High-grade mucoepidermoid carcinoma ex metastasizing pleomorphic adenomas in the parotid gland and parapharyngeal space: a case report

초록

Pleomorphic adenoma (PA) is the most common benign neoplasm of the salivary glands. Its three malignant variants include carcinoma ex PA (carcinoma in preexisting PA), carcinosarcoma, and metastasizing pleomorphic adenoma (MPA). Among the subtypes of carcinoma ex PA, high-grade mucoepidermoid carcinoma (MEC) has rarely been reported. Meanwhile, MPA is rare. We report the imaging findings of a high-grade MEC ex MPA of the parotid gland and parapharyngeal space in a 42-year-old man. The patient had previously undergone neck surgery for a benign lipoma. Contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) revealed a well-defined mass measuring 3.2 × 2.6 cm with heterogeneous enhancement in the left parapharyngeal space. There were multiple small ovoid to round heterogeneously enhancing nodules in the left parapharyngeal space, contiguous with the deep lobe of the parotid gland, infraparotid area, and left neck levels IB, and II. The largest mass in the left parapharyngeal space exhibited an inhomogeneous intermediate to high signal intensity on T2-weighted images, with nonenhancing central portion suggesting cystic change. The other nodules also expressed similar signal intensities, including variable degrees of cystic changes. On diffusion-weighted imaging, the largest mass in the left parapharyngeal space expressed central high- and peripheral low- signal intensities on apparent diffusion coefficient (ADC) mapping images, suggesting central necrosis and hypercellular components, respectively. Other nodal mass and nodules in left level IB-II with cystic changes also exhibited foci of low signal ntensities on ADC mapping images. Considering the intermediate T2 signal intensities and diffusion restriction areas and multiple satellite nodules, carcinoma ex PA with metastases, and multiple co-existing intraparotid PAs was suggested. The patient then underwent subtotal tumor resection surgery using