or without extension into the inferior vena cava.

References

• Kim YJ, Lee JW, Park KW, Yeom JS, Jeong HS, Park JM, Kang HS. Pulmonary cement embolism after percutaneous vertebroplasty in osteoporotic vertebral compression fractures: incidence, characteristics, and risk factors. Radiology. 2009 Apr;251(1):250-9.
• Luetmer MT, Bartholmai BJ, Rad AE, Kallmes DF. Asymptomatic and unrecognized cement pulmonary embolism commonly occurs with vertebroplasty. AJNR Am J Neuroradiol. 2011 Apr;32(4):654-7.

Primary Pulmonary Artery Sarcomas

Primary pulmonary artery sarcomas are rare tumors that always arise from the central pulmonary arteries. The natural history of the disease consists of local tumor growth with superimposed thrombosis and distal tumor emboli, resulting in progressive pulmonary artery obstruction. Clinical symptoms are therefore insidious and often nonspecific, making early diagnosis difficult. Untreated patients progress to decompensated heart failure, with a median survival of as short as 1.5 months.

Histologically, the most common primary pulmonary artery sarcomas are fibrosarcoma and leiomyosarcoma (shown above), but malignant mesenchymoma, angiosarcoma, anaplastic sarcoma, rhabdomyosarcoma, chondrosarcoma, and myxosarcoma have also been reported.

The main differential considerations are bland pulmonary embolus, tumor embolus, and lung cancer.

Pulmonary artery sarcomas can be polypoid intraluminal masses or sessile lesions spreading along the intima. Intimal spread, when extensive, can result in the characteristic appearance of a "lobulated, unilateral hilar mass projecting into the lung parenchyma in an arterial distribution."

In about 50% of cases, there is transmural spread into the adjacent lung, bronchial wall, or lymph nodes, in which case the imaging findings can mimic lung cancer.

CT angiography reveals a low-attenuation filling defect occupying the entire lumen of the proximal or main pulmonary artery with distension of the vessel. However, it can be difficult to distinguish pulmonary emboli from pulmonary artery sarcomas, unless there is extension beyond the lumen. MR imaging can be helpful by revealing enhancement in the tumor.

Pedunculated lesions can move with the cardiac cycle, which may help differentiate these tumors from emboli on conventional angiography.

Pulmonary artery sarcomas can have increased FDG activity, a feature that can be seen with tumor emboli and bland pulmonary emboli (likely due to local inflammation).

The mainstay of treatment is radical resection and distal pulmonary embolectomy. Without the latter, superimposed thrombosis and metastasized emboli in the distal pulmonary arteries can lead to decreased survival. Pneumonectomy, studied in a small retrospective series, has not shown a survival benefit; however, adjuvant chemotherapy and radiation therapy have been shown to increase survival. Endarterectomy techniques, tried earlier, have an unacceptably high local recurrence rate due to incomplete resection.

The images above are from a patient with slowly progressive cough and dyspnea. The CT image shows a low-attenuation filling defect within the left lower lobe pulmonary artery that extended distally into the subsegmental branches (not shown). The FDG-PET image, more caudad to the CT, shows intense activity in the left lung.

References

• Bressler EL, Nelson JM. Primary pulmonary artery sarcoma: diagnosis with CT, MR imaging, and transthoracic needle biopsy. AJR Am J Roentgenol. 1992 Oct;159(4):702-4.
• Chong S, Kim TS, Kim BT, Cho EY, Kim J. Pulmonary artery sarcoma mimicking pulmonary thromboembolism: integrated FDG PET/CT. AJR Am J Roentgenol. 2007 Jun;188(6):1691-3.
• Gladish GW, Sabloff BM, Munden RF, Truong MT, Erasmus JJ, Chasen MH. Primary thoracic sarcomas. Radiographics. 2002 May-Jun;22(3):621-37.
• Gan HL, Zhang JQ, Zhou QW, Xiao W, Gao YM, Liu S, Wang PS. Surgical treatment of pulmonary artery sarcoma. J Thorac Cardiovasc Surg. 2011 Apr 15.
• Mittra ES, Iagaru AH, Leung AN. Case 166: Metastatic left pulmonary artery sarcoma. Radiology. 2011 Feb;258(2):645-8.
• Moffat RE, Chang CH, Slaven JE. Roentgen considerations in primary pulmonary artery sarcoma. Radiology. 1972 Aug;104(2):283-8.

Fibroma of Tendon Sheath

Fibromas of tendon sheath are benign tumors that firmly attach to tendons and are composed of tightly packed spindle cells surrounded by collagen fibers. Imaging findings and clinical presentation can be similar to those of giant cell tumor of tendon sheath.

The lesion tends to afflict patients in the third to fifth decades of life, with a slightly younger median age than that of giant cell tumor of tendon sheath (35 vs. 39) and a stronger male predominance (up to 3 times more common in men than in women). The lesions recur in about 25% of cases, a recurrence rate comparable to that of giant cell tumor of tendon sheath.

Fibroma of tendon sheath almost always (98% of the time) occurs in the extremities, especially the thumb and index and middle fingers. Unlike giant cell tumor of tendon sheath, however, occurrence in the lower extremities is uncommon. Intra-articular location of the lesion has also been described in case reports.

The lesions are lobular in contour and occur adjacent to tendon sheaths. MRI findings are nonspecific. There may be heterogeneously decreased signal on all pulse sequences with little or no enhancement, but the signal characteristics may vary with the cellularity and myxoid content of the lesion.

The images above show a case of recurrent fibroma of tendon sheath. The lesion is centered within the extensor digitorum tendon sheath and splays the extensor tendons. The lesion extends dorsally to the skin and volarly into the carpometacarpal and intermetacarpal joints of the middle and ring fingers. Pressure erosions of the bases of the middle and ring finger metacarpal bones can also be seen. The mass is intermediate signal intensity on proton density (PD) images, intermediate signal intensity on T2-weighted images and demonstrates homogeneous enhancement.

References

• Chung EB, Enzinger FM. Fibroma of tendon sheath. Cancer. 1979 Nov;44(5):1945-54.
• Fox MG, Kransdorf MJ, Bancroft LW, Peterson JJ, Flemming DJ. MR imaging of fibroma of the tendon sheath. AJR Am J Roentgenol. 2003 May;180(5):1449-53.
• Sookur PA, Saifuddin A. Indeterminate soft-tissue tumors of the hand and wrist: a review based on a clinical series of 39 cases. Skeletal Radiol. 2011 Aug;40(8):977-89.

Retroperitoneal Mass with Calcification

Differential considerations for a retroperitoneal mass with calcification can be divided into benign and malignant conditions. Benign causes can be further divided into neoplastic and non-neoplastic.

Non-neoplastic

• Posttraumatic calcified hematoma:
• Myositis ossificans: In the setting of trauma
• Foreign body granuloma: In the setting of penetrating trauma (iatrogenic or otherwise). May have contrast enhancement if there is a significant inflammatory component.

Benign neoplastic

• Tumors of neural origin: Ganglioneuroma, schwannoma, paraganglioma. Usually heterogeneous with T2-hyperintense areas and marked contrast enhancement.
• Hemangioma: Phleboliths. T2-hyperintense.
• Mature teratoma: Heterogeneous contents with with fluid and fat.

