Correlation of MDCT imaging findings with intraoperative findings following acute cholecystitis

 

 

Abstract               Background: The purpose of our study was to describe the CT findings of acute cholecystitis and correlate with intra-operative findings. Material and methodology: retrospective study was undertaken for patients who were referred for CT abdomen with features of cholecystitis, over a period of six months. CT abdomen was performed using a 16 slice GE bright speed MDCT and characteristic findings of gallbladder, and associated complications were observed. Results: highest sensitivity and specificity were pericholecystic effusion, gallbladder wall thickness of 7 mm or more, and local or widespread absence of gallbladder wall enhancement. Absence of gallbladder wall enhancement on the preoperative CT image was accurately associated with the presence of intraoperatively identified and pathologically confirmed gangrenous acute cholecystitis Conclusion: While diagnosing acute cholecystitis CT can be useful. CT findings for acute cholecystitis commonly include wall thickening, pericholecystic stranding, high-attenuation bile, pericholecystic fluid, distention and subserosal edema. With the presence of these findings, diagnosis of acute cholecystitis can be suggested.

Key Word: Radiology, MDCT, Gastrointestinal, Acute cholecystitis

 

 

INTRODUCTION

Acute cholecystitis is an acute inflammatory condition of the gallbladder; acute cholecystitis is mainly due to an obstructing calculus in the neck of gallbladder or cystic duct in 95% of cases.¹ Gallbladder overdistension and increase in intraluminal pressure are results of Obstruction of the cystic duct. This increased pressure, along with cholesterol bile, triggers an acute inflammatory response. Inflammatory response by stimulating prostaglandins I2 and E2 are mainly contributed by Gallstones.² Secondary bacterial infection is present in 20% of cases of acute cholecystitis. Mural ischaemia resulting from the increased intraluminal pressure may also contribute to complications such as gangrenous cholecystitis and perforation.³

There are three stages of inflammatory disease: (a) oedematous cholecystitis; (b) necrotising cholecystitis; and (c) suppurative cholecystitis.¹There is wide availability of computed tomography (CT) scanners in emergency departments, leading to increasing numbers of patients undergoing CT examinations for suspected acute cholecystitis. Patients clinically suspected of having acute cholecystitis ultrasonography (US) is the most common diagnostic method of choice^4,5, it is common practice in France for patients with acute abdominal pain and tenderness to undergo contrast material–enhanced computed tomography (CT) during the initial work-up. According to the Tokyo Guidelines CT has been validated as use in the diagnosis of acute cholecystitis⁶.

Anatomy of Gallbladder: Gallbladder is a pear-shaped sac measuring up to 10 cm long and 3 cm diameter and hangs down from inferior surface of liver (fig 1). Thickness of gallbladder wall measures < 4 mm. Cystic duct arises from neck and runs along liver surface to the porta hepatis. Gallbladder neck and cystic duct have a spiral appearance to folds in the mucosa, it is covered by peritoneum on fundus and inferior surface; and occasionally hangs on its own mesentery.

Biliary tree: Segmental biliary ducts unite to form left and right hepatic ducts, which unite to form the common

hepatic duct (CHD) at the porta hepatis; in two-thirds of individuals, the CHD passes anterior to the right hepatic artery.

The CHD is joined by the cystic duct at a variable position (usually 3.5 cm) to form the CBD.

Divisions and relations of the CBD:

• Upper – above the duodenum within the lesser omentum, anterior to the portal vein and to the right of the hepatic artery
• Middle – posterior to the first part of the duodenum with the gastroduodenal artery, sloping away to the right from the portal vein; immediately anterior to the IVC
• Lower – grooves the posterior aspect of the pancreatic head, anterior to the right renal vein; joined by the main pancreatic duct at the ampulla of Vater, opening into the posteromedial wall of the second part of the duodenum.

Diameter of CBD is variable:

• Up to 5 mm till age of 50 years then 1 mm/decade after that age
• Larger in post-cholecystectomy patient (up to 10 mm)

 

Figure 1: The appearance of the gallbladder on CT. (A) Axial and (B) coronal CT images.

 

Figure 2: Segmental biliary drainage of the liver.

