Acute Small Bowel Obstruction as the First Manifestation of Occult Lung Adenocarcinoma: A Case Report of Jejunal Metastasis.

BACKGROUND Small bowel metastasis from lung adenocarcinoma is a rare clinical entity that may present as an acute abdominal emergency before the primary tumor is diagnosed. Its nonspecific presentation and diagnostic difficulty often delay recognition until surgical exploration. This report describes the case of a 51-year-old man presenting with acute small bowel obstruction due to jejunal metastasis of occult lung adenocarcinoma. CASE REPORT We report the case of a 51-year-old heavy smoker who presented with acute abdominal pain, vomiting, and small bowel obstruction without respiratory symptoms. Computed tomography revealed a jejunal mass causing intestinal obstruction. Emergency segmental jejunal resection with primary jejunojejunal anastomosis was performed. Histopathological examination demonstrated metastatic adenocarcinoma. Immunohistochemical analysis showed positivity for thyroid transcription factor-1 (TTF-1), cytokeratin 7 (CK7), and napsin A, with negative staining for cytokeratin 20 (CK20) and caudal-type homeobox transcription factor 2 (CDX2), confirming a pulmonary origin. Postoperative chest computed tomography revealed an occult necrotic lung mass with mediastinal lymphadenopathy. Despite systemic chemotherapy, the patient experienced rapid disease progression with vertebral and cerebral metastases. CONCLUSIONS Acute small bowel obstruction may rarely represent the initial manifestation of occult lung adenocarcinoma. This case highlights the pivotal role of histopathology and immunohistochemistry in identifying the primary tumor and emphasizes that metastatic lung adenocarcinoma should be considered in the differential diagnosis of unexplained bowel obstruction in high-risk patients to facilitate timely diagnosis and appropriate oncologic management.