Malignant neoplastic

• Undifferentiated pleomorphic sarcoma: Formerly known as malignant fibrous histiocytoma (MFH). Heterogeneous mass with myxoid stroma and/or collagen fibers
• Dedifferentiated liposarcoma: Heterogeneous mass with or without bulky calcification in part of the tumor.
• Malignant mesenchymoma: Heterogeneous mass. By definition has two or more malignant fibrosarcomatous components.
• Malignant teratoma: Heterogeneous mass. Occurs in young patients.
• Extraskeletal osteosarcoma: Variable amount of mineralization with typically intense and amorphous calcification. Nonmineralized areas iso-attenuating to muscle and intermediate signal on T1-weighted images. Variable contrast enhancement.

References

Secil M, Mungan U, Yorukoglu K, Dicle O. Case 89: Retroperitoneal extraskeletal osteosarcoma. Radiology. 2005 Dec;237(3):880-3.

Costal Cartilage Mineralization and Gender

Costal cartilage follows a typical mineralization pattern based on gender. In males, the typical calcification pattern on frontal radiographs consists of parallel lines extending medially from the ends of the anterior ribs (blue arrows). On lateral radiographs, these calcifications appear as circles.

In females, the pattern can be central or globular. The central pattern, also known as the "wagging tongue" pattern, can also be seen in up to 2% of males. These are linear ossific tongues arising from the center of the rib at the costochondral junction (pink arrow).

The globular pattern, may be seen in postmenopausal women and consists of smooth, rounded, centrally indistinct foci of ossification in the central portion of the costal cartilage.

References

Ontell FK, Moore EH, Shepard JA, Shelton DK. The costal cartilages in health and disease. Radiographics. 1997 May-Jun;17(3):571-7.

Traction Spur

A traction spur is a horizontally directed osteophyte on the anterior surface of the vertebral body that arises 2 mm - 3 mm from the endplate. Spinal levels with segmental instability tend to develop these spurs, likely due to abnormal stress placed on the outermost layers of the attachment of the annulus fibrosus, which attach on the vertebral body 2 mm - 3 mm from the endplate and are strongest and most numerous anteriorly.

Early on, radiographs reveal a small horizontally directed bony excrescence immediately above or below the discal edge of the vertebral body. The bony excrescence gets larger as time passes, but never curves at its tip. When the instability is treated with fusion, the traction spur regresses.

The image above shows a small traction spur at the anteroinferior margin of L5. We also see evidence of disc vaccum phenomenon, which is another sign of segmental instability.

The traction spur can be differentiated from the claw or marginal spur by its lack of a curve at the tip.

References

Macnab I. The traction spur. An indicator of segmental instability. J Bone Joint Surg Am. 1971 Jun;53(4):663-70.

Calcified Liver Metastases

The differential diagnosis of calcified liver lesions includes benign and malignant causes. Benign causes include infectious conditions such as tuberculosis and echinococcus, as well as benign masses like hemangiomas. Malignant primary tumors such as hepatocellular carcinoma and cholangiocarcinoma can also cause calcifications.

Calcifications can also be associated with metastases from the following sources:

• Mucinous neoplasms: Colon is the most common, but mucinous neoplasms elsewhere in the gastrointestinal tract can also cause calcifications.
• Serous ovarian cystadenocarcinoma:
• Medullary thyroid carcinoma: Case shown above.
• Sarcomas: Osteosarcoma, leiomyosarcoma.
• Islet cell carcinoma of the pancreas:
• Breast carcinoma: While we're used to seeing calcification in the primary lesion, calcification in metastatic breast cancer is relatively uncommon.

References

• Appleby A, Hacking PM. Calcification in hepatic metastases. Br J Radiol. 1958 Aug;31(368):449-50.
• Katragadda CS, Goldstein HM, Green B. Gray scale ultrasonography of calcified liver metastases. AJR Am J Roentgenol. 1977 Oct;129(4):591-3.

Pubic Spurs

Pubic spurs appear as small, anteroinferiorly directed bumps on the medial aspect of the superior pubic ramus. On frontal radiographs, we see inferiorly pointing bony excrescences projected over the medial aspect of the obturator foramen. Axial CT reveals anterior excrescences at the parasymphyseal region that are seen to point inferiorly on sagittal reformations.

Pubic spurs are common, reported to be present in 85% of patients undergoing CT for reasons other than groin pain. They are thought to represent partial ossification of the tendinous origin of the pectineus muscle. The fibers of the pectineus muscle (from the Latin pecten = comb) then travel down, back, and out to insert onto the posterior surface of the femur, just inferior to the lesser trochanter along the pectineal line.

References

• Cherian PT, Parnell AP. Radiologic anatomy of the inguinofemoral region: insights from MDCT. AJR Am J Roentgenol. 2007 Oct;189(4):W177-83.
• Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease - 8th edition (Mosby, 2004), p 397.

Periosteal (Juxtacortical) Desmoid

Periosteal desmoid is a tumor-like fibrous proliferation of the periosteum at the musculotendinous attachment of the adductor magnus or the medial head of the gastrocnemius muscle on the posteromedial cortex of the distal femur. Because of its location, it also goes by the following names: distal metaphyseal femoral defect or medial supracondylar defect of the femur.

The etiology is thought to be related to repetitive trauma, similar to tug lesions elsewhere in the body. It is, therefore, also called an avulsive cortical irregularity.

The lesion tends to appear in children and young adults between the ages of 12 and 20 years, and usually resolves spontaneously soon thereafter. Patients are usually asymptomatic, but can present with pain.

Radiographic findings include a saucer-like cortical defect at the posteromedial cortex of the distal femur. The base is usually sclerotic, but may be poorly defined and irregular. Small bony spicules at the cortical surface may simulate an aggressive lesion.

Scintigraphy is usually normal, but focal increase in activity can occasionally be seen.

MRI reveals a T1-hypointense, T2-hyperintense lesion with a hypointense base at or near the attachment of the adductor magnus or medial head of the gastrocnemius muscles. Periosseous and marrow edema may also be seen.

Special thanks to Dr. Kavin Malhotra for the case and interesting discussion.

References

• Posch TJ, Puckett ML. Marrow MR signal abnormality associated with bilateral avulsive cortical irregularities in a gymnast. Skeletal Radiol. 1998 Sep;27(9):511-4.
• Resnick D, Greenway G. Distal femoral cortical defects, irregularities, and excavations. Radiology. 1982 May;143(2):345-54.

Rice Bodies: Differential Diagnosis

Rice bodies, named for their macroscopic similarity to polished grains of rice, are made up of central acidophilic material surrounded by collagen and fibrin. Their etiology is debated. One theory suggests that they are due to small synovial infarctions that lead to shedding of synovium and subsequent encasement by fibrin. Another theory posits that rice bodies form independently in synovial fluid and enlarge by aggregation of fibrin.

Rice bodies are iso- or hypointense to skeletal muscle on T1- and T2-weighted images, and can be seen clearly against the background of fluid on T2-weighted images. They tend to blend in with fluid on T1-weighted images.

The image above from a young boy reveal distension of the extensor digitorum tendon sheath with multiple, punctate objects. The objects blend in with fluid signal on the T1-weighted image and are best seen against fluid on the T2-weighted image.

Differential considerations for rice bodies include:

• Infection: First described in the setting of tuberculous arthritis, rice bodies have also been reported with atypical mycobacteria and other infections.
• Chronic synovitis or bursitis: Most commonly seen in rheumatoid arthritis, where it typically presents as a painless mass. It can also be seen in juvenile idiopathic arthritis or in the absence of any underlying systemic disorder.
• Synovial chondromatosis: Can be difficult to differentiate from rice bodies. In general, rice bodies have low signal on both T1- and T2-weighted sequences, making them more visible on T2-weighted images. In contrast, synovial chondromatosis may be intermediate to high signal intensity on T1-weighted images and bright on T2-weighted images, making them more visible on T1-weighted sequences.

