Musculoskeletal Imaging

Schwannoma

a tumour of the peripheral nerve sheath, sometimes also called neurilemmoma. Benign neurilemmomas rarely originate in bone, but when they do the manifestations include pain, swelling, impairment of sensory and motor function, and pathologic fractures. Mandible, sacrum, maxilla, femur, and humerus are the most favored sites of involvement. Three radiographic pictures are encountered:

  • central involvement with an osteolytic focus and sclerotic margin;

  • localization to the nutrient canal with formation of a dumbbell lesion; or

  • periosteal involvement leading to cortical erosion.

    Malignant schwannomas may occur alone or in association with neurofibromatosis. These tumours occur most commonly in the trunk and extremities, in the regions of distribution of the sciatic nerve and brachial and sacral plexuses.

    On MR imaging the tumours appear as inhomogeneous masses, usually of low signal intensity on T1-weighted spin-echo images (but of higher intensity than the cerebrospinal fluid), and of high signal intensity on T2-weighted images (but of lower intensity than cerebrospinal fluid). This imaging technique has replaced CT scanning and myelography for diagnosis.

    DR