Perineal Nodule Due to Enterobiasis: An Aspiration Cytologic Diagnosis Neeta Kumar, M.D.,* Prashant Sharma, and Shyama Jain, M.D. M.B.B.S., Ritesh Sachdeva, Subcutaneous swelling due to Enterobious vermicularis infection is rare. Their presence in perineal subcutaneous tissue is unusual and a clinical curiosity. A case of subcutaneous nodule in the perineum due to E. vermicularis infection diagnosed on fine-needle aspiration is described. Tissue reaction was granulomatous with neutrophils and eosinophils. Lack of familiarity with the morphology of parasites or its eggs, degeneration, and inadequate sampling may make the diagnosis difficult. This case report provides the morphologic clues to cytopathologists toward rendering a diagnosis and alerts them to the possibility of parasitic infection in unusual locations. Diagn. Cytopathol. 2003;28:58 – 60. © 2002 Wiley-Liss, Inc. Key Words: perineal nodule; intestinal parasite; helminths; aspiration cytology Subcutaneous and soft tissue nodules due to inflammatory response to parasitic larvae like microfilaria and cysticercus are well known and described in the cytological literature.1,2 However, such a swelling due to the eggs of intestinal parasites has rarely been diagnosed and documented.3 The ease with which cytological specimens are procured has resulted in the need for rapid and accurate interpretation to ensure prompt treatment. The present article describes a rare case of subcutaneous nodule in the urogenital triangle of perineum, far from the usual site of the perianal region in which eggs and body parts of the adult worm of Enterobius vermicularis (EV) were detected on fine-needle aspiration (FNA). The aim is to highlight the unusual clinical presentation and uncommon cytological features. Cytopathology Laboratory, Department of Pathology, Maulana Azad Medical College and Lok Nayak Hospital, New Delhi, India *Correspondence to: Dr. Neeta Kumar, 178 Haus Khas Apartments (SFS), New Delhi, 110016, India. E-mail: kumar_neeta@hotmail.com Received 9 April 2002; Accepted 10 September 2002 DOI 10.1002/dc.10228 Published online in Wiley InterScience (www.interscience.wiley.com). 58 Diagnostic Cytopathology, Vol 28, No 1 M.B.B.S., Case Report A 26-yr-old male presented with a painless nodule in perineum of 4 mo duration. On examination the nodule was superficial, firm, nontender, had well-defined margins, and measured 1⫻1.5 cm. It was located in the urogenital triangle of perineum very close to the base of the scrotal sac, which was lifted up to visualize the nodule. Overlying skin was normal. There was no inguinal lymphadenopathy. Systemic examination was normal. FNA from this swelling done 15 days ago at another center was reported as acute suppurative lesion. The swelling did not subside with antibiotic treatment and hence was referred to our institution for a repeat FNA. Aspiration yielded whitish purulent material. Smears were stained with Papanicolaou, Giemsa, and Ziehl Neelsen (ZN) stains. Smears showed predominantly neutrophils, eosinophils, and foamy macrophages. The interesting feature was the presence of many eggs amid the inflammatory exudate. Each egg was plano-convex, 50 – 60 ␮m in length, and 18 –22 ␮m in diameter. They had a distinct, translucent shell. Some of these eggs had a coiled larva inside and a clear space between larva and shell (Fig. 1). Many degenerated eggs were identified by their characteristic shape, shell, and peripheral palisading of neutrophils (Fig. 2). A foreign body giant cell with engulfed egg (Fig. 3) and occasional epithelioid cell granuloma were also present. These eggs were characterized as those of EV. On careful search a fragment of cuticle with rectangular plates was identified as the body wall of the adult worm (Fig. 4). ZN stain did not reveal any acid-fast bacilli. The coiled larva inside the egg could be easily identified by its dark blue nuclei stained with methylene blue. Thus, a cytologic diagnosis of EV infection with granulomatous reaction was made. The patient was not conscious of any perianal itching or scratching. Subsequent stool examination on three occasions was negative. Patient was referred to the physician for appropriate treatment. © 2002 WILEY-LISS, INC. ENTEROBIASIS Fig. 1. Embryonated egg amid dense inflammatory exudate showing a coiled larva with prominent nuclei (Giemsa stain, ⫻400). Fig. 2. Degenerated egg with peripheral palisading by neutrophils (Papanicolaou stain, ⫻300). Discussion EV infection is worldwide, with a greater prevalence in temperate regions than in the tropics. It is the most common intestinal nematode in the United States, where