References

• Chau CL, Griffith JF, Chan PT, Lui TH, Yu KS, Ngai WK. Rice-body formation in atypical mycobacterial tenosynovitis and bursitis: findings on sonography and MR imaging. AJR Am J Roentgenol. 2003 May;180(5):1455-9.
• Chen A, Wong LY, Sheu CY, Chen BF.Distinguishing multiple rice body formation in chronic subacromial-subdeltoid bursitis from synovial chondromatosis. Skeletal Radiol. 2002 Feb;31(2):119-21.
• Cuomo A, Pirpiris M, Otsuka NY. Case report: biceps tenosynovial rice bodies. J Pediatr Orthop B. 2006 Nov;15(6):423-5.
• Martini G, Tregnaghi A, Bordin T, Visentin MT, Zulian F. Rice bodies imaging in juvenile idiopathic arthritis. J Rheumatol. 2003 Dec;30(12):2720-1.
• Popert AJ, Scott DL, Wainwright AC, Walton KW, Williamson N, Chapman JH. Frequency of occurrence, mode of development, and significance or rice bodies in rheumatoid joints. Ann Rheum Dis. 1982 Apr;41(2):109-17.

Ivory Vertebra

An ivory vertebra is a vertebral body with normal size and contour and normal adjacent discs that has increased density on radiographs.

The main differential considerations include:

• Osteoblastic tumor: In children, consider osteosarcoma, metastatic neuroblastoma and medulloblastoma, and osteoblastoma. In adults consider metastatic breast or prostate cancer.
• Lymphoma: Usually Hodgkin lymphoma
• Paget disease: Usually causes expansion of the vertebral body, in which case it doesn't exactly fit the definition.
• Idiopathic segmental sclerosis: Reactive bone formation in response to stress.

References

Graham TS. The ivory vertebra sign. Radiology. 2005 May;235(2):614-5

Pneumoretroperitoneum

Pneumoretroperitoneum, as its name spells out, is gas in the retroperitoneal space. In the bad old days of radiology, insufflation of the retroperitoneal space was an important method of examining retroperitoneal organs such as the pancreas. In modern times, pneumoretroperitoneum is usually due to penetrating trauma or perforation of the retroperitoneal portions of the gastrointestinal tract (duodenum, ascending colon, descending colon, and rectum).

The differential diagnosis for the site of injury can be narrowed or rearranged by noting the location of the gas. Gas in the perirenal space is most commonly due to renal infection. Indeed, focal pneumoretroperitoneum anywhere can be sign of a retroperitoneal abscess.

Gas in the right anterior pararenal space is usually due to pathology in the descending portion of the duodenum, while gas in the left anterior pararenal space is more commonly due to pathology in the descending or sigmoid colon. Bilateral anterior pararenal space gas can be due to sigmoid or rectal perforation or complicated pancreatitis.

Gas in the posterior pararenal space bilaterally can be due to rectal perforation or dissecting gas from above the diaphragm. On the other hand, pneumomediastinum can also be seen secondarily when gas dissects superiorly through the aortic hiatus.

Finally, when gas is isolated to the left posterior pararenal space, one can consider pathology related to the sigmoid colon.

Radiographic findings of pneumoretroperitoneum include gas along the psoas margins and around the kidneys and other retroperitoneal organs. However, CT nicely shows the gas confined to the retroperitoneal space. A CT finding related to colonic perforation is the so-called dirty mass, a focal collection of extraluminal fecal matter close to the perforation site.

In the case above, we see gas dissecting along the aortic hiatus and outlining the proximal portions of the psoas muscles. The CT shows gas predominantly in the right anterior pararenal space, but also seen on the left. A stent is present in the descending colon in this patient with carcinoma of the colon.

References

• Dalrymple NC, Leyendecker JR, Oliphant M. Problem Solving in Abdominal Imaging. Elsevier Health Sciences, 2009. Page 153.
• Saeki M, Hoshikawa Y, Miyazaki O, Nakayama F, Okamoto E, Ishikawa T. Computed tomographic analysis of colonic perforation: "dirty mass," a new computed tomographic finding. Emerg Radiol 1998; 5: 140-145.

Transformation of Multiple Myeloma to High-Grade Lymphoma

Multiple myeloma can rarely transform to large-cell lymphoma. This may represent dedifferentiation of the original plasma cell tumor or the emergence of a different clone.

Patients present with rapidly enlarging soft tissue masses and/or marrow involvement. This transformation has a poor prognosis with a median survival of 4 months. It has been suggested that these patients may be more effectively treated with regimens for non-Hodgkin lymphoma than standard myeloma regimens.

The imaging appearance can be mimicked by the more common extraosseous myeloma. Indeed, lymph nodes are common sites of extraosseous involvement, with gross involvement of the lymph nodes seen in 5% of patients with extraosseous myeloma on autopsy.

References

• Mintzer D, Bagg A. Clinical syndromes of transformation in clonal hematologic disorders. Am J Med. 2001 Oct 15;111(6):480-8.
• Moulopoulos LA, Granfield CA, Dimopoulos MA, Kim EE, Alexanian R, Libshitz HI. Extraosseous multiple myeloma: imaging features. AJR Am J Roentgenol. 1993 Nov;161(5):1083-7.
• Suchman AL, Coleman M, Mouradian JA, Wolf DJ, Saletan S. Aggressive plasma cell myeloma. A terminal phase. Arch Intern Med. 1981 Sep;141(10):1315-20.
• Wahlin A, Roos G, Hörnsten P. Multiple myeloma--transformation to high-grade malignant lymphoma. Acta Oncol. 1988;27(4):411-3.

Posterior Dynamic Stabilization

Posterior dynamic stabilization, also known as soft stabilization, attempts to stabilize the spine while maintaining some intersegmental motion. The theory is that the reduction, rather than elimination, of segmental motion can result in alleviation of back pain.

The most widely used posterior dynamic stabilization device is the Dynesys system. As seen in the video below, the system decompresses the neural foramina without the need for interbody or posterolateral fusion.

The system consists of titanium pedicle screws connected vertically by a polyethylene-terephthalate cord. Between the screws, the polyethylene cord is surrounded by a polycarbonate urethane spacer.


During flexion, the cord acts as tension band and limits flexion. During extension, the spacers engage the screw heads and limit extension. The system may be a bit too good at limiting motion, however. As Kim et al have recently reported in a small series of patients, the average post-operative range of motion at the treated levels was about 4 degrees, compared to about 13 degrees pre-operatively.

The most frequently observed complication in this system is pedicle screw loosening, being seen in about 5% of screws and 20% of patients. The screw loosening tends to occur at marginal levels (above and below) rather than the middle level. The loosening, however, does not appear to change clinical outcome, with patients experiencing improvement regardless of screw loosening.

Radiographs of this system can be puzzling at first, appearing as if the surgeon put in the screws, but had to close before the rods could be placed. The reason for this is that the cord and the spacers are conveniently radiolucent. On CT, the attenuation of the cord/spacer system is almost the same as the surrounding muscle, but a subtle target appearance, representing the central cord and the outer spacer, can be appreciated. The cord has a slightly higher attenuation in this case. The T1-weighted MR image shows the structure to better advantage.

Note that the facets are preserved, one of the touted benefits of this system. Also note the absence of bone graft material, which means less donor-site morbidity from autologous iliac graft.

