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 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 IOUS 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 invaluable15 .
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.
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Demonstrating a margin of tissue of only 2 or 3 mm between the metastasis and the hepatic vein.
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Metastasis in segment 8, at the confluence of the hepatic veins

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