Spontaneous infarction of pleomorphic adenoma of the parotid gland: A case report.

Infarction after the fine-needle aspiration (FNA) procedure is a well-recognized phenomenon of salivary gland lesions. Though extremely rare, spontaneous infarction without previous FNA can occur in pleomorphic adenoma (PA). The present report describes a fourth cytological case of spontaneous infarction of PA of the parotid gland using immunocytochemical analysis, to the best of our knowledge, for the first time. A 57-year-old Japanese female presented with persistent swelling of the right neck region. Physical examination revealed a tumour in the right parotid gland, and FNA examination of the tumour was performed following surgical resection. The Papanicolaou smear demonstrated the presence of fully necrotic cell clusters of varying sizes in a necrotic background. Only a few viable cell clusters were observed. These cells were polygonal to spindle-shaped, and exhibited large round to oval nuclei with a conspicuous nucleoli. Although nuclear pleomorphism was noted, the nuclear chromatin was fine. No neoplastic myoepithelial cells were observed. Therefore, it was suspected that these cells were malignant. Immunocytochemical analysis indicated that these atypical cells were positive for p40. Histopathological examination of the resected parotid gland tumour revealed infarcted PA. Our study revealed that the presence of atypical squamous metaplastic cells in a necrotic background was a characteristic cytological feature of infarcted PA, and that these atypical squamous cells can have large nuclei with conspicuous nucleoli and exhibit pleomorphism. Although cytological diagnosis of infarcted PA is difficult, pathologists and cytopathologists must consider the presence of atypical metaplastic squamous cells in benign salivary gland tumours, including infarcted PA.