Microwave ablation of colorectal liver metastases adjacent to the cardiophrenic angle: Parallel versus non-parallel placement of the antenna relative to the diaphragm

PURPOSE: Microwave ablation (MWA) is difficult to perform in colorectal liver metastases (CRLMs) adjacent to the cardiophrenic angle. Therefore, a modified approach involving antenna array placement parallel to the diaphragm was initially attempted. Its safety and efficacy were compared with those involving non-parallel placement. METHODS: Sixty-three patients with CRLMs adjacent to the cardiophrenic angle (lesions within 10 ​mm of the diaphragm) who underwent MWA were included in the study. All patients were further classified into parallel and non-parallel groups according to the method of antenna placement. The distance between the lesion and diaphragmatic surface before MWA, complications, and local tumor progression (LTP) at the last imaging follow-up were recorded. LTPs in the two groups were compared using the log-rank test. Prognostic factors for LTP were assessed using the Cox proportional hazards regression model. RESULTS: Thirty and 33 lesions were ablated using parallel and non-parallel antenna placement, respectively. During the mean follow-up duration of 19.7 ​± ​8.2 months, the LTP rate in the parallel and non-parallel placement groups were 3.3% (1/30) and 24.2% (8/33), respectively. The log-rank test showed that parallel antenna placement was associated with delayed LTP (p ​= ​0.018). Multivariate Cox regression analysis showed that parallel antenna placement was an independent predictor of delayed LTP after adjusting for possible risk factors, including age, sex, tumor size, and KRAS mutation (hazard ratio, 0.1; 95% confidence interval, 0.00, 0.80; p ​= ​0.034). CONCLUSION: The placement of the antenna parallel to the diaphragm is an alternative and effective method for MWA of CRLMs near the cardiophrenic angle and can contribute to the reduction of the LTP rate.