A Diagnostic Dilemma of Esophageal Duplication Cyst in a Patient With Rectal Cancer: A Case Report.

Mediastinal masses include a diverse group of entities arising from the different structures within or close to the mediastinum. We report a 60-year-old female with a history of rectal bleeding who was diagnosed with rectal cancer. During the staging computed tomography scan, a round hypodense mass was seen in the left upper lobe region in close contact with the superior mediastinum, with differential diagnoses of metastatic lesions and duplication cysts. In order to clarify the nature of the referred lesion, an ultrasonography-guided fine-needle aspiration was performed, and the cytology was negative for malignancy. The patient underwent posterolateral thoracotomy, and pathologic evaluation of the resected mass showed epithelial squamous cells and smooth muscle layers in the cyst wall compatible with esophageal duplication cyst (EDC). Our study aimed to alert physicians to take EDCs into account for the differential diagnosis of mediastinal masses. A comprehensive understanding of the clinical characteristics, diagnostic techniques, and therapeutic options of duplication cysts is crucial for early detection and appropriate management in the adult population.