Computed Tomography in acute cholecystitis

Abdominal CT scans are inferior to ultrasonography in diagnosing gallstones. The major application of CT scans is to define the course and status of the extrahepatic biliary tree and adjacent structures. It is the test of choice in evaluating the patient with suspected malignancy of the gallbladder, the extrahepatic biliary system, or nearby organs, in particular, the head of the pancreas. Use of CT scan is an integral part of the differential diagnosis of obstructive jaundice . Spiral CT scanning provides additional staging information, including vascular involvement in patients with periampullary tumors.
                 In many institutions, the initial noninvasive imaging modality of choice for patients with suspected biliary obstruction is CT, specifically helical CT scanning (Fig. 100-2). The latter provides rapid imaging. The disadvantages include
(1) the requirement for intravenous contrast administration (not always possible in patients with renal dysfunction)
(2) the use of ionizing radiation
(3) additional cost as compared to US


               CT scanning is less “operator dependent” than US. Thus, it is reproducible and studies are easily compared. It is therefore important for follow-up after biliary surgical or interventional procedures. When correctly performed, CT provides valuable information not only of the intrahepatic and extrahepatic bile ducts but also of structures outside the biliary system (e.g., liver parenchyma, adjacent lymph nodes, the presence of choledocholithiasis, neoplasms).
               To optimize biliary tract imaging with helical CT, a 3- to 5-mm collimated scan (pitch 1:1) should be performed from the porta hepatis through the pancreatic head during the portal venous phase of contrast enhancement. Overlapping axial reconstructions of the helical acquisition can aid interpretation. The extrahepatic bile duct is typically visualized throughout its entire course in the hepatoduodenal ligament as a water-density tubular structure. At the level of the pancreatic head, the distal common bile duct has a round or oval configuration. Although normal intrahepatic bile ducts can occasionally be seen with current CT technology, it usually is not difficult to differentiate normal intrahepatic bile ducts from true dilated ducts. Normal intrahepatic ducts should be less than 2 mm and not confluent.                  Multidetector CT technology shortens acquisition time. This has the advantage of allowing single breath-hold imaging, which is important when scanning pediatric or critically ill patients. Multidetector CT also allows the ability to obtain a three-dimensional data set, which enables image reconstruction for CT angiography and cholangiography

Ultrasonography in acute cholecystitis

Ultrasonography
US is a relatively inexpensive, noninvasive imaging modality used to confirm the presence of biliary ductal dilation . US, when performed correctly, may provide considerable information to assist the internist, surgeon, gastroenterologist, or interventional radiologist in the management of patients with hepatobiliary disease.

Though operator dependent, US is generally readily available in most medical institutions caring for patients with biliary disease. The normal gallbladder is an anechoic (fluid-filled) oval structure. The position of the gallbladder fundus is variable; however, the gallbladder neck has a fixed relationship with the main interlobar fissure of the liver. The wall of the gallbladder is a thin, smooth, echogenic line that should not exceed 3 mm. The gallbladder wall may appear abnormally thickened in the nonfasting state. Pathologic gallbladder wall thickening may be secondary to cholecystitis, hepatitis, hepatic failure, congestive heart failure, renal failure, neoplasm, or human immunodeficiency virus. The common hepatic duct is easily visualized in the porta hepatis as it crosses the undivided right portal vein. In most cases, the hepatic artery passes between the common hepatic duct and portal vein; however, in 10% to 15% of patients, the hepatic artery is located anterior to the common hepatic duct. The joining of the cystic duct with the common hepatic duct forms the common bile duct. The cystic duct is generally located posterior to the common hepatic duct and may travel a variable distance before joining the common hepatic duct. Within the hepatoduodenal ligament, the common bile duct is anterior and lateral to the portal vein. As the common bile duct travels caudally to the second portion of the duodenum, it assumes a more posterior position. On US, the normal diameter of the extrahepatic bile ducts may range from 4 to 8 mm. The size of the extrahepatic bile ducts may increase slightly with increasing patient age, after cholecystectomy, or bile duct surgery, or after endoscopic manipulation of the duct. The maximum upper limit of normal in the extrahepatic biliary tree after cholecystectomy is 10 mm. However, it is generally accepted that a duct that measures 6 mm or greater in symptomatic patients warrants further investigation. Intrahepatic bile ducts can be considered normal if they are less than 40% of the diameter of the accompanying portal vein or if they are 2 mm or less in diameter. Intrahepatic biliary dilation may appear as an alteration in the normal anatomic relationships in the portal triads and a confluence of tubular structures near the hilum of the liver. The appearance of peripheral intrahepatic duct dilation has been called the parallel channel sign Color-flow Doppler US is useful in this setting to confirm the presence of biliary dilation. Using color-flow Doppler US, one may differentiate between vessels and dilated biliary ducts. US accurately predicts the level of biliary obstruction in the majority of cases (92%), but it is less accurate in suggesting the correct cause (71%). There are many causes of biliary obstruction. These include stones, neoplasms, inflammatory disease, and congenital causes (rare). Newer noninvasive techniques include the use of tissue harmonic imaging to improve visualization of the bile ducts. US coupled with the use of CT or MRCP to determine extent of disease assists the interventional radiologist, gastroenterologist, or surgeon in planning therapy.

