Colorectal Quiz: Episode 48 - Anal Stenosis

When pediatricians refer patients with suspected anorectal abnormalities, 9 out of 10 times the exam is completely normal and the patient needs only constipation management.

A Hagar dilator can slide through a stenotic area even when a digital rectal exam detects abnormal, tight, scarred tissue; the only way to know is to put your finger in.

A real anal stenosis can be very tight and small, but you can also have an anal stenosis that fits an 11 Hagar dilator.

A 5-year-old followed by three gastroenterologists for difficult constipation was found on first digital rectal exam to have both anal stenosis and a presacral mass that had never been diagnosed.

A Hagar dilator inserted only about 4 millimeters may miss a distal rectal stenosis or atresia; a digital rectal exam to a couple of knuckles' depth is necessary to check out the distal hindgut.

Anal stenosis is the appropriate term for a narrow opening; rectal atresia (a segment with no lumen and dilated rectum above) would present in the newborn period with failure to pass stool.

Rectal atresia exists where the anal canal is pretty normal and normally located, but there is a segment where there is nothing, and then normal dilated rectum above.

If there is proximal dilatation, a narrowing is clinically relevant; this principle applies to assessing whether an anastomotic problem or other obstruction is significant.

When abnormal anatomy (such as anal stenosis) is identified, a biopsy should not be performed because sometimes you get information you really don't want to know.

It is very unlikely to have both anal stenosis and Hirschsprung disease in the same patient.

If you biopsy near a stenotic area, you will probably be biopsying the narrowed area, which typically might show no ganglion cells, and patients have been misdiagnosed with Hirschsprung disease when they never had it.

Patients misdiagnosed with Hirschsprung disease may have their rectum removed, and because of an underlying anorectal malformation they really needed that rectum for the proprioception it provided.

If you sample an area with no ganglion cells and hypertrophic nerves, savvy pathologists should run a calretinin stain; if calretinin is present, it means there are ganglion cells nearby and it is not Hirschsprung disease.

In colonic atresia (most commonly right colon only), there is somewhere between 1% and 3% or 7% (mixed data, low single-digit percentage) of associated Hirschsprung disease, so a biopsy should be performed.

Clues that a rectal biopsy was taken too low include: no ganglion cells with no comment on the nerves, or identification of squamous epithelium.

Anal stenosis has about a 40% risk of an associated presacral mass.

If a presacral mass is present (approximately 40% of anal stenosis cases), you need to know if it is connected to the dura, which requires both a pelvic MRI and a spinal MRI.

If you just order a pelvic MRI, you might not get information about dural involvement of a presacral mass, and you could get yourself in a lot of trouble.

For a very low, skin-level anal stenosis, dilation might solve the problem, but that is exceedingly rare.

For most anal stenoses, especially those a little bit in (maybe 1 centimeter or so), dilations are not going to be successful and the stenosis will recur.

For skin-level stenoses, a strictureplasty (like those done for strictures after PSARP) can be performed at the skin level where you can barely get a finger or Hagar in.

The surgical approach for anal stenosis is to open only the posterior part of the anal canal (like half of a PSARP), keeping the anterior 180° in continuity.

By working posteriorly in anal stenosis repair, you avoid the danger area anteriorly where you could injure the vagina or urethra (male or female), and you have more freedom to do work.

In anal stenosis repair, you advance a pliable part of the distal rectum to do a coloanal anastomosis, preserving at least 50% or more of the dentate line and the sensation in that area, which gives a better chance of long-term continence.

The technical principle is: do not get rid of the anal canal.

When you open the stenotic anal canal posteriorly, it flops open from a circle to a hemicircle; that anal canal stays a hemicircle. You fill the posterior hemicircle by mobilizing the rectal wall forward, so the posterior part is columnar epithelium to skin and the anterior part is the original anal canal.

Patients with anal stenosis always have good sphincters, so preserving the anal canal and good sphincters will preserve continence.

Once the distal obstruction (anal stenosis) is relieved, the dilated rectosigmoid should be given time to recover; sigmoid resection can always be performed later if needed, but the anal problem must be solved first.

A dilated colon proximal to a relieved obstruction will not get back to normal from an anatomic standpoint; a contrast study two years later will still show dilatation.

The more important question is whether the dilated colon will function; most will function well, possibly with some motility agents to help move stool along, and you should be able to get by without resection.

Fisher has been performing tapering of balloon-animal-type rectums and sigmoids that become dilated because of distal obstruction.

In a series of about 111 patients with dilated colon managed with Malone only, 97% did not need a sigmoid resection; only 3% underwent sigmoid resection.

The 3% of patients who underwent sigmoid resection in the Malone-only series had pelvic floor dyssynergia on anorectal manometry; in retrospect, those patients probably should have received pelvic floor physical therapy and might have avoided sigmoid resection.