Cannonballs in Trichomonas vaginalis Infection: Morphologic Evidence of Parasite-Associated Neutrophilic Aggregates

Cannonballs, compact aggregates of neutrophils observed in Papanicolaou (Pap) smears, are frequently associated with Trichomonas vaginalis (T. vaginalis) infection but are generally regarded as nonspecific inflammatory findings. To clarify their morphologic features, we analyzed cervicovaginal liquid-based cytology specimens from 29 cervicitis cases, including six positive for T. vaginalis. Cannonballs were evaluated using immunocytochemistry for T. vaginalis and cytokeratin, cell block analysis, and morphometric analysis, with negative cases as controls. All positive cases contained T. vaginalis-associated cannonballs, with a mean positivity rate of 58.5%. Parasites were intermingled with aggregated neutrophils, and cell block analysis demonstrated parasite-centered neutrophilic aggregates. Cytokeratin staining patterns differed morphologically between positive and negative cases. In addition, T. vaginalis-associated cannonballs were significantly smaller than adjacent squamous epithelial cells. These findings suggest that some cannonballs in trichomoniasis may represent parasite-associated neutrophilic structures and provide insight into host–parasite interactions in cervicovaginal inflammation.