Ascariasis-induced cholecystitis: sonographic diagnosis

Abdominal ultrasound (US) revealed a distended gallbladder (GB) with a very thick (1.3cm) and oedematous wall with hypoechoic foci (Fig. 1). The lumen contained sludge and an ill-defined, curvilinear echogenic structure, without acoustic shadowing (Fig. 2). A diagnosis of acute acalculous cholecystitis was made, with a suspicion of GB ascariasis.

Follow-up US a week after conservative treatment, revealed a long helical echogenic structure inside the lumen of the GB (Fig. 3). Two parallel hyperechoic bands were detected, with a hypoechoic centre that corresponded to the alimentary canal of the worm, pathognomonic findings for ascaris (Fig. 4). In addition, a clumped fluke's end was easily visible, probably demonstrated the parasite's anterior end, with the three prominent "lips" (Fig. 5).

Infection from ascaris was confirmed by parasitological examination, with the presence of characteristic eggs in the patient's faeces.

On US, an individual worm, viewed along its longitudinal axis, appears as a hypoechoic tubular structure with well-defined, echogenic walls. The alimentary canal of the worm is seen either as a single central echogenic line (when in a collapsed state) or as two parallel hyperechoic bands with a hypoechoic centre (when distended); the latter effect is known as "the inner tube" sign. In cross-section the individual worm presents a "target" sign with its circular, echogenic body wall and its central dot-like alimentary canal. On prolonged scanning, the worms always show curling movements. It has been reported that a bolus of worms mixed with faecal matter and air produces an unusual appearance of a complex, echogenic mass (helminthoma).

Ascariasis is a rare cause of appendicular colic, peritonitis, cholecystitis, pancreatitis, obstruction of the bile duct, liver abscess, and recurrent pyogenic cholangitis.

Biliary ascariasis is best shown by US, which sometimes distinctly depicts the worm's segments and shows the worm's movement inside the gallbladder in real-time (when alive), thus presenting a big advantage over CT and MRI.

The initial treatment of biliary ascariasis is conservative management with intravenous fluids, oral antihelminthics (mebendazol), analgesics and follow-up ultrasonography.