Figure 6. Small bowel intussusception caused by metastatic leiomyosarcoma. A 42-year-old man with malignant leiomyosarcoma of the left atrium, which had been partially resected 3 months earlier. He was admitted with abdominal pain and weight loss. (a) CT of the chest shows a round hypodense lesion in the left atrium (arrowheads), representing the residual leiomyosarcoma. (b) CT of the abdomen shows a hypodense area in the centre of a small bowel loop in the left abdomen (white arrow), characteristic of invaginated mesenteric fat. The proximal bowel loops are dilated, some with an air–fluid level. Orally administered contrast medium is seen in the colon (open arrows) as evidence of only partial small bowel obstruction.