Ya-Wei Xu, Hong Fu

Department of Hepatobiliary Surgery, S haoxing People’s Hospital, Shaoxing Hospital of Zhejiang University, Shaoxing 3120 0 0, China

With the development of color Doppler and laparoscopic ultra-sound, now intraoperative ultrasound (IOUS) plays an important role in liver surgery. Compared to percutaneous ultrasound (US), IOUS is conducted directly on the liver surface, with no blind spots or dead ends, thus improves the detection, localization and char-acterization of lesions without influencing factors, such as obesity, ascites and meteorism [1] . Besides, most IOUS uses high frequency ultrasonic probe which provides high resolution so that it can find smaller lesion than computed tomography (CT) and magnetic res-onance imaging (MRI) [ 2,3 ]. This is very helpful in patients with liver cirrhosis because it is very difficult to distinguish the lesion from normal liver tissue. IOUS detects up to 30% more nodules in cirrhotic livers. But since such nodules are more often regen-erative nodules than tumors, IOUS may overestimate the disease. Contrast-enhanced intraoperative ultrasound (CEIOUS) becomes an important supplemental measure in recent years. It may be used for the differentiation of small lesion which is difficult for IOUS by observing the dynamic image of micro perfusion. It is a useful di-agnostic tool in both benign pathologies, such as regenerative nod-ules, and malignant liver lesions. The advantage of this approach is the possibility of intraoperative characterizing lesions that could not be diagnosed by preoperative imaging, based on vasculariza-tion patterns, resulting in modification of the surgical therapy de-cision and expansion of the resection or intraoperative ablation [4] . Huf et al. [5] reported that CEIOUS offers the substantial advantage of locating additional liver lesions compared to preoperative MRI and preoperative contrast-enhanced US.

IOUS improves intraoperative diagnosis, especially in colorec-tal liver metastases (CRLM). It can find the missed lesions in-tra operatively and consequently change the preoperative surgi-cal plan. Nowadays, both contrast-enhanced CT and MRI with or without liver-specific contrast agent have greatly improved the de-tection and characterization of liver tumors [ 6,7 ]. But preoperative chemotherapy may negatively affect the accuracy of preoperative staging and intraoperative staging due to the chemotherapy-related changes in liver parenchyma and modification of CRLM features. IOUS improves staging in patients undergoing resection for CRLM even in the era of liver specific MRI [8] . In addition to improved tumor detection, in patient with neuroendocrine liver metastases, IOUS was found to be associated with features of tumor biology, specifically tumor grade and risk of recurrence [9] . IOUS helps to determine the insection margins and transection planes. IOUS is now strongly recommended by the 2018 Southampton Consensus Guidelines to be available in every laparoscopic liver surgery case, as it potentially helps in planning the resection line and precise tumor location [10] . It is essential to guide the resection although its reported impact varies among the published series depending on the type of the liver tumors considered and more importantly on the surgical policy applied. Hiroyoshi et al. [11] reported that CEIOUS might contribute to precise assessment of macroscopic in-trabiliary growth of CRLM, leading to oncological benefits by en-abling accurate R0 resection. The more conservative the surgery the more profitable the impact of IOUS. Under the guide of IOUS, surgeons use balloon catheter, vessel compression and dye-staining techniques to make anatomical segmental and subsegmental resec-tion possible. IOUS allows for real-time monitoring of the transec-tion plan to avoid positive margin. It can be used repeatedly, with few contraindications and does not expose patients to radiation. Also, IOUS can monitor the major vessels in order to protect or ligate them. Besides, it can assess the patency to elevate the suc-cess rate of vascular remodeling. Chandra et al. [12] used saline as a contrast agent in IOUS which accurately identifies small iso-lated segmental bile ducts and helps in surgery of the biliary tract. 3D printed model has been employed in recent years to support clinicians from various fields. Igami et al. [13] displayed feasibil-ity of using 3D printed models in choosing liver partition line and earlier in determining resection line before small hepatectomy of tumor invisible in IOUS. 3D printed model may serve as a useful adjunct to IOUS which led to changes in surgical approach in 26.3% in Witowski’s study [14] .

Under the guidance of IOUS, surgeons also can carry out biopsy and treatment of liver nodules. IOUS helps to elevate the accuracy of location and guide the radiofrequency or microwave ablation. It is essential especially in deep lesions. Incorrect targeting on imag-ing causes inadequate placement of the radiofrequency ablation needle which, in turn, leads to the need of more treatment ses-sions or more frequent local recurrence after radiofrequency abla-tion. Dupre et al. [15] designed a high-intensity focused ultrasound device for intraoperative use which can achieve precise ablations of biological tissues without incisions or radiation. It enables an ab-lation rate higher than any other treatment and is independent of perfusion.

There are several barriers to the routine use of IOUS includ-ing time pressure, perceived learning curve, and cost of implica-tions. Most of the IOUS are operated by sonographers while others by surgeons. In our opinion, surgeons are more familiar with the anatomy and surgical procedure. They are competent with IOUS after adequate training so that it could be avoided to pause the operation and to call sonographers intra operatively. With the de-velopment of three-dimensional ultrasound, hepatectomy will be more accurate and safer.

Acknowledgments

None.

CRediT authorship contribution statement

Ya-Wei Xu :Conceptualization, Data curation, Investigation, Writing original draft.Hong Fu :Conceptualization, Data curation, Writing original draft, Writing review & editing.

Funding

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Ethical approval

Not needed.

Competing interest

No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the sub-ject of this article.