Diagnostic ultrasound ( PDFDrive )

222 PART II Abdominal and Pelvic Sonography
guide management and for those who have a contraindication
to CECT.
Endoscopic ultrasound is more sensitive than abdominal
ultrasound for the detection of common bile duct stones and
can be useful in suspected gallstone pancreatitis. 60 Endoscopic
ultrasound is also valuable in diagnosing microlithiasis and
pancreas divisum. 61
Because of its complications (including pancreatitis) and
expense, ERCP, formerly both a diagnostic and a therapeutic
modality, is now usually reserved for therapy. 62 Sometimes coupled
with endoscopic sphincterotomy and stone removal, ERCP is a
valuable therapeutic modality in choledocholithiasis with jaundice,
dilated common bile duct, acute pancreatitis, or cholangitis. 63
Ultrasound Findings
Evaluation of the gallbladder and bile ducts is the focus of most
sonographic examinations performed in patients with acute
pancreatitis. Nevertheless, understanding pancreatic and extrapancreatic
abnormalities associated with acute pancreatitis is
important. he combined use of serum amylase and serum lipase
yields sensitivity and speciicity of 90% to 95% in diagnosing
acute pancreatitis, 64 but mild cases may be missed. In mild acute
pancreatitis the patient may present for diagnosis ater transient
elevated amylase and lipase levels have resolved; thus no serologic
indicators of pancreatitis may be present. 65 In these patients the
diagnosis of mild acute pancreatitis is clinical. On the other
hand, the diagnosis may be missed in patients with severe
pancreatitis because pain is absent or masked by other, more
severe symptoms. Analyzing fatal pancreatitis between 1980 and
1985, Lankisch et al. 66 reported that 30% of cases were not
diagnosed until autopsy.
Ater a careful search of the gallbladder and bile duct for
stones, the entire pancreas should be scanned. Ater scanning
the pancreas, peripancreatic pathology should be sought in the
lesser sac, anterior pararenal spaces, and transverse mesocolon.
he reported prevalence of sonographic abnormality in acute
pancreatitis varies from 33% to 92%. In a retrospective evaluation
of patients with acute pancreatitis, using a deined scanning
protocol to look for pancreatitis-associated indings, Finstad
et al. 37 found that sonography revealed abnormalities in 45 of
48 patients (92%) (Table 7.2).
Pancreatic echogenicity typically decreases in patients who
have acute pancreatitis because of interstitial edema. In some
patients, echogenicity is normal. In rare cases, echogenicity may
increase, possibly because of hemorrhage, necrosis, or fat
saponiication. Cotton et al. 67 noted that, compared with the liver,
the pancreatic echogenicity was increased in 16% of normal
individuals and 32% of patients with acute pancreatitis. Finstad
et al. 37 found no acute pancreatitis patients with globally increased
echogenicity, although focal areas of increased echogenicity and
inhomogeneity did occur.
Enlargement of the pancreas is almost universal in acute
pancreatitis. Unfortunately, enlargement may be diicult to
judge, because pancreatic size before the onset of pancreatitis
is usually unknown and varies widely. In 1995 Guerra et al. 7
found that the thickness of the body of the normal pancreas
in 261 adults was 10.1 mm (±3.8 mm; range, 4-23 mm). In
TABLE 7.2 Sonographic Abnormalities in
Patients With Acute Pancreatitis
Abnormality
No. of Patients
(48 Total)
Prevalence
Peripancreatic
29 60%
inlammation
Heterogeneous
27 56%
parenchyma
Decreased gland
21 44%
echogenicity
Indistinct ventral
16 33%
margin
Pancreas enlarged a 13 27%
Focal intrapancreatic
11 23%
echo change
Peripancreatic luid
10 21%
collections
Focal mass 8 b 17%
Perivascular
5 10%
inlammation
Pancreatic duct dilation 2 4%
Venous thrombosis 2 4%
a Anteroposterior dimension was ≥23 mm at superior mesenteric
artery.
b Five of eight were hypoechoic.
Modiied from Finstad TA, Tchelepi H, Ralls PW. Sonography of acute
pancreatitis: prevalence of indings and pictorial essay. Ultrasound Q.
2005;21(2):95-104. 37
2005, Finstad et al. 37 in his series of patients with acute pancreatitis
found that the mean anteroposterior measurement of
the pancreatic body at the SMA level was 21.1 mm (±6.4 mm;
range, 12-45 mm), almost twice the average found in normal
individuals by Guerra et al. It seems reasonable, therefore, to
use 22 mm (mean plus 3 standard deviations) as the upper limit
of normal pancreatic thickness, understanding that this is likely
to be an insensitive parameter for diagnosing acute pancreatitis
(Fig. 7.22).
he classic inding of decreased gland echogenicity is present
in only 44% of patients. In addition, when there is fatty iniltration
of the liver, the normal pancreas may appear hypoechoic, a pattern
called “pseudopancreatitis” (Fig. 7.23). Pancreatic heterogeneity
is a subjective but common inding, present in more than 50%
of patients (Fig. 7.24). Focal hypoechoic regions are noted in
some patients (Fig. 7.25).
he least subjective, most common, and thus most useful
inding is pancreatitis-associated inlammation (Fig. 7.26; see
also Figs. 7.22 and 7.24). Extrapancreatic inlammatory changes
may be detected even when the pancreatic contour is normal
and the pancreas is not obviously enlarged. Pancreatic inlammation
is typically hypoechoic or anechoic (Fig. 7.27) and
conforms to a known retroperitoneal or peritoneal space (Video
7.2). It may be diicult or impossible to distinguish inlammation
from luid (Fig. 7.28). In contrast to inlammation, luid collections