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INTERVENTIONAL AND OTHER TECHNIQUES 271
main uses is in staging pancreatic tumours, predicting
their resectability, identifying small lymph
node metastases and assessing vascular invasion. 37
It is particularly accurate in identifying small pancreatic
insulinomas, 38 often difficult or impossible
to identify on conventional cross-sectional imaging
despite a documented biochemical abnormality,
and thus guiding subsequent surgical procedures.
Endoscopic ultrasound is also used in the detection
of biliary calculi, particularly in the normal-calibre
common bile duct, with a much higher accuracy
than other imaging techniques and without the
potential additional risks of ERCP. 39
Further, less-established uses of endoscopic
ultrasound include gastrointestinal examinations,
in which invasion of gastric lesions into and
through the wall of the stomach can be assessed, 40
anal ultrasound, which is used to visualize the
sphincter muscles in cases of sphincter dysfunction,
the staging of colorectal carcinomas and the
demonstration of bowel wall changes in inflammatory
bowel conditions. 41
The miniprobe has a higher frequency (20–30
MHz) and may be passed down a conventional
endoscope. It therefore has the advantage of a onestage
gastrointestinal tract endoscopy/ERCP,
rather than requiring a separate procedure. It may
be inserted into the common duct of the biliary
tree to assess local tumour invasion and to clarify
the extent and/or nature of small lesions already
identified by other imaging methods. It shows
remarkable accuracy in the detection of common
bile duct tumours and other biliary tract disease
when compared with other imaging modalities. 42
It may be used in the staging of oesophageal and
gastric cancer, and is especially useful when a tight
oesophageal stricture prevents the passage of the
endoscope. 41 The layers of the oesophageal or gastric
wall and the extent of tumour invasion can be
accurately assessed.
The miniprobe is also used in patients with suspected
pancreatic carcinoma, for example in patients
with a negative CT but who have irregularity of the
pancreatic duct on contrast examination. The probe
can be passed into the pancreatic duct during ERCP
to detect small lesions, assess the extent of the
tumour and predict resectability. 43 It is superior to
conventional endoscopic ultrasound in the detection
of the smaller, branch tumour nodules, and can
also detect local retroperitoneal or vascular invasion
in areas adjacent to the probe.
The use of endoscopic ultrasound is currently
limited to a few specialist centres. A steep learning
curve together with the expense of the equipment
is likely to restrict its widespread use; however, as
its applications expand and its value becomes
proven, it is likely to become a more routine investigation
at many centres. 41
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