Diagnostic ultrasound ( PDFDrive )

CHAPTER 7 The Pancreas 221
3% in patients with nonnecrotic (interstitial) pancreatitis and
17% for those with necrotizing pancreatitis. he same review
noted 30% mortality with infected necrosis versus 12% for
uninfected necrosis. Organ failure is even more skewed; there
was no mortality with no organ failure, 3% with single-organ
failure, and 47% mortality with multiorgan failure. 32
he causes of acute pancreatitis are numerous and diverse.
One problem in evaluating and treating acute pancreatitis has
been the lack of a universally accepted classiication system. he
International Symposium on Acute Pancreatitis (Atlanta, 1992)
attempted to address these problems by proposing a classiication
system that is clinically oriented. 33 With better understanding
of the disease, improved imaging options, and myriad new
treatments, the Atlanta classiication of acute pancreatitis was
updated and revised. 28,34,35 he predominant causes of acute
pancreatitis are gallstones and alcohol abuse, accounting for about
80% of all cases 36 (Table 7.1).
All patients, including known alcoholics, who present with
their irst episode of acute pancreatitis should have sonography
to evaluate the biliary tree for gallstones. 37 Evaluation of the
biliary tree is crucial in patients with acute pancreatitis because
cholecystectomy with removal of common duct stones prevents
recurrence of acute pancreatitis, 38 which can be fatal. Gallstones
afect about 15% of the US population, 39 but prevalence varies
widely by ethnicity. Ater a careful search of the gallbladder
for stones, the bile duct should be evaluated for choledocholithiasis
and obstruction. Reports vary, but the prevalence of
common duct stones in patients with symptomatic gallstones is
likely 10% to 20%. If the ducts are not dilated sonographically,
however, the prevalence of common duct stones is probably
about 5%. 40 With careful technique, ultrasound can identify
common duct stones with a sensitivity of approximately 75% in
expert hands. 41,42
When biliary dilation or choledocholithiasis is present
sonographically, a stone may be impacted in the distal common
duct. It seems reasonable to assume that urgent intervention to
relieve the obstruction is necessary in these patients. here is
conlicting evidence, however, whether patients beneit from
intervention in the acute setting. 43-47 Acosta et al. 48 reported results
from a prospective randomized clinical trial of patients with
biliary pancreatitis that showed better outcomes with decompression
of the duct within 48 hours from the onset of symptoms.
It made no diference if the decompression was spontaneous or
from surgical treatment or ERCP.
How gallstones cause acute pancreatitis is unknown, although
it is somehow related to passage of stones into and through the
TABLE 7.1 Causes of Acute Pancreatitis
Cause
Acute Pancreatitis Cases
Gallstones 40%
Alcoholism 40%
Idiopathic 10%
Other 10%
common duct. Gallstones cause 30% to 50% of acute pancreatitis
attacks, whereas only 3% to 7% of patients with gallstones develop
pancreatitis. 38 Another important cause of acute pancreatitis is
biliary sludge (microlithiasis). hese cases comprise most of
what was previously characterized as “idiopathic” pancreatitis. 49
he myriad other causes of acute pancreatitis include neoplasm, 50,51
infection, pancreas divisum, toxins, drugs, and genetic, traumatic,
and iatrogenic (endoscopy, postoperative) factors. 36 From 5% to
7% of patients with pancreaticobiliary tumors, benign or malignant,
present with acute pancreatitis. 47
Approach to Imaging
Abdominal sonography and contrast-enhanced computed
tomography (CECT) are the two most useful imaging modalities
in patients with acute pancreatitis. Other useful, but usually
secondary diagnostic and therapeutic studies include MRI, MRCP,
ERCP, and endoscopic ultrasound. he choice of modality depends
on the clinical situation. Ultrasound should be performed to
detect gallstones and bile duct obstruction in all patients in whom
biliary acute pancreatitis is possible. CECT is indicated early in
the clinical course of patients with severe pancreatitis, mainly
to diagnose pancreatic necrosis. 52 Pancreatic necrosis is considered
signiicant when more than 30% of the gland is afected or an
area larger than 3 cm is present. Patients with pancreatic necrosis
must be observed closely for clinical deterioration and treated
with prophylactic antibiotics. 53-55 Sharma and Howden 56 found
that antibiotic prophylaxis signiicantly reduced sepsis by 21%
and mortality by 12% compared with no prophylaxis. CT is also
the most accurate examination when seeking delayed complications
of acute pancreatitis.
MRCP is an accurate means of detecting stones in the gallbladder
and bile ducts of patients with acute pancreatitis. 36,57
Abdominal MRI can provide information similar to CECT,
including the diagnosis of pancreatic necrosis. 58,59 Because of
expense, MRCP and MRI are oten reserved for patients in whom
CT or ultrasound does not provide adequate information to
Imaging in Acute Pancreatitis
ROLE OF ULTRASOUND
Detect gallstones as a cause of acute pancreatitis
Detect bile duct dilation and obstruction
Diagnose unsuspected acute pancreatitis or conirm
diagnosis of acute pancreatitis
Guide aspiration and drainage
ROLE OF COMPUTED TOMOGRAPHY
Detect pancreatic necrosis (patients with suspected severe
pancreatitis)
Detect complications of acute pancreatitis
Diagnose unsuspected acute pancreatitis or conirm
diagnosis of acute pancreatitis
Diagnose conditions mimicking acute pancreatitis,
including gastrointestinal ischemia, ulceration, or
perforation and ruptured abdominal aortic aneurysm
Guide aspiration and drainage