Efficacy and Safety of Angioplasty Balloon Interposition in CT-Guided Percutaneous Thermal Ablation of Hepatic Malignancies to Protect Adjacent Organs

Purpose To evaluate the feasibility and safety of placing angioplasty balloons between the liver surface and adjacent organs in CT-guided thermal ablation of subcapsular liver malignancies in case of inadequate success of conventional dissection techniques. Materials and Methods A retrospective, single-centre database query identified 327 hepatic malignancies in 153 patients treated in 215 sessions from 2016 to 2018 by thermal ablation. Demographic data, tumour size, distance to adjacent structures, complications and long-term outcomes were assessed when ancillary procedures were performed to protect adjacent organs. Results In 21 of 327 (6.4%) ablations, thermal protection was necessary. Balloon interposition was successfully performed in 9 cases in 8 patients after hydrodissection or gas insufflation failed to separate adherent organs. Median pre- and post-balloon insertion distance was 0 mm [0–2 mm] and 17 mm [8–20 mm]. No balloons were damaged, ruptured or slid away from their initial position. Technical success of MWA and protection of adherent structures were achieved in all procedures. In a median follow-up of 11.5 months [0–49 months], the local control rate was 88.9% as 1 patient was treated twice with an interval of 3 months for local recurrence. Three non-process-related major complications and 1 minor complication occurred. Conclusion Balloon interposition is a safe and feasible method to enable thermal ablation to a greater number of patients, even after established thermo-protective techniques fail to separate the colon or stomach from the liver surface.


Introduction
Thermal ablation is a well-established, minimally invasive alternative to resection of HCC and liver metastases. It is considered safe with a recent meta-analysis showing minor complications in 5.7% and major complications in 4.6% with a mortality rate of 0.23% [1]. Nevertheless, performing percutaneous ablation near adjacent organs results in the risk of thermal damage, potentially leading to serious complications such as gastrointestinal perforation. Therefore, thermo-protective techniques like gas insufflation, hydrodissection, levering the adherent organ with blunt-tip needles and bile aspiration have been established [2][3][4]. If foregoing measures fail to displace adherent structures, single case reports imply that the balloon interposition technique may be a feasible second-line procedure for organ protection [5][6][7]. Relevant case series to evaluate technical feasibility, safety and success do not exist for now. This retrospective, single-centre case series presents nine cases. 1

Study Population
From 2016 to 2018, all patients who underwent CT-guided thermal ablations were identified in a retrospective database query. If preceding traditional dissection methods did not achieve to adequately isolate the adherent structures, balloon catheter interposition was performed as secondline treatment at our institution. The study was approved by the institutional review board. Preinterventional CT scan of a 73y patient with a HCC (black arrows) in S3 adjacent to the stomach (a, b). Insufficient technical success of gas dissection (white arrow, c, d). Positioning of guiding needles in between the liver and the stomach by using blunt trocars (e, f). Advancing angioplasty balloons via 8F sheaths over guiding wires (g, h, i). Placement of the microwave antenna (j, k). CT scan immediately (l, m) and 2 days after thermoablation (n, o) shows the periablational zone covering the entire HCC (white arrows). Complete ablation was confirmed by follow-up. No complication to the stomach occurred

