Internal Herniation Through the Transverse Mesocolon Causing Small Bowel Obstruction: A Case Report.

Internal hernias are one of the rare causes of small bowel obstruction. Among them, transmesocolic hernias are particularly uncommon and pose a diagnostic challenge due to their non-specific clinical and radiological features. We report the case of a 68-year-old female with known metastatic invasive lobular carcinoma of the breast, who presented with right flank pain, nausea, and constipation. Imaging suggested small bowel obstruction without a clear etiology. Emergency laparotomy revealed a transmesocolic hernia with two jejunal loops herniated through a 6 cm × 3 cm mesocolic defect. The herniated bowel was viable and reduced, and the defect was repaired. No bowel resection was necessary. Transmesocolic hernias may be congenital or acquired. In this case, the defect was likely secondary to peritoneal carcinomatosis or mass effect from metastatic disease. Diagnosis is often delayed due to non-specific signs. Early surgical intervention is essential to prevent bowel ischemia and infarction. Transmesocolic hernia, though rare, should be considered in patients with small bowel obstruction and no prior surgical history, especially in the setting of peritoneal malignancy. High clinical suspicion and timely operative management are critical for favorable outcomes.