Part of the TeachMe Series

Pseudo-Obstruction

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Original Author(s): Ryan Cohen
Last updated: November 24, 2019
Revisions: 6

Original Author(s): Ryan Cohen
Last updated: November 24, 2019
Revisions: 6

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Pseudo-obstruction, also known as Ogilvie syndrome in the acute setting, 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 bowel. It is a rare condition, yet is most common in the elderly.

In this article, we shall look at the causes, key clinical features, investigations and management of acute colonic 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 toxic megacolon, bowel ischaemia, and perforation.

There are a variety of causes of pseudo-obstruction, including:

  • Electrolyte imbalance or endocrine disorders
    • Including hypercalcaemia, hypothyroidism, or hypomagnesaemia
  • Medication
    • Including opioids, calcium channel blockers, or anti-depressants
  • Recent surgery, severe illness, or trauma
    • Includes cardiac ischaemia
  • Neurological disease
    • Includes Parkinson’s disease, Multiple Sclerosis, and Hirschsprung’s disease
By Blausen gallery 2014 [CC BY 3.0] and OpenStax College [CC BY 3.0], via Wikimedia Commons

Figure 1 – (A) the anatomy of the large bowel (B) the macroscopic features of the large intestine

Clinical Features

Most patient’s will present with the clinical features of mechanical bowel obstruction:

  • Abdominal pain
  • Abdominal distension
  • Constipation
    • Due to an adynamic bowel, whilst not passing ‘normal’ stool, often patients may have paradoxical diarrhoea
  • Vomiting
    • Typically a late feature due to the colon being most distal in the GI tract

On examination, the abdomen will be distended and tympanic; whilst often soft and non-tender, the presence of focal abdominal tenderness* should be assessed.

*Focal tenderness indicates ischaemia and is a key warning sign; patients with bowel obstruction may be uncomfortable on palpation due to the discomfort from pressing on a distended abdomen, but there should be no focal tenderness, guarding, or rebound tenderness unless ischaemia is developing

 Differential Diagnosis

  • Mechanical obstruction
  • Paralytic ileus
  • Toxic megacolon

Investigations

A wide range of initial blood tests should be performed to assess for biocehmical or endocrine causes of pseudo-obstruction, including U&Es, Ca2+, Mg2+, and TFTs

Plain abdominal films (AXR) will show bowel distension, however this will be much the same as mechanical obstruction, hence has limited use in definitive diagnosis of the condition.

Patients presenting with features of pseudo-obstruction should undergo an abdominal-pelvis CT scan with IV contrast (Fig. 2). This will show dilatation of the colon, as well as definitively excluding a mechanical obstruction and assessing for any complications (e.g. perforation).

Motility studies will often be required in the long-term and potential biopsy of the colon at colonoscopy.

Figure 2 – Coronal view from a CT abdomen-pelvis scan, demonstrating acute pseudo-obstruction

Management

Most cases can be managed conservatively and do not require surgical intervention. Treatment of the underlying cause will be required, where applicable.

Patients should be made nil-by-mouth and started on intravenous fluids, with a fluid balance chart started; if the patient is vomiting, an nasogastric tube should be inserted to aid decompression*.

In most cases of pseudo-obstruction that do not resolve within 24-48 hours, endoscopic decompression will be the mainstay of treatment. This involves the insertion of a flatus tube and allowing the region to decompress. If there is limited resolution, use of intravenous neostigmine (an anticholinesterase) may also be trialled if suitable.

Patient should be reviewed regularly to assess the condition’s progression. Nutritional support should be considered early in these patients, particularly if recurrent, as this may lead to weight loss and malnutrition.

*As pseudo-obstruction affects the distal part of the GI tract, vomiting is a late-stage of the disease progression hence may not always be warranted

Surgical Management

In the absence of perforation or ischaemia, non-responding cases may require segmental resection +/- anastomosis, however unless all the affected areas are removed, this will not be curative.

Alternative procedures can also be performed to decompress the bowel in the long-term, such as caecostomy or ileostomy.

Key Points

  • Pseudo-obstruction is a disorder characterised by acute dilatation of the colon in the absence of a mechanical obstruction
  • Causes include electrolyte imbalance, medication, and trauma
  • It is important to differentiate from mechanical bowel obstruction, most often warranting CT imaging
  • Management includes supportive measures, selective use of neostigmine and endoscopic decompression
  • Surgical decompression should be reserved for patients with peritonitis or perforation and for those failing endoscopic and medical therapy