Neurilemmoma (benign Schwannoma)

Schwannomas are benign tumours of nerve sheath origin, most often occurring in subcutaneous tissue.

Histopathology

Classic benign Schwannoma are encapsulated. They show both Antoni A and Antoni B areas in varying proportions. Antoni A areas are cellular, composed of spindle cells with serpentine nuclei. The nuclei palisade to form Verocay bodies. Antoni B areas are composed of similar cells but are hypocellular with myxoid matrix. Within both components, there may be thick-walled hyalinised vessels.

Variants

• Ancient Schwannoma

• Cellular Schwannoma

• Plexiform Schwannoma

• Melanotic Schwannoma

• Epithelioid Schwannoma

• Hybrid Schwannoma/perineuroma

• Hybrid Schwannoma/neurofibroma

• Glandular Schwannoma

• Microcystic/reticular Schwannoma

• Gastrointestinal Schwannoma: unencapsulated with pushing margins; there is a discontinuous cuff of lymphocytes, sometimes forming germinal centres; Verocay bodies are usually absent.

Immunohistochemistry

• S-100; strongly positive, especially in Antoni A areas

• CD57 (Leu-7)

• GFAP

• Myelin basic protein has given variable results

The positivity for cytokeratins may be due to cross reactivity with GFAP.

Cytogenetics

Monosomy 22, eliminating one of the NF-2 alleles, has been reported in Schwannomas, neurofibromas and perineuromas¹.

Differential diagnosis

See the immunohistochemistry of the differential diagnosis of spindle cell tumours of the pleura.

• leiomyoma: may also be positive for S-100 and CD57. Desmin and SMA will be positive.

References

Diagnostic Immunohistochemistry edited by Professor D. J. Dabbs, page 72

¹ Hahn HP, Fletcher CDM. The role of cytogenetics and molecular genetics in soft tissue tumour diagnosis - a realistic approach. Current Diagnsotic Pathology 2005;11:361-370.

² Fanburg-Smith JC, Majidi M,Miettinen M. Keratin expression in schwannoma; a study of 115 retroperitoneal and 22 peripheral schwannomas. Mod Pathol 2006; 19:115-21

©SMUHT/PW Bishop