Rapidly destructive articular disease

Rapidly destructive articular disease refers to the rapidly progressive osteoarthritis and destruction of the hip, typically seen in elderly women. The disease is almost always unilateral, but bilateral hip and concomitant shoulder involvement have also been reported.

Destruction of the hip is usually seen an average of 14 months after the onset of symptoms; however, no significant osteonecrosis, inflammatory change, bacteria or crystals are seen on histological evaluation.

Radiographs reveal progressive loss of joint space and subchondral bone. Eventually, there is flattening and deformity of the femoral head and superolateral subluxation of the femoral head. Mild sclerotic changes may be seen; however, there is minimal or absent osteophytosis.

Differential considerations include

• Osteonecrosis
• Septic arthritis
• Neuroarthropathy
• Crystal-induced arthropathies

References

Llauger J, Palmer J, Rosón N, Bagué S, Camins A, Cremades R. Nonseptic monoarthritis: imaging features with clinical and histopathologic correlation. Radiographics. 2000; 20 Spec No:S263-278.

Milwaukee Shoulder

Milwaukee shoulder is the combination of

• Complete tear of the rotator cuff
• Osteoarthritic changes
• Noninflammatory joint effusion with calcium hydroxyapatite and calcium pyrophosphate dihydrate crystals
• Synovial hyperplasia
• Destruction of cartilage and subchondral bone
• Multiple osteochondral loose bodies

It typically affects older women with a history of trauma who present with rapidly progressive, destructive arthritis of the shoulder.

Imaging studies reveal joint space narrowing, subchondral sclerosis with cyst formation, destruction of subchondral bone, soft-tissue swelling, capsular calcifications, and intraarticular loose bodies. Calcium pyrophosphate dihydrate crystal deposition of the knees is also commonly seen.

The process is also known as cuff arthropathy in the orthopedic literature, where the etiology is thought to be chronic rotator cuff tear that results in upward migration of the humeral head and subsequent changes in the humeral head and inferior surface of the acromion.

References

• McCarty DJ, Halverson PB, Carrera GF, et al. "Milwaukee shoulder": association of microspheroids containing hydroxyapatite crystals, active collagenase, and neutral protease with rotator cuff defects. Arthritis Rheum 1981; 24:464-473.
• Llauger J, Palmer J, Rosón N, Bagué S, Camins A, Cremades R. Nonseptic monoarthritis: imaging features with clinical and histopathologic correlation. Radiographics. 2000; 20 Spec No:S263-278.

Takotsubo Cardiomyopathy

Takotsubo cardiomyopathy (TC), also known as stress cardiomyopathy and broken-heart syndrome, is a rare, reversible cardiomyopathy that is seen in conditions of extreme emotion or medical stress. It is characteristically seen in elderly or postmenopausal women and can mimic acute coronary artery syndrome.

There is reversible left akinesis of the apical and distal anterior wall together with hypercontraction of the basal wall in the absence of angiographically significant coronary artery narrowing. The shape of the heart apparently resembles that of a "takotsubo," a Japanese pot used in trapping octopus. How much pot one has to smoke for this resemblance to appear is currently unknown, but under intense investigation.

It is thought that the apex is disproportionately vulnerable due to any or all of the following:

• Lack of a 3-layered myocardial configuration
• Limited elasticity reserve
• Relatively limited coronary circulation
• Increased responsivity to adrenergic stimulation

Cardiac MRI has been used to evaluate these patients. T2-weighted sequences have shown edema in the majority of patients in the acute setting. At least one group found a statistically significant relationship between the amount of edema and the severity of regional systolic dysfunction. Delayed gadolinium enhancement is not typically seen in the acute setting; however, there are reports of minute foci of delayed enhancement in a minority of cases, and presence of delayed enhancement should not exclude TC. Apical thrombi have also been reported in a minority of cases (either by MRI or echocardiography).

