Dropped gallstones: spectrum of imaging findings, complications and diagnostic pitfalls

Abstract

Spillage of gallstones into the abdominal cavity, referred to as "dropped gallstones" (DGs), occurs commonly during laparoscopic cholecystectomy. The majority of these spilled stones remain clinically silent; however, if uncomplicated DGs are not correctly identified on subsequent imaging, they may mimic peritoneal implants and cause unduly concern. A small percentage of DGs cause complications, including abscess and fistula formation. Recognising the DG within the abscess is critical for definitive treatment. This pictorial review illustrates the imaging appearances and complications of DGs on CT, MRI and ultrasound and emphasises pitfalls in diagnosis.

Figure 1.

Multiple tiny dropped gallstones 3 years after laparoscopic cholecystectomy. Axial contrast-enhanced CT, soft tissue window, shows tiny dense foci (arrow) clustered in Morison's pouch (a) and the gallbladder fossa (b). It is easier to differentiate the calcified stones from the metallic clips on wider windows (c, d). Note the surgical clip (arrowhead) in the gallbladder fossa (b, d).

Figure 2.

Incidentally detected dropped gallstones 14 years after laparoscopic cholecystectomy. (a) Axial contrast-enhanced CT shows two rounded peripherally calcified nodules adjacent to the liver (arrows). (b) Axial T₁ weighted three-dimensional gradient echo MR shows two rounded foci in Morison's pouch.

Figure 3.

An 80-year-old male presenting 3 years after laparoscopic cholecystectomy (LC) with a perihepatic abscess. (a) Axial unenhanced CT, performed 5 days after LC owing to abdominal pain and fever, shows two calcified dropped gallstones (DGs) posterior to the right lobe of the liver. Residual air bubbles (black arrow) reflect recent laparoscopy. The DGs were not removed at that time because the patient's symptoms were not attributed to the stones, and most DGs remain clinically silent. (b) Axial unenhanced CT 3 years after LC, when the patient presented with fever and right upper quadrant pain, shows a round 5-cm fluid collection containing two calcified-dependent foci, typical of a perihepatic abscess secondary to DGs. High-density branching structures within the liver represent opacified bile ducts following recent endoscopic retrograde cholangiopancreatography which was performed to evaluate the biliary tree (black arrow). (c) Ultrasound shows a hypoechoic fluid collection containing rounded echogenic foci (arrow) with posterior acoustic shadowing. (d) Axial T₂ weighted MR demonstrates dependent round hypointense foci within a 5-cm rounded hyperintense fluid collection posterior to the right lobe of the liver.

Figure 4.

A 54-year-old female with abdominal pain, 6.8-kg weight loss and night sweats 7 months after laparoscopic cholecystectomy (LC). (a) Axial contrast-enhanced CT 7 months after LC shows a biconvex heterogeneous complex collection (arrow) abutting the right lobe of the liver. No calcified stone to suggest a dropped gallstone is seen. (b) Contrast-enhanced CT 1.5 years later, when the patient presented with persistent symptoms, shows marked interval increase in size of the large, heterogeneous complex collection compatible with a perihepatic abscess (arrow). Again, no calcified stone is seen within the abscess. (c) Drainage (arrow) of the abscess 5 months later (30 months after LC) did not result in its resolution. The patient underwent laparoscopic debridement of the perihepatic abscesses and removal of retained gallstones with subsequent resolution of her symptoms.

Figure 5.

A 50-year-old male with several months of severe fatigue, lack of appetite and low-grade fever that started 7 months after laparoscopic cholecystectomy (LC). (a) Axial contrast-enhanced CT 7 months after LC shows a large heterogeneous collection compatible with an abscess adjacent to the right lobe of the liver. No calcified stone is seen to suggest a dropped gallstone (DG). (b) Follow-up axial unenhanced CT several weeks later shows no significant change in size of the perihepatic abscess. However, a faint calcific density is now seen in the centre of the collection, raising the possibility of a DG as a nidus for the abscess formation. The dense focus was initially overlooked, probably owing to the administration of intravenous contrast in the first study.

Figure 6.

Fistula formation owing to dropped gallstones (DGs). Patient presenting with a draining wound in the anterior abdominal wall several months after laparoscopic cholecystectomy (LC). (a) Photograph of the anterior abdominal wall demonstrates an indurated focal defect superior to the umbilicus at a trocar entry site from prior LC (arrow). (b) Axial contrast-enhanced CT shows a 1.8-cm peripherally calcified stone (long arrow) within the anterior abdominal wall with stranding of the adjacent subcutaneous fat. Note surgical clips in the gallbladder fossa (short arrow).

Figure 7.

Dropped gallstones (DGs) mimicking perihepatic nodules. (a) Axial contrast-enhanced CT shows punctuate high-density foci adjacent to the liver, initially interpreted as “enhancing perihepatic nodules”. (b) Repeat unenhanced axial CT study demonstrates that the foci surrounding the liver are also hyperdense in the absence of intravenous contrast. Therefore, these high-density foci more likely represent calcifications, compatible with dropped gallstones, rather than enhancing soft tissue nodules. (c) Pre-operative ultrasound shows multiple tiny stones (arrows) within the gallbladder, with a similar appearance to the “perihepatic nodules” seen on CT, supporting the diagnosis of post-operative DGs in (b).

Figure 8.

Dropped gallstones (DGs) misinterpreted as perihepatic lymph nodes. A 68-year-old female with gallbladder cancer incidentally detected in resected specimen. (a) Axial contrast-enhanced CT for staging gallbladder cancer shows a round subcentimetre nodule adjacent to the liver (arrow), interpreted as a suspicious lymph node. (b) Image at the level of the pelvis shows several similar round foci (arrows) adjacent to the uterus. Subsequent surgery proved these “nodules” to be DGs.

Figure 9.

Metastatic ovarian cancer with multiple calcified perihepatic metastatic implants. Axial unenhanced CT demonstrates multiple high-density foci abutting the liver (arrowheads), and at least one round 1-cm focus of fluid density with peripheral calcification (arrow), mimicking a small abscess adjacent to a DG.

Figure 10.

Loose body in a 53-year-old male without prior cholecystectomy. (a, b) Axial contrast-enhanced CT images obtained 4 months apart demonstrate a round peripherally calcified soft tissue 1-cm nodule (arrow) located anteriorly in the pelvis (a) and in the rectovesical pouch on the subsequent study (b), such mobility between the two studies is typical of a loose body.

Figure 11.

Multiple colonic diverticula. Axial unenhanced CT demonstrates four rounded hyperdense foci (arrows), some with lucent centres, representing colonic diverticula with inspissated dense fluid or contrast material, mimicking dropped gallstones.

Figure 12.

Dropped appendicolith. (a) Axial contrast-enhanced CT 3 days after laparoscopic appendectomy shows a dense opacity (arrow), not present on pre-operative CT (not shown), in Morison's pouch, representing a dropped appendicolith. (b) Axial contrast-enhanced CT obtained 13 months later, when patient presented with fever and abdominal pain, shows a heterogeneous fluid collection surrounding the dropped appendicolith (arrow). Note intact gallbladder (arrowhead).