August Challenge: What is the likely cause of this radiographic abnormality?

August Challenge: What is the likely cause of this radiographic abnormality?

Maria Flynn, MD

Suffolk Radiology Associates

Suffolk, VA

Each month, Dr. Maria Flynn issues a Radiology Challenge, presenting images from one of a variety of imaging modalities and a case report. Can you diagnose the condition? Follow the link to find out whether your answer was correct, what was really wrong with the patient, and how the patient was treated. Then, come back next month to test your radiographic reading skills on a new case!

Case report

A previously healthy 36-year-old man presented to the emergency department because of diffuse abdominal pain, which had started several days earlier. A contrast-enhanced computed tomography (CT) scan of his abdomen and pelvis ruled out an intra-abdominal infection or mesenteric ischemia (Figure 1). Right upper quadrant ultrasonography was undertaken (Figures 2 and 3).

Challenge: Based on the diagnostic images and the patient?s history, acute cholecystitis is the most likely cause of his abdominal pain. The ultrasound images show the gallbladder wall to be irregularly thickened, with abnormal echogenic material in the nondependent portion. What is the likely cause of this radiographic abnormality?

1. Adherent gallstones
2. Cholesterol crystals
3. Gallbladder polyps
4. Gangrenous cholecystitis
5. Emphysematous cholecystitis

>Click to view answer

Answer: d. Gangrenous cholecystitis

Gangrenous cholecystitis is a progression of acute cholecystitis in which the increased intraluminal pressure leads to necrosis of the gallbladder wall. Various series report that 2% to 38% of acute cholecystitis cases can progress to gangrenous cholecystitis.¹ The condition is more prevalent among older patients, men, patients who have cardiovascular disease but not diabetes, and those with leukocytosis of more than 17,000 white blood cells/mL.^2-4 The complication rate for gangrenous cholecystitis is between 16% and 22% and its mortality rate can approach 22%, compared with a complication rate between 6% and 15% and a mortality rate between 0.5% and 6% for nongangrenous acute cholecystitis.⁵ Because of the increased morbidity and mortality rates of gangrenous cholecystitis, it is important to distinguish this condition from its nongangrenous counterpart preoperatively to ensure rapid surgical intervention.

The clinical picture of gangrenous cholecystitis can be confusing, with up to 50% of patients presenting with only generalized abdominal pain and 6% presenting with no abdominal pain.⁵ Generalized abdominal pain is thought to be secondary to generalized peritonitis from inflammation of the parietal peritoneum. Imaging studies can be extremely helpful with these patients. Both ultrasonography and contrast-enhanced CT scanning have been used as first-line modalities. Typically, if the clinical picture is more consistent with acute cholecystitis, ultrasonography will be used first. In more confusing cases, a contrast-enhanced CT scan may be the initial imaging modality, as was the case with our patient.

Ultrasonography findings for acute nongangrenous cholecystitis include cholelithiasis, Murphy?s sign (ultrasonographically localized maximum tenderness over the gallbladder), a notably distended gallbladder, a thickened gallbladder wall (> 3 mm), and pericholecystic fluid.⁶ Of these findings, the most sensitive is the combination of cholelithiasis and a positive Murphy?s sign.⁶ Although it is not always possible to distinguish uncomplicated acute cholecystitis from gangrenous cholecystitis using ultrasonography, the presence of intraluminal membranes or marked irregularity of the gallbladder wall are specific for gangrenous cholecystitis.^1,2 The intraluminal membranes are from the desquamated gallbladder mucosa.² In up to 66% of patients with gangrenous cholecystitis, the ultrasonographic Murphy?s sign will be absent.⁵ This is thought to be secondary to denervation of the gallbladder wall.⁵ The absence of a Murphy?s sign on ultrasonography increases the likelihood of gangrenous cholecystitis in patients with other ultrasonographic signs of acute cholecystitis.

Sensitive contrast-enhanced CT findings for gangrenous cholecystitis include gas in the lumen wall, intraluminal membranes, an irregular or absent wall, hemorrhage into the gallbladder wall and lumen, and pericholecystic abscess.² Other findings associated with gangrenous cholecystitis include lack of mural enhancement, pericholecystic fluid, marked gallbladder distension, and gallbladder wall thickening.²

References

1. Jeffrey RB, Laing FC, Wong W, et al. Gangrenous cholecystitis: diagnosis by ultrasound. Radiology. 1983;148(1):219-21.
2. Bennett GL, Rusinek H, Lisi V, et al. CT findings in acute gangrenous cholecystitis. AJR Am J Roentgenol. 2002;178(2):275-281.
3. Merriam LT, Kanaan SA, Dawes LG, et al. Gangrenous cholecystitis: analysis of risk factors and experience with laparoscopic cholecystectomy. Surgery. 1999;126(4):680-686.
4. Hunt DR, Chu FC. Gangrenous cholecystitis in the laparoscopic era. Aust N Z J Surg. 2000;70(6):428-430.
5. Simeone JF, Brink JA, Mueller PR, et al. The sonographic diagnosis of acute gangrenous cholecystitis: importance of the Murphy sign. AJR Am J Roentgenol. 1989;152(2):289-290.
6. Hanbidge AE, Buckler PM, O?Malley ME, et al. From the RSNA refresher courses: imaging evaluation for acute pain in the right upper quadrant. Radiographics. 2004;24(4):1117-1135.