Wednesday, January 31, 2018

Dilated Cisterna Chyli: A Potential Mimicker of Lymphadenopathy

  ryan schwope
ryan schwope
Axial (top) and coronal (bottom) contrast-enhanced CT images
demonstrate a retrocrural fluid-filled tubular structure with imperceptible walls
 (black arrows), the classic imaging features of a cisterna chyli
    Ryan Schwope
    Coronal T2-weighted MRI shows the tubular cystic structure of the cisterna chili
    and it's continuity with the thoracic duct (white arrow)
  • The cistern chyli is a dilated lymphatic sac ommonly located in the right retrocrural region, at the level of L1-L2, extending 5-7 cm in CC dimension. It classically receives draining lymph from two lumbar trunks and an intestinal trunk, and continues cephalad as the thoracic duct
  • Can enhance on delayed MRI >5 min
  • Has an average size of 7.4 mm in the AP dimension, although some authors consider it dilated when ≥6 mm
  • Dilatation can be secondary to lymphatic damage from prior gastroesophageal or retroperitoneal surgery, uncompensated cirrhosis, hypoalbuminemialymphangioleiomyomatosis, elevated central venous pressure, and biliary obstruction
  • Size changes can vary depending on phase of respiration, hydration, and lower thoracic duct peristalsis
  • Important to know of this entity because it can mimic retrocrural lymphadenopathy in the oncologic setting
  • Mulitplanar reformations and MRI can help demontrsate the tubular cystic nature of the cistern chyli and its continuity with the thoracic duct 

References 





Re

Gout of the extensor mechanism of the knee

MRI of gout of the extensor tendons of the knee, with nodules in the distal quadriceps and proximal patellar tendons. Lateral conventional radiograph does not show any calcifications.
Patient with leukemia (note abnormal marrow signal) who presented with acute knee pain and pre-patellar soft tissue swelling. Imaging shows gouty tophi involving the extensor tendons of the knee, with nodules in the distal quadriceps and proximal patellar tendons (yellow arrows). Lateral conventional radiograph does not show any calcifications. Patients with cancer are pre-disposed to gout due to hyperuricemia in the setting of high cell turnover or treatment-related tumor lysis.

Tophaceous masses of gout at the knee are most commonly located on the medial aspect of the infrapatellar fat pad and anterior joint recess (~90% of cases), at the lateral femoral condyle at the attachment site of the popliteus tendon (~80%), and the intercondylar fossae (~70%). Involvement of the extensor mechanism (distal quadirceps tendon and the patellar tendon) is less common, but characteristic.

Gouty tophi present as lobulated or amorphous masses. On MRI, they are isointense on T1-WI and heterogeneously intermediate-to-hypointense on T2-WI, with variable enhancement. Well-defined erosions of the patella can be seen with large tophi. Large erosions can mimick malignancy. Calcifications, when present can help narrow the differential diagnosis; however, as in the case above, they may not always be present.

Differential considerations include:
  • Post-traumatic or reactive enthesopathy, hydroxyapatite deposition: Will have calcifications.
  • Tenosynovial giant cell tumor: Can have low signal due to hemorrhage. No calcifications.
  • Amyloid deposition: Typically low signal. Can have calcifications.
  • Sarcoma: Gouty tophi can get very aggressive and erode into the patella, mimicking a soft tissue sarcoma.

References

Saturday, December 23, 2017

Myxofibrosarcoma Recurrence

tail-like recurrence of myxofibrosarcoma (MFS)
Serial contrast-enhanced axial images of the forearm in a patient with recurrent myxofibrosarcoma (MFS). Arrows indicate slowly enlarging, tail-like recurrence along the superficial fascia in the resection bed.

Myxofibrosarcoma (MFS, previously myxoid malignant fibrous histiocytoma) is an intermediate-grade soft-tissue sarcoma with fibroblastic and myxoid components. Patients are typically in the sixth to eighth decades of life.

These lesions can range from round and well-defined (like most soft tissue sarcomas) to predominantly infiltrating, with tails extending along fascial planes. They have high T2 signal intensity related to their myxoid content and heterogeneous enhancement that can be feather-like (typically seen with myxoid neoplasms).

