Brain Pathology Case of the Month - June 2001

DIAGNOSIS:    MALIGNANT SOLITARY FIBROUS TUMOR

DISCUSSION

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.

References

1. Carneiro SS, Scheithauer BW, Nascimento AG, Hirose T, Davis DH (1996) Solitary fibrous tumor of the meninges; a lesion distinct from fibrous meningioma. Amer J Clin Pathol 106: 217-224.
2. Challa VR, Kilpatrick SE, Ricci P, Wilson JA, Kelly DL (1998) Solitary fibrous tumor of the meninges. Clin Neuropathol 17 (2):73-8.
3. Perry A, Scheithauer B, Nascimento A (1997) The immunophenotypic spectrum of meningeal heamangiopericytoma: a comparison with fibrous meningioma and solitary fibrous tumor of meninges. Am J Surg Pathol 21(11): 1354-1360.
4. Prayson RA, McMahon J, Barnett G (1997) Solitary fibrous tumor of the meninges. J Neurosurg 86:1049-1052.
5. Slavik T, Bentley RC, Gray L, McLendon RE (1998) Solitary fibrous tumor of the meninges occurring after irradiation of a mixed germ cell tumor of the pineal gland. Clin Neuropathol 17(1):55-60.
6. Vallat-Decouvelaere AV, Dry SM, Fletcher CD (1998) Atypical and malignant solitary fibrous tumors in extrathoracic locations. Amer J Surg Pathol. 22:1502-1511.

Acknowledgments

Dr. Ken Berean, Vancouver General Hospital, for his clinical expertise.
Laurel Hammond and Kris Milne, UWO, for assistance preparing the report and graphics.

Contributed by J Barron MD, SP Lownie MD, DH Lee MD, and RR Hammond MD

International Society of Neuropathology