References

• Kim CH, Chung CK, Jahng TA. Comparisons of outcomes after single or multilevel dynamic stabilization: effects on adjacent segment. J Spinal Disord Tech. 2011 Feb;24(1):60-7.
• Murtagh RD, Quencer RM, Castellvi AE, Yue JJ. New techniques in lumbar spinal instrumentation: what the radiologist needs to know. Radiology. 2011 Aug;260(2):317-30.
• Ko CC, Tsai HW, Huang WC, Wu JC, Chen YC, Shih YH, Chen HC, Wu CL, Cheng H. Screw loosening in the Dynesys stabilization system: radiographic evidence and effect on outcomes. Neurosurg Focus. 2010 Jun;28(6):E10.

Post-Traumatic Exostosis

Solitary osteochondromas are commonly thought of as neoplasms. But, there is a theory that they may be the result of injury, with experiments in rabbits showing osteochondroma formation following resection of the periosteum of the metaphysis or diaphysis.

A common location for avulsion injuries in children is at the apophyses, which can result in a prominent exostosis. The best known of these are seen with Osgood–Schlatter and Sinding-Larsen-Johansson diseases.

Apophyses in the pelvis can also be affected. The case above shows a post-traumatic exostosis at the anterior inferior iliac spine, the site of origin of the rectus femoris muscle.

References

• Goodwin MA. Myositis ossificans in the region of the hip-joint. Br J Surg. 1959 Mar;46(199):547-9.
• Hwang SK, Park BM. Induction of osteochondromas by periosteal resection. Orthopedics. 1991 Jul;14(7):809-12.
• Irving MH. Exostosis formation after traumatic avulsion of the anterior inferior iliac spine. Report of two cases. J Bone Joint Surg Br. 1964 Nov;46:720-2.
• Richardson RR. Variants of exostosis of the bone in children. Semin Roentgenol. 2005 Oct;40(4):380-90.

Well-Differentiated Liposarcoma, Atypical Lipomatous Tumor, and Friends

Atypical lipomatous tumor and well-differentiated liposarcoma refer to the exact same tumor (see below for more synonyms). They are intermediate-grade malignant neoplasms with a mature lipomatous proliferation that are locally aggressive, but which do not metastasize (unless they dedifferentiate).

The choice of terminology depends on the urgency the pathologist or radiologist wants to convey in the record, as well as the consensus between them and the surgeon in order to prevent either inadequate or excessive therapy.

This vagueness/flexibility is due to the fact that the location of this tumor make a big difference on the possibility of getting tumor-free margins, and consequently, a difference in local recurrence and prognosis.

For example, in the retroperitoneum, mediastinum, and the spermatic cord, getting a tumor-free margin is usually impossible, and, as a result, local recurrence is common and often fatal, with a mortality rate of 80%. The same tumor in the extremities is far more easily resected with clear margins, with a mortality rate of close to 0%.

For this reason, the use of the term well-differentiated liposarcoma conveys the correct level of urgency when the tumor is located in the retroperitoneum or mediastinum, while the term atypical lipomatous tumor is more suited for lesions in the extremities.

The WHO lists the following as old synonyms for atypical lipomatous tumor and well-differentiated liposarcoma:

• Atypical lipoma
• Adipocytic liposarcoma
• Lipoma-like liposarcoma
• Sclerosing liposarcoma
• Spindle cell liposarcoma
• Inflammatory liposarcoma

On MRI, atypical lipomatous tumors are fatty tumors that are differentiated from lipomas by the presence of thickened or nodular septa, associated nonadipose masses, prominent foci of high T2 signal, and prominent areas of enhancement (pink arrows).

References

• Gaskin CM, Helms CA. Lipomas, lipoma variants, and well-differentiated liposarcomas (atypical lipomas): results of MRI evaluations of 126 consecutive fatty masses. AJR Am J Roentgenol. 2004 Mar;182(3):733-9.
• Tos APD, Pedeutour F. Atypical lipomatous tumour / Well differentiated liposarcoma. in Pathology and Genetics of Tumours of Soft Tissue and Bone. Fletcher CDM, Unni KK, Mertens F (eds). IARCPress Lyon, 2002. pp 35-37.
• Weiss SW, Rao VK. Well-differentiated liposarcoma (atypical lipoma) of deep soft tissue of the extremities, retroperitoneum, and miscellaneous sites. A follow-up study of 92 cases with analysis of the incidence of "dedifferentiation". Am J Surg Pathol. 1992 Nov;16(11):1051-8.

Staging in Multiple Myeloma

Two main staging systems exist for multiple myeloma: the Durie-Salmon staging system and the International Staging System. The systems have low concordance with each other (36%), but both seem to be predictive of progression-free and overall survival.

Durie-Salmon Staging System

The older Durie-Salmon staging system uses a combination of 4 factors: immunoglobulin levels, hemoglobin, calcium levels, and the number of bone lesions on radiographs.

• Stage I: All of the following:
  • Hgb > 10 g/dL, AND
  • Calcium ≤ 12 mg/dL, AND
  • Low M-component production rates: IgG < 5 g/dL, IgA < 3 g/dL, Urine light chain M-component on electrophoresis < 4 g/24 hours, AND
  • Radiographs normal or with a single bone plasmacytoma.
• Stage II: neither Stage I or Stage III
• Stage III: One or more of the following
  • Hgb < 8.5 g/dL, OR
  • Calcium > 12 mg/dL, OR
  • High M-component production rates: IgG > 7 g/dL, IgA > 5 g/dL, Urine light chain M-component on electrophoresis > 12 g/24 hours
  • Advanced lytic bone lesions

Each stage is further divided into A and B based on renal function:

• A: Relatively normal renal function, with serum creatinine < 2.0 mg/dL
• B: Abnormal renal function, with serum creatinine ≥ 2.0 mg/dL

International Staging System

This newer staging system uses serum albumin and β2-microglobulin levels to divide patients into 3 stages.

• Stage I: β2-microglobulin < 3.5 mg/L; albumin ≥ 3.5 g/dL
• Stage II: Neither stage I or III.
  Has two categories: β2-microglobulin < 3.5 mg/L but albumin < 3.5 g/dL, or β2-microglobulin 3.5 mg/L - 5.5 mg/L irrespective of the albumin level.
• Stage III: β2-microglobulin ≥ 5.5 mg/L

References

• Durie BG, Kyle RA, Belch A, Bensinger W, Blade J, Boccadoro M, Child JA, Comenzo R, Djulbegovic B, Fantl D, Gahrton G, Harousseau JL, Hungria V, Joshua D, Ludwig H, Mehta J, Morales AR, Morgan G, Nouel A, Oken M, Powles R, Roodman D, San Miguel J, Shimizu K, Singhal S, Sirohi B, Sonneveld P, Tricot G, Van Ness B; Scientific Advisors of the International Myeloma Foundation. Myeloma management guidelines: a consensus report from the Scientific Advisors of the International Myeloma Foundation. Hematol J. 2003;4(6):379-98.
• Greipp PR, San Miguel J, Durie BG, Crowley JJ, Barlogie B, Bladé J, Boccadoro M, Child JA, Avet-Loiseau H, Kyle RA, Lahuerta JJ, Ludwig H, Morgan G, Powles R, Shimizu K, Shustik C, Sonneveld P, Tosi P, Turesson I, Westin J. International staging system for multiple myeloma. J Clin Oncol. 2005 May 20;23(15):3412-20.
• Hari PN, Zhang MJ, Roy V, Pérez WS, Bashey A, To LB, Elfenbein G, Freytes CO, Gale RP, Gibson J, Kyle RA, Lazarus HM, McCarthy PL, Milone GA, Pavlovsky S, Reece DE, Schiller G, Vela-Ojeda J, Weisdorf D, Vesole D. Is the International Staging System superior to the Durie-Salmon staging system? A comparison in multiple myeloma patients undergoing autologous transplant. Leukemia. 2009 Aug;23(8):1528-34.