Despite best efforts at acquiring negative margins (made difficult by infiltrating tails), MFS has a propensity for repeated local recurrence, with rates of up to 79%. Recurrence can be tricky to detect. As seen in the image above, tail-like recurrence can be easily dismissed as being related to inflammation or trauma. Our group has found no association between the appearance of MFS at presentation (well-defined vs. tail-like) and the pattern of recurrence, so it's important to watch out for tails regardless of the initial tumor presentation.

In summary, the key to early detection of recurrent MFS is
  1. Know that you're dealing with MFS (look at the path report, and know that some pathologists may still call these "myxoid MFH").
  2. Be aware of propensity for tail-like recurrence.
  3. Make sure to compare to multiple studies dating back to post-operative baseline to increase sensitivity for detection of these slowly growing lesions.

References

Daniels C , Wang WL , Madewell JE, Wei W, Amini B. Pattern of Recurrence of Myxofibrosarcoma is not Associated with Pattern at Presentation or Rate of Delayed Diagnosis. Iran J Radiol. 2017 ;14(1):e13469.

Monday, December 11, 2017

Pleomorphic adenoma

Magnetic resonance imaging (MRI) of parotid pleomorphic adenoma. T1- and T2-weighted and post-contrast sequences

Pleomorphic adenoma (also known as benign mixed tumor) is the most common tumor of the major salivary glands, and the most common benign tumor of the parotid glands (~75% of all benign salivary gland tumors). Prior head and neck irradiation is a risk factor. They are typically solitary, slowly growing, and asymptomatic. They are typically diagnosed after palpation by the patient or incidentally on imaging studies. Surgical resection is advised due to risk of malignant transformation.

On MRI, pleomorphic adenomas, have polylobulated margins a rim of low T2 signal corresponding to a fibrous capsule. They have heterogeneous low-to-intermediate signal intensity on T1-weighted images. High T2 signal and avid, solid enhancement are considered relatively specific features, especially when present in a younger patient (< 57 years). Dynamic contrast-enhanced (DCE) MRI shows gradual enhancement. On diffusion-weighted imaging (DWI), pleomorphic adenomas tend to have very high ADC values; however, DWI is not able to differentiate between benign and malignant parotid gland tumors.

On ultrasound, pleomorphic adenomas are typically hypoechogenic. They can have mild to moderate uptake on FDG PET.

Differential considerations include:
  • Warthin tumor: 10–15% are bilateral. Can have proteinaceous cystic components with high T1 signal ranging from a few millimeters to 1–2 cm. Solid components have rapid enhancement and washout.
  • Adenoid cystic carcinoma: Small, low-grade lesions can be mistaken for pleomorphic adenomas. Variable signal intensity on T2-weighted depending on type. Low-grade tumors have high T2 signal in the solid parts. Large tumors can have cystic areas of hemorrhagic necrosis.
  • Myoepithelial adenoma: Also tend to have very high ADC values
  • Basal cell adenoma: More commonly in the superficial lobe of the parotid gland. Tend to be round and well-circumscribed tumors. Have heterogeneous enhancement on CT.
  • Carcinoma in pre-existing pleomorphic adenoma (carcinoma ex pleomorphic adenoma): Typically less well-circumscribed than benign pleomorphic adenoma. Tends to occur after 10–15 years of an existing pleomorphic adenoma, with sudden rapid growth (3–6 months) in patients in the sixth-to-eighth decades of life.
  • Lymphoma: Tend to be multiple. Can have well-defined and lobulated margins. Tend to have low T2 signal and slight enhancement.
  • Sarcoid: Can be placed in any differential, including this one.

References

Monday, December 4, 2017

Osseous Pseudoprogression after Spine Stereotactic Radiosurgery

Osseous Pseudoprogression after Spine Stereotactis Radiosurgery

One of the issues we run into when assessing response to radiation therapy is pseudoprogression: Enlargement of the area of abnormality that is not truly progression. This phenomenon is best known in brain lesions following gamma knife therapy, but has also been seen in lung lesions after stereotactic body radiotherapy (SBRT).

In the spine, we can see pseudoprogression after spine stereotactic radiosurgery (SSRS) in bone lesions (osseous pseudoprogression, or OPP), as well as in the epidural soft-tissue components of bone lesions.

