Overview
Definition:
Intraoperative ultrasound (IOUS) mapping of liver lesions is a real-time imaging technique used during surgery to precisely identify, localize, and delineate the extent of liver tumors or other abnormalities
It assists surgeons in planning the optimal surgical approach, ensuring complete resection, and avoiding vital structures.
Epidemiology:
Liver lesions are common, with primary hepatocellular carcinoma (HCC) and metastatic disease being the most frequent
The incidence of liver lesions requiring surgical intervention varies geographically and by underlying etiology, impacting operative strategy significantly.
Clinical Significance:
Accurate localization of liver lesions intraoperatively is critical for successful surgical resection, particularly for small, multifocal, or deeply situated lesions
IOUS reduces the risk of incomplete resection, preserves healthy liver parenchyma, and can identify unexpected lesions not evident on preoperative imaging.
Indications
Primary Indications:
Resection of primary liver tumors (HCC, cholangiocarcinoma)
Resection of liver metastases (colorectal, neuroendocrine, etc.)
Evaluation of indeterminate lesions found on preoperative imaging
Guidance for ablation procedures
Confirmation of lesion location prior to incision.
Secondary Indications:
Assessment of vascular involvement
Identification of vascular anatomy variations
Detection of occult lesions
Evaluation of disease recurrence
Intraoperative assessment of resection margins.
Contraindications:
Generally, IOUS has no absolute contraindications during surgery
Relative contraindications may include extensive adhesions that limit probe access or severe coagulopathy affecting maneuverability.
Preoperative Preparation
Imaging Review:
Thorough review of all preoperative imaging (CT, MRI, angiography) is essential to correlate findings with intraoperative ultrasound
Understanding lesion number, size, and precise location relative to vascular and biliary structures is key.
Patient Assessment:
Assessment of liver function (Child-Pugh score, MELD score) to determine surgical candidacy and potential for liver resection
Evaluation of comorbidities that may impact surgical risk.
Informed Consent:
Ensuring comprehensive informed consent covering the procedure, potential risks, and the role of intraoperative ultrasound in guiding the surgery.
Intraoperative Ultrasound Technique
Equipment:
Sterile ultrasound probe covers are mandatory
High-frequency linear and sector probes are typically used, depending on the depth and resolution required
Ultrasound machine should be readily accessible and operated by a trained sonographer or surgeon.
Probe Manipulation:
Gentle manipulation of the probe is crucial to avoid damaging liver parenchyma or causing bleeding
Applying liberal amounts of sterile coupling gel is necessary for optimal image acquisition.
Scanning Protocols:
Systematic scanning of the liver parenchyma in multiple planes (transverse, sagittal, coronal) is performed
Careful attention is paid to segmental anatomy of the liver
B-mode, Doppler, and sometimes contrast-enhanced ultrasound (CEUS) are utilized.
Real Time Correlation:
Continuous correlation between ultrasound findings and the surgical field
The surgeon may palpate the liver while the sonographer scans to confirm lesion location
Marking the skin with sterile markers based on ultrasound localization is common.
Interpretation And Guidance
Lesion Characterization:
IOUS can help differentiate cystic from solid lesions and assess margins
Doppler ultrasound is crucial for evaluating vascularity of lesions and their relationship to hepatic vessels (portal vein, hepatic artery, hepatic veins).
Margin Assessment:
Accurate delineation of lesion margins is vital for ensuring complete tumor removal
IOUS can identify tumor infiltration into surrounding parenchyma or vessels, guiding resection planes.
Unexpected Findings:
IOUS may reveal additional lesions not seen on preoperative imaging, impacting the extent of resection
It can also identify unexpected vascular anomalies or biliary ductal dilatations.
Guidance For Resection:
The ultrasound image is used to guide the surgeon’s incision, resection line, or ablation needle
It helps define safe margins and avoid critical structures like major vessels, bile ducts, and the diaphragm.
Postoperative Care And Follow Up
Immediate Postoperative:
Standard postoperative care following liver surgery
Monitoring for bleeding, bile leaks, and liver dysfunction
Pain management and fluid balance are crucial.
Imaging Follow Up:
Postoperative imaging (CT or MRI) is typically performed to confirm the extent of resection, assess for residual disease, and monitor for recurrence
The findings are correlated with IOUS data.
Long Term Monitoring:
Regular follow-up with imaging and tumor markers (e.g., AFP for HCC) is essential for early detection of recurrence
Surveillance protocols depend on the primary tumor type and stage.
Complications
IOUS Related Complications:
Potential complications are rare but can include iatrogenic bleeding or injury to vascular/biliary structures if probe manipulation is not careful
False positives or negatives can occur, leading to suboptimal resection or unnecessary procedures.
Surgical Complications:
Standard surgical complications of liver resection: bleeding, bile leak (biloma, biliary fistula), liver insufficiency (post-hepatectomy liver failure), infection, ascites, thromboembolic events.
Prevention Strategies:
Meticulous surgical technique, adequate preoperative assessment, thorough understanding of liver anatomy, utilization of IOUS by experienced personnel, and adherence to established surgical guidelines for liver resection.
Key Points
Exam Focus:
Understanding the role of IOUS in tumor localization, margin assessment, and identification of multifocal disease
Knowing when IOUS is indicated and its limitations
Correlation of IOUS with preoperative imaging
Doppler assessment of vascular invasion.
Clinical Pearls:
Always correlate IOUS findings with preoperative scans and the surgeon's tactile sense
Use a systematic scanning approach
Remember that IOUS is a dynamic tool to supplement but not replace preoperative imaging
Never biopsy blindly based solely on IOUS without clear visualization of the lesion.
Common Mistakes:
Inadequate review of preoperative imaging
Insufficient scanning planes
Over-reliance on a single image
Failure to correlate findings with surgeon's palpation
Misinterpretation of vascularity or lesion margins
Inadequate probe sterility leading to infection.