Pseudo-Obstruction

Clinical Features

Patients with pseudo-obstruction will present with abdominal distension, abdominal pain, and absolute constipation. Vomiting is often a late clinical feature, due to the distal location of the colon in the alimentary tract.

There may be a concurrent illness present that may have triggered the episode, such a severe infection or electrolyte derangement.

On examination, the abdomen will be distended and tympanic, with absent bowel sounds. Whilst patients may have a generalised mild tenderness, any signs of peritonism may suggest developing bowel ischaemia

 Differential Diagnosis

In patients with suspected pseudo-obstruction, the main differential to consider is a mechanical large bowel obstruction, such as from an obstructing colorectal cancer or diverticular stricture. Other differentials include a toxic megacolon or paralytic ileus (of the small bowel).

Investigations

Patients with a suspected pseudo-obstruction should have routine blood tests performed, including full blood count, urea & electrolytes, Ca²⁺ and Mg²⁺, and thyroid function tests

The diagnosis can be confirmed via CT scan of abdomen pelvis with intravenous contrast. In pseudo-obstruction, often the entire colon is dilated, with no obvious narrowing or transition point evident (i.e. no mechanical obstruction). Any radiological evidence of bowel ischaemia can also be assessed for

Whilst less sensitive, plain film abdominal radiographs (AXR) can be performed, which will show evidence of bowel distension. However, as AXR cannot distinguish between a pseudo-obstruction and a mechanical obstruction, their use in aiding definitive diagnosis is limited.

In unclear cases, between pseudo-obstruction and a mechanical obstruction, endoscopic assessment (i.e. flexible sigmoidoscopy) may be required for direct visualisation and concurrent bowel decompression for symptomatic relief (see Management)

By Milliways / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Figure 1
CT imaging demonstrating an acute pseudo-obstruction

Management

Patients with confirmed pseudo-obstruction are often intravascularly fluid deplete therefore need aggressive fluid resuscitation.

Ensure a nasogastric tube is placed, especially if the patient is vomiting, and a urinary catheter is inserted for fluid balance assessment. Adequate analgesia should be prescribed and ensure any electrolyte abnormalities are corrected.

Conservative Management

In cases that do not resolve within 24-48 despite correcting any known underlying cause hours (or those with features suggestive of developing ischaemia), decompression by flexible sigmoidoscopy and insertion of a flatus tube is required.

If there is limited resolution, use of intravenous neostigmine (an anticholinesterase) may also be trialled if suitable. This must be done in a high-dependency monitored setting, due to its side effect of severe bradycardia (amongst other side effects)

Surgical Management

Emergency surgery is required for patients with pseudo-obstruction in those with any evidence of bowel ischaemia or perforation (or recurrent or non-responding cases).

Given the entire large bowel is involved in pseudo-obstruction, this invariably may involve a laparotomy and subtotal colectomy being performed.

Less commonly, to simply decompress the bowel in recurrent or non-responding cases, a caecostomy or defunctioning ileostomy (if incompetent ileocaecal valve) may be formed.