DIAGNOSIS: MALIGNANT SOLITARY FIBROUS TUMOR
The solitary fibrous tumor was first described as a pleural lesion but has subsequently been reported in numerous extrathoracic sites. Meningeal examples have been reported but are rare (1,2,4,5). Extrathoracic malignant solitary fibrous tumors are extremely rare and have not been reported previously intracranially. Anaplastic features including areas of increased cellularity, necrosis, nuclear atypia, and greater than 4 mitoses/10 high power fields are felt to be associated with aggressive behavior (6) although the collective experience is limited.
The differential diagnosis includes hemangiopericytoma, anaplastic meningioma and malignant fibrous histiocytoma. As with any poorly differentiated tumor, cell lineage must be extensively investigated using immunohistochemistry and electron microscopy. CD34 immunostaining is helpful in distinguishing solitary fibrous tumors from other considerations. Solitary fibrous tumors display diffuse strong CD34 expression in contrast with other entities in the differential where CD34 staining is mostly limited to the vascular bed (3).
In follow-up 2 months after surgery, the patient's dementia had improved markedly. She was completely oriented, although short-term memory was still impaired. She was independent in daily activities. CT scans showed no residual tumor. Cerebral angiography at 3 months postoperatively remarkably showed near complete spontaneous thrombosis of the right carotid-ophthalmic aneurysm. Adjuvant radiotherapy was given. At the time of submission, 10 months postoperatively, she continues to do well with only mild occasional headaches.
Contributed by J Barron MD, SP Lownie MD, DH Lee MD, and RR Hammond MD