Sonography of gangrenous cholecystitis.

Gangrenous cholecystitis is an acute surgical emergency, which requires early cholecystectomy. Differentiation of patients with gangrenous cholecystitis from those with non-gangrenous cholecystitis can be difficult, both clinically and with imaging. Careful attention to the following sonographic signs suggests the presence of gangrenous cholecystitis decreased focal wall perfusion on Color Doppler, irregular gall bladder mucosal outline, gall bladder wall thickening with signs of de-lamination, gas within the gall bladder, absence of calculi, and large peri-cholecystic collections. Both sonogram with color flow imaging and contrast-enhanced Computed tomography are complementary investigations to establish this important diagnosis in critically ill patients.

INTRODUCTION

Gangrenous acute cholecystitis is an uncommon form of cholecystitis, which if undiagnosed, is rapidly fatal. The incidence varies from 2% to 30% in most surgical series of acute cholecystitis.[1] Gangrenous cholecystitis is more likely to occur in older patients, especially men who with cardiovascular disease or diabetes, with an elevated white cell count, viz., greater than 14 900 cells/mm3.[23] The clinical diagnosis can be extremely challenging as the differentiation from acute cholecystitis may be very difficult pre-operatively as laboratory and imaging results may be non specific.[4] Murphy's sign of right upper quadrant tenderness on palpation over the distended gall bladder may actually be absent in two thirds of the patients due to the denervation of the gall bladder from necrosis of the wall.[5] For effective management, prompt open cholecystectomy is often the treatment of choice, rather than laparoscopic cholecystectomy. There is an increased prevalence of gall bladder perforation in up to 10% of patients with associated peritonitis, fistula and intra-peritoneal abscess formation.[12] Therefore, it is important to have a high index of suspicion of gangrenous cholecystitis, especially in patients who are diabetic and/or have renal and cardiac impairment.[367] This review emphasizes the value of sonography in the diagnosis of gangrenous cholecystitis and its complementary role with other imaging investigations, especially computed tomography of the upper abdomen.

Early reports using gray- scale sonography found that abdominal sonography was insensitive in detecting gangrenous cholecystitis. Emphasis was placed on detecting a thickened “striated” gall bladder wall as a sign of wall necrosis [Figure 1].[89] However, this sign is also found in acute cholecystitis and more commonly represents edema of the gall bladder wall rather than necrosis or intramural hemorrhage. Other signs suggesting gall bladder wall necrosis include intra-luminal membranes and asymmetrical wall thickness.[9] Therefore, there is considerable overlap between the sonographic findings of gangrenous cholecystitis and those of cholecystitis: in both conditions, gall bladder wall thickening with “striation” greater than 3 mm occurs, and there is distention of the gall bladder lumen greater than 6 cm in transverse diameter, presence of peri-cholecystic fluid collections and the presence of cholelithiasis. However, Murphy's sign may only be present in one third of the patients with gangrenous cholecystitis compared to over 95% of the patients with cholecystitis.[5] Mok et al.,[10] emphasized the loss of the gall bladder mucosa/wall interface echo as a sensitive predictive sign in a small prospective series of 6 patients. With color flow Doppler ultrasound, and along with the ability to visualize and quantify gall bladder wall perfusion, the sensitivity to detect wall necrosis has improved considerably [Figures 2 and 3]. In gangrenous cholecystitis, focal perfusion defects are present within the necrotic wall of the gall bladder;, this is not present in patients with cholecystitis, where perfusion is actually increased from wall inflammation. This important sign was confirmed by Wu et al.,[11] when reviewing Computed tomography (CT) imaging of 25 patients with gangrenous cholecystitis. They found that there was a significant correlation between CT perfusion defects of the gall bladder wall and the presence of gall bladder wall necrosis. The only other CT signs of value were the presence of peri-cholecystic “stranding” of the surrounding fat in the gall bladder fossa and the absence of gall bladder calculi. Radio-nuclide biliary imaging with Technetium99m di-isoimmino-diacetic acid (DISIDA) can be falsely negative in patients with gangrenous cholecystitis, although a “rim” sign surrounding the gall bladder from peri-hepatic uptake of isotope has also been reported in some patients.[1213]

Figure 1

Sonogram of a patient with gangrenous cholecystitis demonstrates a striated irregular thickened gall bladder wall with a calculus in the neck of the gall bladder

Figure 2

Color flow Doppler sonogram of a patient with gangrenous cholecystitis with absent color flow within the necrotic wall of the gall bladder

Figure 3

Sonogram of a small peri-cholecystic collection in patients with gangrenous cholecystitis following perforation from wall necrosis

The initial investigation is sonography with Doppler color flow imaging. This will identify those acutely ill patients will with gall bladder focal perfusion defects, as well as those with the sonographic signs of cholecystitis. To confirm the diagnosis, an un-enhanced and contrast-enhanced CT scan of the abdomen is recommended, especially in the high-risk patient.