Overview
Definition:
Intraoperative ultrasound (IOUS) is a real-time imaging technique utilized during surgical procedures to visualize anatomical structures, particularly in complex regions like the biliary tree
It allows surgeons to identify critical structures, assess tissue characteristics, and guide surgical maneuvers with enhanced precision.
Epidemiology:
IOUS is increasingly employed in hepatobiliary and pancreatic surgery, as well as in laparoscopic cholecystectomies
Its use is advocated in cases of suspected aberrant biliary anatomy, challenging dissections, or when pre-operative imaging is inconclusive, estimated in 5-15% of elective cholecystectomies and a higher proportion of complex hepatobiliary resections.
Clinical Significance:
Accurate identification of biliary anatomy intraoperatively is paramount to prevent bile duct injuries, which can lead to significant morbidity, mortality, and long-term complications
IOUS provides immediate, dynamic visualization, augmenting the surgeon's understanding beyond static pre-operative imaging, thereby improving patient safety and surgical outcomes.
Indications For IOUS Biliary
Suspected Aberrant Anatomy:
Pre-operative suspicion of variations in cystic duct insertion, common hepatic duct formation, or accessory ducts
Cases with previous abdominal surgery or inflammation leading to distorted anatomy.
Difficult Cholecystectomy:
Dense adhesions, inflammation, difficult Calot's triangle dissection, or when identification of the cystic duct and artery is challenging
Suspected choledocholithiasis requiring intraoperative confirmation or stone clearance.
Biliary Reconstruction:
Guiding biliary-enteric anastomoses, assessing ductal patency, and identifying appropriate recipient ducts during reconstructive procedures like Roux-en-Y hepaticojejunostomy.
Liver Resection:
Mapping intrahepatic bile ducts and their relationship to tumors or vascular structures during liver resections to prevent inadvertent bile duct transection.
Intraoperative Guidance:
Confirming lesion margins, identifying unexpected pathology, or guiding needle placement for drainage or biopsy.
IOUS Technique And Equipment
Equipment Selection:
Sterilizable ultrasound probes (linear and curvilinear) are essential, typically of higher frequency (7-12 MHz) for superficial structures and lower frequency (3-5 MHz) for deeper visualization
A sterile sheath or drape is mandatory.
Probe Handling:
Gentle manipulation with sterile gel or saline
Avoiding excessive pressure to prevent artifact or displacement of structures
Constant communication between the sonographer (often the surgeon or assistant) and the operating surgeon.
Scanning Planes:
Transverse, sagittal, and oblique planes are used to obtain a comprehensive view
Dynamic scanning with slight probe angulation and patient repositioning can enhance visualization
Focus on identifying key landmarks like the portal vein, hepatic artery, and their branching patterns relative to the bile ducts.
Image Optimization:
Adjusting gain, depth, focus, and using Doppler to identify vascular structures and differentiate them from bile ducts
Harmonic imaging can improve resolution and reduce artifact.
Interpreting Biliary Anatomy With IOUS
Cystic Duct:
Visualized as a tubular structure connecting the gallbladder to the common hepatic duct
Its insertion point and angle are critical
Doppler can help differentiate it from the cystic artery.
Common Hepatic Duct:
Formed by the confluence of the left and right hepatic ducts
IOUS can delineate its course and any potential obstructions or tributaries.
Common Bile Duct:
Formed by the union of the common hepatic duct and the cystic duct
Its length, diameter, and relation to the pancreatic duct and the duodenum are assessed
Doppler helps differentiate it from the gastroduodenal artery and portal vein.
Intrahepatic Ducts:
Visualization of segmental and subsegmental bile ducts, especially crucial in liver resections
Their branching patterns can be complex and require careful dynamic scanning.
Gallbladder Bed:
Assessing for any residual stones or thickened mucosa, and ensuring adequate visualization of the cystic duct stump during cholecystectomy.
IOUS In Specific Surgical Scenarios
Laparoscopic Cholecystectomy:
Confirming identification of the cystic duct and artery before clipping/ligation
Visualizing stones in the cystic duct or common bile duct
Identifying aberrant right hepatic ducts entering the gallbladder bed
Reducing the risk of bile duct injury.
Open Cholecystectomy:
Assisting in dissection in cases of severe inflammation or adhesions
Identifying retracted clips or lost stones
Guiding common bile duct exploration.
Hepatobiliary Resection:
Mapping intrahepatic ducts relative to the tumor
Identifying the origin of major intrahepatic ducts to guide transection planes
Assessing vascular invasion and its relation to biliary structures.
Pancreaticoduodenectomy:
Visualizing the common bile duct and its stump during pancreaticojejunostomy
Assessing ductal patency and identifying any anomalies in the pancreatic duct.
Complications And Limitations Of IOUS
Technical Limitations:
Limited field of view, operator dependency, potential for artifacts (e.g., reverberation, shadowing), and difficulty in visualizing small structures or stones in tortuous ducts
Poor acoustic windows due to bowel gas or patient positioning.
Missed Injuries:
Despite IOUS, bile duct injuries can still occur if critical structures are obscured or if the interpretation is inaccurate
Complete visualization of all biliary anatomy is not always achievable.
Learning Curve:
Requires significant practice and experience to master the technique and interpretation
Correlation with pre-operative imaging and intraoperative findings is essential.
Equipment Failure:
Malfunction of the ultrasound machine or probe, or failure of the sterile covering, can necessitate a change in surgical strategy.
Key Points
Exam Focus:
Understanding the indications for IOUS in biliary surgery
Recognizing key biliary structures and their sonographic appearance
Knowing how IOUS helps prevent bile duct injuries
Awareness of its limitations.
Clinical Pearls:
Always correlate IOUS findings with pre-operative imaging and direct visualization
Use Doppler to differentiate vessels from ducts
Dynamic scanning is crucial for understanding spatial relationships
If anatomy is unclear, consider intraoperative cholangiography or operative cholangioscopy.
Common Mistakes:
Mistaking the cystic artery for the cystic duct
Overlooking small or aberrant ducts
Insufficient scanning of the entire biliary tree
Relying solely on IOUS without adequate surgical judgment
Not recognizing the limitations of the technology.