Dropped Gallstone with fistulous tract formation

A 60-year-old male patient presented with history of abdominal pain and pus discharge from a sinus in right lumbar region for 6 months. He had a past history of laparoscopic cholecystectomy 6 years back and pigtail insertion for drainage of post-op collection.

Non-contrast Magnetic resonance imaging (MRI) and computed tomography (CT) of abdomen were done.

MRI of the abdomen showed non-visualization of the gallbladder suggestive of post-cholecystectomy status (Fig-1), an ill-defined area of T1 hypointense, T2FS heterogeneously hyperintense signal in the sub-hepatic space with central T1 and T2 hypointense signal (Fig- 2a, 2b, 2c) and a fistulous tract extending from the sub-hepatic space (hepatorenal pouch) through the lateral abdominal wall muscles into the subcutaneous planes (Fig -3a, 3b).

These findings could possibly represent a dropped gallstone with adjacent chronic inflammatory reaction and fistulous tract formation.

For the confirmation of findings, plain CT abdomen was done which showed a small hypodense mass in the subhepatic region with tiny central hyperdense foci representing dropped GB calculi (Figures 4 and 5).

The fistulous tract was at the site of the previous pigtail insertion track.

Laparoscopic cholecystectomy is the current surgical technique of choice for treatment of symptomatic cholelithiasis, due to lower number of complications compared to open cholecystectomy, as well as shorter hospital stay and postoperative recovery period. Complications of laparascopic cholecystectomy are infrequent, but they have high morbidity [1].

Laparoscopic cholecystectomy has an overall complication rate of 1.6%–5.3%. The most common surgical complications requiring imaging are bile duct injury and retained common bile duct stones, which occur in 0.32%–0.52% and 0.5% of cases, respectively. Up to 40% of laproscopic cholecystectomies result in gallbladder perforation and subsequent gallstone spillage into the peritoneum (ie, “dropped stones”)[2].

Due to peritoneal insuffulation and irrigation during surgery, retained gallstones are widely disseminated throughout the abdominopelvic cavity. A dropped gallstone acts as an inflammatory nidus, causing an inflammatory response. This is most common with pigment stones, which may contain viable pathogens. The most common complication of dropped gallstones is abscess formation; other complications include sinus track and fistulous communication with the skin or the bowel. The perihepatic space (particularly hepatorenal pouch) is the most common location for a dropped gallstone and subsequent abscess formation [3].

At imaging, the appearance of dropped gallstones vary depending on the stone composition, size, and number of stones spilled. On CT, gallstones may be seen as radio densities within an abscess or inflammatory mass.

On Ultrasound the radiolucent stones can be visualized within an abscess as echogenic foci with post-acoustic shadowing.

MRI can be helpful in these cases, with stones showing hypointense signal on T1 and T2W sequences, whereas pigment stones can be T1 hyperintense with no enhancement on contrast administration[2].

The treatment of dropped gallstone and its consequences depends on the clinical perspective. It primarily entails the removal of causative agent via percutaneous or open technique.

 It is recommended to remove all the dropped gallstones during surgery; if not it must be documented [4].

Teaching point:

A Radiologist may be the first person to suggest the diagnosis of dropped gallstone.

A dropped gallstones should be considered as a potential source of recurrent intraabdominal/ intrathoracic abscesses or fistula formation in any patient who presents months to years after laparoscopic cholecystectomy.

Written informed patient consent for publication has been obtained.