The Disappearing Act
The AXR was read by both the emergency physician and radiologist as normal. There was no radiological evidence of intestinal obstruction; until we put the ultrasound probe on the patient’s tender abdomen. These were what we saw, the bowel in short and long axis.
The small bowel was fluid filled and dilated (>2.5cm). There was no peristaltic activity noted at the bedside (but remember that akinesis can only be confirmed after 5 mins of continuous observation – a luxury not found in the Emergency Department).
Two worrisome features striked us though, suggesting that this was not a simple IO: the bowel wall was thickened (>3mm, yellow arrow) and there was fluid adjacent to the oedematous bowel wall (red arrow). These are suggestive of strangulation.
An urgent CTAP was performed and confirmed the diagnosis of strangulated small bowel, and the patient was sent to the theatre. The culprit was an adhesion band in the RIF, causing closed loop obstruction. Around 100cm of the bowel was already gangrenous and had to be resected. The patient stayed in the SICU for 4 days and eventually was discharged home on the 12th post op day.
Why doesn’t the IO show up on AXR?
The reason is simple: one can only see bowel obstruction on plain film if it is distended by gas. If the bowel is distended by fluid (as is in this case), it looks like and blends in with its surrounding soft tissue, and “disappears”.
Fluid, on the other hand, is easily recognized using ultrasound. In fact, when you can see entire circumference of the bowel wall in short axis, or both the near and far walls in long axis, you know that there is no air in that lumen of the bowel.
Ultrasound can pick up fluid filled intestinal obstruction missed by AXR. If you suspect an IO in a patient with normal AXR, sound the patient.
The reasoning for doing point of care ultrasound (POCUS) for a patient with suspected IO is the same as ordering an AXR. Whichever is better to make the same diagnosis depends only on what distends the lumen.
As much as AXR does not replace CT, neither does POCUS
Features suggestive of strangulation in IO includes the following:
Increased wall thickness (>3mm)
Adjacent free fluid
Don’t waste time looking for an akinetic loop – it takes >5 mins.
Ogata M, Mateer JR, Condon RE. Prospective evaluation of abdominal sonography for the diagnosis of bowel obstruction. Ann Surg. 1996 Mar;223(3):237-41.
Dr. Toh Hong Chuen
Acute and Emergency Care Centre, Khoo Teck Puat Hospital. Singapore