Gallstone ileus: a challenging ultrasound diagnosis

An 87-year-old female patient presented to the emergency department with a one-day history of generalized abdominal pain. She denied urinary symptoms and intestinal habits alterations.

Her past medical history was insignificant.

A physical examination showed a distended abdomen with mild tenderness.

A plain abdominal film was performed and no evidence of considerable intestinal distention was found. Hydro-aereo levels were questioned (Fig. 1). An abdominal ultrasound (US) was requested to further clarify this case. The US examination showed multiple small bowel loops distended, with some ascitic fluid between them. These findings were suggestive of a probable occlusive/subocclusive process, thus a contrast-enhanced computed tomography (CT) was performed which demonstrated pneumobilia at biliary tree (Fig. 2a) and thickening of gallbladder wall with a fistulous traject to the duodenum (Fig. 2b). The jejunal small bowel loops were distended, with a transition point in the hypogastrium, without an apparent cause (Fig. 2c). Small bowel and colon loops distal to transition point were normal.  A second US examination was performed which identified a 2.5 cm gallstone at the transition point of intestinal distention (Fig. 3). The diagnosis of gallstone ileus was purposed.

Gallstone ileus is an infrequent cause of mechanical bowel obstruction, caused by the impaction of a gallstone in the intestinal tract after being passed through a biliary-enteric fistula. [1]. Fifty to 70 per cent of gallstones impact in the ileum, which is the narrowest segment of the intestine. Rarely, the gallstone becomes impacted within the pyloric channel or duodenum, causing gastric outlet obstruction (Bouveret's syndrome). Female and older patients are disproportionally affected [1,2].

The following sequence is probably responsible for most cases of fistula formation that lead to gallstone ileus. Pericholecystic inflammation after cholecystitis leads to the development of adhesions between the biliary and enteric systems. Pressure necrosis by the gallstone against the biliary wall then causes erosion and fistula formation.  Ninety per cent of obstructing stones are greater than 2 cm in diameter, with the majority measuring over 2.5 cm [3].

There is an association between the existence of colecystoenteric fistula and coexisting Mirizzi syndrome, which may explain the initial evidence of biliary tree dilatation in this patient [4].

The classic clinical presentation of gallstone ileus is typically observed in older women with episodic subacute obstruction.  In this case, the patient had no previous history of subacute obstruction or transient abdominal pain, and the clinical symptoms started the day before to the admission.

In patients suspected of having gallstone ileus, abdominal imaging is needed to confirm the diagnosis, identify the location of bowel obstruction, and look for complications related to the obstruction (e.g. ischemia, necrosis, perforation).

Our patient was suspected of having an acute abdomen with the initial evaluation. CT remains the best imaging modality for evaluation of patients suspected of acute abdomen. Besides that, she also performed first a plain abdominal film and an US which were inconclusive for the diagnosis, supporting that these imaging modalities, however, could complement the evaluation, are not necessary.  The CT scan performed showed several findings consistent with gallstone ileus such as pneumobilia, a collapsed gallbladder with wall thickening and isoattenuating gallstones inside viewed in US realized before, and intestinal obstruction. However, it was not able to demonstrate the gallstone responsible for the obstruction, as it was isoattenuating. In this particular case, repeating the US evaluation was an opportunity to confirm the suspected diagnosis of gallstone ileus.

The patient was submitted to surgical treatment, performing an enterolithotomy with gallstone removal (Figure 4).

Written informed patient consent for publication has been obtained.