Benign Epithelioid Schwannoma

Abstract

Benign schwannoma (neurilemoma) has various morphologic patterns that may cause problems in differential diagnosis. Although an epithelioid variant of malignant schwannoma simulating carcinoma and melanoma is well recognized, a benign counterpart has not yet been defined. In the current study, we describe five cases of benign epithelioid schwannoma that were in the subcutis (four cases) and the neck of the urinary bladder (one case). The tumors occurred in adults 28-73 years of age, were 1-4.5 cm in diameter, were well circumscribed and cellular, and were composed of epithelioid cells arranged in cords and nests. The benign nature of the lesions was evident by a constellation of features, including small size, sharp circumscription, bland morphology, low proliferative activity (four of five had < or =1% Ki67 immunostaining), and a benign clinical course after either marginal or intralesional excision. All cases had some features of classic schwannoma light microscopically and a high degree of Schwann cell differentiation both ultrastructurally and immunohistochemically. The recognition of benign epithelioid schwannoma is important because it may be misinterpreted as a malignant neuroectodermal, mesenchymal, epithelioid, or melanocytic tumor.

Epithelioid schwannoma or ossifying fibromyxoid tumour?

“…The similarities in morphological and immunohistochemical features may result in confusion of the two tumours (Kindblom et al, 1998;Miettinen et al, 2008;Laskin et al, 2005). In OFMTs, the presence of a peripheral ossification rim, the uniform appearance of the cells and the absence of a peripheral nerve section are indicative findings in differential diagnosis (Kindblom et al, 1998). In addition to epithelioid schwannoma, other tumour types should be considered in differential diagnosis, including malignant peripheral nerve sheath tumours, osteosarcoma, myoepithelioma and extraskeletal myxoid chondrosarcoma (Miettinen et al, 2008).…”

“…Although there is no clear information on the origin of OFMT, some researchers suggest that these tumours are neural in origin on the basis of having similar morphological and immunohistochemical characteristics to neural tumours (Kindblom et al, 1998;Saad et al, 2005). In this sense, the cases defined as epithelioid schwannoma can be seen as having an intermediate morphology that falls between classic schwannoma and OFMT (Kindblom et al, 1998).…”

“…In this sense, the cases defined as epithelioid schwannoma can be seen as having an intermediate morphology that falls between classic schwannoma and OFMT (Kindblom et al, 1998).…”

“…Both epithelioid schwannoma and ossifying fibromyxoid tumour (OFMT) have recently been defined as two different entities, often confused with each other due to their similar morphological and immunohistochemical features (Kindblom et al, 1998). While epithelioid schwannoma can be described as a benign nerve sheath tumour of peripheral nerves, OFMT is considered to be a intermediate (borderline) malignant soft tissue tumour.…”

“…While epithelioid schwannoma can be described as a benign nerve sheath tumour of peripheral nerves, OFMT is considered to be a intermediate (borderline) malignant soft tissue tumour. There are differing opinions regarding the origin of the tumour (Kindblom et al, 1998;Miettinen et al, 2008).…”