Subcapsular colorectal liver metastasis adjacent to the gallbladder
A 67-year-old man, 3 years after sigmoid colectomy for pT3N1 cancer, has a rising CEA of 18 ng/mL. CT and PET show a single 3.2 cm metastasis in segment IVb, 6 mm from the gallbladder fossa and 1 cm from the diaphragmatic dome. There is no extrahepatic disease and colonoscopy is normal. Liver function is normal, platelets 105 × 10^9/L and INR 1.2. He has hypertension and a BMI of 34. The multidisciplinary team considers resection, ablation or stereotactic body radiotherapy. A surgeon offers wedge resection but warns of bile leak and a positive margin near the gallbladder. The patient prefers a minimally invasive treatment. You are asked to assess ablation. There is no ascites. The lesion is subcapsular and adjacent to the gallbladder wall.
1. Compare microwave ablation, radiofrequency ablation and stereotactic body radiotherapy for this lesion, and state your recommendation.
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All three are reasonable locally destructive options for a solitary 3.2 cm colorectal metastasis. Surgical resection remains the reference standard if a clear margin can be achieved safely, but this lesion is centrally located near the gallbladder and diaphragm, so a wedge resection may risk bile leak or a positive margin. Radiofrequency ablation is heat-sink sensitive and less effective near large vessels; it also risks biliary injury near the gallbladder. Microwave ablation achieves higher temperatures, larger zones and less heat-sink effect, making it attractive for a 3.2 cm lesion, but it carries a real risk of gallbladder and diaphragmatic injury. SBRT is non-invasive and avoids needle risk, but local control for a 3.2 cm lesion may be slightly lower and it requires a longer course.
My recommendation is microwave ablation with hydrodissection, provided a safe window can be created and the patient accepts the risk. If the gallbladder cannot be separated, SBRT or surgical resection in a hepatobiliary centre should be reconsidered.
2. What technical adjuncts would you use to protect the gallbladder and diaphragm, and how would you confirm adequate coverage?
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Use image guidance with CT and, if available, cone-beam CT or fusion. Position the patient to move the gallbladder away from the needle path, for example left lateral or prone. Perform hydrodissection with 5% dextrose or sterile water rather than saline, because non-ionic fluid creates a better thermal barrier; inject through a fine needle to separate the gallbladder from the tumour and to displace the diaphragm. If needed, create artificial ascites. Place the microwave antenna under stepwise imaging, avoiding the gallbladder lumen and pleural space. Use a power and time protocol appropriate for a 3.2 cm lesion, and consider multiple antennae if the predicted zone is insufficient. Confirm coverage with immediate post-ablation contrast CT: the ablation zone should encompass the tumour with a 5–10 mm margin. Assess for gallbladder wall thickening, pneumothorax and pleural effusion.
3. What complications would you anticipate and how would you follow this patient?
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Anticipate bile leak, cholecystitis, gallbladder perforation, diaphragmatic injury, pneumothorax, pleural effusion, liver abscess, bleeding and, rarely, needle-track seeding. Warn the patient about fever and pain, and give prophylactic antibiotics according to local protocol. If cholecystitis occurs, manage with antibiotics and consider drainage or cholecystectomy. Follow with contrast CT or MRI at 1, 3 and 6 months, then periodically, plus CEA. At 1 month, expected post-ablation changes can mimic residual tumour, so compare with the immediate post-ablation scan. If there is residual or local progression, repeat ablation, SBRT or resection may be considered depending on the pattern and the patient’s fitness.