Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

Table 8.2. Causes of diffuse gallbladder wall thickening

Local conditions

Acute cholecystitis

Chronic cholecystitis

Hepatitis

Associated with portal hypertension

Portal vein thrombosis

Acute viral hepatitis

AIDS cholangitis

Systemic disorders

Hypoalbuminemia

Renal failure

Ascites

Chemotherapy

Severe congestive heart failure

Graft-versus-host disease

tis, other conditions show minimal gallbladder wall enhancement and pericholecystic liver enhancement.

Scintigraphy

Cholescintigraphy with Tc-99m-HIDA or one of the other IDA derivatives assesses gallbladder function. For this test to be valid, however, reasonably normal hepatic uptake and excretion is necessary. Cholescintigraphy results are not meaningful in a setting of severe hepatocellular dysfunction or common bile duct obstruction. The test should also be interpreted with caution after sphincterotomy because some of these patients have gallbladder nonvisualization even without acute cholecystitis. Likewise, gallbladder nonvisualization is found in patients with cystic fibrosis and in a setting of a choledochal cyst.

Several hours of fasting are normally required before cholescintigraphy is performed; otherwise, resultant gallbladder contraction prevents radiotracer and bile flow into the gallbladder, thus leading to a false-positive test. One disadvantage of cholescintigraphy is that it generally requires several hours to perform this test, a fact accentuated by ultrasonographers.

Gallbladder ejection fraction is measured during cholecystokinin cholescintigraphy and by US. In most institutions an ejection fraction of <35% is considered abnormal, although this limit varies depending on injection method used. In general, a normal gallbladder ejection fraction excludes dysfunction. Both scintigra-

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phy and US are reproducible techniques in studying gallbladder contraction, but these two tests are not directly interchangeable.

A fatty meal induces gallbladder emptying, and, in general, a standardized liquid fatty meal results in good intraindividual reproducibility of gallbladder emptying; there is, however, considerable interindividual variability. Aside from CCK-dependent effects, other mechanisms probably are involved in gallbladder emptying. Gallbladder US in young, nulliparous women reveals fasting volume and postprandial ejection fractions to be slightly greater during the luteal phase than during the follicular phase. Gallbladder volume roughly doubles during pregnancy and then decreases postpartum. Gallbladder motility and gallbladder ejection fraction are significantly impaired in late pregnancy.

Gallbladder visualization during cholescintigraphy (or oral cholecystography) essentially excludes acute cholecystitis. Normally nonvisualization is defined as a lack of gallbladder activity up to 4 hours after radiotracer administration.

Some patients have increased tracer activity in liver parenchyma adjacent to the gallbladder—the pericholecystic rim sign. This activity is associated with acute cholecystitis in most but not all patients and is believed to be secondary to increased blood flow to parenchyma adjacent to an inflamed gallbladder. It is not to be confused with tracer within the gallbladder.

What is the significance of gallbladder nonvisualization but the presence of a pericholecystic rim sign? Morphine-augmentation is helpful in visualizing the gallbladder in some and thus excluding acute cholecystitis, although even then there are false-positives.

Gallbladder contractility is decreased in patients with a prior vagotomy. Likewise, the gallbladder does not contract normally in patients with achalasia or those on octreotide therapy.

Gallbladder contraction before injecting Tc-99m-IDA allows subsequent tracer material to accumulate within the gallbladder and decreases the number of false-positive results. A common drug used to stimulate gallbladder contraction is cholecystokinin-octapeptide (CCK-8). It is used selectively; for instance, in some institutions patients who have been fasting for 24 hours or longer are pretreated

GALLBLADDER AND BILE DUCTS

with CCK while others are not. Slow infusion of a physiologic dose of CCK-8 results in more complete gallbladder emptying than a bolus injection.

