In this study of 2084 ablation sessions performed over 5 years, we showed that thermal ablation is a safe treatment for liver malignancies, with a mortality rate of 0.1% (2/2084) and an overall major complication rate of 5.6% (117/2084), which is similar to the results of previous studies[8–14]. In this study, the most frequent major complication was symptomatic pleural effusion (51.3%, 60/117), which we found at higher rates than what has been reported in previous studies[13–15, 20]. The reason for this discrepancy might be selection bias of tumours. Our previous study concluded that the frequency of subphrenic tumours was 24%[21], a higher frequency than other studies had previously reported 6.3–13.5%[22, 23]. Thermal ablation of liver tumours abutting the diaphragm poses a risk of diaphragmatic injury, and symptoms range from mild, such as pleural effusion and right shoulder pain, to severe, such as diaphragmatic perforation[22, 24]. Mild diaphragmatic injury is self-limiting and asymptomatic pleural effusion can resolve on its own. However, thoracentesis or diuresis is required if the patient experiences dyspnea or chest tightness. In addition, when tumours were located in the subphrenic region, artificial pleural effusion was used to improve the sonic window of tumours, to visualize and ablate the tumour completely and, to decrease the damage to diaphragm. The thoracic drainage tube was kept in for several days to observe the drainage of the pleural effusion. There were no diaphragmatic perforations in this study, and all symptomatic pleural effusions were significantly relieved after 3–5 days of thoracic drainage.
The results showed that the only independent predictive factors for major complications were: total maximum diameter of the lesions > 3 cm; thermal ablation method used, including MWA and MWA + RFA; and ICC and postoperative SIRS. PLT counts < 100⋅109/L, although statistically significant, appeared to be a trend to increase the incidence of major complications.
The present study suggested that the ablation of larger size tumours leads to more major complications, which is consistent with the published literature[9]. It is conceivable that larger tumours require more ablation treatments and require the administration of higher ablation energy. Single ablation usually fails to achieve sufficient coverage of larger tumours, and multiple overlapping ablations are necessary[25], which may increase the complications caused by puncture. A larger ablated zone may have a greater impact on the liver function reserve. For tumours larger than 3 cm, MWA is preferred due to its high thermal efficiency, higher capability for coagulation of blood vessels and faster ablation time[26]. When large tumours were located adjacent to vital organs, such as the gallbladder and gastrointestinal tract, we combined RFA on the side of the tumour close to vital organs to completely ablate the tumour while reducing damage to vital organs. Although the results showed that when the total maximum diameter of the lesions was > 3 cm and thermal ablation methods including MWA and MWA + RFA, increased the occurrence of major complications, half of the complications were symptomatic pleural effusion, and the thermal damage caused by ablation was relatively limited.
Compared with HCC, ICC is more aggressive and requires a larger ablative range to avoid local tumour progression[27], which may damage adjacent structures. In addition, ICC usually causes obstruction of the biliary tract by inhibiting adequate drainage of bile leading to increased probability of liver abscess due to retrograde infection. Su et al.[28] reported that 42.8% of patients with ICC developed abscesses after ablation procedures due to the increased risk of ascending biliary infection. In this study, the incidence of liver abscess in patients with ICC was 4.4% (4/91), higher than the incidence in patients with HCC (1.1%, 21/1959).
Although the results showed that p value of patients with PLT count < 100×109/L was less than 0.05 (p = 0.047), this factor may only has a trend to increase the incidence of major complications after thermal ablation. More than half of the patients in our study developed within cirrhosis. As cirrhosis progressed, some patients’ platelet counts were reduced due to hypersplenism, which could increase the risk of haemorrhage[29, 30]. However, in our study, the incidence of haemorrhage was only 0.2% (5/2084). Our previous study showed that with some preventive measures, thermal ablation is a safe method for patients with decreased PLT count[31].
SIRS is the body's excessive defensive stress response to pathogenic factors, which eventually transforms into a clinical syndrome in the pathological process of systemic inflammatory damage[32]. For many years, SIRS was used to define sepsis. However, the concept of SIRS is too sensitive and lacks specificity, and the SIRS criterion is recognized to be limited as a prognostic tool in the general population[33]. Thermal ablation can instantaneously induce massive production of necrotic tumour tissues and increase the risk of systemic inflammatory response, manifesting as elevated body temperature, leukocytosis, and increased C-reactive protein levels[34, 35], which are all assumed to participate in organ injuries such as hepatic abscesses and liver dysfunction. Thus, we included SIRS as a variable, and the results showed that it significantly increased the risk of major complications after thermal ablation. Therefore, close supervision of SIRS is expected to be necessary to implement interventional preventive measures as early as possible.
There are some limitations of this study, including its retrospective design and single treatment centre bias, which reduces the generalizability of our data. In addition, 35% of ablation sessions in this study were multifocal, and included more than two lesion locations, thus we did not analyse the impact of lesion location on complications in the study. Finally, since this study was a retrospective analysis, the power and frequency of thermal ablation could not be controlled, and there may have been selection biases.