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