Schwannoma-Like Pleomorphic Adenoma: A Case Report with Review of the Literature

Abstract

Pleomorphic adenoma is a common benign salivary gland tumor, which represents about 66 % of benign neoplasms of the salivary glands. Although it can occur in any salivary gland, it is most frequently found in the parotid. Pleomorphic adenomas are renowned for their cytomorphological and architectural heterogeneity that are characterized by intermixed epithelial and mesenchymal-like components. We report a rare case of pleomorphic adenoma of the parotid gland with prevalent schwannoma-like features mimicking a benign schwannoma. Microscopically the tumor showed a prevalence (about 95 %) of schwannoma-like areas with focal (about 5 %) epithelial component with tubular organization. The tumor showed positive immunoexpression for cytokeratin, S-100 protein, and focal expression of p63, CD10 and smooth muscle actin. To the best of our knowledge only six cases of schwannoma-like pleomorphic adenoma have been reported in the literature. The differential diagnosis between this entity and neurogenic and myogenic tumors is discussed.

Divergent Schwannoma-Like Phenotype in a Pleomorphic Adenoma

“…Further, this ambiguity is extended histopathologically when PAs show a divergent schwannoma-like phenotype as demonstrated in our case and previous reports [4][5][6][7][8]. Examples of epithelioid schwannomas of the parotid gland diagnosed as PAs have also been reported [31].…”

“…S100, a marker that is most useful in the diagnosis of a schwannoma finds no application in its differentiation from a schwannoma-like PA because S100 also stains myoepithelial cells [11,14]. Unlike previous two studies [7,8], AE1/AE3 pankeratin was not used in this case. A study by Fanburg-Smith et al showed that although 22 peripheral schwannomas examined were negative for AE1/AE3 pankeratin, 72/104 (69%) cases of retroperintoneal schwannomas were positive for AE1/AE3 [15].…”

“…Five other cases were asymptomatic. This information was available in two cases [6,8]. Imaging studies were available in three cases including our case.…”

“…This information was not available in four cases. Schwannomatous areas with nuclear palisading were predominant in five cases [4,7,8…”

“…The overall impression was of Antoni type A tissue as in a schwannoma (Figs. 7,8,11). Limited amount of Antoni type B-like tissue mixed with fibrofatty connective tissue was also seen (Fig.…”