Teaching Case

64-year-old woman with chronic kidney disease on haemodialysis, long-standing cholelithiasis underwent cholecystectomy to manage an episode of acute cholecystitis. Discharged after uneventful early postoperative course, seen again at Emergency Department two weeks later because of low-grade fever, worsening abdominal pain and right-sided peritonism. Elevated C-reactive protein at routine laboratory tests.

Ultrasound (Fig. 1) detected a well-demarcated, ovoid subhepatic collection measuring approximately 7x5 cm, with a markedly inhomogeneous internal structure, mostly hypo-anechoic with dependent echoes.
Further investigation with CT (Fig. 2) confirmed suspicion of abscess collection extending from the surgical bed, with predominantly fluid-attenuation content, some nondependent air and thin enhancing peripheral wall; the abscess contained a centimetric fragment consistent with faintly calcific, sonographically unrecognisable dropped gallstone. Correlation with surgical description revealed that laparoscopic cholecystectomy was intraoperatively converted to open surgery following gallbladder perforation during manoeuvres that caused intraperitoneal spillage of purulent content.
The patient underwent percutaneous CT-guided drainage (Fig. 3a), including an attempt to fragment the stone, and rapidly improved. Drained pus tested positive for extended-spectrum beta-lactamase-producing (ESBL+) Escherichia coli. Before hospital discharge, repeated CT (Fig. 3b) showed collapsed abscess after drainage, and the dropped gallstone was not visible anymore.

Laparoscopic cholecystectomy (LC) represents the preferred treatment for symptomatic cholelithiasis, acute and chronic cholecystitis, empyema and gallstone pancreatitis. Albeit generally regarded as a safe procedure, LC is associated with a non-negligible morbidity (overall complication rate 6.5%) and occasionally mortality [1]. Considering the large number of LC surgeries performed, operated patients who fail to make the predictable rapid recovery may be requested to undergo emergency imaging before or shortly after hospital discharge. Therefore, radiologists should be familiar with potential complications after LC to avoid misinterpretation and allow appropriate management [2-4].
Despite careful maneuvers and use of retrieval bags, spillage of bile commonly (10-40% of interventions) occurs during either dissection, tearing or extraction of the gallbladder. The incidence is even higher in elderly or obese male patients, in acute cholecystitis and in presence of adhesions. Dropped gallstones (DGs) occur less commonly (roughly 4-6%), but may be displaced to any part of the abdominal cavity spread and form a nidus for infection [4-8]. Therefore, surgeons should try to retrieve DGs and irrigate the peritoneum to dilute any infected bile. Conversion to open surgery should be considered but is controversial, since some authors claim that retained DGs caused no harm after long-term follow-up evaluation, while others reported complications and suggested close follow-up of patients [6, 9, 10].
Even if unaware of operative notes, radiologists should remember DGs as potential source of postsurgical abscesses in patients presenting with unspecific clinical symptoms such as fever, persistent pain, bowel obstruction over a period of days to a few months after LC. Following gallstone spillage, the risk of abscess development has been estimated to reach 3%. At CT, intra-abdominal inflammatory masses with fluid-like purulent content and peripheral enhancing rim are mostly encountered in the gallbladder fossa, Morison’s pouch and right parietocolic space. However, the use of pneumoperitoneum and peritoneal irrigation may result in unusual locations such as the pelvis, retroperitoneum and abdominal wall at trocar site or incisional hernia. Within abscesses, DG with high calcium content appear as one or more, central or eccentric hyperattenuating foci, best recognised with wide window settings. As in this patient, poorly or non-calcified stones (such as those made of cholesterol) easily go undetected. Compared to CT, DG are difficult to recognise at MRI due to low signal intensity [2-4, 11].
Abscesses require surgical or percutaneous drainage, and DG may be removed using nephroscope or baskets, since untreated DG may result in recurrence [4-8].