Fig. 1

A, B A 76-year-old female complained of abrupt onset of abdominal pain with progressive muscle guarding, which started on postoperative day 1 after lumbar decompression and posterior instrumentation at L4–5. A Supine lumbar lateral radiograph showed intra-abdominal free air without disruption upon examining the bowel gas pattern (black arrow). B Axial computed tomography (CT) revealed intraperitoneal free air and fluid in the right paracolic gutter (white arrow). C A 70-year-old male experienced sudden abdominal pain with abdomen distension, which started on postoperative day 3 after lumbar decompression and posterior instrumentation of L3-S1 Intra-abdominal free air and an air-fluid level were observed on the left lateral decubitus view (black arrow)