Anoscopy

Article Author:
Shawn London
Article Editor:
Matthew Tichauer
Updated:
6/10/2018 4:37:20 PM
PubMed Link:
Anoscopy

Introduction

Anoscopy is a bedside procedure which is inexpensive, can be performed quickly without bowel preparation or the need for sedation. With this method, the examiner can visualize the internal portions of the anal sphincter and the distal rectum. Prospective studies suggest that anoscopy has a higher sensitivity for anorectal lesions such as internal hemorrhoids, proctitis, lacerations, fistulas, ulcers and masses than flexible sigmoidoscopy. Up to 50% of rectal bleeding can be falsely attributed to hemorrhoids without internal examination to confirm this diagnosis.

Anatomy

The most significant visible structures of the lower gastrointestinal (GI) tract including:

  • The four cm-long anorectal canal
  • The midpoint of the anorectal canal known as the dentate line (the transition between the distal squamous and proximal columnar epithelium)
  • The anal glands
  • Longitudinal mucosal folds of the columns of Morgagni which terminate in small crypts (of consequence since they can become obstructed and subsequently infected). 

Hemorrhoids are clusters of vascular, connective, and smooth muscular tissue which exist in the left lateral, right anterior, and right posterior portion of the anal canal. While internal hemorrhoids drain into the middle and superior rectal veins, patients with portal hypertension nonetheless do not have an increased incidence of varies. Since internal hemorrhoids lie above the dentate line, they have visceral innervation and are not painful, but they may become symptomatic due to bleeding and/or prolapse from the rectal canal. Severely prolapsed internal hemorrhoids may be painful if strangulated, and secondarily ischemic Conversely, external hemorrhoids emerge inferior to the dentate line and have somatic innervation from the perianal skin and can cause significant discomfort. Anoscopy can be useful to characterize the presence of enlarged internal hemorrhoids, but external hemorrhoids may preclude anoscopy due to discomfort.

Indications

This procedure can be useful in individuals experiencing rectal/anal discomfort to evaluate for common lower gastrointestinal pathology which can cause pain such as anal fissures, sexually transmitted infection, anal condylomata, or bleeding such as internal hemorrhoids, rectal ulceration/inflammation, rectal varices or trauma. Anoscopy can be useful in evaluating for anal cancer, particularly in high-risk groups such as in men who have sex with men and have co-existing HIV infection. This translates to a lifetime risk of 7% to 8% in a male infected in his 20s. There are no current routine screening guidelines at this time. 

Contraindications

Contraindications include patient inability to tolerate the examination due to discomfort, apprehension, significant active bleeding which could prevent adequate visualization by the examiner, or the presence of a known mass in the distal rectum which could be damaged or irritated by the introduction of the rigid anoscope.

Equipment

Anoscopes come in the slotted and non-slotted variety, both with an obturator or occlusion device which is left in place during insertion. Both devices are then gradually removed with the obturator removed, enabling visualization. The non-slotted variety has the benefit of allowing 360-degree visualization of the entire anal passage versus the slotted version which provides a view of only a small portion of the distal rectum and anal opening at a time. As a consequence, the slotted version may require several passes to provide complete visualization if the patient is unable to tolerate rotation of the device. Most commercially available anoscopes do not include a built-in light source, leaving providers to use either a head-mounted light source or to enlist an assistant in directing the light source to allow adequate visualization. High-resolution anoscopy is a specialized procedure involving camera-assisted magnification and is typically considered to be out of the scope of practice of practitioners who have not received specialized training in its use.

Preparation

As with all procedures in which the examiner may come into contact with bodily fluids, personnel should wear personal protective equipment including gloves, a gown, and eye protection. The risks, benefits, and alternatives of the procedure should be discussed with the patient before initiation of anoscopy. The patient should be counseled regarding the expectation of some discomfort during the examination.

Technique

Typically, the examiner will perform a digital rectal exam first to ensure that no mass or tissue is obstructing the anal canal which could be injured during insertion of the device. There is insufficient evidence to comment on the efficacy of topical pre-procedure lidocaine application to provide analgesia during anoscopy, but in the absence of known lidocaine allergy, many practitioners consider this a reasonable measure to adopt. The water-soluble lubricant is applied to the anoscope itself pre-insertion to facilitate insertion.This may be accomplished using the topical anesthetic as a de-facto lubricant, thereby providing an opportunity for the lidocaine to be distributed along the path of the anoscope before its introduction. Typically, the device is introduced with the obturator in place which is then removed, allowing the examiner to visualize the anal canal and distal rectum as the anoscope is slowly withdrawn. In the case of slotted anoscopes, which only allow a visualization of a portion of the mucosa at the time, the obturator should be reinserted before reinserting or rotating the device due to the discomfort associated with placing traction of the segment of tissue which bulges into the slotted segment.

Complications

Complications include discomfort, mucosal irritation, mechanical trauma, and worsening of hemorrhoidal bleeding.

Clinical Significance

While anoscopy appears to be the superior procedure for identifying distal anorectal pathologies such as internal hemorrhoids, proctitis, or ulcerations (which cannot be reliably identified or differentiated from one another on digital rectal exam) which may lead patients to present with complaints of bleeding or discomfort, there are significant limitations to this procedure. While anoscopy is highly sensitive for identifying pathology such as internal hemorrhoids, findings seen on anoscopy does not allow practitioners to rule out a proximal source of GI bleeding, which is identified subsequently on endoscopy up to 50% of the time. Therefore, the finding of a potential source of GI bleeding such as internal hemorrhoids in isolation does not allow the examiner to exclude an additional source of bleeding.

Ultimately, anoscopy is a useful adjunct for screening for anorectal pathology which is inexpensive and can be accomplished quickly and without preparation. However, the procedure must not be unduly relied upon in evaluation of a patient with rectal bleeding, since the presence of rectal pathology does not rule out a proximal source of bleeding.