Anorectal cytology as a screening tool for anal squamous lesions: cytologic, anoscopic, and histologic correlation.

BACKGROUND: Anorectal cytology has been increasingly used as a screening method for anal squamous lesions, particularly in high-risk, homosexual, patients with human immunodeficiency virus infection. The diagnostic cytologic, anoscopic, and histologic criteria bear some resemblance to the criteria used in cervicovaginal samples with few differences. It is important to recognize these differences because they can lead to an erroneous diagnosis of dysplasia and unnecessary procedures.

METHODS: Seventy-eight anorectal cytology specimens from 51 patients were reviewed blindly. Of the 51 patients, 33 were HIV positive. The cytology specimens consisted of 75 ThinPrep (Cytyc, Boxborough, MA) and 3 conventional Papanicolaou-stained smear specimens. The revised diagnosis was compared with the original diagnosis, corresponding histology specimens, and anoscopic results, when available.

RESULTS: Six specimens were unsatisfactory for review. The revised diagnosis was negative in 15 patients, atypical squamous cells of undetermined significance in 3 patients, low-grade squamous intraepithelial lesions in 24 patients, high-grade squamous intraepithelial lesions in 28 patients, and squamous cell carcinoma (SQC) in 2 patients. Five patients with an original diagnosis of SQC had the diagnosis revised upon review of their specimens. It is noteworthy that these five specimens showed the presence of atypical parakeratotic cells. Thirty-two patients had anoscopic evaluation and 30 patients had histologic correlation. Twenty-seven patients with abnormal anoscopic findings had confirmed abnormal histologic findings. Twenty- five of the 32 (78%) patients had abnormal cytology that correlated with abnormal anoscopic findings.

CONCLUSIONS: Anorectal cytology is an accurate method for screening patients for anal squamous lesions. Atypical parakeratotic cells represent a potential pitfall. Anoscopy is important in confirming the presence of a lesion, but only a biopsy can accurately determine the grade of a lesion.