Anal Intraepithelial Neoplasia: Performing High-Resolution Anoscopy

Michelle D. Inkster

Eric D. Willis

James S. Wu

Perioperative Considerations

Anal squamous intraepithelial lesion (SIL) precedes anal squamous cell carcinoma. The causative agent is human papillomavirus (HPV) in the majority of cases.
Anal squamous cell cancer arises between the anal verge and the anorectal line (Fig. 18-1).
Although groups at high risk include HIV-positive individuals, especially men who have sex with men; solid-organ transplant recipients; and those with a history of cervical, vulvar, penile, or vaginal dysplasia, anal SIL can occur in anyone.
Anal SIL detection, necessary for diagnosis and treatment, is facilitated by inspection of at-risk epithelium with adequate lighting, magnification, and chemical enhancement.
- Diagnostic techniques used are derived from colposcopy described by Hinselmann et al. in 1925.
- In 1989, Scholefield et al. prospectively used a microscope to examine the anal canal to detect premalignant lesions.
- In 1997, Jay et al. reported high-resolution anoscopy (HRA) using a colposcope in conjunction with an anoscope to describe the appearance of anal SILs and their relationship to histopathology.
- In 2017, Oette and coworkers described anal chromoendoscopy (ACE) using gastroenterological video endoscopes.
- Inkster et al. described chromoendoscopy with narrow-band imaging (NBI) and NBI with acetic acid (NBIA) using both en face and retroflexed views to detect anal dysplasia.

Preprocedural Interview

A history is obtained and physical examination is performed. Risk factors for anal HPV disease are identified.
Baseline anal cytology is typically obtained.
The perianal skin and anal canal are examined by inspection, palpation, and 1× anoscopy. Perianal condyloma, as shown in Figure 18-2, is noted.
Lesions of the mouth, nares, eyelids, penis, or gynecologic areas are referred for appropriate follow-up.

Sterile Instruments/Equipment

Colposcope
Dilute acetic acid (3% solution)

Lugol iodine solution

FIGURE 18-1 ▪ A. The epithelium at risk for anal SIL extends from the anal verge to the anorectal line. B. The anorectal line defines the junction between the ATZ and the columnar epithelium of the rectum. The ATZ, derived from the embryonic cloaca, extends from the anorectal line to the dentate line. Distal to the dentate skin is the pecten that has no or few sweat glands and extends from the dentate line to the anal verge. Distal to the anal verge is the hair-bearing perianal skin or anal margin. C. Retroflexion with the scope delineating the anatomy. A, anterior; ATZ, anal transitional zone; PEC, pecten; R, right; Scope, endoscope; SIL, squamous intraepithelial lesion. (Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2019. All Rights Reserved.)

FIGURE 18-2 ▪ Perianal or anal margin condyloma acuminata (arrows) are located on the hair-bearing skin.

Cotton-tip applicators
Forceps/needle driver/scissors
Biopsy forceps
Electrocautery
3-0 Vicryl or chromic suture
Colonoscope with NBI
Clear self-lighted plastic disposable anoscope

Technique

DETECTION OF ANAL DYSPLASIA

Anal Colposcopy/High-Resolution Anoscopy

The patient undergoes a full cathartic bowel preparation with miralax prior to the procedure.
The procedure is performed in the operating room under general anesthesia.
The patient is placed in the lithotomy position utilizing yellow-fin stirrup.
The perianal skin and anal canal are examined through a colposcope to identify lesions (Fig. 18-3).

FIGURE 18-3 ▪ Anal colposcopy (highresolution anoscopy). The anoderm is inspected through an anoscope with a colposcope.
Treatment of the anoderm with dilute acetic acid makes abnormal epithelium appear white (“acetowhite”). This is performed using a cotton tip applicator soaked in the acetic acid and applied to the anoderm.
Treatment with Lugol iodine solution stains the glycogen-containing normal epithelium brown; abnormal epithelium, depleted of glycogen, does not take up the stain. A saturated cotton tip applicator is soaked in Lugol’s solution and it is applied directly to the area.
The appearance of anoderm stained with Lugol iodine is shown in Figure 18-4.

FIGURE 18-4 ▪ Treatment of the anoderm with Lugol iodine stains normal anoderm brown (arrows).
Lesion detection is enhanced using a green filter.
Biopsy of abnormal-appearing epithelial lesions is done to establish their histopathologic identity.
The appearance of anal low-and high-grade lesions, as seen through a colposcope, is shown in Figures 18-5 and 18-6, respectively.

FIGURE 18-5 ▪ A. Diffuse low-grade anal lesion (white arrows) seen through a colposcope. B. Histopathologic appearance of the lesion seen in A. The squamous epithelium shows prominent koilocytes, characterized by enlarged, hyperchromatic, and angulated nuclei (arrow) showing perinuclear halos. Binucleation is common (arrowhead). The cells maintain an overall low nuclear-to-cytoplasmic ratio, and there is no significant expansion of the basal layer (curved arrow). The overall findings are diagnostic of low-grade squamous intraepithelial lesion.

FIGURE 18-6 ▪ A. Examination of the anoderm through a colposcope with a green filter after treatment with acetic acid reveals a raised lesion (arrow). B. The squamous epithelium of this lesion shows partial thickness atypia (arrows), characterized by disorganized polygonal cells with eosinophilic cytoplasm, increased nuclear-to-cytoplasmic ratio, nuclear hyperchromasia, numerous mitoses (curved arrow), and dyskeratotic keratinocytes. The upper third of the squamous epithelium (arrowhead) shows maturation with evenly spaced nuclei and a low nuclearto-cytoplasmic ratio. This would previously have been classified as AIN II; however, it is now classified as HSIL per the LAST consensus.¹ AIN, anal intraepithelial neoplasia; HSIL, high-grade squamous intraepithelial lesion.

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