Extraskeletal Osteosarcoma

Extraskeletal osteosarcomas are rare, malignant soft tissue tumors that produce osteoid or bone matrix. They can be primary, or secondary to radiation, occurring 2-40 years following exposure.

Unlike osteosarcomas of bone, which tend to affect children and adolescents, extraskeletal osteosarcomas tend to affect adults, with a mean age at presentation of about 50 years. Extraskeletal osteosarcoma is rare in children, but recent data suggests that children may have a more favorable response to treatment than adults.

Like intraosseous osteosarcomas, extraskeletal osteosarcomas can be classified histologically as osteoblastic, chondroblastic, fibroblastic, telangiectatic, or small cell.

Extraskeletal osteosarcomas have a predilection for the lower extremities, followed by the upper extremity, and retroperitoneum. They are usually located deep and well-attached to surrounding tissue, but superficial or subcutaneous lesions have also been described.

Radiographs may reveal variable mineralization and a dense fluffy area of increased density, but up to half of cases have no calcification on radiographs. The mineralization pattern is distinguished from that of the much more common myositis ossificans by, which is ossified, well-defined, and peripherally sclerotic.

The adjacent bone is usually not involved in extraskeletal osteosarcoma.

CT can better demonstrate mineralization and necrosis within the lesion. MRI is nonspecific, and may reveal a poorly defined, heterogeneous lesion on T1- and T2-weighted sequences. Dynamic sequences reveal intense, early enhancement. The MRI appearance may be similar to that of giant cell tumour of the tendon sheath.

The masses are hypervascular, as revealed on angiography and nuclear medicine bone scans.

References

• Beall DP, Ly J, Bell JP, Parker EE, John CM, Babb JC, Stapp AM. Pediatric extraskeletal osteosarcoma. Pediatr Radiol. 2008 May;38(5):579-82.
• Kind M, Stock N, Coindre JM. Histology and imaging of soft tissue sarcomas. Eur J Radiol. 2009 Oct;72(1):6-15.
• Kransdorf MJ, Meis JM. From the archives of the AFIP. Extraskeletal osseous and cartilaginous tumors of the extremities. Radiographics. 1993 Jul;13(4):853-84.

Calcaneal Trabecular Bone Architecture

Familiarity with the normal trabecular architecture of the calcaneus is important for detecting subtle fractures on radiographs and avoiding mistaking a pseudo-cyst of the calcaneus (more below) for a true lesion.

Five trabecular groups have been defined in the calcaneus. These may be lumped into compressive and tensile trabeculae.

Compressive

• Thalamic (yellow): Greek for room or chamber. These are the primary compressive trabeculae and extend from the articular surface of the subtalar joint to the cortex of the posterior tuberosity in a concave anteroinferior curve.
• Anterior apophyseal (red): These are the secondary compressive trabeculae. Curved trabeculations fan out from the region of the sinus tarsi anteroinferiorly to the anterior tuberosity.

Tensile

• Inferior plantar (cyan): These are the primary tensile trabeculae. Curved trabeculations extend from the inferior cortex to the cortex of the posterior tuberosity.
• Anterior plantar (green): These are the secondary tensile trabeculae. Trabeculations extend from the anterior part of the inferior cortex anterosuperiorly to the anterior tuberosity.
• Posterior achillean (purple): Also known as the tendotuberosity group, these tensile trabeculae run parallel to the posterior tuberosity.

Subtle disruptions in these trabecular patterns can alert you to the possibility of a fracture. Keats has also described a prominent trabeculation along the inferior aspect of the calcaneus on the lateral view that can simulate a stress fracture.

A relatively lucent triangular window bounded superiorly by the primary and secondary compressive trabeculae and inferiorly by the tensile trabeculae is referred to as the foramen calcaneus or Ward's triangle. When prominent, it can be mistaken for a lesion, and is referred to as the pseudocyst or pseudolesion of the calcaneus.

References

• Aggarwal ND, Singh GD, Aggarwal R, Kaur RP, Thapar SP. A survey of osteoporosis using the calcaneum as an index. Int Orthop. 1986;10(2):147-53.
• Diard F, Hauger O, Moinard M, Brunot S, Marcet B. Pseudo-cysts, lipomas, infarcts and simple cysts of the calcaneus: are there different or related lesions? JBR-BTR. 2007 Sep-Oct;90(5):315-24.
• Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease. 8th edition, page 886; Mosby (2004).

SAPHO Syndrome

SAPHO syndrome refers to a broad spectrum of diseases involving the musculoskeletal system and skin. SAPHO stands for synovitis, acne, pustulosis, hyperostosis, and osteitis.

SAPHO hass been described multiple times by investigators in different countries and specialties, and like the story of the blind men and the elephant, has collected quite a few names over the years, including bilateral clavicular osteomyelitis with palmar and plantar pustulosis (Japanese orthopedists), subacute and chronic symmetric osteomyelitis (French radiologists), sterno-costo-clavicular hyperostosis (German physicians), chronic recurrent multiftseal osteomyelitis (Scandinavian pediatricians), and pustulotic arthro-osteitis (Japanese rheumatologists).

When taken together, these different parts of the elephant combine to give us the recurring features of the condition:

• Distinctive skin lesions: Severe acne and palmoplantar pustules.
• Distinctive bone lesions: Painful and tender sclerosis and hyperostosis. Characteristic sites include the anterior chest wall in adults and the metaphyses of long tubular bones in children. Histologic analysis reveals nonspecific inflammatory changes, with the occasional positive culture of indolent organisms (e.g., Propionibacterium acnes).
• Indolent clinical course: Usually chronic and self-limited.

Different diagnostic criteria have been developed for SAPHO. One developed by Kahn et al. requires one or more of the following to make the diagnosis:

• Chronic recurrent multifocal sterile and axial osteomyelitis, with or without dermatosis.
• Acute, subacute or chronic arthritis associated with palmoplantar pustulosis, pustulous psoriasis or severe acne.
• Sterile osteitis associated with palmoplantar pustulosis, pustulous psoriasis or severe acne.

References

• Boutin RD, Resnick D. The SAPHO syndrome: an evolving concept for unifying several idiopathic disorders of bone and skin. AJR Am J Roentgenol. 1998 Mar;170(3):585-91.
• Kahn MF, Khan MA. The SAPHO syndrome. Baillieres Clin Rheumatol. 1994 May;8(2):333-62.

Solitary Fibrous Tumor of the Soft Tissues

Solitary fibrous tumors are rare spindle cell neoplasms that were first described in the pleural space, but which can occur anywhere in the body, including the retroperitoneum, deep soft tissues of the proximal extremities, abdominal cavity, and head and neck.

Solitary fibrous tumors are a distinctive mesenchymal neoplasm that have hemangiopericytoma-like microscopic features. Indeed, many tumors previously classified as hemangiopericytomas are now called solitary fibrous tumors.

Unlike thoracic tumors, solitary fibrous tumors elsewhere tend to be symptomatic. Like their thoracic cousins, solitary fibrous tumors of the soft tissues are benign tumors that are cured by surgical resection in almost all cases. Lipomatous hemangiopericytoma, a rare variant of the solitary fibrous tumor, contains mature adipose tissue, and will be discussed at a later date.

On CT and MRI, solitary fibrous tumors have well-defined margins and usually lobulated contours. Solitary fibrous tumors can exert mass effect on and displace adjacent structures, but local invasion is rare. Post-contrast images reveal avid contrast enhancement in the majority of cases, usually with a heterogeneous pattern. Calcification is uncommon.

