Electromagnetic Navigation System with a Marker Option for Computed Tomography-Guided Microwave Ablation of Undetectable or Inconspicuous Hepatic Tumors in Non-Enhanced Scans: A Feasibility Study

<b>Objectives</b>: Primary objective was to report the feasibility, safety and efficacy of percutaneous ablation of hepatic malignant tumors that are undetectable or inconspicuous in non-enhanced computed tomography (CT) scans using an electromagnetic navigation system with a marker option. Secondary objectives included the evaluation of technical parameters including the accuracy of needle placement, the number of control CT acquisitions, and procedural duration. <b>Methods</b>: This prospective study (performed from 1 March 2022 until 30 November 2024) included all patients with hepatic tumors (not visible or poorly defined on non-enhanced CT) who underwent percutaneous microwave ablation (MWA). Technical efficacy was assessed with contrast-enhanced CT immediately post-ablation, and oncologic outcomes (overall and progression-free survival) were evaluated with MRI at 1, 3, and 6 months. <b>Results</b>: Fifteen patients (12 males, 3 females; mean age of 66 years) with 16 tumors (median diameter of 15 mm) were treated in 16 sessions. Tumor types included hepatocellular carcinoma (<i>n</i> = 7), colorectal metastasis (<i>n</i> = 4), ocular melanoma (<i>n</i> = 1), neuroendocrine tumor (<i>n</i> = 1), intrahepatic cholangiocarcinoma (<i>n</i> = 1), and breast cancer metastasis (<i>n</i> = 1). Median procedure time was 53 min, scans number was nine, needle length was 12 cm, and median deviation was 1 mm. No complications were reported. Primary efficacy rate was 94% (15/16), rising to a secondary (assisted) technique efficacy of 100% after re-ablation (one session). During median follow-up of 23 months, local tumor progression-free survival was 100%; distant progression-free survival was 80%, and two patients (13.3%) died, one being cancer-related. <b>Conclusions</b>: Electromagnetic navigation with a marker option enables safe, accurate, and effective MWA of inconspicuous hepatic tumors, achieving excellent local control with favorable oncologic outcomes.