Enterobius vermicularis worm granuloma mimicking like a pseudo tumor in the anal canal: An unusual clinical presentation.

Enterobius vermicularis is one of the most common intestinal nematode worldwide. Enterobius rarely causes a symptomatic disease. We report here an unusual case of a 60-year old man who came with a polypoidal growth in the anal canal increasing in size for past 20 years. He had pain and intense itching over the mass. The differential diagnosis of squamous papilloma, fibroma and foreign body granuloma were considered. The mass lesion was excised surgically and sent to the pathology laboratory. The mass turned out to be an "E. vermicularis worm granuloma" by histopathologic examination. Thus, timely reporting and surgical resection of such lesion is necessary to prevent further complications. This case is reported here for the unusual presentation of pinworm as a pseudoneoplasm in the anal canal. Incidence of these cases reflected the poor personal hygiene and improper disposal of human excreta in the rural areas. We insist that health education is the only way to control the spread of helminthic infections that causes a heavy disease burden to our country.

INTRODUCTION

Enterobius vermicularis (pinworm) is an intestinal nematode most often encountered in the temperate zones especially in areas of poor faecal sanitation.[1] More than 200 million people are infected worldwide. In India the prevalence of intestinal enterobiasis infection among children is more than 61%. Herewith we are reporting a case of E. vermicularis with an unusual presentation, which caused a diagnostic challenge to the surgeons and the pathologists.

CASE REPORT

A 63-year old male from a rural area came to the surgical OPD with a polypoidal mass in the anal region. The mass was gradually increasing in size for past 20 years. He gave the complaint of pain and intense itching over the mass. On examination, the growth was from the anal wall, with skin covered and firmness in consistency measuring about 4 × 3 cm [Figures 1 and 2]. All the basic investigations done were within normal limits except a slight increase in the eosinophil count. Stool examination was negative for any worm or its ova. A differential diagnosis of squamous papilloma, fibroma, and foreign body granuloma were considered. Patient was admitted into the hospital and mass from the anal region was excised completely. Lateral sphincterotomy and Balal's stitch was done. Then the specimen was sent to the department of pathology where it was examined and processed.

Figure 1

External surface of the excised anal canal growth measuring 4 × 3 cm

Figure 2

The cut surface of the granuloma that is homogeneously white with few yellow specks

To our surprise, histopathologic examination of the skin-covered lesion revealed the fragments of dead E. vermicularis worms surrounded by granulomatous reaction composed of epithelioid macrophages, foreign body type of giant cells and lymphocytes [Figures 3 and 4]. The granuloma was of the noncaseating type. Sections also showed stacks of pinworm eggs which are D-shaped with double contoured hyalinized shell. Eggs are also surrounded by many large foreign body-type giant cells and granulomas [Figures 5 and 6]. Thus, the deposition of eggs by the female gravid worm in the anal wall penetrating through the breaches elicited a severe foreign body type of granulomatous reaction. In the end, the anal canal growth turned out to be a “E. vermicularis worm granuloma with eggs.” This rare interesting case is presented here to stress the fact that worm granuloma can mimic a pseudo tumor in the anal region if untreated for a longer duration.

Figure 3

The fragmented dead worms surrounded by a granulomatous reaction and foreign body type of giant cells. (H and E, ×100)

Figure 4

The appearance of the worm granuloma containing macrophages, giant cells and lymphocytes under higher magnification (H and E, ×400)

Figure 5

The stacks of pinworm eggs surrounded by giant cells. (H and E, ×100)

Figure 6

Photomicrograph shows the stacks of pinworm eggs with typical double-contoured hyalinized wall under higher magnification (H and E, ×400)

DISCUSSION

E. vermicularis “pinworm” is a common nematode of the gastrointestinal tract. Enterobiasis is usually an asymptomatic disease except for intense perianal pruritus that often gets worse at night. Pinworms are relatively harmless and innocuous within the intestine, but the worms if found in the ectopic locations can elicit a severe granulomatous inflammation.[23]

Life cycle of the worm is simple and completed in a single host. Man is the only host and it does not need a second host. Transmission occurs through ingestion of embryonated eggs, through inhalation of the airborne eggs dislodged from contaminated clothing and autoinfection through the contaminated finger nails (hand to mouth spread). The adult worms live in caecum and colon. The female adult worms are small white, spindle shaped, 8-13 mm size, visible to the naked eye. Male worms are 2-5 mm in size, and dies after fertilizing the female worms.[1] Female gravid worms sometimes come out through the anus to lay her eggs in the perianal area. The migration of the female worms in the perianal area creates a crawling sensation and the deposited eggs cause severe itching and irritation in the perianal area.

Although E. vermicularis is an intestinal nematode, it can be seen in ectopic locations causing urinary tract infections, perianal cellulitis, perianal abscesses, anal canal granuloma, salpingitis, peritonitis, vulvovaginitis, and acute appendicitis.[4] Very few case reports are there in which live pinworms are found in the conjunctival sac of eye and in nares.[5]

Diagnosis is usually made by looking at the typical plano-convex eggs of size 50-60 μ in length, 20-20 μ in width with thick double-contoured hyalinized sheath. NIH swab, cellophane swab, or scotch tape swab method is used to collect the eggs from the perianal skin. Stool examination may not be helpful at times because eggs are not often released in the faeces. Occasionally eggs are detected in the urine and vaginal smears.[6] The adult worms are identified by the double bulb esophagus and a pair of cervical alae in the anterior end.

Infected children and adults should be treated with mebendazole (100 mg once), albendazole (400 mg once), or pyrantel pamoate (11 mg/kg once; maximum, 1 g), with the same treatment repeated after 2 weeks. Whole family of the infected person has to be treated to eradicate the reservoir of infection. Good personal hygiene, proper disposal of human excreta, and rural health education is necessary to control and prevent enterobiasis.