Atypical findings of small intestinal adenocarcinoma with mesenteric extension.

Primary small intestinal cancer is a rare malignancy, accounting for 0.1%-0.3% of all gastrointestinal cancers. Its nonspecific presentation often delays diagnosis and worsens prognosis. This case report presents a patient with small intestinal cancer exhibiting mesenteric invasion and atypical features. We emphasize that mesenteric invasion is a rare finding, and the achieved 5-year recurrence-free survival in a Stage ⅡB small intestinal adenocarcinoma represents an exceptionally favorable outcome. The patient was a 78-year-old female who was referred to our hospital with a chief complaint of anorexia, vomiting, and abdominal pain. A palpable lower abdominal mass and intestinal obstruction were identified. Detailed evaluation confirmed small intestinal cancer with mesenteric metastasis. Laparotomy revealed a mass located in the small intestinal mesentery, encircled by folded small intestine. The mass demonstrated strong adherence to both the sigmoid colon and bladder walls. Surgical resection was performed, including excision of the mass, partial sigmoid colon resection, and partial bladder resection. Histopathological analysis confirmed a neoplasm of the small intestine. The patient received postoperative adjuvant chemotherapy with FOLFOX and remains alive without recurrence 5 years postoperatively. Small intestinal adenocarcinoma with mesenteric invasion is a rare finding and may present with vague symptoms and mimic other pathologies. Early use of imaging and multidisciplinary management are crucial for achieving favorable outcomes.