[Adenocarcinoma in the Lung Detected Due to the Development of Perforative Peritonitis Caused by Small Intestinal Metastasis-A Case Report].

: Previous studies have reported that perforations of the small intestine caused by metastatic tumors prior to the diagnosis of primary lung cancer are very rare. A 79-year-old man was admitted to our hospital with acute lower abdominal pain. Abdominal computed tomography revealed intraperitoneal free air around the bowel wall thickening in the small intestine. The patient was diagnosed with acute peritonitis caused by perforation of the small intestine, and an emergency operation was performed. Laparotomy revealed perforation in the jejunum without any palpable tumor in the abdomen. Partial resection of the jejunum revealed an ulcerating lesion at the perforation site. Histological examination indicated small intestinal metastasis secondary to lung adenocarcinoma. Positron emission tomography performed after discharge showed a small reticular opacity with intense accumulation of FDG in the left lung. The patient was diagnosed with perforation of the small intestine metastasis secondary to lung adenocarcinoma. The postoperative course was uneventful; the patient received chemotherapy, and is alive 6months after the operation.