An ultrasonography of the gallbladder. Arrows indicate the acoustic shadows from stones in the gallbladder

GENERAL APPROACH TO THE PATIENT WITH OBSTRUCTIVE JAUNDICE

GENERAL APPROACH TO THE PATIENT WITH OBSTRUCTIVE JAUNDICE

A patient presenting with signs and symptoms of obstructive jaundice undergoes clinical evaluation and a diagnostic work-up. Included in the latter are laboratory data (i.e., blood studies) and imaging. The goals of imaging include the following:

	1.	Confirmation of the presence of obstructive jaundice using cross-sectional imaging (i.e., US, CT, or MRI)
	2.	Precisely defining biliary anatomy to determine the severity and the level of obstruction, using the techniques of MRCP (noninvasive); percutaneous transhepatic cholangiography (PTC or PTHC) and percutaneous biliary drainage (PBD or PTBD) (invasive); and endoscopic retrograde cholangiopancreatography (ERCP) (invasive)
	3.	Image-based assistance in the staging of malignant disease
	4.	Image-based guidance for possible nonsurgical therapy

Diagnostic Studies :Blood Tests

Blood Tests

When patients with suspected diseases of the gallbladder or the extrahepatic biliary tree are evaluated, a complete blood count and liver function tests are routinely requested. An elevated white blood cell (WBC) count may indicate or raise suspicion of cholecystitis. If associated with an elevation of bilirubin, alkaline phosphatase, and aminotransferase, cholangitis should be suspected. Cholestasis, an obstruction to bile flow, is characterized by an elevation of bilirubin (i.e., the conjugated form), and a rise in alkaline phosphatase. Serum aminotransferases may be normal or mildly elevated. In patients with biliary colic or chronic cholecystitis, blood tests will typically be normal.

Physical examination of acute cholecystitis

           Physical examination may be normal, but mild epigastric or right upper quadrant tenderness as well as mild icterus are common.
          The symptoms may also be intermittent, such as pain and transient jaundice caused by a stone that temporarily impacts the ampulla but subsequently moves away, acting as a ball valve.A small stone may pass through the ampulla spontaneously with resolution of symptoms

          Tenderness  and  a positive Murphy’s sign help distinguish acute cholecystitis from biliary colic,  in which there  is no  infammatory process. Given that the common bile duct is not obstructed, profound jaundice in the setting of a picture of acute cholecystitis is rare and should raise  the suspicion  of  cholangitis,  with  obstruction  of  the common bile duct, or Mirizzi syndrome, in which infammation or a stone in the gallbladder neck leads to infammation of the adjoining  biliary  system,  with  obstruction  of  the  common hepatic duct.

Murphy’s sign

Presentation of acute Calculous Cholecystitis

             About 80% of patients with acute cholecystitis give a history compatible with chronic cholecystitis. Acute cholecystitis begins as an attack of biliary colic, but in contrast to biliary colic, the pain does not subside; it is unremitting and may persist for several days.
            The pain is typically in the right upper quadrant or epigastrium, and may radiate to the right upper part of the back or the interscapular area. It is usually more severe than the pain associated with uncomplicated biliary colic. The patient is often febrile, complains of anorexia, nausea, and vomiting, and is reluctant to move, as the inflammatory process affects the parietal peritoneum. This process will cause an arrest of  inspiration with gentle pressure under the right costal margin,  a  fnding  known  as Murphy’s  sign. Tenderness  and  a positive Murphy’s sign help distinguish acute cholecystitis from 
biliary colic,  in which there  is no  infammatory process. Given that the common bile duct is not obstructed, profound jaundice

                                                             Murphy’s sign

Acute Calculous Cholecystitis

Acute cholecystitis results from obstruction of the cystic duct, usually secondary to a gallstone. Local inflammatory responses may also result in edema and inflammation of the gallbladder
- 90% to 95% of cases of cholecystitis are calculous in origin.
- 5% to 10% of the cases and is acalculous cholecystitis more common in critically ill trauma, burn, and sepsis patients and individuals with cardiac, diabetic, and acquired immunodeficiency syndrome conditions.This type is higher incidence of gangrene, emphysematous infection, perforation, and mortality

Stagnation of bile and resultant infection from an impacted gallstone was once thought to be the main pathophysiology in the development of cholecystitis. However, studies investigating bile cultures have shown that only 15% to 30% of patients undergoing cholecystectomy for cholecystitis have positive bile cultures. This indicates that inflammation of the gallbladder is not simply an infectious process but rather a multifactorial series of events that are initiated by gallstone obstruction of the cystic duct. A well-described “ball-valve” mechanism has been attributed to the characteristic pain. Initially, a gallstone impacts at the neck of the gallbladder leading to obstruction and wall edema. This leads to the formation of lysolecithin, a mucosal toxin. Prostaglandin synthesis increases and amplifies the inflammatory response. The edema and inflammation can then result in the lifting of the gallbladder wall away from the stone, thereby disimpacting the stone and effecting drainage through the cystic duct. In most patients this series of events plays through and conservative management is effective. In some patients, however, disimpaction does not occur, and this results in continued cystic duct obstruction and leads to venous congestion, gallbladder ischemia, biliary stasis, and a systemic inflammatory response that necessitates operative intervention.

                                             Anatomic relationships of the gallbladder