Hyperchromatic crowded groups: pitfalls in pap smear diagnosis.

A problem in the diagnosis of Papanicolaou smears--the interpretation of "hyperchromatic crowded groups" (HCGs)--is identified and analyzed. HCGs usually represent benign entities such as endometrial cells, syncytial aggregates in severe atrophy, or fragments of endocervical tissue, the latter being seen with increasing frequency due to the use of the endocervical brush. Tubal metaplasia is another common, benign source of HCGs. However, occasionally HCGs represent serious lesions, such as carcinoma in situ, invasive squamous cell carcinoma, and glandular neoplasia, either in situ or invasive. The distinction among these various entities is not always easy, but guidelines are presented.