The take-away messages are:
  • We have so far only seen OPP after single-fraction SSRS. This is likely due to the higher biological dose of single-fraction therapy.
  • If you see an enlarging bone lesion on MRI performed within 3-6 months after single-fraction SSRS, you can't be confident that it represents true progression, because about 1/3 of these enlarging bone lesions will represent OPP.
  • The only finding on conventional MRI that has been shown to be associated with OPP is tumor growth confined to the 80% iso-dose line and the slope of enlargement (earlier time to tumor enlargement).

References

Sunday, July 9, 2017

Hemochromatosis: Hand Manifestations

X-ray of hand in hemochromatosis
50-year-old man with subtle manifestations of hemochromatosis arthropathy. Note narrowing of the metacarpophalangeal (MCP) joints, more advanced at the index and middle fingers. Other features of hemochromatosis arthropathy are not present, specifically, there is no subchondral cyst formation, hook-like osteophytes, osteoporosis, or chondrocalcinosis and the radiocarpal articulation is unaffected.

Hemochromatosis: General
  • Autosomal recessive disorder
  • Several genes implicated
  • Body has mechanism for dealing with low Fe (increased intestinal absorption), but no effective way of dealing with excess Fe
  • Fe accumulates in organs
  • Damage via Fe2+ -> Fe3+ -> Oxidation -> Free radicals


Arthropathy
  • Present in 50% of patients when rigorous criteria are used to define arthritis
  • Males affected earlier and more severely
  • Associated with use of joint
  • Typically a chronic process
  • Acute episodes of inflammatory arthritis may occur: May be associated with recovery of CPPD crystals from joint fluid aspiration.
  • Rare syndrome of septicemia accompanied by monoarticular or oligoarticular septic arthritis caused by Yersinia species described: Prosthetic joints seem especially susceptible to this infection.


Pathophysiology
  • Hemosiderin found in superficial synovial lining cells and macrophages (phagocytosis of iron loaded synoviocytes)
  • Very little iron detected in deeper synovial layers, and only occasionally in macrophages.
  • Arthropathy generally non-inflammatory. Chronic inflammatory cell infiltrate rarely seen.
  • Minimal to no iron deposition in cartilage.
  • Chondrocalcinosis a frequent finding
  • No close spatial relationship between iron and CPPD crystals, and crystals can be found even in the absence of iron deposits.


Imaging Features
  • Overlap with those of idiopathic OA and CPPD
  • Joint space narrowing
  • Subchondral sclerosis
  • Subchondral cysts
  • Osteophyte formation (hook-like osteophytes can be seen)
  • Chondrocalcinosis in articular and non-articular cartilage
  • Osteoporosis


The deal with chondrocalcinosis
  • Fe2+ (but not Fe3+) inhibits pyrophosphatase
  • Leads to diminished hydrolyzation of inorganic pyrophosphate
  • Contributes to precipitation of inorganic pyrophosphate with calcium.

References

  • Dallos T, Sahinbegovic E, Aigner E, Axmann R, Schöniger-Hekele M, Karonitsch T, Stamm T, Farkas M, Karger T, Cavallaro A, Stölzel U, Keysser G, Datz C, Schett G, Manger B, Zwerina J. Validation of a radiographic scoring system for haemochromatosis arthropathy. Ann Rheum Dis. 2010 Dec;69(12):2145-51.
  • Frenzen K, Schäfer C, Keyßer G. Asymmetrical hemochromatosis arthropathy in a patient with a history of poliomyelitis. Rheumatol Int. 2012 Apr;32(4):1045-7.
  • van Vulpen LF, Roosendaal G, van Asbeck BS, Mastbergen SC, Lafeber FP, Schutgens RE. The detrimental effects of iron on the joint: a comparison between haemochromatosis and haemophilia. J Clin Pathol. 2015 Aug;68(8):592-600.

Sunday, July 2, 2017

Chordoma Drop Metastases

MRI of spine with chordoma drop metastasis

Chordoma drop metastases are extremely rare, with ~11 reported cases. Of these, 1 was present at the time of initial presentation and 3 were only seen at autopsy. The naturally slow growth of chordomas, lack of symptoms in several cases, and late age of onset may mask true incidence of intradural drop metastases.

The imaging features are nonspecific and tend to mirror those of the primary neoplasm.

References

Martin MP, Olson S. Intradural drop metastasis of a clival chordoma. J Clin Neurosci. 2009 Aug;16(8):1105-7.