Megacolon. The term megacolon describes both congenital and acquired forms of colon dilation. In all younger patients with megacolon, the possibility of Hirschsprung disease should be excluded. Hirschsprung disease manifests in the first years of life caused by absence of parasympathetic ganglion cells in myenteric (Auerbach) and submucosal (Meissner) plexuses in the rectum. The absence of ganglion cells results in constipation and bowel obstruction.
■ Clinical Picture
Congenital megacolon (Hirschsprung disease). Congenital meg-acolon manifests from birth as persistent constipation. If the aganglionic intestinal segment is short, it is usually possible to empty the bowel using enemas and laxatives. If the affected seg-
Fig. 17.1 Extrinsic compression (stenosis).
a Compression in ascending colon from retroperitoneal lymph nodes. b Compression in ascending colon due to kidney tumor; mucosa is reddened.
Fig. 17.4 Dilation of colon: pseudoobstruction. Radiograph image shows considerable colon distention, especially in the ascending colon, and spare or lacking haustration. Increased vulnerability of the mucosa and risk of perforation (courtesy of Dr. Volker Remplik, Institute for Radiology, Augsburg Clinic).
ment is longer, there is complete blockage of the bowels and the infant will die without early surgical intervention.
Acquired megacolon (secondary). Acquired (secondary) megacolon develops at any age as a result of stenosis in the rectum or sigmoid caused by a tumor, scarring, or spasms related to chronic anal fissures.
Functional megacolon (actual pseudo-obstruction). In functional megacolon (no anatomical cause), the colon is dilated up to the rectum. Unlike in Hirschsprung disease the rectum is filled with stool. Functional megacolon can be constitutional and may be familial. Distention usually affects the entire sigmoid colon, though it can also involve the whole colon.
Additional examinations. An abdominal radiograph can demonstrate the exact extent of bowel distention in the acute phase as well as decompression after placement of a decompression tube (Figs. 17.4, 17.5).
In Hirschsprung disease, manometry can be used to detect defective relaxation of the internal rectal sphincter. Disease can be eliminated by resection of the aganglionic rectal segment.
Radiographic contrast studies are essential in all forms of megacolon for further treatment planning.
Differential diagnosis. Hormonal and medication-induced causes must be excluded. These include: hypothyroidism, acro-megaly, diseases of the brain and spinal cord, morphine abuse, vitamin B1 deficiency, acute potassium deficiency, and anti-cholinergic use.
The colon is distended and elongated. Stagnation of bowel contents can lead to secondary colitis.
Endoscopic diagnostic criteria
► In Hirschsprung disease, the rectum is empty and narrowed from increased muscle tone in the rectal wall.
► A full thickness rectal biopsy is performed with special dye techniques for detecting the absence of ganglion cells in the submucosal plexus. The frozen biopsy is sent to a special laboratory for evaluation (staining technique) of acetylcholinesterase (AChE) activity, which is increased in Hirschsprung disease. Using the safer method of suction biopsy, the mucosa can be biopsied and the specimen evaluated using enzyme histochemical staining to determine (only) cholinesterase activity.
► Pseudo-obstruction appears as a dilated colon/rectum rather than as a narrow rectal segment. Clinical picture can be acutely worsened by volvulus (an ischemic and/or edematous dark-red narrowed segment in the sigmoid colon).
In Hirschsprung disease, resection of the aganglionic rectal segment is unavoidable. Other forms of megacolon ("slow transit") are treated conservatively.
If there is massive dilation with lacking intestinal tone and distention of the transverse diameter exceeding six centimeters, placement of a decompression tube (e.g., Cook, Wilson-Cook Medical Inc., Winston-Salem, NC, USA) using a long guidewire inserted through the endoscope (4.80 m long, 0.035 inches wide) is necessary. Decompression occurs immediately (Fig. 17.5). After carefully building up food intake, beginning with tea and plain toasted bread, after a few days the patient may have foods higher in fiber along with ample amounts of water. In some cases, high fiber bulk laxatives (Indian Plantago, etc.) must be prescribed. Laxatives should only be used in severe cases. Osmotic laxatives (magnesium sulfate, lactulose, lactitol, mac-rogol) have limited side effects. Macrogol (polyethylene glycol) does not cause gas and thus does not increase bowel distention.
If the patient has obstructive constipation (e.g., rectocele) surgical intervention is the only option.
Follow-up surveillance should be performed every 4-6 months to monitor the continued effectiveness of treatment and, if necessary, treatment should be adjusted. Attention should be paid to regularity of bowel movements.
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