INTRAOPERATIVE ULTRASOUND IMAGING
Category: Diagnostic Radiology
Abstract : INTRAOPERATIVE ULTRASOUND (IOUS) IOUS is increasingly used in the abdomen,
in both the diagnosis and treatment of lesions. Its applications are varied and
its dynamic nature, mobility and high resolution make it ideal for surgical
work. Hepatic intraoperative ultrasound imaging IOUS The most frequent
application in the abdomen is in diagnosing and locating liver metastases pri
INTRAOPERATIVE ULTRASOUND (IOUS)
IOUS is increasingly used in the abdomen,
in both the diagnosis and treatment of lesions. Its applications are varied and
its dynamic nature, mobility and high resolution make it ideal for surgical
work.
Hepatic intraoperative ultrasound imaging IOUS
The most frequent
application in the abdomen is in diagnosing and locating liver metastases prior
to surgical resection.
Resection of metastases, particularly from colorectal
tumours, is a potential cure, but results are unsuccessful if small lesions,
undetected preoperatively, are not removed at operation.
The direct
contact of the intraoperative ultrasound imaging probe with the liver surface,
avoiding attenuative subcutaneous tissue, enables a high-frequency (7.5 MHz)
probe to be used. IOUS can demonstrate lesions too small to be detected on
preoperative imaging, and as a result can change operative management in terms
of altering the resection line to include more tissue, removing additional
hepatic segments or even abandoning the operative procedure altogether.
A
combination of surgical palpation, which detects small surface lesions, and
IOUS, which detects small, deep lesions, has the highest diagnostic accuracy.
IOUS is quick to perform in the hands of an experienced operator and its
contribution to the success of surgery is invaluable. IOUS is particularly
useful when there has been a delay between preoperative imaging and surgery, as
progression of disease may have occurred during this interval, or when
preoperative imaging is equivocal (for example, differentiating tiny cystic from
solid lesions). IOUS is often able to offer a definitive diagnosis and when
doubt still exists guided biopsy under ultrasound control may be
performed.
In addition to lesion detection it is able to demonstrate
vascular invasion by tumour and to demonstrate clearly, in real time, the
relationship of the tumour to adjacent vascular structures; this is essential
for planning a resection line. The greater the margin of normal tissue around
the resected tumour, the better the long-term prognosis, and a margin of greater
than 1 cm normal tissue is preferred. IOUS can also be used to locate deep
lesions for ultrasound-guided biopsy or ablation.
Other applications of
intraoperative ultrasound imaging IOUS
There are numerous extrahepatic
applications for IOUS in the abdomen, including urological, vascular and
gastrointestinal tract scanning. Ultrasound evaluation of the common duct for
calculi following cholecystectomy can identify small fragments which may not be
easily palpable through the duct wall. Using this technique the duct is less
susceptible to injury which may be associated with direct examination or the
introduction of X-ray contrast agents. Pancreatic scanning is particularly
useful in identifying small tumours of the body and tail of pancreas for
curative resection16 and in differentiating small pancreatic retention cysts
from solid nodules.
The treatment of tumours by percutaneous
ultrasound-guided techniques, rather than surgical resection, is becoming more
common. However, it may not always be possible to achieve success percutaneously
and techniques have been developed to ablate tumours during open surgery.
Cryotherapy, in which the lesion is frozen by introducing a cryoprobe into the
centre of the lesion under intraoperative ultrasound guidance, has been
successfully used, but is now largely superseded by radiofrequency and microwave
ablation.
These techniques have resulted in long-term survival in
patients with hepatocellular carcinoma and multiple liver metastases. The
success of such techniques depends to a large extent upon patient selection.
Those with very large and/or multiple lesions tend to have a poor prognosis
compared with patients with smaller, well-confined disease. However these
techniques continue to develop and are likely to offer hope to many patients
currently untreatable with conventional methods.
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