References

• Virani SS, et al. Takotsubo Cardiomyopathy, or Broken-Heart Syndrome. Tex Heart Inst J. 2007; 34(1): 76–79.
• Leurent G, Larralde A, Boulmier D, Fougerou C, Langella B, Ollivier R, Bedossa M, Le Breton H. Cardiac MRI studies of transient left ventricular apical ballooning syndrome (takotsubo cardiomyopathy): a systematic review. Int J Cardiol. 2009 Jun 26;135(2):146-9.

Silastic Arthropathy

Silastic arthropathy is caused by reaction to silicone particles from silastic arthroplasty and manifests as erosion and osteolysis. Silastic arthroplasty is performed in the small joints of the hands and feet, with the first metatarsophalangeal joint being the most common site of surgery, and the most commonly affected by silastic arthropathy.

References

Gentili A. Silastic Arthropathy.

Ulnar Capping

Ulnar capping refers to productive bone changes that may be seen at the ulnar stylus in a minority of patients with long-term rheumatoid arthritis (RA). It is the exception to the rule that productive changes are not seen in RA.

References

Manaster BJ, Disler DG, May DA, Sartoris DJ. Musculoskeletal Imaging, The requisites. Second Edition. pp106-107.

Chronic Infantile Neurologic, Cutaneous, and Articular Syndrome

Chronic infantile neurologic, cutaneous, and articular (CINCA) syndrome, also known as neonatal-onset multisystem inflammatory disease (NOMID), is a rare inflammatory disease characterized by a persistent migratory skin rash, articular symptoms, and chronic aseptic meningitis. There are recurrent episodes of fever and inflammation.

References

OMIM.

Dysplasia Epiphysealis Hemimelica

Dysplasia epiphysealis hemimelica (DEH), also known as Trevor-Fairbank disease or Trevor disease, refers to an osteochondroma arising from an epiphysis or sesamoid, tarsal or carpal bone. It is thought that there is abnormal cartilage proliferation with associated enchondral ossification.

Dysplasia epiphysealis hemimelica is almost always seen in the lower extremity. Upper extremity involvement has been reported, but is thought to be extremely rare. "Hemimelia" refers to the tendency of dysplasia epiphysealis hemimelica to involve either the medial (more common) or lateral aspect of the ossification center of a single extremity. Bilateral involvement has been reported, but is thought to be extremely rare.

Dysplasia epiphysealis hemimelica may is classified into

• Localized type: Affects a single bone.
• Classic type: 2/3 of cases. Affects more than one area in a single lower extremity.
• Generalized (severe) type: An entire lower limb is involved.

Dysplasia epiphysealis hemimelica presents between the ages of 2 and 14 years, and is three times more common in boys. The most common sites are the distal femur > proximal tibia > talus > tarsal navicular > first cuneiform.

Radiolographs and CT reveal a single or multiple irregular mass(es) with focal ossification arising from one side of the affected epiphysis or sesamoid bone. These lesions enlarge with skeletal growth and may ossify and become confluent with the underlying bone.

Dysplasia epiphysealis hemimelica may result in the following:

• Joint deformity
• Premature closure of the physis with deformity and limb length discrepancy
• Early secondary osteoarthritis from articular surface irregularity
• Undertubulation of bone from secondary involvement of the metaphysis

Differential Diagnosis

• Myositis ossificans
• Infection
• Chronic infantile neurologic, cutaneous, and articular (CINCA) syndrome
• Tumoral calcinosis
• Synovial osteochondromatosis
• Vascular calcifications
• Parasitic calcifications

References

Araujo CR, et al. Best Cases from the AFIP: Dysplasia Epiphysealis Hemimelica of the Patella. RadioGraphics 2006 26:581-586.

