Overview
Definition:
Microwave ablation (MWA) is a minimally invasive thermal ablation technique used to destroy cancerous tissue in the liver by generating electromagnetic waves
The perioperative role encompasses the entire patient journey, from pre-procedural assessment and planning to intra-procedural management and immediate postoperative care, aiming to optimize outcomes and minimize complications.
Epidemiology:
Liver tumors, including hepatocellular carcinoma (HCC) and colorectal liver metastases (CRLM), are common worldwide
MWA is increasingly utilized for unresectable or localized tumors, especially in patients with limited hepatic reserve or comorbidities
Its application is growing as a palliative or curative treatment modality.
Clinical Significance:
Understanding the perioperative aspects of MWA is crucial for surgeons and interventional radiologists to effectively manage patients
Optimal patient selection, precise technique, and vigilant postoperative monitoring are key to achieving successful tumor destruction while preserving liver function and patient well-being, directly impacting oncologic outcomes and quality of life.
Indications And Contraindications
Indications:
Primary HCC in patients unsuitable for resection or transplantation
Small unresectable HCCs (typically <3 cm)
Recurrent HCC after surgery
Colorectal liver metastases not amenable to resection
Palliation of symptomatic liver lesions
Patients with Child-Pugh A or B liver function
Tumors amenable to percutaneous or laparoscopic access.
Contraindications:
Large or multifocal tumors (>3-4 lesions or tumors >5 cm)
Tumors with major vascular involvement (e.g., portal vein invasion)
Diffuse infiltrative HCC
Severe coagulopathy (INR > 1.5, platelets < 50,000/µL)
Uncontrolled sepsis or ascites
Inability to tolerate procedure or anesthesia
Tumors located adjacent to critical structures like bowel or gallbladder (relative contraindication, requires careful planning)
Extrahepatic disease.
Preoperative Assessment And Planning
Patient Selection:
Comprehensive assessment of liver function (Child-Pugh score, MELD score)
Evaluation of tumor burden, number, size, and location
Assessment of comorbidities and performance status (ECOG/KPS)
Review of imaging (contrast-enhanced CT, MRI with hepatobiliary phase contrast, multiphasic angiography)
Discussion with multidisciplinary tumor board.
Imaging And Staging:
Detailed imaging to define tumor margins, proximity to vessels, diaphragm, and other organs
Accurate staging to exclude extrahepatic disease
Baseline laboratory tests including complete blood count, liver function tests, coagulation profile, and tumor markers (AFP, CEA).
Anesthetic Considerations:
Anesthesia typically involves sedation or general anesthesia
Factors include patient comorbidities, procedural duration, and need for patient immobility
Regional anesthesia may be considered for specific cases
Consultation with anesthesiology team is essential.
Procedural Technique And Intraoperative Management
Access Methods:
Percutaneous access under image guidance (ultrasound, CT, or fluoroscopy)
Laparoscopic approach for better visualization and access to specific lesions
Open surgical approach is rare but may be used in complex cases.
Ablation Parameters:
Selection of appropriate microwave antenna(e) and placement based on tumor size and location
Optimization of ablation time and power output to achieve adequate tumor margin coverage (often aiming for a 0.5-1 cm margin)
Use of overlapping ablation zones for larger or irregular tumors.
Intraoperative Monitoring:
Continuous monitoring of vital signs
Real-time imaging (ultrasound or CT) to confirm antenna placement and assess ablation zone
Careful attention to heat dissipation to adjacent organs, particularly bowel and gallbladder, to prevent thermal injury
Use of saline or air cooled systems to protect nearby structures.
Postoperative Care And Complications
Immediate Postoperative Care:
Close monitoring of vital signs, pain control, and fluid balance
Assessment for signs of bleeding, infection, or thermal injury
Routine laboratory monitoring (CBC, LFTs)
Pain management typically with oral analgesics
Mobilization as tolerated.
Common Postoperative Issues:
Post-ablation syndrome (fever, malaise, abdominal pain) is common and usually self-limiting
Mild elevation of liver enzymes
Potential for minor bleeding or hematoma at the access site.
Management Of Complications:
Major complications are rare but can include hemorrhage, infection, unintended thermal injury to adjacent organs (bowel perforation, gallbladder injury, diaphragmatic injury), pleural effusion, pneumothorax, and tumor seeding along the needle tract
Management depends on the type and severity of complication, ranging from conservative measures to surgical intervention
Prompt recognition and management are critical.
Follow Up And Long Term Outcomes
Imaging Surveillance:
Regular follow-up imaging (contrast-enhanced CT or MRI) at 1, 3, and 6 months post-ablation, then every 6 months thereafter
Assessment of local tumor recurrence, new tumor development, and overall treatment response
Response evaluation criteria (e.g., mRECIST) are used.
Prognostic Factors:
Tumor characteristics (size, number, histology), baseline liver function, completeness of ablation (achieving adequate margin), and development of complications all influence prognosis
Patients with small, solitary HCCs and good liver function tend to have better outcomes.
Long Term Results:
MWA can achieve durable local tumor control for selected patients, with reported local recurrence rates varying between 5-20%
Overall survival depends on the underlying liver disease, tumor type, and extent of disease
MWA is a valuable option for improving survival and quality of life in carefully selected patients.
Key Points
Exam Focus:
Indications for MWA in HCC and CRLM
Contraindications and patient selection criteria
Imaging modalities for assessment and follow-up
Principles of intraoperative thermal protection
Management of common post-ablation syndrome and major complications
Role of MWA in liver tumor management algorithms.
Clinical Pearls:
Always assess liver reserve before ablating significant tumor burden
Overlapping ablations are crucial for larger or irregular tumors to ensure complete coverage
Proximity to bowel and gallbladder requires careful planning and use of protective measures
Postoperative fever and pain are common
rule out serious complications systematically
Close multidisciplinary team (MDT) discussion is vital for optimal patient management.
Common Mistakes:
Inadequate ablation margin leading to local recurrence
Over-aggressive ablation in patients with poor liver reserve
Failure to protect adjacent vital structures
Misinterpretation of imaging findings during follow-up
Poor patient selection for the procedure.