Pathology of Epithelioid Schwannoma - A rare variant of Nerve Sheath Tumour [Infographic]

In 1981 Taxy et al described first two cases of epithelioid schwannoma.

The clinical, gross, and light microscopic features of two epithelioid tumours were not typical of either benign or malignant schwannoma.

Electron microscopic features were indicative of benign Schwann cell tumours.

In 1985 Frank et al described electron microscopic features of Schwann cells in epithelioid schwannoma.

It was first reported as cutaneous epithelioid schwannoma by Kindblom et al in 1998.

The tumors are predominantly dermal/subcutaneous in location and involve the lower limb, upper limb, trunk and head/neck.

These tumors may cause diagnostic errors due to their increased cellularity and epithelioid morphology.

Typical histologic features of classic schwannoma such as Antoni A and B areas, Verocay bodies, and hyalinized vessels are either absent or only present in focal areas.

Strong and diffuse S-100 protein expression is seen in both benign and malignant counterparts of epithelioid schwannoma.

Type IV collagen encircle individual cells in the tumour, indicating a continuous basal lamina. HMB-45 is negative.

The findings that are suggestive of the benign nature of the lesion are long-term clinical history, small size, superficial localization, encapsulation, bland morphology, lack of mitosis and necrosis, and a benign clinical course after complete excision.

Pathologists should be aware of the epithelioid variant of schwannoma to avoid false diagnosis of malignancy.

Differential diagnosis include epithelioid variant of malignant peripheral nerve sheath tumour, myopericytoma, leiomyoma, benign fibrous histiocytoma, cellular blue naevus, cellular neurothekeoma, palisaded encapsulated neuroma.

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