Reverse Shoulder Arthroplasty

The reverse shoulder prosthesis, also known as the Grammont prosthesis, reverses normal shoulder anatomy. Instead of reproducing the normal anatomy of the humeral head as ball and glenoid fossa as cup, the reverse shoulder arthroplasty replaces the humeral head with a cup and the glenoid fossa with a ball. This design moves the center of rotation of the shoulder joint distal and medial compared with the anatomic center of rotation. This improves the leverage of the deltoid muscle and allows it to compensate for deficient rotator cuff musculature and provide an increased range of motion.

References

Roberts CC, et al. Radiologic Assessment of Reverse Shoulder Arthroplasty. RadioGraphics 2007 27:223-235.

Primary Synovial Chondromatosis

Primary synovial chondromatosis is a benign neoplastic process that typically affects adult men in their 20s to 40s, with the knee being the most commonly affected site. It is characterized by hyaline cartilage nodules of variable calcification in the subsynovial tissue of a joint, tendon sheath, or bursa, which may break off from the synovial surface into the joint.

Radiographs and CT reveal multiple intraarticular chondral bodies and extrinsic, well-marginated erosion of bone on both sides of the joint. The chondral bodies are usually of similar size and demonstrate variable calcification, ranging from tiny speckles to large, round, and lamellated. MRI findings are variable due to the variable calcification of these chondral bodies. However, erosions are seen in 80% of patients on MR. Post-contrast imaging reveals hyperplastic, enhancing synovium.

The extraarticular form typically affects the hands or feet, where there are calcifications in tendon sheaths or bursae with or without saucerization of adjacent bone.

Differential considerations include:

• Intraarticular or juxtacortical chondroma
• Synovial chondrosarcoma
• Pigmented villonodular synovitis
• Secondary synovial osteochondromatosis

References

Murphey MD, et al. From the Archives of the AFIP: Imaging of Synovial Chondromatosis with Radiologic-Pathologic Correlation. RadioGraphics 2007 27:1465-1488.

Schatzker Classification of Tibial Plateau Fractures

The Schatzker classification divides tibial plateau fractures into six types:

Type (%)	Definition	Associated injuries
I (6%)	Lateral plateau fracture without displacement and with less than 4 mm of depression1	May be associated with a distraction-type injury to the medial collateral ligament or anterior cruciate ligament
II (25%)	Lateral plateau fracture with greater than 4 mm of depression	20% of patients have associated distraction injuries to the medial collateral ligament or medial meniscus
IIIA	Compression fracture of the lateral plateau
IIIB	Compression fracture of the central aspect of the tibial plateau	May result in joint instability
IV (10%)	Medial plateau fracture with a split or depressed component	Worst prognosis. Increased likelihood of injury to the peroneal nerve or popliteal vessels. Frequently associated with distraction injury to the lateral compartment2
V (3%)	Bicondylar plateau fracture (wedge fractures of the medial and lateral tibial plateau	Articular depression typically seen in lateral plateau. May see associated fracture of the intercondylar eminence. 50% have peripheral meniscal detachment. 30% have anterior cruciate ligament avulsion injury. Status of soft tissues dictates management.
VI (20%)	Transverse subcondylar fracture with dissociation of the metaphysis from the diaphysis	30% are open. There is frequently extensive soft-tissue injury. Increased risk of compartment syndrome. Status of soft tissues dictates management.

¹ Lateral tibial plateau depression is measured as the vertical distance between the lowest point on the intact medial plateau and the lowest depressed lateral plateau fracture fragment
² e.g., lateral collateral ligament complex injury, posterolateral corner injury, or fracture or dislocation of proximal fibula

References

Markhardt BK, Gross JM, Monu J. Schatzker Classification of Tibial Plateau Fractures: Use of CT and MR Imaging Improves Assessment. RadioGraphics 2009 29:585-597.

Disseminated Pulmonary Ossification

Disseminated pulmonary ossification (DPO) refers to the formation of mature bone in the lung parenchyma. It is usually seen in men between 40 and 60 years of age, predominantly in the lower lobes.