an estimated 20 – 40 million people are infected.4 Humans are the only host and no reservoir host is known. Infection occurs by ingesting fully developed embryonated eggs, which hatch in small intestine and subsequently develop in large intestine. Adult worm primarily resides in cecum. Gravid female migrates to the anal region and releases eggs from its reproductive opening or after its disintegration on the skin. The freshly laid eggs containing an immature first-stage larva are sticky, and thus adhere to the skin and attain full development. These may stick to the patient’s hand and are ingested with contaminated food. The hatching of eggs may also occur on the skin at the site of deposition and larvae migrate into cecum or vagina to establish retrograde or aberrant infection.4,5 Fig. 3. Foreign body giant cell with engulfed egg (Papanicolaou stain, ⫻400). Fig. 4. Body wall of adult worm with rectangular cuticular plates (Giemsa stain, ⫻400). Usually, EV infections are asymptomatic. The commonest symptom is the perianal itching due to secretion and excretion of the female worm associated with its movement to the anal region. Severe complications occur only when the worm reaches into the peritoneum via intestinal perforation or erratic migration through the female genital tract. Dead worms and eggs have been identified incidentally in histological sections from several ectopic sites, i.e., vagina, cervix, fallopian tube, omentum, peritoneum, liver, lung, spleen, kidney,6,7 and perianal abscesses,8 –13 but their detection in cytological samples is documented only occasionally.3,14 –16 Enterobiasis diagnosed by cytologic examination of pus discharge from postoperative enterocutaneous fistula and by intraoperative cytology from ovarian and tubo-ovarian masses is described in single case reports. In none of these cases was infection by EV suspected clinically.14 –16 Intact skin is a barrier to invading parasite. Infection of skin and subcutaneous tissue can occur by ectopic migration followed by the death of the worm in sites damaged by cuts, Diagnostic Cytopathology, Vol 28, No 1 59 KUMAR ET AL. wounds, or scratching. The same might have happened in the present case, although there was neither such history nor any evidence of fistula. To the best of our knowledge, subcutaneous abscess due to EV infection in the urogenital triangle of perineum (as in the present study) has not been diagnosed and documented before in either cytological and histological samples. The only case of subcutaneous abscess due to enterobiasis diagnosed by FNA cytology was located in the natal cleft.3 Avolio et al.13 described one case and reviewed 12 other cases of perianal abscesses reported up till then. All 13 cases were located within the anal triangle of perineum at or near the anal verge and diagnosis of EV infection was established postoperatively in histologic sections. Entry of EV through mucosal breach and perianal crypt or gland has been postulated as the pathogenetic mechanism in perianal abscess.11,13 The noteworthy features of our case which have not been reported previously include unusual location of nodule and uncommon cytologic findings of ingestion of egg by giant cell, peripheral palisading of degenerated eggs by neutrophils. Cuticular plates of body wall seen in our case resembled that reported earlier.3 Lack of familiarity with the morphology, poor preservation of worms, eggs, and inadequate sampling may make the cytologic diagnosis difficult. Any of these could be responsible for missed diagnosis at first FNA in the present case. Stool examination also may not be helpful, as it provides diagnosis only in 5–15% cases and was negative in our case.5 To conclude, parasites rarely identified in the past are more frequently diagnosed in cytological specimens today. Familiarity with their morphologic clues and high index of suspicion are necessary for cytopathologist to initiate an intensive and careful screening for parasites. This is valuable in rendering a correct diagnosis to ensure prompt and adequate medical treatment and avoiding unnecessary surgery. The patient and family should be treated with antihelminthic drugs. Treatment should be repeated after 2–3 wk to ensure complete cure.4,5 60 Diagnostic Cytopathology, Vol 28, No 1 Acknowledgment The authors thank Mr. S. Ghosh for microphotography. References 1. Jain S, Sakhuja P, Kumar N, Sodani P, Gupta S. Cytomorphology of filariasis revisited. Acta Cytol 2001;45:186 –191. 2. Khurana N, Jain S. Cytomorphological spectrum of cysticercosis: A review of 132 cases. 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