Rapid onsite cytologic evaluation and diagnosis of hydatidosis from soft-tissue swelling in neck on unstained wet mount preparation

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Hydatid disease (HD) is an infection caused by larval forms of tapeworm, Echinococcus species, for which dogs are definite hosts whereas humans are intermediate hosts.^[1] It is more common in Asia, Australia, South America, Greece, Middle East, and Southern Europe.^[2] Primary hydatid cyst in soft tissue and muscle, without involvement of liver or lungs, is very rare.^[3] The cyst wall consists of an outer, thick laminated membrane, and an inner, thin, nucleated germinal layer. Protoscolices are usually produced singly into the lumen of bladder or also within the brood capsule, each having 10–30 protoscolices.^[4]

Cytology plays an important role in the diagnosis of hydatidosis. Diagnosis is mainly based on demonstrating scolices, hooklets, and laminated membrane, which is very well described in the literature. Herein, we report a case of HD diagnosed on examination of unstained wet mount preparation, presenting as a solitary subcutaneous swelling in the neck. This is a rare occurrence in the absence of visceral involvement.

A 22-year-old female presented with a painless, cystic swelling in the neck for the past 4 months. On examination, a well-defined cystic swelling measuring 1 × 1 cm was noted in the upper neck region. Fine-needle aspiration (FNA) yielded few drops of clear fluid along with whitish granular material. Air-dried smears were prepared for Giemsa staining. A wet mount preparation was also evaluated microscopically. It revealed scolex with hooklets [Figure 1a]. Thereafter, smears were stained with Giemsa, which showed numerous protoscolices along with hooklets and acellular laminated membrane [Figure 1b and c].

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Figure 1:

(a) Fine-needle aspiration (FNA) smear showing scolex (wet preparation × 400) and hooklets (Inset, Giemsa stain × 400). (b) FNA smear showing laminated membrane (Giemsa stain × 400). (c) FNA smear showing four scolex and hooklets (arrowed) (Giemsa stain × 400).

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Hydatid cyst presenting as a neck swelling is a rarity. Hence, FNA of neck swelling harboring hydatid cyst is unintentional, as in this case. Aspiration may lead to anaphylactic reaction due to spillage of the hydatid fluid. The mechanism of these reactions is complex. In some cases, it is typically a hypersensitivity reaction type I associated with immunoglobulin E in response of a high plasma concentration of antigens Echinococcus.^[5] Anaphylactic or anaphylactoid reactions may also be secondary to complement activation with liberation of anaphylatoxins.^[6] Fortunately, no such reaction occurred in this case. The purpose of this report is to document identification of the scolex and hooklets from a hydatid cyst on unstained wet mount preparation.