Primary hydatid cyst of the neck diagnosed by aspiration cytology.

Primary hydatid cyst of the neck is of extremely rare occurrence even in endemic regions. Clinically mimicking a cold abscess, we report such a case which was diagnosed by fine needle aspiration cytology. The lesion was removed surgically and at 6-month follow-up visit, the patient was a symptom-free.

INTRODUCTION

Hydatid disease is a serious helminthic disease in humans with a world-wide distribution and is particularly prevalent in the cattle rearing regions. Essentially a zoonotic disease, it is caused by the larval tapeworm of the genus Echinococcus granulosus, Echinococcus multilocularis and Echinococcus oligarthus. However, most human cases occur due to infection of E. granulosus.[1] Commonly affecting liver and lungs, affection of various other organs has been reported. Such affection can be primary or secondary following liver or lung involvement. Here, we report a rare case of the primary hydatid cyst in the neck accidentally diagnosed by fine-needle aspiration cytology (FNAC).

CASE REPORT

A 58-year-old male farmer reported to the outpatient clinic of the Department of Surgery with a 45 × 30 mm swelling in the right posterior triangle of the neck. The patient stated that he first noticed the swelling one month back, the size of which then was that of a pea. It was gradually increasing but was painless. There was no history of fever or cough. On examination the swelling was soft and cystic with well-defined margin and was non-tender. It was also non-reducible and non-fluctuant. The overlying skin was free and was mildly hyperemic. There was no attachment to the deeper tissue. A clinical diagnosis of cold abscess was made and the patient was sent for FNAC which was performed with a 24 gauge needle attached to 10 cc syringe. The aspiration yielded 5 ml of mildly dirty fluid with some white granularity. The fluid was centrifuged, smears were made and stained with Hematoxylin and eosin (H and E) stain and May-Grunwald-Giemsa stain. The microscopic examination revealed scolices and hooks with few fragments of lamellar membrane in a dirty background of pus cells and cell debris [Figures 1 and 2]. A diagnosis of the hydatid cyst was made. The patient then underwent chest X-ray, abdominal ultrasound and computed tomography scan to rule out any other organ involvement. The complete blood counts were unremarkable. Indirect hemagglutination test for E. granulosus was positive. The results of all the other tests were negative indicating that this was a case of primary hydatid cyst in the subcutanoeus tissue of the neck. The patient was treated with oral Albendazole and the intact cyst was removed surgically with no complication. The histopathology confirmed the diagnosis. The case was followed up for 6 months and there was no recurrence.

Figure 1

Microphotograph showing scolices and hooks of Echinococcus granulosus(H and E, ×100)

Figure 2

Microphotograph showing a closer look at scolices and hooks. Inset shows high power view of hook (H and E, ×400)

DISCUSSION

Hydatid disease or Echinococcosis is a zoonotic disease which may affect humans. Further more, known as a hydatid cyst due to the cystic nature of the lesion, it is caused by the larval forms of Echinococcus most commonly E. granulosus. Hydatid disease is seen endemically in Middle East as well as in other parts of the world, including Africa, India, South America, Turkey, and Southern Europe[1] in cattle and sheep-rearing regions. Cystic hydatid disease or hydatid cysts usually affects the liver (70%) and the lungs (25%) but can occur anywhere in the body, including spleen, kidneys, bile ducts, mesentery, heart, brain, and musculoskeletal or soft tissue.[23] Localization in soft tissues is extremely rare accounting for only 2.3% in the largest published series consisting of only 24 out of 1056 cases.[4] Even in regions where Echinococcosis is endemic, hydatid cyst in the neck is rare and its incidence is unknown.[56] Iynen et al.,[6] Eroglu et al.,[7] Kesici et al.[8] and Hmidi et al.[9] reported one case each of a primary hydatid cyst in the neck region. The larval stage (metacestode) of Echinococcus usually resides in the small intestine of dogs. Humans, who get infected by ingestion of eggs of Echinococcus, serve as the accidental intermediate host where the life-cycle of the Echinococcus reaches a dead end. In humans, the parasite eggs hatch in the small intestine, pass into the portal venous system or lymphatic system to reach the liver and lungs and form hydatid cyst lesions. Moreover, they can cross the hepatic sinusoid or pulmonary capillary barrier enters the systemic circulation and can affect all the parts of the body.[6] Our case was unique as the patient suffered from the primary subcutaneous hydatid cyst of the right posterior triangle of the neck with no involvement of lungs and liver. FNAC although generally discouraged as a diagnostic tool in suspected hydatid cases due to the risk of anaphylaxis, accidentally clinched the diagnosis in this case. To conclude, we report this case for its unique presentation, to emphasize the fact that hydatid cyst should remain in the differential diagnosis of cystic lesions in unusual locations particularly in the endemic regions and also to highlight the role of FNAC in detection of hydatid cysts.