A case of intracapsular carcinoma ex pleomorphic adenoma of the parapharyngeal space with cervical lymph node metastasis

Carcinoma ex pleomorphic adenoma is a rare aggressive malignant carcinoma developing in a pre-exisiting pleomorphic adenoma. Capsular invasion has an oppressive prognosis. On the other hand, intracapsular carcinoma ex pleomorphic adenoma is known to have a benign clinical behavior. We report a rare case of intracapsular carcinoma ex pleomorphic adenoma of a minor salivary gland in the parapharyngeal space revealed by prior cervical lymph node metastasis. A 35-year-old male presented with a month-long history of progressive enlargement of the left cervical mass. We performed a biopsy of the mass and the diagnosis of a metastatic adenocarcinoma of undetermined origin was made. To detect the primary tumor, several investigations were performed using various diagnostic modalities. We found a tumor in the left parapharyngeal space. But, unlike the metastatic cervical lymph node, this tumor showed neither FDG uptake nor enhancement on either CT or MRI. These imaging findings did not favor this tumor as the primary site. We were unable to confirm that the tumor in the parapharyngeal space was the primary carcinoma. We performed a left modified radical neck dissection, removal of the tumor in the parapharyngeal space and hemithyroidectomy of the left lobe. Histological examination revealed that the tumor in the parapharyngeal space was carcinoma ex pleomorphic adenoma. We diagnosed it as the primary carcinoma. Despite the absence of capsular invasion, this case featured high-grade malignancy with cervical lymph metastasis.