DPO is usually seen in association with chronic heart or lung diseases and has been classified into nodular and branching types. Differential considerations include:

• mitral stenosis and other diseases that cause pulmonary venous hypertension: Most common association. Seen in 15-50% of these patients. The appearance is nodular.
• interstitial pulmonary fibrosis: May be seen in up to 9% of these patients.
• chemotherapy: e.g., busulfan
• hemodialysis
• acromegaly
• metastatic cancer

References

• Luschka H. Verastigte Knockenbildung im Parenchym der Lunge. VirchowsArch [PatholAnat] 1856;10:500-505.
• Gevenois PA, Abehsera M, Knoop C, Jacobovitz D, Estenne M. Disseminated pulmonary ossification in end-stage pulmonary fibrosis: CT demonstration. AJR Am J Roentgenol. 1994 Jun;162(6):1303-4.

Differential Diagnosis of Unilateral Tibial Bowing

Anterolateral bowing

• Neurofibromatosis type 1 (shown above): Can be unilateral. Fibula may or may not be hypoplastic.
• Congenital anterolateral tibial bowing and polydactyly (CATBP)

Anteromedial bowing

• Fibular hemimelia: Linked to the sonic hedge-hog gene. May also see skin dimpling over the tibia, equinovalgus foot, missing lateral toes, and tarsal coalition.

Posteromedial bowing

• Calcaneovalgus foot deformity: resolves with growth. Also associated with limb-length inequality and triceps surae weakness.

Lateral bowing

• Physiologic in infants
• Abnormalities of the medial physis: Fracture malunion, Blount disease, Turner syndrome, rickets, hypophosphatasia
• Fibrocartilaginous dysplasia At the site of pes anserinus tendon insertion.

Special thanks to Dr. James Dimaala for the case of anterolateral tibial bowing in a patient with neurofibromatosis type I.

Rasmussen Encephalitis

Rasmussen encephalitis (RE) is an inflammatory unilateral brain disorder with progressive tissue and function loss and epilepsy.

Patients (mainly, but not exclusively, children) pass through a prodromal period of minor signs and symptoms, followed by the acute stage, characterized by progressive decline of functions associated with the affected hemisphere (hemiparesis, hemianopia, cognitive deterioration and/or aphasia), as well as seizures. About 50% of patients experience epilepsia partialis continua: unilateral myoclonic twitching of the distal extremities or the face for at least 1 hour with intervals of no more than ten seconds. The patient passes into the residual phase of stable neurological deficit and decreased frequency of seizures after about 8 months.

Pathologically, there is infiltration of T lymphocytes. Cytotoxic T-cells are thought to lead to apoptosis of neurons and astrocytes.

Imaging shows progressive unilateral (usually precentral and inferior frontal) atrophy. CT and MRI are often initially normal, followed by findings of cortical swelling and then atrophy. FLAIR may show small areas of hyperintensity that increase over time. MR spectroscopy shows decreased NAA and choline and increased myoinositol and glutamine/glutamate.

Functional imaging (e.g., PET) may reveal decreased activity in the affected lobe(s) or hemisphere when MRI is normal. PET and SPECT may also show crossed cerebellar diaschisis.

Differential considerations include:

• Sturge-Weber syndrome: Also will see progressive hemispheric atrophy, but there may be cortical calcifications and enhancing of pial angiomas. Clinically, there is a port wine facial nevus.
• MELAS: Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes. Will see cortical atrophy in the chronic phase. Look for lacunar infarctions.
• Hemispheric infarction (Dyke-Davidoff-Masson): Will also have unilateral atrophy, but there may be compensatory calvarial thickening, elevation of the petrous ridge and hyperaeration of the paranasal sinuses.

References

Bien CG, Schramm J. Treatment of Rasmussen encephalitis half a century after its initial description: Promising prospects and a dilemma. Epilepsy Res. 2009 Jul 15.

