Mediastinal Teratoma With Somatic-Type Adenocarcinoma: An Enigmatic Discovery by Fine Needle Aspiration Cytology

Mediastinal masses often present acutely as medical emergencies, necessitating prompt and accurate diagnosis. Imaging-guided fine needle aspiration cytology (FNAC) plays a pivotal role in rapidly identifying rare mediastinal tumours and differentiating them from other potential aetiologies, enabling timely intervention. Primary mediastinal germ cell tumours (PMGCTs) constitute approximately 15% of adult mediastinal neoplasms. The development of somatic-type malignancies, particularly colonic-type adenocarcinoma, in PMGCTs is rare and typically associated with a poor prognosis. Combining cytological findings with imaging, serum tumour marker analysis and immunohistochemistry can facilitate the detection of various germ cell components and aid in diagnosing GCTs. We report the case of a 35-year-old male presenting with symptoms of mediastinal compression. Contrast-enhanced computed tomography (CECT) revealed an ill-defined anterior mediastinal lesion measuring 9.2 cm in maximum dimension with a heterogeneous appearance. Emergency ultrasound-guided FNAC was performed, yielding highly cellular smears that showed malignant epithelial cell clusters with intracytoplasmic and extracellular mucin, as well as strips and clusters of benign intestinal epithelial cells. Based on the cytomorphological features, the patient's age and imaging findings, a diagnosis of somatic-type adenocarcinoma arising in a background of teratoma was suggested. Histopathological examination of the excised mass confirmed the cytological diagnosis. Adenocarcinoma in the mediastinum may arise from primary sites such as the aerodigestive tract or represent metastatic disease. However, in this case, the presence of a benign intestinal epithelial component strongly indicated a teratomatous origin. This report underscores the utility of imaging-guided FNAC as a minimally invasive and effective diagnostic tool, enabling early diagnosis and timely treatment initiation in patients presenting with acute mediastinal obstruction.