A Case of Pleomorphic Adenoma of the Submandibular Gland Radiologically Suspected to be Malignant

Pleomorphic adenoma (PA) is the most common benign salivary gland tumor, typically arising from the parotid gland. PA of the submandibular gland is relatively uncommon and may present diagnostic challenges, particularly when imaging findings raise suspicion of malignancy. A 66-year-old woman presented with a painless mass in the left submandibular region. Imaging studies including unenhanced computed tomography (CT), magnetic resonance imaging (MRI), ultrasonography (US), and positron emission tomography (PET) revealed a lobulated mass with irregular margins, heterogeneous internal architecture, and partially disrupted capsular structures. PET showed abnormal fluorodeoxyglucose (FDG) accumulation with a maximum standardized uptake value (SUVmax) of 3.70. Based on these findings, malignancies such as adenoid cystic carcinoma or carcinoma ex pleomorphic adenoma (CXPA) were strongly suspected. The tumor was resected under general anesthesia with careful preservation of the capsule and excised en bloc together with the submandibular gland and a portion of the sublingual gland. Histopathological and immunohistochemical analyses revealed no evidence of malignancy, and a final diagnosis of PA was made. This case highlights the diagnostic difficulty of submandibular PA, especially when capsular structures appear ambiguous on imaging. It underscores the limitations of relying solely on imaging modalities and reaffirms the importance of integrating clinical history, imaging, and pathological findings to achieve accurate diagnosis.