 

Figure 3: Normal MRCP. Highly T2-weighted MR sequence which shows fl uid within the pancreaticobiliary system.

Acute cholecystitis pathophysiology: Acute cholecystitis is mostly associated with gallstones (90–95%). In Western societies It is estimated that approximately 10–20% of people have cholelithiasis and out of that one third of those with gallstones usually develop cholecystitis⁷. Mechanism is transient or persistent gallbladder outlet obstruction due to calculus, which leads to cholestasis and subsequent mechanical, chemical, or infectious irritation of the gallbladder wall. Bile breakdown products (lysolecithin), prostaglandins, bacterial infection (present in 40–70%), and mechanical erosion from calculus are thought to be key factors in mucosal irritation.

CT Findings in Acute Cholecystitis: CT findings in acute cholecystitis include distention of gallbladder, wall thickening, hyperenhancement of mucosa, pericholecystic fat stranding or fluid, and gallstones with a sufficient attenuation difference from bile to be visualized (about 65–75%). A mixed cholesterol or pigment stones have similar attenuation to bile and are not identified by standard CT kilovoltage settings^8-11. Reactive hyperaemia resulting in increased enhancement of the hepatic parenchyma of the gallbladder fossa may also be present (CT rim sign). The gallbladder is considered distended if it measures greater than 5 cm in the short axis and greater than 8 cm in length. Wall thickening was defined at greater than 4 mm in a non-collapsed gallbladder (short axis greater than 2 cm)⁹. Diffuse gallbladder wall thickening is a nonspecific finding that is associated with a wide variety of disease states including hypoalbuminemia, ascites, chronic cholecystitis, hepatitis, and unrelated inflammatory processes elsewhere in the abdomen (such as pancreatitis)^12,13.

 

METHODOLOGY

We had reviewed hospital discharge records of the past one year period to identify patients with a discharge diagnosis of acute cholecystitis. This list of patients was cross-referenced with radiology files to identify patients who had CECT scans before cholecystectomy. All of these patients had subsequent pathologic documentation of acute cholecystitis. All CT scans were performed using 16 slice GE bright speed MDCT and all of the patients had received IV contrast material. The CT scans were reviewed by two other abdominal imagers in consensus for the presence of gallstones, gallbladder size, bile attenuation, gallbladder wall thickening, pericholecystic fluid, subserosal edema, pericholecystic stranding, gas within the lumen or wall of the gallbladder, and sloughed membranes. Patients with other diagnoses, such as acute diverticulitis of the right sided colon or acute appendicitis, were excluded.

 

Table 1: Intraoperative findings of 54 patients with acute cholecystitis

 

Table 2: CT findings of 54 patients with acute cholecystitis

* Gallbladder wall thickness at CT was compared with a pathologic measurement of the gallbladder wall specimen.

† Absence of gallbladder wall enhancement was evaluated after intravenous administration of contrast agent.

 

Table 3: CT findings of 54 patients with acute cholecystitis

Data in parentheses are numerators and denominators. * Gallbladder wall thickness at CT was compared with a pathologic measurement of the gallbladder wall specimen. † Absence of gallbladder wall enhancement was evaluated after intravenous administration of contrast agent.

DISCUSSION

In a study conducted by Morris et al he had reported 17 patients had developed gallbladder perforation in association with emphysematous cholecystitis, gangrenous acute cholecystitis, or both ¹⁴. The MDCT features of these patients included mainly poor definition and irregularity of the gallbladder wall with or without a defect ¹⁵. One patient in our study had a disrupted gallbladder wall and pericholecystic abscess. However, 6 of the 11 non selected patients who were diagnosed with severe acute cholecystitis had gallbladder perforation.

 

CONCLUSIONS

While diagnosing acute cholecystitis, CT can be useful. CT findings for acute cholecystitis commonly include wall thickening, pericholecystic stranding, high-attenuation bile, pericholecystic fluid, distention and subserosal edema. With the presence of these findings, diagnosis of acute cholecystitis can be suggested. Widespread absence of gallbladder wall enhancement on CT image can be associated with gangrenous acute cholecystitis.

 

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