MRI reveals nonspecific features: high signal intensity on T2-weighted images and intermediate signal intensity on T1-weighted images. Large collateral feeding vessels can be seen as perilesional flow voids.

Differential considerations include highly vascular soft-tissue lesions such as high-grade sarcomas, angiosarcoma, and a solitary vascular metastasis.

References

• Gengler C, Guillou L. Solitary fibrous tumour and haemangiopericytoma: evolution of a concept. Histopathology. 2006 Jan;48(1):63-74.
• Wignall OJ, Moskovic EC, Thway K, Thomas JM. Solitary fibrous tumors of the soft tissues: review of the imaging and clinical features with histopathologic correlation. AJR Am J Roentgenol. 2010 Jul;195(1):W55-62.

Shallow Sella Turcica

A shallow sella turcica can be a normal variant seen in about 15% of the population. It can also be associated with certain congenital anomalies and syndromes, such as Cockayne syndrome, Prader-Willi syndrome, basal cell nevus syndrome, Down syndrome, Hallerman-Streiff syndrome, and myotonic dystrophy. It can also be due to underdevelopment of the pituitary or decreased intracranial pressure.

References

• Castriota-Scanderbeg A and Dallapiccola B. Abnormal skeletal phenotypes: from simple signs to complex diagnoses (Springer, 2005), p 67.
• Keats TE and Anderson MW. Atlas of Normal Roentgen Variants That May Simulate Disease - 8th edition (Mosby, 2004), p 115.

Evolution of Signal Abnormality in Femoral Neck Stress Injuries

The image sequence above shows 3 sets of MRI examinations for a 75-year-old woman who began experiencing left hip pain after favoring that side due to contralateral knee pain. Initial MR examination at t=0 shows signal abnormality in the left femoral neck. Approximately 2 months later (t=51 days) patchy small areas of abnormal signal remain, but there has been significant improvement. 5 months after the initial scan (t=145 days), we see resolution of signal abnormality in the femoral neck.

Knowing the expected evolution of post-traumatic bone marrow signal abnormalities can be helpful in the setting of persistent pain or concern for neoplasm. In a patient presenting with persistent pain after the initial MRI, new signal abnormalities could represent reinjury or progressing injury. Persistent signal changes in the absence of new trauma may indicate a neoplasm.

In a study of 10 patients with (9 men, 1 woma, between the ages of 19 to 49), Slocum et al found that STIR signal abnormalities in nondisplaced, compressive-side femoral neck stress fractures resolved 6 months after the first imaging study in 90% of their patients.

Interestingly, they also found that most patients continued to be symptomatic even after resolution of the edema.

References

Slocum KA, Gorman JD, Puckett ML, Jones SB. Resolution of abnormal MR signal intensity in patients with stress fractures of the femoral neck. AJR Am J Roentgenol. 1997 May;168(5):1295-9.

Dermatofibrosarcoma Protuberans

Dermatofibrosarcoma protuberans is an uncommon soft tissue tumor of intermediate- to low-grade malignancy that arises in the dermis and spreads into the subcutaneous tissues and muscle. Metastases are rare.

The tumor tends to affect patients in the second and the fifth decades of life and has a predilection for the trunk, followed by the extremities and head and neck.

Dermatofibrosarcoma protuberans is a slowly growing tumor with an excellent prognosis after complete resection. Local recurrence, however, is relatively common with incomplete surgical resection.

MRI usually reveals a multilobuilar, well-defined, and superficial mass that is hypointense on T1-weighted images and iso- to slightly hyperintense on T2-weighted images. Areas of high signal on T1-weighted images representing hemorrhage can also be seen.

Atypical imaging findings include a deep location, deep extension of a large soft tissue mass, and ill-defined margins.

References

• Lee SJ, Mahoney MC, Shaughnessy E. Dermatofibrosarcoma protuberans of the breast: imaging features and review of the literature. AJR Am J Roentgenol. 2009 Jul;193(1):W64-9.
• Torreggiani WC, Al-Ismail K, Munk PL, Nicolaou S, O'Connell JX, Knowling MA. Dermatofibrosarcoma protuberans: MR imaging features. AJR Am J Roentgenol. 2002 Apr;178(4):989-93.

Desmoplastic Fibroma of Bone

Desmoplastic fibroma of bone (desmoid tumor of bone), a locally aggressive lesion related to desmoid tumors of the abdominal wall, is characterized by abundant collagen formation. This rare tumor, variably classified as benign or intermediate, accounts for less than 0.1% of all bone tumors. The tumor has a predilection for The long bones, mandible, and pelvis.

Patients are usually younger than 40 and present with nonspecific signs and symptoms. The insidious onset of signs and symptoms means that the tumor can get pretty large before presentation. Pathologic fractures, as seen in our case, are be the first presnting symptom in about 10% of cases.

Radiographs reveal a lucent lesion with a fusiform expansion of the bone. In the long bones, the lesions are metaphyseal or metadiaphyseal. Epiphyseal involvement is less common, but may occur after closure of the physis.

Internal pseudo-trabeculation, seen in 75% of cases, is due to uneven bone destruction, leaving ridges of intact bone near the periphery of the tumor.

The borders are usually non-sclerotic and sharp, but a wide zone of transition can be seen in some cases. No significant periosteal reaction is seen, but the cortex itself may be either thinned or thickened. Bone destruction and soft tissue invasion can be seen with locally aggressive forms and can mimic a malignant bone tumor.

Radiographic differential considerations include:

• Unicameral bone cyst: Can be identical to desmoplastic fibroma on radiographs. CT and MR can be used to exclude this possibility.
• Aneurysmal bone cyst: Eccentric expansion (blow-out) of bone is seen in aneurysmal bone cysts, compared to the more fusiform expansion of bone usually seen with desmoplastic fibroma.
• Fibrous dysplasia: Tends to occupy a longer segment of bone than desmoplastic fibroma, has a mineralized matrix, and may have a sclerotic rim.
• Chondromyxoid fibroma: Chondromyxoid fibroma is usually more eccentric and may have a scalloped border with thin marginal sclerosis. Pseudotrabeculations tend to be more curvilinear.
• Giant cell tumor: Can extend into the epiphysis, but is usually round rather than oval and does not have a sclerotic margin.
• Low-grade fibrosarcoma: Usually has a permeative pattern of bone destruction, a wider zone of transition, and no sclerotic margin.
• Low-grade central osteosarcoma: A typical appearance is a large, intramedullary, fibro-osseous lesion with focal areas of cortical disruption, which can mimic the appearance of a desmoplastic fibroma. Typically associated with areas of mineralized tumor matrix.
• Chondrosarcoma: Desmoplastic fibromas can contain enchondroma-like nodules that can mimic chondrosarcoma.

MRI can be helpful in further characterizing the lesion, but can be confusing in the presence of a pathologic fracture. On T1-weighted images, the lesions are isointense or hypointense to adjacent normal muscle. On T2-weighted images, the lesions have components that are iso- to hypointense to skeletal muscle. Cortical disruption and soft tissue extension are seen in about 50% of cases. Ridges of bone may result in linear areas of signal void on T2-weighted images.

Post-contrast images reveal heterogeneous enhancement, with areas of intense enhancement mixed with areas of minor to no enhancement.