Hemimegalencephaly

Hemimegalencephaly is the hamartomatous overgrowth of all or part of a cerebral hemisphere with defects of cellular organization and neuronal proliferation, migration, and organization. Hemimegalencephaly may be associated with pachygyria, polymicrogyria, heterotopia, and balloon cells.There is usually an inverse relationship between the size of the affected hemisphere and the severity of its malformation.

It has been suggested that hemimegalencephaly is a disorder of the entire brain that is more evident on one side.

Clinical Presentation and Classification

The classical triad is psychomotor retardation, contralateral motor deficit, and epilepsy. Prognosis depends on severity of epilepsy and associated neurological deficits.

Three clinical types have been described:

• Isolated form: The classic and most common type. Sporadic without evidence of cutaneous or systemic involvement
• Systemic form: Associated with partial or total hemigigantism and/or several neurocutaneous syndromes, including epidermal nevus syndrome (sporadic spectrum of disorders that includes linear sebaceous nevus syndrome and the Proteus syndrome)
• Total hemimegalencephaly: The least common form, in which there is involvement of the ipsilateral cerebellum and brainstem.

Imaging

MRI will show the obvious enlargement of one hemisphere, as well as disorders of cortical migration and development, such as agyria, pachygyria, micropolygyria, and lissencephaly. Because the treatment for seizures is hemispherectomy, it is important to also make note of any cortical abnormalities on the contralateral side, as hemispherectomy in such cases would likely not be effective.

MRA may show anomalies of vascular structures, including hypoplasia of the deep venous system, hypertrophy of the veins draining into the sagittal sinus, abnormal extension of the sylvian veins up to longitudinal superior sinus, and arterial hypervascularization of the affected hemisphere

Differential Diagnosis

• Disorders of neuronal migration
• Tuberous sclerosis
• Hemiatrophy
• Gliomatosis cerebri
• Unilateral cortical edema

References

Di Rocco C, Battaglia D, Pietrini D, Piastra M, Massimi L. Hemimegalencephaly: clinical implications and surgical treatment. Childs Nerv Syst. 2006 Aug;22(8):852-66.

Alexander Disease

Alexander disease is a rare, nonfamilial, leukoencephalopathy that is characterized by white matter abnormalities primarily in the frontal lobes.

Three clinical subtypes have been described:

• Neonatal: There is extremely rapid deterioration.
• Infantile: This is the most common. There is early onset macrocephaly and rapid deterioration.
• Adult: The least common and mildest subtype.

On CT, there is low attenuation within the frontal white matter, internal capsule, and caudate heads. There is intense enhancement in early disease in the periventricular rim, frontal lobe white matter, basal ganglia, thalami, brainstem (periaqueductal area), dentate nuclei, fornix, and optic chiasm. MRI shows white matter changes in the frontal white matter. The periventricular rim is high intensity on T1- and low intensity on T2-weighted images.

Colloid Cyst

Colloid cysts are benign, congenital, mucus-containing, epithelium-lined cysts that almost always arise in the anterior third ventricle in the region of the foramina of Monro. They present in the third or fourth decade. The most common symptom is heaache.

CT findings in the characteristic location are usually enough for diagnosis. The attenuation on CT depends on hydration state, but approximately 2/3 demonstrate high attenuation. On T1-weighted images, the signal correlates with cholesterol concentration in the cyst. 2/3 are hyperintense on T1. On T1-weighted images, the signal correlates with water concentration in the cyst. The majority are isointense to brain on T2-weighted images. No suppression or restriction is seen on FLAIR and DWI, respectively. Usually no enhancement is seen.

Atypical Findings

Less than 1% can be seen in the lateral or 4th ventricles, cerebellum, or extraxial space. They are rarely low attenuation. Hemorrhage, enhancement, and calcification are also uncommon findings. About 25% have mixed attenuation/signal. Fluid-fluid levels are also uncommonly seen.

