Diagnostic ultrasound ( PDFDrive )

194 PART II Abdominal and Pelvic Sonography
Causes of Sonographic Nonvisualization of
Gallbladder
Previous cholecystectomy
Physiologic contraction
Fibrosed gallbladder duct—chronic cholecystitis
Air-illed gallbladder or emphysematous cholecystitis
Tumefactive sludge
Agenesis of gallbladder
Ectopic location
is also absent. he lack of visualization of the gallbladder on
sonography in symptomatic patients warrants CT or MRCP
to avoid an unnecessary surgical procedure. he gallbladder
may also lie in ectopic positions, including suprahepatic, suprarenal,
within the anterior abdominal wall, or in the falciform
ligament. 11
he gallbladder may fold unto itself, the body onto the neck,
or the fundus onto the body. he latter is called a phrygian cap
and has no clinical importance. A septate gallbladder is composed
of two or more intercommunicating compartments divided by
thin septa. 11 his is distinguished from the hourglass gallbladder
(see “Adenomyomatosis”), which has thick septa separating the
components. Duplication of the gallbladder oten occurs with
duplication of the cystic duct and may be diagnosed prenatally.
Variations of the cystic duct are discussed in the section on
anatomy of the biliary tree.
he gallbladder derives its blood supply from the cystic artery,
which arises from the right hepatic artery, or less oten from the
gastroduodenal artery. In acute cholecystitis an enlarged, prominent
cystic artery may be identiied on sonography.
Sonographic Technique
Evaluation of the gallbladder is usually performed with routine
sagittal and transverse sonograms. If the gallbladder is not
visualized, however, maneuvers to evaluate the gallbladder fossa
are essential to avoid missing gallbladder disease. his is done
primarily with subcostal oblique sonograms, performed with
the let edge of the transducer more cephalad than the right
edge. he face of the transducer is directed toward the right
shoulder. A sweep from cephalad to caudad shows the middle
hepatic vein superiorly and the gallbladder fossa inferiorly in a
single plane. hey form the anatomic boundary separating the
right and let liver lobes. he fossa runs from the anterior surface
of the right portal vein obliquely to the surface of the liver. It
may have a variable appearance, mainly inluenced by the state
of the gallbladder, and ater gallbladder removal the fossa appears
as an echogenic line as a result of the remaining connective
tissues.
Ingestion of food, particularly fatty food, stimulates the
gallbladder to contract. he contracted gallbladder appears thick
walled and may obscure luminal or wall abnormalities. herefore
the examination of the gallbladder should be performed ater a
minimum of 4 hours of fasting.
Gallstone Disease
Gallstone disease is common worldwide. he prevalence of
gallstones is highest in the European and North American
populations (≈10%) and lowest in the East Asian (≈4%) and
sub-Saharan African (2%-5%) populations. 75 Common risk factors
are age, female gender (but not in Asian populations), fecundity,
obesity, diabetes, and pregnancy. Although most patients are
asymptomatic, about one in ive develops a complication, oten
biliary colic. he risk of acute cholecystitis or other serious
complications of gallstones in patients with a history of biliary
colic is about 1% to 2% per year. 76
Sonography is highly sensitive in the detection of stones
within the gallbladder. he varying size and number of stones
within the gallbladder lead to a variable appearance on sonography
(Fig. 6.36, Video 6.9). he large diference in the acoustic impedance
of stones and adjacent bile makes them highly relective,
which results in an echogenic appearance with strong posterior
acoustic shadowing. Small stones (<5 mm) may not show shadowing
but will still appear echogenic. Mobility is a key feature of
stones, allowing diferentiation from polyps or other entities.
Various maneuvers may be used to demonstrate mobility of a
stone; scanning with the patient in the right or let lateral decubitus
or upright standing position may allow the stone to roll within
the gallbladder.
Multiple stones may appear as one large stone, producing
uniform acoustic shadowing. When the gallbladder is illed with
small stones or a single giant stone, the gallbladder fossa will
appear as an echogenic line with posterior shadowing. his can
be diferentiated from air or calciication in the gallbladder wall
by analysis of the echoes. With stones the gallbladder wall is
irst visualized in the near ield, followed by the bright echo of
the stone, followed by the acoustic shadowing, called the wallecho-shadow
complex (Fig. 6.36B). When air or calciication is
present, the normal gallbladder wall is not seen, and only the
bright echo and the posterior dirty shadowing are seen.
Milk of calcium bile, also known as limey bile, is a rare
condition in which the gallbladder becomes illed with a pasty,
semisolid substance of mainly calcium carbonate. 77 It is oten
associated with gallbladder stasis and in rare cases may cause
acute cholecystitis or migrate into the bile ducts. he appearance
on sonography is highly echogenic material with posterior acoustic
shadowing, forming a bile calcium level on various patient
positions (Fig. 6.37).
Biliary Sludge
Biliary sludge, also known as biliary sand or microlithiasis,
is deined as a mixture of particulate matter and bile that
occurs when solutes in bile precipitate. Its existence was irst
recognized with the advent of sonography. he exact prevalence
of sludge is unknown in the general population because most
studies have examined high-risk populations. he predisposing
factors in development of sludge are pregnancy, rapid weight
loss, prolonged fasting, critical illness, long-term total parenteral
nutrition, cetriaxone or prolonged octreotide therapy,
and bone marrow transplantation. In one study, over a 3-year
period, about 50% of cases resolved spontaneously, 20% persisted
asymptomatically, 5% to 15% developed gallstones, and 10% to