When free air is not under the diaphragm

A 52-year-old woman presented to the emergency department with 3 days of abdominal pain. The pain began 1 day after undergoing a screening colonoscopy. On examination, her vital signs were normal and she had significant tenderness to the lower abdomen. Laboratory work revealed a white count of 22 K/µL and a normal lactate (0.8 mmol/L). An upright chest and abdominal x-ray were normal. Computed tomography (CT) of the abdomen with intravenous (IV) contrast was then performed.

Intestinal perforation is a potentially life-threatening complication that may arise from diverse etiologies, including instrumentation.^1-4 The initial step in workup of suspected intestinal perforation is often looking for free air under the diaphragm on an upright abdominal x-ray to evaluate for pneumoperitoneum.¹ We would not see this finding in our patient because she had pneumoretroperitoneum, where the gas pattern is different from that of pneumoperitoneum.⁵ Ultimately, CT scan showed retroperitoneal air tracking along the aorta and inferior vena cava (IVC) (Figures 1 and 2). She underwent exploratory laparotomy with creation of a diverting end descending colostomy.

Colonoscopy-related perforation (CRP) is rare; the incidence ranges from 0.016% to 0.2% following diagnostic procedures and up to 5%, if the colonoscopy is therapeutic.^2-4 Rectal perforations, as in this case, have been reported to have an incidence ranging from 0.003% to 0.01%.^{2, 6} CRP can be managed conservatively or surgically. It is important to note that up to 31% of patients with CRP present for treatment more than 24 h after their colonoscopy.^{3, 4}