Pathology Quiz Case 3

A 59-YEAR-OLD MAN PRESENTED WITH A long history of a right parotid mass, which had gradually enlarged over the past 2 years. The lesion had initially been evaluated 8 years earlier, when the findings of fine-needle aspiration were suggestive of pleomorphic adenoma. Although surgical excision was offered, the patient declined. On presentation to our clinic, he reported no symptoms and denied pain, numbness, and facial weakness. He had no other medical problems, had quit smoking 20 years earlier, and denied alcohol use. The physical examination was notable for a palpable 4 3-cm mass at the tail of parotid gland, with elevation of the auricular lobule. The mass was mobile within the parotid gland and not attached to the overlying skin. Facial nerve function was intact, and there was no palpable cervical lymphadenopathy. Contrast-enhanced computed tomography revealed a 4.5 3.4 3.3-cm solidcystic, heterogeneous mass in the superficial aspect of the right parotid gland extending inferiorly into the tail (Figure 1). Extension into the stylomandibular tunnel indicated deep lobe involvement. No cervical adenopathy was seen. The patient underwent a near-total parotidectomy with facial nerve preservation. Intraoperatively, the superior component of the mass was delivered from the stylomastoid foramen without violation of the specimen. Histopathologic examination revealed a neoplasm that was composed of cytologically bland myoepithelial cells within a loose myxoid matrix (Figure 2). Centrally, there was a large area of dense hyalinized stroma (Figure 3) merging with benign myoepithelial cells (Figure 3, right), while adjacent areas of the tumor contained cohesive groups of glandular cells (Figure 3, upper left) with marked nuclear atypia and necrosis (Figure 4). The tumor was noninvasive (contained within the mixed tumor capsule) and well circumscribed. The patient underwent postoperative radiation therapy and 3 years later was still without evidence of disease. What is your diagnosis? Figure 1.