Perianal nodule due to Enterobius vermicularis: Cytomorphological spectrum on fine needle aspiration cytology with a review of literature

Enterobius vermicularis (EV), an intestinal nematode, causes lesions at ectopic sites also. Although lesions are fully curable with antihelminthic drugs, patients may require surgical intervention in clinically unsuspected cases to arrive at correct diagnosis and appropriate treatment. Accurate diagnosis of these lesions on fine needle aspiration cytology (FNAC) has an advantage of avoiding unwanted surgery. To the best of our literature search, there are few case reports of EV diagnosed on cytology, but none of them describes the various stages of development of eggs and hatching of larvae. Dealing cytopathologist should be cognizant of them as parasite can be present in any of these forms/stages. Recently, we came across an interesting case of young boy who presented with perineal nodule and on FNAC from the lesion showed EV larvae and its eggs in various stages of hatching and development. The patient responded to antihelminthic treatment (AHT). Morphological clues with a review of cytological literature are discussed.