Silent Sinus Syndrome

Silent sinus syndrome (SSS), also known as Maxillary atelectasis with enophthalmos and imploding antrum, is the painless (silent) involution of the maxillary sinus with associated enophthalmos due to gradual collapse of the orbital floor.

It is thought that SSS is caused by hypoventilation of the maxillary sinus due to obstruction of the ostiomeatal complex. The trapped gas is resorbed into capillaries, creating negative pressure. There is also accumulation of secretions and chronic inflammation, resulting in maxillary atelectasis and wall collapse.

Patients present with enophthalmos (2-5 mm). Diplopia and other ocular symptoms are uncommon, likely due to the gradual course of the disease.

CT findings include:

• Complete or near-complete unilateral obstruction of the maxillary sinus
• Obstruction of the ostiomeatal unit
• Lateral retraction of the uncinate process, resulting in relative enlargement of the middle meatus
• Nasal septal deviation
• A variable degree of retraction and collapse of all the walls of the maxillary sinus, manifested as concavity, resulting in inferior displacement of the globe and orbital contents into the maxillary sinus
• Demineralization of sinus walls
• Increased retroantral fat pad on the affected side

References

• Annino DJ Jr, Goguen LA. Silent sinus syndrome. Curr Opin Otolaryngol Head Neck Surg. 2008 Feb;16(1):22-5.
• Waqar S, Dhir L, Irvine F. Silent sinus syndrome: a cause of unexplained enophthalmos. Can J Ophthalmol. 2010 Oct 24;45(5):547-548.

Bizarre Parosteal Osteochondromatous Proliferation

25-year-old man with 2 years of progressively worsening pain at the small finger with recent loss of range of motion.  

Bizarre parosteal osteochondromatous proliferation (BPOP), also known as Nora lesion, is an osteochondromatous proliferation that arises from the periosteal aspect of an intact cortex. The lesion occurs most commonly in the hands and feet (proximal and middle phalanges, and metacarpals/metatarsals) of young adults. About 25% of cases occur in the long bones.

It is thought to be part of a spectrum of reactive changes in response to trauma, initially presenting as soft-tissue swelling.

The stage after soft-tissue swelling is florid reactive periostitis, where there is a laminated or mature periosteal reaction and often minimal periosteal elevation. There is juxtacortical soft tissue calcification, without disruption of the underlying cortex or medullary changes.

The next stage is BPOP, where there is a well-marginated mass of heterotopic mineralization arising from an intact cortex without periosteal reaction or medullary changes.

The final stage is acquired osteochondroma or turret exostosis, where the focus of ossification matures and a bony base is formed with a cartilage cap.

Histologically, BPOP is composed of variable amounts of cartilage (usually predominant), bone, and fibroblastic spindle cells and is similar to fracture callus. The cartilagenous component can have areas of ossification, and large immature chondrocytes can raise concern for malignancy. The rest of the lesion consists of trabeculae of woven bone mixed with fibroblastic spindle cells.

Differential Considerations

• Osteochondroma: There is continuity of the intramedullary cavity with the lesion in osteochondroma. BPOP, as described above, is not continuous with the medullary cavity. In addition, there is absence of the characteristic orientation away from the physis in BPOP.
• Myositis ossificans: There is ossification along the periphery of the lesion, which is located in the peripheral soft tissues.
• Parosteal osteosarcoma: There is cortical and soft-tissue infiltration and periosteal elevation, which are not seen in BPOP.

References

• Bush JB, Reith JD, Meyer MS. Bizarre parosteal osteochondromatous proliferation of the proximal humerus: case report. Skeletal Radiol. 2007 Jun;36(6):535-40.
• Dhondt E, et al. Nora's lesion, a distinct radiological entity? Skeletal Radiol. 2006 Jul;35(7):497-502.
• Hoch B, Montag A. Reactive bone lesions mimicking neoplasms. Semin Diagn Pathol. 2011 Feb;28(1):102-12.

