Introduction
Pseudo-obstruction is a disorder characterised by dilatation of the colon due to an adynamic bowel, in the absence of mechanical obstruction.
The disorder most commonly affects the caecum and ascending colon, however can affect the whole of the large colon.
Whilst it is a rare condition, it is more common in older patients, especially in the context of multiple risk factors. In acute cases, it can also known as Ogilvie syndrome.
In this article, we shall look at the clinical features, investigations and management of pseudo-obstruction.
Pathophysiology
The exact mechanism is unknown, yet it is thought to be due to an interruption of the autonomic nervous supply to the colon resulting in the absence of smooth muscle action in the bowel wall.
As with mechanical obstruction, untreated cases can result in an increasing colonic diameter, leading to an increased risk of bowel ischaemia and bowel perforation.
There are a variety of causes of pseudo-obstruction, including:
- Electrolyte imbalanceor endocrine disorders, such as hypercalcaemia, hypothyroidism, or hypomagnesaemia
- Medication, including opioids, calcium channel blockers, or anti-depressants
- Recent surgery, severe systemic illness, or trauma
- Neurological disease, including Parkinson’s disease or Multiple Sclerosis
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)
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.
Key Points
- Pseudo-obstruction is a disorder characterised by acute dilatation of the colon in the absence of a mechanical obstruction
- There are multiple causes, including electrolyte imbalances, medication, or neurological conditions
- Diagnosis is made via CT imaging and endoscopic assessment
- Management includes treatment of the underlying cause and endoscopic decompression in non-responding cases
- Surgical intervention should be reserved for those with bowel ischaemia, bowel perforation, or recurrent or non-responding cases