If the gallbladder is not visualized in 60 to 90 minutes, often 0.04mg/kg morphine sulfate is injected IV and additional images are obtained for 30 to 60 minutes. Intravenous morphine increases sphincter of Oddi pressure and thus bile accumulates within the gallbladder. If the gallbladder still does not visualize during morphine-augmented cholescintigraphy, in the appropriate clinical setting a diagnosis of acute cholecystitis is reasonable. If, on the other hand, the gallbladder is not visualized within an initial 90 minutes but is observed after morphine, abnormal gallbladder function should be suspected.

A variant of the above technique is to combine cholecystokinin pretreatment together with morphine augmentation. Imaging is performed in patients after Tc-99m-BrIDA until gallbladder activity is identified or up to 90 minutes postinjection; if no gallbladder is identified, a second dose of BrIDA is followed by morphine sulfate.

Gallbladder scintigraphy can be performed using indium-111–labeled autologous white blood cells. Labeled white blood cells accumulate within the gallbladder wall in acute cholecystitis. In some patients, however, delayed imaging is required, thus delaying the diagnosis.

Perforated Cholecystitis

Neglected cholecystitis evolves into gallbladder perforation. Most perforations are walled-off and result in pericholecystic fluid or a right upper quadrant abscess, a common location being between the gallbladder and adjacent liver. Free perforation into the peritoneal cavity results in bile peritonitis, while an occasional perforation into the liver evolves into a liver abscess.

Chronic perforations have evolved into a cholecystocutaneous or cholecystoenteric fistula, and even a cholecystogastric fistula (Fig. 8.7). Some cholecystoenteric fistulas are secondary to gallstones eroding into the gut (discussed in Chapter 4).

Detection of gallbladder perforation is not straightforward. Adherent omentum, fat, or

adhesions often mask a recent perforation. Computed tomography visualizes only about half of gallbladder wall defects, and US even less. Pericholecystic fluid and gallbladder wall thickening are often the only pertinent imaging findings.

Gangrenous Cholecystitis

Gangrenous cholecystitis is a sequela of either calculus or acalculus cholecystitis.

Computed tomography and US reveal similar findings. The gallbladder wall is irregular and thick. Sloughed gallbladder mucosa is seen as thin intraluminal linear echoes parallel to the gallbladder wall and a striated wall edema pattern seen with US should suggest gangrenous cholecystitis. Often inflammation extends to surrounding structures. A sonographic Murphy’s sign is less often elicited in these patients than with more conventional acute cholecystitis.

Color Doppler US reveals no flow within a thickened gallbladder wall in acute necrotizing cholecystitis.

Occasionally a thin rim of increased scintigraphic activity, a rim sign, is seen adjacent to the gallbladder fossa, a sign associated with gallbladder wall gangrene. The presence of a

Figure 8.7. Spontaneous cholecystocutaneous fistula (arrow) secondary to cystic duct obstruction by a stone.

rim sign, together with subsequent gallbladder visualization after administration of morphine, does occur with gallbladder gangrene. The rim sign should be distinguished from tracer activity in adjacent liver parenchyma.

Empyema/Abscess

Empyema, consisting of an obstructed, pusfilled gallbladder lumen, leads to marked gallbladder distention. Ultrasonography shows a markedly distended, hyperechoic sludgecontaining gallbladder. Computed tomography reveals this pus-filled gallbladder content to have greater attenuation than bile. At times a frank abscess is identified (Fig. 8.8).

Laparoscopic cholecystectomy is difficult in the setting of gallbladder empyema and many of these patients undergo conventional cholecystectomy.

Emphysematous Cholecystitis

Emphysematous cholecystitis is a severe form of acute cholecystitis manifesting with gas (not air) in the gallbladder lumen, wall, bile ducts, or pericholecystic tissues, and no abnormal communication between the biliary tree and gastrointestinal tract. It develops if gas-forming bacteria predominate as the infectious organism. Diabetes mellitus is a common underlying condition. Some of these patients do not appear systemically ill, and unless imaging suggests the condition, conservative therapy may be initially

Figure 8.8. Salmonella cholecystitis resulting in a gallbladder abscess (arrow). The abscess was drained percutaneously. (Courtesy of Georgine DeMarino, M.D., University of Iowa.)

