Clinical History
A 93-year-old women was referred to the emergency department by her general practitioner because of decreased appetite and general fatigue for one week. The only relevant finding in the medical history was the presence of a gallstone for several years. There was no history of biliary or hepatic surgery.
Imaging Findings
Plain abdominal radiography shows a round calcified structure in the right lumbar region (Fig. 1). It projects lateral and caudal to the gallbladder fossa. There is a normal bowel gas pattern.
Contrast enhanced CT images (Fig. 2) show a hyper-attenuating inflamed gallbladder wall. The abdominal fat around the gallbladder is infiltrated. There is a normal outlining of the liver. At the fundus of the gallbladder there is a defect in the gallbladder wall. A fistula trajectory arises from this wall defect, goes through the muscles of the abdominal wall and extends to the subcutaneous fat (Fig. 3). The radio-opaque round structure can be seen in the subcutaneous compartment of the fistula (Fig. 4). It is a calcified gallstone that has eroded through the inflamed gallbladder wall. This process has been named ‘spontaneous cholecystocutaneous fistula’.
Discussion
Before the modern age of antibiotic therapy and cholecystectomy procedures, spontaneous cholecystocutaneous fistula was a more common finding [1]. Today, it is a rare complication of cholecystitis. The accepted theory for the pathophysiology is that the high intraluminal pressure leads to impaired blood flow of the gallbladder wall, which causes mural necrosis and perforation. This allows the gallstone to erode through the gallbladder wall [2]. Malignancy of the gallbladder or acalculous cholecystitis have also been reported as a cause of spontaneous cholecystocutaneous fistula [3]. In contrast to this case, the gallstone can perforate into adjacent abdominal organs, such as the duodenum or small bowel [3].
This pathology occurs in an elderly population. Presentation is atypical, with a long-standing low-grade infectious process and indistinct complaints. The patient can become septic if the infection is not contained. Imaging is needed to recognize this rare infectious process and to evaluate the extent.
Computed Tomography (CT) and ultrasound (US) are the modalities of choice to evaluate this abdominal infectious process [1]. These modalities can demonstrate radio-opaque gallstones if present. Imaging typically shows a thickened and hyper-attenuating gallbladder wall (Fig. 2). Pericholecystic inflammatory fat stranding is an indirect sign. The fistula trajectory has a characteristic hyper-attenuating wall with a relatively hypo-dense content that extends from the gallbladder to the subcutaneous abscess (Fig. 3). If the fistula has already drained externally, a fistulography can be performed.
The expected evolution of this inflammatory process would be a spontaneous evacuation of the abscess through the skin. If evacuation has not yet occurred, drainage of the abscess would be the therapy of choice. In this elderly population, a conservative approach is often preferred because of the high risk for an emergency surgical intervention and extensive co-morbidity. Imaging can evaluate the extent of the infectious process and will contribute to therapy planning. In this case, a surgical cutaneous incision was made, the gallstone was removed and pus was drained. There was persistent bile drainage through the cutaneous incision. Given the age and clinical condition of the patient, the treating physicians opted for a conservative approach.
Typically, the patient is an elderly woman with a chronic neglected, calculous and contained cholecystitis. The patient often has an atypical clinical presentation without fever or pain. US and CT are the modalities of choice to evaluate the extent of the infectious process and to demonstrate the fistula. A conservative approach to treatment is often preferred.
Differential Diagnosis List
Spontaneous cholecystocutaneous fistula with subcutaneous gallstone.
Cholecystocutaneous fistula with subcutaneous gallstone
Infectious cutaneous abcess with calcification
Corpus alienum with surrounding infectious abcess
Final Diagnosis
Spontaneous cholecystocutaneous fistula with subcutaneous gallstone.
