"Collagen balls" in peritoneal washings. Prevalence, morphology, origin and significance

Peritoneal washings obtained at laparotomy from women undergoing surgery for neoplasms of the genital tract may contain "collagen balls," consisting of tissue fragments composed of collagen covered with mesothelial cells. Collagen balls were found in 19 (4.5%) of 418 peritoneal washings and were more prevalent in specimens labeled pelvic washings (17 of 294, or 5.8%) than in those labeled peritoneal washings (2 of 124, or 1.6%). In 15 of the 19 cases in which we found collagen balls, at least one ovary was available for microscopic examination. In 14 of the 15 cases minute nodular papillary stromal projections covered with mesothelium were found on the surface of the ovaries. We conclude that collagen balls, a nonspecific entity, most probably originate on the surface of the ovaries. Their significance lies in their being mistaken for mucin-distended cells exfoliated from a neoplasm or from detached fragments of a papillary ovarian neoplasm.