The interpretation of high-grade squamous intraepithelial lesion on anal cytology: a comparative analysis with the cervical Papanicolaou test.

INTRODUCTION: Prior studies have shown that high-grade squamous intraepithelial lesion (HSIL) tends to be underdiagnosed on anal cytology. Our study aims to decipher the interpretative challenges of HSIL that are more specific to anal cytology specimens by comparing them to cervical Papanicolaou tests.

MATERIALS AND METHODS: One hundred cases each of anal and cervical cytology specimens with HSIL interpretation and concordant histologic follow-up were retrieved and diagnostically confirmed. Patient demographic data were obtained from the electronic medical record. The cytologic specimens were reviewed and statistically compared in terms of proportion of HSIL cells, HSIL patterns and types, and cytoplasmic area of HSIL cells (with digital image analysis). A P value of <0.05 was considered statistically significant.

RESULTS: Of the patients with anal HSIL, 97% were human immunodeficiency virus-positive and 60% were men who have sex with men. The anal cytology specimens significantly differed from the cervical ones in several respects: proportion of HSIL cells, cytoplasmic area of HSIL cells, cases with HSIL cells in syncytial groups (10 versus 57) and cases with keratinizing HSIL (45 versus 10). The P value was <0.0001 for all comparisons except for the proportion of HSIL cells (P = 0.001).

CONCLUSIONS: Anal cytologic HSIL, in contrast to its cervical counterpart, exhibits fewer abnormal cells and smaller size of the diagnostic cells with a higher percentage of keratinizing lesions. A careful scrutiny of the sample with an enhanced understanding of the morphology and better sampling may help improve the detection of anal HSIL on cytology.