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WHO Classification of Tumours
Schwannoma, NOS
Adrenal gland


Definition

Schwannoma is a benign nerve sheath tumour that is typically encapsulated and composed entirely of well-differentiated neoplastic Schwann cells. The vast majority of schwannomas follow a benign clinical course (WHO grade I)
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Louis DN, Ohgaki H, Wiestler OD, Cavenee WK (Eds.)
WHO Classification of Tumours of the Central Nervous System.
4th Edition
International Agency for Research on Cancer: Lyon 2007



. Multiple schwannomas are associated with neurofibromatosis type II (NF2) or schwannomatosis .

Histological variants:

> Cellular schwannoma
This variant is hypercellular, composed exclusively or predominantly of Antoni A tissue and devoid of well-formed Verocay bodies. The most common location is at paravertebral sites in the pelvis, retroperitoneum and mediastinum. Cranial nerves, especially the fifth and eighth, may be also affected

Click for details
Louis DN, Ohgaki H, Wiestler OD, Cavenee WK (Eds.)
WHO Classification of Tumours of the Central Nervous System.
4th Edition
International Agency for Research on Cancer: Lyon 2007



.

> Plexiform schwannoma
This schwannoma grows in a plexiform or multinodular manner and can be of either conventional or cellular type. The vast majority arise in skin or subcutaneous tissue of an extremity, head and neck, or trunk. Cranial and spinal nerves are usually spared. There is a low association with schwannomatosis and NF2 , but not NF1.

> Melanotic schwannoma
This is a rare, circumscribed but unencapsulated, grossly pigmented tumour, composed of cells having the ultrastructure and immunophenotype of Schwann cells that contain melanosomes and are reactive for melanoma markers. Cytologic atypia is not uncommon. The vast majority of non-psammomatous tumours affect spinal nerves and paraspinal ganglia, whereas the psammomatous lesions also involve autonomic nerves of viscera, such as the intestinal tract and heart. Cranial nerves may also be affected.
Approximately 50% of patients with psammomatous melanotic schwannoma have the rare inherited autosomal-dominant disorder Carney complex type I (CNC) .