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Neuroradiology Case of the Week

Case 181

Samuel Madoff, MD, and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: The patient is a 39-year-old male presenting status post assault with loss of consciousness.

Radiological Findings: There is an expansile, predominantly sclerotic lesion involving the left frontal bone and greater wing of the sphenoid (Figs 1 & 2).

Diagnosis: Fibrous dysplasia

Discussion: Fibrous dysplasia is a benign, metaplastic process which replaces normal bone with abnormal, moderately dense fibrous tissue containing immature, erratically distributed bony trabeculae. Of the two types, in the monostotic form (ie. involves a single bone) the typical locations are the femur (neck), tibia and ribs. In contrast, the polyostotic type (>1 bone involved) is considered to be more aggressive, often unilateral and usually involves the pelvis, long bones, skull and ribs. Approximately 10% of cases are craniofacial. In the compact anatomy of the head, the expansile nature of fibrous dysplasia may result in a variety of symptoms/signs via mass effect, such as proptosis due to orbital encroachment. Commonly, however, fibrous dysplasia is identified incidentally. Complications of either form include pathologic fracture or, very rarely, sarcomatous transformation.
     Associated disorders include McCune-Albright Syndrome (an endocrinopathy in females with café au lait spots), Mazabraud Syndrome (polyostotic fibrous dysplasia and soft-tissue myxomas) or Cherubism (multiple jaw lesions which give a rounded appearance to the face and typically regress in adulthood).
     Imaging findings on plain films or CT reveal an expansile lesion of varied qualities. If the lesion has a high osseous content, then it appears dense and sclerotic. Contrastingly, if it has a high fibrous content then it looks lytic with a classically described “ground glass” or “smoky” matrix. On MRI, findings are again variable. It is usually hypointense on T1 and may range from hypo- to hyperintense on T2. The “rind sign” is a low signal sclerotic rim seen on either T1 or T2. Scintigraphy demonstrates increased activity in 90% of cases, with the remainder undetected.

References:

1. Brant W. & Helms C. Fundamentals of Diagnostic Radiology. 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 1999: 962-964.
2. Greenspan A. Orthopedic Imaging: A Practical Approach. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 2004: 630-643.