Pleomorphic adenomas rarely form a giant cyst. In this report, we describe the case of 44-year-old man who had a pleomorphic adenoma of the submandibular gland with a giant cyst. Extraoral examination showed an elastic hard, movable mass measuring 45 × 27 mm in the left submandibular region. Magnetic resonance imaging revealed a mass with high intensity in the left submandibular region, associated with border irregularity and internal heterogeneity on both T1-weighted images and T2-weighted images. Enhanced computed tomography showed a low-density area in the mass. Fine-needle aspiration cytology was subsequently performed, but a tentative diagnosis was not obtained. We then planned to surgically resect the tumor according to the pathological diagnosis obtained on intraoperative frozen section analysis, performed with the patient under general anesthesia. Resection of the mass was planned if the lesion was benign, and resection with upper neck dissection was planned if the lesion was a malignant tumor. A pleomorphic adenoma was diagnosed on intraoperative frozen section analysis, and the tumor was surgically resected. Histopathological examination of the excised specimen finally showed a pleomorphic adenoma with hematoma in the cyst-like cavity.
