Duodenal diverticulum metastasis from pulmonary squamous cell carcinoma diagnosed by EUS-FNA

A 76-year-old male with pulmonary squamous cell carcinoma achieved complete response by chemoradiotherapy and subsequent systemic chemotherapy. During follow-up, fluorodeoxyglucose positron emission tomography/computed tomography showed strong fluorodeoxyglucose accumulation near the duodenal papilla. Elevated lesions were observed in the duodenal diverticulum upon lateral-viewing endoscopy, and a curved linear array echoendoscope showed a hypoechoic mass. Since it was difficult to obtain adequate tissue samples by endoscopic biopsy, endoscopic ultrasound-guided fine needle aspiration was performed for the hypoechoic mass. The pathological findings were squamous cell carcinoma, which was similar to the past histology of primary lung cancer. These findings indicated the diagnosis of duodenal diverticulum metastasis from pulmonary squamous cell carcinoma. Duodenal metastasis of pulmonary squamous cell carcinoma is a rare disease, and there have been no reports of duodenal diverticulum metastasis.