Neurofibromatosis 2 : Vestibular Schwannoma
Histologically, vestibular schwannomas seen in the setting of neurofibromatosis 2 (NF2) are similar to the sporadic lesions. The image shows Antoni A areas composed of interlacing bundles of spindle cells (Schwann cells) with wavy or oval nuclei, eosinophilic cytoplasm, and indistinct cytoplasmic borders. There is nuclear palisading with a hint of Verocay bodies. Molecular Genetics of NF2: NF2 results from inactivating germline mutations in the tumor suppressor gene NF2 on chromosome 22q12.2. About 50% of NF2 cases have de novo mutations. The type of mutations present (nonsense, missense, frameshift, or large deletions) affects the disease severity. NF2 codes for Merlin (also known as Schwannomin) – a 595 amino acid protein expressed in Schwann cells, meningeal cells, and eye lens. It belongs to moesin-ezrin-radixin family of cytoskeletal-associated proteins. Merlin interacts with several cytoskeletal proteins and cell membrane-associated signaling complexes. It appears to play an important role in contact-dependent inhibition of cellular proliferation. Prognosis: There is no risk of malignant transformation in schwannomas of NF2, however they cause significant morbidity due to their location in brain and spinal cord. Patients develop deafness, vision loss, imbalance and gait abnormalities, muscle weakness, paralysis, pain, and seizures.