Multiple Meningiomas

Meningiomas are multiple in up to 10% of imaged cases and up to 17% in autopsy series. However, the presence of multiple meningiomas in different neuraxial compartments is rare. In about 30% of cases, different histological types of meningioma are seen in the different lesions.

Cushing and Eisenhardt used the term "multiple meningiomas" to refer to the occurrence of multiple meningiomas in the absence of neurofibromatosis or vestibular schwannomas.

References

• Cushing H, Eisenhardt L. Meningiomas; their Classification, Regional Behaviour, Life History, and Surgical End Results. Springfield III., Charles C Thomas, 1938, 785.
• Bhatoe HS. Simultaneous occurrence of multiple meningiomas in different neuraxial compartments. Neurol India. 2003 Jun;51(2):263-5.

Scheuermann Disease

Scheurmann disease refers to vertebral wedging, end-plate irregularity, and disc height loss, with or without Schmorl nodes, classically resulting in thoracic (75%) kyphosis. The thoracolumbar (25%) and lumbar (5%) spine may also be involved. Cervical spine involvement is rare. It is seen in adolescents and young adults, found in 30% of boys and 20% of girls with back pain. 15% of patients also have scoliosis.

The criteria for the diagnosis of Scheuermann disease are:

• Greater than 5-degree wedging of at least three adjacent vertebrae at the apex of the kyphosis
• Irregular and narrowed endplates
• Thoracic kyphosis of greater than 45 degrees

References

Davies A, Saifuddin A. Imaging of painful scoliosis. Skeletal Radiol. 2009 Mar;38(3):207-23.

Differential Diagnosis of Painful Scoliosis in a Child

Scoliosis in adults often presents with pain. Idiopathic scoliosis in children, on the other hand, is often painless. When children present with painful scoliosis, especially if there is a left-sided curve, the following conditions should be considered:

• Vertebral tumours: osteoid osteoma, osteoblastoma, aneurysmal bone cyst, Langerhans cell histiocytosis
• Intraspinal tumours: neurofibroma; astrocytoma
• Infection: tuberculosis, discitis, osteomyelitis
• Scheuermann kyphosis
• Disc disease: disc herniation, Schmorl nodes
• Spondylolysis: spondylolisthesis
• Degenerative: facet joint arthritis, spinal stenosis, nerve root compression

References

• Taylor LJ, Painful scoliosis: a need for further investigation. Br Med J (Clin Res Ed). 1986 January 11; 292(6513): 120–122.
• Davies A, Saifuddin A. Imaging of painful scoliosis. Skeletal Radiol. 2009 Mar;38(3):207-23.

Double "Density" Sign on Bone Scan

The double "density" sign, more properly referred to as the double uptake sign, is the scintigraphic pattern on osteoid osteoma on bone scan. The more intense central uptake on blood-flow, blood-pool and delayed phases of the bone scan represents the nidus of the lesion, while the lower, peripheral uptake, represents activity in the surrounding sclerotic reactive bone. The main differential considerations on radiographs include osteomyelitis, which has a more uniform pattern of radiotracer uptake, and abscess, which has decreased activity in the central cavity.

Epiphyseal Lesions: Differential Diagnosis

• Giant cell tumor:
• Chondroblastoma:
• Langerhans cell histiocytosis:
  
  
• Subchondral cyst:
• Infection: Pediatric osteomyelitis
• Lymphoma:
• Metastasis:
• Osteoid osteoma: Rarely involves the epiphysis
• Clear cell chondrosarcoma: Rare

Tumor Margin Differential Diagnosis

• IA: Geographic with sclerotic border (non-aggressive, benign)
• IB: Geographic without sclerotic border (non-aggressive)
• IC: Geographic with wide zone of transition (Aggressive)
• II/III: Moth-eaten/permeative (Aggressive)

