Fluoro-2-Deoxyglucose (FDG)-Avid Adenoid Cystic Carcinoma of the Larynx: A Rare Case and Diagnostic Insight Obtained Using Positron Emission Tomography/Computed Tomography (PET/CT) Imaging.

Adenoid cystic carcinoma (ACC) is a relatively uncommon tumor among head and neck cancers, with laryngeal involvement, typically subglottic, being exceptionally rare. While ACC usually originates in the salivary glands, its occurrence in the larynx is highly unusual. Laryngeal adenoid cystic carcinoma (LACC) is characterized by indolent growth, frequent perineural invasion, and a tendency for local recurrence. Moreover, distant metastasis can occur with the lungs being the most common site of metastasis. We present a case of a 28-year-old male patient with a progressively enlarging right neck mass, uncovering a rare case of infiltrative LACC invading the thyroid gland. Post thyroidectomy, the 18-fluoro-2-deoxyglucose (F-18-FDG)-positron emission tomography (PET)/computed tomography (CT) scan revealed FDG-avid right posterior subglottic residual disease with invasion into adjacent structures, including the trachea. This represents one of the few documented cases of FDG-avid LACC, contributing to the sparse literature on this rare and aggressive malignancy. This case highlights the diagnostic challenge and clinical significance of FDG-PET/CT in evaluating rare and aggressive malignancies like LACC.