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initiated. Nevertheless, mortality is about 15%. Gallstones are absent in some of these patients. In some, a superimposed pneumoperitoneum suggests a perforation. Rarely, simultaneous emphysematous pyelonephritis and emphysematous cholecystitis develop.

The diagnosis is straightforward with conventional radiography and CT, revealing gas in the gallbladder lumen, wall, or pericholecystic tissues (Fig. 8.9). Ultrasono-graphy can miss emphysematous cholecystitis due to gallbladder nonvisualization; intramural gas can be confused with gas within the bowel. If the gallbladder is identified, US reveals highly reflective echoes from nondependent gallbladder wall segments. Exten-sive gas mimics gallbladder wall calcifications. Ultrasonography in one patient revealed gas bubbles rising within the gallbladder and floating to the surface, an appearance called effervescent gallbladder

(30).

Cholescintigraphy may or may not detect cystic duct obstruction in these patients.

Although successful percutaneous gallbladder drainage has been performed in these patient, most are managed surgically.

Eosinophilic Cholecystitis

Histologically, eosinophilic cholecystitis consists of a transmural eosinophilic infiltrate. It is associated with allergic conditions, parasites, hypereosinophilic syndromes, and even with calculous acute cholecystitis. Tissue infiltration with eosinophils and eosinophilic granulomas occurs in necrotizing granulomatous vasculitis involving the gallbladder; similar features are found in allergic granulomatous angiitis of Churg and Strauss.

Therapy

In Pregnancy

Traditionally, a pregnant woman with acute cholecystitis has undergone an open cholecystectomy, although a laparoscopic cholecystectomy is feasible. If warranted, cholangiography is performed.

A pneumoperitoneum is induced during a typical laparoscopic cholecystectomy; gasless laparoscopic cholecystectomy has been performed in pregnant women.

A

Ultrasonography-guided percutaneous cholecystostomy may have a role in pregnancy; biliary decompression is maintained during pregnancy and an elective cholecystectomy performed after delivery.

Percutaneous Cholecystostomy/Aspiration

Does percutaneous transhepatic gallbladder drainage have a role in patients with acute suppurative cholecystitis? A common indication for percutaneous cholecystostomy is in a high surgical risk patient with suspected acute cholecystitis. Ultrasonography is commonly used for guidance. Following successful cholecystostomy most patients improve, the exception being those who have either transmural gallbladder inflammation or gangrene.

Gallbladder aspiration is an alternate procedure to percutaneous cholecystostomy in some patients. In a comparison, 82% of gallbladder aspirations and 100% of percutaneous cholecystostomies were technically successful (31); viscid sludge or pus prevented aspiration through a 21-gauge needle in some patients. Complications are more common with percutaneous cholecystostomy than aspiration. A typical scenario is US-guided percutaneous gallbladder drainage followed by laparoscopic cholecystectomy several days later, after clinical

Figure 8.9. Emphysematous cholecystitis. Radiograph (A) and CT

(B) in two different patients. Gas is present in the gallbladder wall and lumen (arrow). Pneumobilia was identified on other images.

improvement. Inflammation subsides after drainage and the cystic duct often becomes patent, as shown by cholescintigraphy performed after percutaneous gallbladder drainage.

In general, for most patients with acute acalculous cholecystitis a percutaneous cholecystostomy is curative; in the presence of stones, however, a percutaneous cholecystostomy simply provides drainage and an eventual definitive procedure is necessary in most patients.

Open Cholecystectomy

This is not the place to discuss the relative merits and indications of open versus laparoscopic cholecystectomy. Rather, the emphasis here is on the role of imaging. In general, selective rather than routine intraoperative cholangiography is performed. Intraoperative fluoroscopic cholangiography is becoming more popular than static images. A fluoroscopic study can be performed faster than a comparable static study; whether the information obtained with a fluoroscopic image is sufficient is debatable. Quality control of intraoperative images remains a problem.