	IA	IB	IC	II/III
Brodie abscess	X
Benign Fibrous Histiocytoma of Bone	X
Non-ossifying fibroma	X
Osteoid osteoma	X
Chondroblastoma	X	X
Enchondroma (inactive)	X	X
Fibrous dysplasia	X	X
Aneurysmal bone cyst	X	X	X
Chondromyxoid fibroma	X	X	X
Giant cell tumor		X	X
Enchondroma (active)			X
Chondrosarcoma	LG		X
Langerhans cell histiocytosis	X		X	X
Myeloma/metastasis		X	X	X
Brown tumor			X	X
MFH/fibrosarcoma			X	X
Osteomyelitis			X	X
Osteosarcoma			X	X
Ewing				X
Round cell tumors				X
LG, low-grade

References

• Musculoskeletal Radiology: The Requisites, 3rd edition, p 408.
• AFIP 2009-2010 syllabus, pp 812-814.

Elastofibroma

Elastofibroma is a slowly growing reactive process that is thought to result from friction between the scapula and chest wall. The lesion arises from periosteal fibroblasts, and is found in up to 25% of autopsies in patients older than 55. On CT, however, elastofibromas are seen in only 2% of patients, a difference thought to result from the small size of lesions reported on the autopsy series. The majority are asymptomatic. The overwhelming majority (99%) occur between the chest wall and inferior scapular tip and up to 66% are bilateral.

On CT, elastofibroma appears as a poorly defined, crescent-shaped, heterogeneous soft tissue mass with that has the same attenuation as muscle and contains linear fat-attenuation streaks. On MRI, the lesion is isointense to skeletal muscle and contains streaks that are isointense to fat. Elastofibromas have also been reported to have homogeneous attenuation and signal intensity without visible foci of fat. Other atypical imaging features include bone destruction and intense contrast enhancement, and should prompt further investigation to exclude neoplasm (liposarcoma or metastatic disease, for example).

Reference

• Kransdorf MJ, Meis JM, Montgomery E. Elastofibroma: MR and CT appearance with radiologic-pathologic correlation. AJR Am J Roentgenol. 1992 Sep;159(3):575-9.
• Ochsner JE, Sewall SA, Brooks GN, Agni R. Best cases from the AFIP: Elastofibroma dorsi. Radiographics. 2006 Nov-Dec;26(6):1873-6.

Sacroiliitis: Differential Diagnosis

Conditions Associated with a Tethered Cord

The following conditions are associated with tethered cords

• Dorsal lipoma
• Tight filum terminale
• Diastematomyelia
• Myelomeningocele

Gorlin Syndrome

Gorlin Syndrome, also known as basal cell nevus syndrome, is characterized by multiple odontogenic keratocysts (OKC), prominent dural calcifications, and macrocephaly. Other findings include, hyperaerated paranasal sinuses, rib anomalies (splayed, fused, or bifid), kyphosis, platybasia, and Sprengel deformity of the scapula.

The image shows dural calcifications (blue arrow), at least one odontogenic keratocyst (pink arrow), a bifid left second rib (green arrow), and a Sprengel deformity of the left scapula (yellow arrow).

Fatty Intradural Tumors: DDx

Fatty intradural, extramedullary tumors

• Lipoma
• Lipomyelomeningocele
• Filum terminale fibrolipoma

Pseudomeningocele

Pseudomeningoceles are CSF-filled sacs contiguous with thecal sac, but not lined with meninges; they are lined by reactive fibrous tissue.

Pseudomeningoceles are post-traumatic and most commonly occur at the cervical spine, where flexibility predisposes to nerve root avulsion. Iatrogenic trauma can be caused by dural laceration with resultant CSF leak and formation of a fibrous pseudocapsule. Infants with Erb palsy can also demonstrate pseudomeningoceles.

Differential considerations include:

• Paraspinous abscess
• Post-operative hematoma
• Soft tissue tumor
• True meningocele
• Plexiform neurofibroma