From the Guidelines
Diagnosis of megacolon should be based on radiographic evidence of total or segmental colonic distention of > 6 cm, presence of systemic toxicity, and inflammatory or infectious etiology, as outlined in the WSES-AAST guidelines 1. The diagnostic approach to megacolon involves a combination of clinical evaluation, imaging studies, and laboratory tests.
- Clinical evaluation: begins with a thorough history and physical examination, looking for symptoms like severe constipation, abdominal distension, and decreased bowel movements.
- Imaging studies:
- Plain abdominal X-rays are typically the first imaging study, showing dilated colon segments with a diameter exceeding 6 cm in adults.
- Contrast studies such as barium enema may reveal the extent of colonic dilation and identify transition zones in cases of acquired megacolon.
- CT scans provide more detailed information about bowel wall thickness, surrounding structures, and potential complications.
- Laboratory tests:
- Complete blood count, electrolytes, and inflammatory markers help assess for complications like infection or metabolic disturbances.
- In cases where toxic megacolon is suspected, laboratory tests should be performed frequently to monitor for signs of deterioration, such as persistent fever after 48–72 h of steroid therapy 1. The diagnostic workup should be tailored to distinguish between different types of megacolon, including toxic megacolon, which is a rare but severe and potentially fatal complication of colonic inflammation 1.
- Key characteristics of toxic megacolon include radiographic evidence of colonic distention, presence of systemic toxicity, and inflammatory or infectious etiology 1.
- Management of toxic megacolon requires coordination between medical and surgical services, with aggressive attempts at medical therapy and early surgical intervention in the absence of improvement, development of complications, or deterioration 1.
From the Research
Diagnosis of Megacolon
The diagnosis of megacolon involves several key steps and considerations, as outlined in the following points:
- Megacolon is defined as cecal dilatation above 12 cm and above 6.5 cm of the sigmoid colon, measured at the pelvic brim 2.
- The initial tasks in diagnosing megacolon include excluding mechanical obstruction, discontinuing enabling medications, and correcting metabolic disturbances 2.
- A hypaque enema can be used to exclude mechanical obstruction 2.
- The rectum should be decompressed with an indwelling tube and tap water enemas 2.
- Intravenous neostigmine is generally effective and safe for patients with colonic distention unresponsive to conservative therapies 2, 3.
- Endoscopic decompression is necessary for patients who do not respond to, or relapse after neostigmine, or in whom neostigmine is contraindicated 2, 3.
- Signs of peritonitis may imply colonic perforation, and surgery will be needed, often on an emergent basis 2, 4.
Types of Megacolon
There are several types of megacolon, including:
- Acute megacolon (Ogilvie's syndrome), which is attributed to a sympathetically mediated reflex response to serious medical or surgical conditions in elderly patients 2, 3.
- Toxic megacolon, which is secondary to an identifiable inflammation of the colon 2, 3, 4.
- Chronic megacolon, which may be congenital (due to Hirschsprung's disease) or may represent the end-stage of any form of refractory constipation (slow transit constipation or pelvic floor dysfunction) 2, 3, 5.
Diagnostic Tools
Several diagnostic tools can be used to diagnose megacolon, including:
- Plain radiographs of the abdomen 4.
- Sigmoidoscopy 4.
- Rectal suction biopsy to detect hypertrophic nerve trunks and the absence of ganglion cells in the colonic submucosa, confirming the diagnosis of Hirschsprung's disease 5.
- Colonoscopy, which can be used to decompress the colon and treat nontoxic megacolon 6.