MRI differential considerations of a predominantly osteolytic lesion with a large area of low T2 signal not corresponding to calcium include:

• Lymphoma:
• Primary leiomyosarcoma of bone:
• Fibrous dysplasia:
• Non-ossifying fibroma:
• Giant cell tumor:

References

• Bahk WJ, Kang YK, Lee AH, Mirra JM. Desmoid tumor of bone with enchondromatous nodules, mistaken for chondrosarcoma. Skeletal Radiol. 2003 Apr;32(4):223-6.
• Crim JR, Gold RH, Mirra JM, Eckardt JJ, Bassett LW. Desmoplastic fibroma of bone: radiographic analysis. Radiology. 1989 Sep;172(3):827-32.
• Frick MA, Sundaram M, Unni KK, Inwards CY, Fabbri N, Trentani F, Baccini P, Bertoni F. Imaging findings in desmoplastic fibroma of bone: distinctive T2 characteristics. AJR Am J Roentgenol. 2005 Jun;184(6):1762-7.
• Greenspan A, Jundt G, Remagen W. Fibrogenic, Fibroosseous, and Fibrohistiocytic Lesions. In Differential Diagnosis of Orthopaedic Oncology, 2nd Edition. 2007 Lippincott Williams & Wilkins; pp 292-297.
• Shuto R, Kiyosue H, Hori Y, Miyake H, Kawano K, Mori H. CT and MR imaging of desmoplastic fibroblastoma. Eur Radiol. 2002 Oct;12(10):2474-6.
• Vanhoenacker FM, Hauben E, De Beuckeleer LH, Willemen D, Van Marck E, De Schepper AM. Desmoplastic fibroma of bone: MRI features. Skeletal Radiol. 2000 Mar;29(3):171-5. Review.

The Femoral Neck and Periosteum

Before we get to the femoral neck in specific, a general review of the lowly periosteum:

Periosteum, which covers most bones except for the articular surfaces, tendon insertions, and sesamoid bones, is divided into two layers. The outer fibrous layer contains fibroblasts.

The inner cellular layer, also referred to as the cambium (Latin for a change) layer, contains progenitor cells that develop into osteoblasts and chondroblasts. This is the layer that is responsible for forming lamellar bone to increase bone width, and forming woven bone in response to injury.

The periosteum is attached to bone by Sharpey’s fibers, collagen fibers that penetrate the full width of the cortex at sites exposed to high tension forces.

A recent quantitative study Allen and Burr showed that the periosteum of the human femoral neck is predominantly fibrous, with significantly less cellular periosteum than diaphyseal bone. They found mineralizing tissue in the expected location of this cellular layer. This replacement of the cellular layer by mineralization is also found along the diaphyses of long bones as people age.

All of this means that there may be little if any callus formation with femoral neck fractures. This comes into play in assessing post-fixation healing in adults. Contrary to intertrochanteric fractures, which show increasing callus formation and sclerosis with progression of healing, femoral neck fractures show no such association, making radiographic assessment of healing difficult

References

• Allen MR, Burr DB. Human femoral neck has less cellular periosteum, and more mineralized periosteum, than femoral diaphyseal bone. Bone. 2005 Feb;36(2):311-6.
• Szechinski JW, Grigorian MA, Grainger AJ, Elliott JM, Wischer TK, Peterfy CG, Genant HK. Femoral neck and intertrochanteric fractures: radiographic indicators of fracture healing. Orthopedics. 2002 Dec;25(12):1365-8; discussion 1368.

Longitudinal Stress Fracture

Longitudinal stress fractures are uncommon fractures that are thought to be related to rotational stress. While they most commonly occur in the tibia, cases have also been reported in the femur and fibula.

The diagnosis is most readily made on CT by noting a fracture plane oriented along the long axis of the bone. MRI may also allow visualization of the fracture plane, but has a lower sensitivity. MRI can, however, suggest the diagnosis by revealing bone marrow edema starting at the entry of the nutrient foramen of the tibia, eccentric periosteal reaction and new bone formation, and eccentric soft tissue edema. The relationship between the nutrient foramen and the fracture plane is an interesting one. It has been suggested that the foramen may be a potential area of weakness in some patients, with some tibial longitudinal fracture planes starting within the foramen.

The image above shows the CT and MRI from a patient with a longitudinal stress fracture. The CT demonstrates the fracture plane with endosteal and periosteal callus formation along the anteromedial margin of the tibia. No communication between the nutrient foramen and the fracture plane was noted on CT. The first axial STIR image shows the medullary end of the nutrient foramen (yellow arrow). The second axial STIR image is just distal to the first and shows marrow edema and eccentric soft tissue edema. No fracture plane could be seen on MRI. The radigraphs, even in retrospect, were normal.

References

• Allen GJ. Longitudinal stress fractures of the tibia: diagnosis with CT. Radiology. 1988 Jun;167(3):799-801.
• Craig JG, Widman D, van Holsbeeck M. Longitudinal stress fracture: patterns of edema and the importance of the nutrient foramen. Skeletal Radiol. 2003 Jan;32(1):22-7. Devas MB. Longitudinal stress fractures. Another variety seen in long bones. J Bone Joint Surg Br. 1960 Aug;42-B:508-14.
• Feydy A, Drapé J, Beret E, Sarazin L, Pessis E, Minoui A, Chevrot A. Longitudinal stress fractures of the tibia: comparative study of CT and MR imaging. Eur Radiol. 1998;8(4):598-602.
• Goupille P, Giraudet-Le Quintrec JS, Job-Deslandre C, Menkes CJ. Longitudinal stress fractures of the tibia: diagnosis with CT.
• Saifuddin A, Chalmers AG, Butt WP. Longitudinal stress fractures of the tibia: MRI features in two cases. Clin Radiol. 1994 Jul;49(7):490-5.

Extensively Calcified Synovial Sarcoma

Synovial cell sarcomas, discussed earlier, can present with calcifications in about 30% of cases. The calcifications are often diffuse and punctate. Extensive calcification simulating a cartilaginous or bony tumor is uncommon, but has been reported to have a better prognosis, with higher survival rates.

The image above shows such a case. The radiograph of the shoulder shows an extensively calcified lesion adjacent to the scapula. A discontinuity in the pattern of calcification superiorly is better appreciated on CT as a soft tissue component anteriorly that is metabolically active on the PET/CT fused image. MRI shows hypointensities corresponding to the calcification posteriorly, as well as a T1-hypointense, T2-hyperintense, enhancing soft tissue component anteriorly.

The radiographic differential diagnosis includes soft tissue chondroma, extra-articular synovial chondromatosis, ossifying myositis, tumoral calcinosis, and even extraskeletal osteosarcoma.

The CT suggests a more aggressive process due to the presence of the soft tissue component, which is confirmed on PET and MRI imaging.

Cases of ossifying synovial sarcomas have also been described, containing not simply calcification, but ossified matrix.

References

• Hisaoka M, Matsuyama A, Shimajiri S, Akiba J, Kusano H, Hiraoka K, Shoda T, Hashimoto H. Ossifying synovial sarcoma. Pathol Res Pract. 2009;205(3):195-8.
• Maxwell JR, Yao L, Eckardt JJ, Doberneck SA. Case report 878: Densely calcifying synovial sarcoma of the hip metastatic to the lungs. Skeletal Radiol. 1994 Nov;23(8):673-5.
• Sánchez Reyes JM, Alcaraz Mexia M, Quiñones Tapia D, Aramburu JA. Extensively calcified synovial sarcoma. Skeletal Radiol. 1997 Nov;26(11):671-3.
• Winnepenninckx V, De Vos R, Debiec-Rychter M, Samson I, Brys P, Hagemeijer A, Sciot R. Calcifying/ossifying synovial sarcoma shows t(X;18) with SSX2 involvement and mitochondrial calcifications. Histopathology. 2001 Feb;38(2):141-5.

