Infarcted Warthin tumor with mucoepidermoid carcinoma-like metaplasia: a case report and review of the literature

Abstract

BackgroundWarthin tumor is a common, benign, painless salivary gland neoplasm. Rarely, Warthin tumors show large areas of squamous metaplasia; such Warthin tumors are called metaplastic or infarcted Warthin tumors because they are occasionally accompanied with tumor necrosis. The histological distinction between mucoepidermoid carcinomas and the metaplastic portions of Warthin tumors can be challenging; without a genetic study, mucoepidermoid carcinomas can be misdiagnosed as metaplastic Warthin tumors. We report a case of infarcted Warthin tumor partly showing mucoepidermoid carcinoma-like epithelial metaplasia. Only two cases of infarcted Warthin tumor similar to our case have been reported.Case presentationA 69-year-old Japanese man presented with a right parotid tumor. He had noticed the swelling on his right buccal region 1 year previously; the lesion had rapidly enlarged, with associated pain, 1 month previously. A radiological examination revealed a mass in the tail of the right parotid gland. Superficial parotidectomy was performed. On histological examination, the mass showed typical focal features of Warthin tumor; other areas showed coagulation necrosis of the tumor. These areas were surrounded by non-oncocytic epithelium comprising squamous and mucinous epithelial cells. Although cellular atypia of the non-oncocytic epithelium was not observed, a mixture of squamous and mucinous cells and lack of abundant lymphoid tissue mimicked low-grade mucoepidermoid carcinoma. Based on the results of fluorescence in situ hybridization, MAML2 gene rearrangement was not present in the typical portions of Warthin tumor and the mucoepidermoid carcinoma-like lesion. Therefore, a metaplastic or infarcted Warthin tumor was diagnosed. Our patient was disease-free 8 months after surgery.ConclusionsClinicians need to know that pain is a clinical symptom of infarcted/metaplastic Warthin tumor. Pathologists should be aware that a metaplastic Warthin tumor can mimic a low-grade mucoepidermoid carcinoma. Our case showed a mucoepidermoid carcinoma-like lesion that was confined near the area of tumor necrosis, and neither cytological atypia nor apparent invasive growth was present. These findings appeared to be histological clues of a metaplastic Warthin tumor rather than a mucoepidermoid carcinoma. Careful clinicopathological evaluation as well as genetic studies are needed to clarify the distinction between mucoepidermoid carcinoma and metaplastic portions of Warthin tumors.

MAML2 rearrangement as a useful diagnostic marker discriminating between Warthin tumour and Warthin-like mucoepidermoid carcinoma

“…Nevertheless, another study detected split signals indicative for MAML2 rearrangement in squamous epithelium in two cases of WT with squamous metaplasia, without any accompanying abnormalities in the oncocytic epithelium, lymphocytes and mucinous metaplasia [29]. Recently, Yorita et al described a case of Warthin tumour with a MEC-like component, in which the lack of MAML2 rearrangement led to the diagnosis of infarcted WT with metaplastic changes [3]. In contrast, mucoepidermoid carcinoma may potentially develop from WT as postulated by Bell et al [46].…”

“…Metaplastic cells may be atypical and grow in pseudoinfiltrative pattern suggestive for malignancy. Perplexingly, mucoid metaplasia may occur as well, which may easily lead to misdiagnosis of MEC [3]. However, metaplastic changes in WT are usually focal and admixed with necrosis, haemorrhages and fibrosis associated with prior biopsy [11].…”

“…Conventional WT is characterized by a dense lymphoid stroma and cystic spaces lined by bilayer oncocytic epithelium forming papillary projections. Its metaplastic or infarcted variants display coagulative necrosis, fibrosis, and inflammation along with squamous or mucinous metaplasia, but with no cytological atypia or invasive growth pattern [3]; an association with prior biopsy of the tumour has been postulated [4]. In contrast, WT-like mucoepidermoid carcinoma exhibits atypical bilayer oncocytic epithelium with no "typical" bilayer epithelium of WT along with the presence of dense lymphoid stroma and squamoid or goblet-like cells.…”

Cytopathology and diagnostics of Warthin's tumour

“…The most common type is that in which the epithelium and lymphoid stroma ratio is approximately equal, stroma‐poor type where the epithelial component is above 70%, stroma‐rich type with the lymphoid stromal component above 70% and metaplastic type. In this metaplastic type or variant, the classic oncocytic epithelium and the lymphomatous stroma are partially replaced by squamous metaplasia and haemorrhagic and necrotising areas are also present …”

“…In such a WT type, residual classical WT can be found pointing to the original WT lesion. It is considered that this appearance could reflect pre‐operative FNA …”