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THE PANCREAS 133
head of pancreas. This differentiation, however, is
usually academic at this stage.
Colour Doppler can demonstrate considerable
vascularity within the mass and is also important in
identifying vascular invasion of the coeliac axis,
superior mesenteric artery, hepatic, splenic and/or
gastroduodenal arteries and of the portal and
splenic veins, a factor which is particularly important
in assessing the suitability of the tumour for
curative resection. The recognition of involvement
of peripancreatic vessels by carcinoma with colour
Doppler, together with the ultrasound assessment
of compression or encasement of these vessels, has
been found to be highly sensitive and specific (79%
and 89%) for diagnosing unresectability, 19 thus the
need for further investigative procedures such as
CT may be avoided, particularly in cases of large
tumours. 20
Pancreatic metastases
Pancreatic metastases may occur from breast, lung
and gastrointestinal tract primary tumours. They
are relatively uncommon on ultrasound (Fig. 5.6),
simply because they are a late manifestation in
patients who already have known, widespread disease
and in whom investigations are generally considered
unnecessary.
Widespread metastatic disease can be demonstrated
on ultrasound, particularly in the liver, and
there is often considerable epigastric lymphadenopathy,
which can be confused with the
appearances of pancreatic metastases on the scan.
Pathology of the pancreas, both benign and
malignant, can affect the adjacent vasculature
by compression, encasement or thrombosis.
Doppler of the splenic, portal and superior
mesenteric veins is useful in demonstrating the
extent of vascular complication when pancreatic
abnormalities are suspected.
BENIGN FOCAL PANCREATIC LESIONS
Focal fatty sparing of the pancreas
The uncinate process and ventral portion of the
head of pancreas may sometimes appear hypoechoic
in comparison with the rest of the gland
(Fig. 5.7). This is due to a relative lack of fatty deposition
and is often more noticeable in older
patients, in whom the pancreas is normally hyperechoic.
Its significance lies in not confusing it with
a focal pancreatic mass. The area of fatty sparing is
well-defined, with no enlargement or mass effect,
and is regarded as a normal variation in the ultrasound
appearances. If doubt exists, CT will differentiate
fatty sparing from true neoplasm. 21
Focal pancreatitis
Inflammation can affect the whole, or just part of
the gland. Occasionally, areas of hypoechoic, focal
acute or chronic pancreatitis are present (see
Pancreatitis, above). These are invariably a diagnostic
dilemma, as they are indistinguishable on
ultrasound from focal malignant lesions (Fig. 5.8).
Factors which point towards inflammation include
Figure 5.6 Metastatic deposit from primary breast
carcinoma in the body of the pancreas (arrow).
Figure 5.7 The uncinate process is relatively
hypoechoic (arrows) because of fatty sparing.