Alveolar Soft‐Part Sarcoma

Alveolar soft‐part sarcoma is a rare tumor of unknown origin that tends to affect children and young adults. The tumor has a relatively indolent clinical course, with survival rates of about 75% at 2 years. The ultimate prognosis, however, is poor due to late metastases, with survival dropping to 15% at 20 years. The prognosis, however, seems to be considerably better in children.

Histologically, these tumors are characterized by uniform nests of polygonal tumor cells that are separated by fibrovascular septa and delicate vascular channels. The cells inside the nests are discohesive, which together with the fibrovascular septa, resemble the pattern of alveoli in the lung.

Intravascular tumor extension is seen on histology in most cases.

Alveolar soft‐part sarcoma typically presents in the lower extremities of young women. It also has a predilection for children, in which case the gender ratio appears more equal between males and females. In addition, a substantial percentage of these tumors occurs in the head and neck in children, often occurring in the orbit or tongue. Tumors occurring in these locations tend to have a better prognosis, possibly due to their small size at the time of diagnosis.

Imaging findings are nonspecific. However, features such as myxoid or cystic change and hemorrhage are unusual at histology.

The figure above shows an alveolar soft part sarcoma in the right calf of a young woman. The mass extends along the lateral and posterior compartments of the calf and has engulfed and destroyed the fibula. The tumor is predominantly hypointense on T1-weighted images and hyperintense on T2-weighted images. There is mild, heterogeneous enhancement with central areas of necrosis.

References

Folpe AL, Deyrup AT. Alveolar soft-part sarcoma: a review and update. J Clin Pathol. 2006 Nov;59(11):1127-32

Lymphoma in Bone

Lymphoma can affect bone in a primary or secondary fashion. Primary bone lymphoma is a rare tumor, comprising less than 5% of all bone tumors and less than 1% of all cases os lymphoma.

Primary Bone Lymphoma

Primary bone lymphoma is defined as lymphoma within a single bone with or without regional nodal metastases and the absence of distal lesions within 6 months following the diagnosis. Primary bone lymphoma involving more than one bone without distal metastases is a subgroup of primary bone lymphoma and is called primary multifocal osseous lymphoma or multifocal primary lymphoma of bone.

Hodgkin lymphoma, usually diffuse histiocytic lymphoma, makes up the majority of cases of primary bone lymphoma. Primary bone lymphoma has the best prognosis of all primary bone malignant lesions.

Primary bone lymphoma tends to affect the pelvis and appendicular skeleton, while primary multifocal osseous lymphoma tends to involve vertebrae more often than primary bone lymphoma.

Secondary Bone Lymphoma

Secondary bone lymphoma is more common and can be seen with both Hodgkin and non-Hodgkin lymphoma. Bone involvement can be seen in about 5% of lymphoma cases during the entire course of the disease and is higher in children (25%). The most frequent sites of secondary (metastatic) involvement are the spine, pelvis, and skull.

In Hodgkin lymphoma, secondary involvement may be via hematogenous dissemination or contiguous spread from adjacent lymph nodes, with the sternum being a common site of involvement from adjacent internal mammary lymph nodes. The lesions can be either sclerotic, lytic, or mixed, with sclerotic lesions accounting for almost half of all bone lesions in Hodgkin lymphoma.

Imaging Findings

Imaging findings are nonspecific and similar for primary and secondary forms. Radiographic findings are especially nonspecific and can range from normal, predominantly lytic (most common), sclerotic, to mixed. Cortical destruction, extraosseous soft-tissue masses, and periosteal reaction (usually aggressive) can also be seen and indicate advanced local disease.

Radiography tends to underestimate the true extent of the lesion, making MRI and nuclear medicine necessary for proper evaluation. The radiograph above shows a vague lucency involving the proximal humerus, which underestimates the extent of disease seen on MRI and PET.

A sclerotic pattern is seen more frequently with Hodgkin lymphoma, with the ivory vertebrae being a classic presentation. In non-Hodgkin lymphoma, lytic lesions with a permeative pattern are the most common radiologic presentation. In addition, sclerosis can develop following chemotherapy or radiation.

Bone scans are much more sensitive than radiography in detecting osseous involvement, revealing areas of increased radiotracer uptake. PET and MRI, however, are more effective in detecting marrow involvement and lesions without bone remodeling.

CT may reveal cortical and trabecular disruption, periosteal reaction, sequestra, and extraosseous extension. In the case of sclerotic lesions, the relative lack of cortical destruction on CT favors lymphoma over osteosarcoma and Langerhans cell histiocytosis.

Extraosseous tumor growth with relative preservation of the cortex is another feature of lymphoma best evaluated on CT and MRI, but can also be seen with Ewing sarcoma and primitive neuroectodermal tumor.

Another feature of lymphoma best seen on CT is a sequestrum. Although most often associated with osteomyelitis, sequestra can also be seen in non-matrix forming bone tumors such as lymphoma, fibrosarcoma, malignant fibrous histiocytoma, and Langerhans cell histiocytosis.

Marrow involvement is best seen on MRI as T1 hypointensity, but is not specific for lymphoma. T1-weighted images are best for evaluating the extent of disease. T2-weighted and STIR images may reveal low (uncommon), intermediate, or high signal intensity. While sensitive in detecting marrow involvement, T2-weighted and STIR images may overestimate osseous lesions due to the difficulty in differentiating peri-lesional edema from tumor. There may be areas of entrapped marrow fat within the lesions.

Extraosseous soft tissue masses are T1-hypointense and T2-hyperintense and demonstrate diffuse and homogenous enhancement. Extraosseous tumor growth with relative preservation of the cortex is another feature of lymphoma best seen on CT and MRI, but can also be seen with Ewing sarcoma and primitive neuroectodermal tumor.

Treatment response is best evaluated by histologic analysis, as MRI is not as effective in distinguishing viable tumor from post-treatment changes.
Should be considered in the differential diagnosis of fat-containing bone lesions.

References

• Hwang S. Imaging of lymphoma of the musculoskeletal system. Magn Reson Imaging Clin N Am. 2010 Feb;18(1):75-93.
• Hwang S. Imaging of lymphoma of the musculoskeletal system. Radiol Clin North Am. 2008 Mar;46(2):379-96, x.
• Malloy PC, Fishman EK, Magid D. Lymphoma of bone, muscle, and skin: CT findings. AJR Am J Roentgenol. 1992 Oct;159(4):805-9.

Hemangiopericytoma and Solitary Fibrous Tumor

Hemangiopericytomas are tumors of intermediate aggressiveness that arise from pericytes, specialized cells normally present around capillaries. The histological definition of a hemangiopericytoma in the past has been fairly loose, leading to confusion about what tumors can truly be called hemangiopericytomas.

About 15% of soft tissue neoplasms have at least focal areas that look like hemangiopericytoma on light microscopy; however, when studied by electron microscopy and immunohistochemistry, the majority of these tumors have been shown not to arise from pericytes.

Because of histologic overlap between hemangiopericytoma and solitary fibrous tumor and the lack of evidence of a pericytic differentiation for many of these tumors, pathologists have slowly abandoned the term hemangiopericytoma in favor of solitary fibrous tumor.

The only tumors that can still be called hemangiopericytoma are those that truly have pericytic (myoid) differentiation: myopericytoma, infantile myofibromatosis, and hemangiopericytoma-like lesions of the sinonasal tract showing myoid differentiation.

References

Gengler C, Guillou L. Solitary fibrous tumour and haemangiopericytoma: evolution of a concept. Histopathology. 2006 Jan;48(1):63-74.