The indications for intraoperative cholangiography continue to be debated by surgeons. Risk factors correlating with presence of chole-

docholithiasis include history of jaundice, pancreatitis, hyperbilirubinemia and hyperamylasemia. Other criteria whether to perform intraoperative cholangiography include dilated bile ducts on preoperative US and unclear US findings.

Laparoscopic Cholecystectomy

Compared to open cholecystectomy, laparoscopic cholecystectomy requires a longer operative time, but it leads to less pain, a shorter hospitalization, and earlier recovery, and it is associated with a lower morbidity.

Cirrhosis is generally considered a relative contraindication for laparoscopic cholecystectomy.

Extensive adhesions surrounding the gallbladder make laparoscopic cholecystectomy more difficult. Neither CT nor US can reliably detect these adhesions although MRI may have a role. Nonvisualization of the gallbladder on drip infusion cholangio-graphy appears to have value in predicting extensive adhesions, but this study is rarely performed.

Imaging

Laparoscopic cholecystectomy achieves the same end result as an open cholecystectomy, yet with the former procedure surgeons generally prefer a more specific preoperative diagnosis concerning the presence or absence of bile duct stones; although these stones are readily detected by operative cholangiography, their removal during laparoscopic cholecystectomy is problematic and is one of the causes of conversion to an open cholecystectomy. The luxury of T-tube insertion if bile duct stones are detected and their later removal via the T-tube tract by interventional radiologists is not a viable option during laparoscopic cholecystectomy.

Preoperative US aids in predicting whether intraoperative difficulties are encountered. Preoperative US detection of gallbladder wall thickening was found to be the most sensitive and pericholecystic fluid the most specific indicator of a difficult laparoscopic cholecystectomy and the possible need for conversion to laparotomy (32).

Is ERC necessary prior to routine laparoscopic cholecystectomy? Prior to laparoscopic cholecystectomy, ERC not only detects bile duct

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stones but also outlines any anomalous biliary anatomy. If stones are found, a sphincterotomy and stone extraction are then performed. Patients having normal biliary US and normal liver function tests have a >95% negative ERC rate, and for these patients preoperatively ERC appears unnecessary. Some surgeons thus argue that endoscopic sphincterotomy prior to laparoscopic cholecystectomy should be reserved only for seriously ill patients or a suspected malignancy, because laparoscopic transcystic duct exploration can be successful in over 90% of cholecystectomies and is safe. Even if laparoscopic cystic duct exploration is not successful, then either open choledochotomy or postoperative endoscopic sphincterotomy is considered.

The role of operative cholangiography during laparoscopic cholecystectomy is not settled and depends, in part, on whether preoperative imaging is performed. Some surgeons obtain it almost routinely, while others use it selectively. The study is safe and adds little to patient morbidity, but it does prolong surgery. A learning curve exists in performing successful intraoperative cholangiography. A success rate of over 90% can be achieved. Digital C-arm fluoroscopy is a useful guide for intraoperative cholangiography. In general, laparoscopic cholangiography and, if needed, common bile duct exploration obviate a need for a later second procedure such as endoscopic sphincterotomy in patients with retained stones.

Intraoperative cholangiography detects biliary tract complications, and often conversion to an open laparotomy can be performed to repair a visualized injury. Such conversion results in earlier detection of injuries and fewer subsequent procedures to correct the injury.

Operative cholangiography performed primarily to detect bile duct stones is discussed later (see Biliary Stones).

Complications

General: Complications occur during laparoscopic cholecystectomy, with postoperative complication rates of 4% to 6% being typical. Initially, after the introduction of laparoscopic cholecystectomy, bile duct injuries were more common than during the previous open cholecystectomy era. Nevertheless, most recent