Balloon Interposition Technique
All procedures were performed under general anaesthesia and with CT guidance by using dedicated software for 3D CT guided interventions (Adaptive 3D Interventional Suite, Siemens, Forchheim, Germany). The abdomen was punctured with a 17-gauge coaxial biopsy needle (TruGuideÒ, BARDÒ Peripheral Vascular Inc., Tempe, AZ, USA) which contains an optional blunt-tip stylet. After accessing the peritoneum, the trocar-tip stylet was replaced by the blunt-tip stylet in order to minimize the risk of damage to peritoneal organs when gradually advancing the needle in between the liver surface and adjacent organs [8]. A 0.035 ''J-tip PTFE guiding wire (EmeraldÒ, Cordis, Santa Clara, CA, USA) was then placed 5-10 cm beyond the needle and an 8-9 Fr sheath (RadifocusÒ, Terumo Corporation, Shibuya, Tokyo, Japan) was advanced over the wire just into the peritoneal cavity. An angioplasty balloon (16/40 mm, 18/40 mm or 20/40 mm, ATLASÒ Percutaneous Transluminal Angioplasty Balloons, Bard Peripheral Vascular, Inc., Tempe, AZ, USA) was placed through the sheath and was inflated manually with air with a 5 ml Luer Lock Syringe when in correct position (Figs. 1, 2 and 3). In case of insufficient separation of the adjacent organ from the liver surface, a second angioplasty balloon was placed in parallel to the first balloon by using the same technique. Finally, the MWA antenna was placed in the intended liver position and the ablation including track ablation was performed with standard ablation protocols [9].

Data Analysis
CT scans, treatment protocols and physician letters were reviewed for demographic data, tumour type, lesion size, liver segment, type of organ in need of protection, pre-and post-balloon insertion distance between liver and adjacent organ, number of balloons used, displacement of balloon, time to insert balloons, technical success, complications and local control rate at last available follow-up. Adequacy of organ protection was judged bases on the distance between liver surface and the adjacent by the interventionalist. Technical success was defined as complete ablation of the lesion plus an ablative margin of 5 mm for HCC and 10 mm for metastases on first follow-up CT imaging 2 days and second follow-up CT or MRI 8 weeks after the procedure. Complications were defined according to the CIRSE classification.

Results
In 21 of 327 lesions (6.4%) treated from 2016 to 2018, ancillary procedures were necessary to perform thermal ablation (Table 1). Consecutive balloon interposition was performed in 9 cases in 8 patients when preceding gas-or hydrodissection failed to separate adjacent organs from the liver capsule (42.9%). The treated patients suffered from HCC (n = 4), and metastases from either CRC (n = 3) or oesophageal adenocarcinoma (n = 1). Median tumour size was 31.5 mm [21-42 mm]. Six malignancies were located in segment 3, the other 3 tumours sited in segments 2, 4b and 6. In 7 procedures, the stomach was the adjacent organ,

Discussion
Even though thermal ablation is rated as an effective and safe method, its use is limited by several factors like tumour size or distance between the ablation zone and crucial structures, as they determine both the technical success and the risk of complications, such as bowel perforation [10][11][12]. As most neoplasms can be separated effectively from the adjacent organ by traditional dissection methods, these methods are considered first-line procedures [7,9,[13][14][15][16]17]. However, their technical success might be limited if post-operative adhesions are present or if the administered gas or fluids disperse away from the intended site [6,7,13]. In these cases, balloon interposition  Fig. 3 a, b Preinterventional CT-scan of a 60-year old male patient with liver cirrhosis and multifocal HCC (black arrows). Short distance between HCC tumours in S6 and the right colonic flexure. c MW ablation of the lesion in S6 following interposition of an angioplasty balloon (white arrow) between the liver and the colon. seems to emerge as a valuable additional option to finalize complex ablative liver procedures as the given data indicates that 9 of 21 ablations could not have been successfully treated without balloon interposition. Furthermore, it may also help to achieve complete ablation by enabling a more aggressive treatment of the tumour.
So far, only an animal model and single case reports have been published on this technique [5,18]. The tendency of the balloon to dislocate from its intended position might has been discussed as the main disadvantage of the procedure [7]. In our experience, the displacement of the balloon usually results from advancing the guiding wire too deeply into the peritoneal space leading to contact of the wire tip to peritoneal structures and hence, a lateral movement of the wire body (Fig. 4). Therefore, the dislocation of the balloon could be prevented by advancing the wire only a few centimetres beyond the targeted balloon position.
This study has certain limitations. Firstly, this singlecentre case series contains only 9 procedures in which balloon interposition was performed. Hence, to evaluate technical success and safety further in-depth data are needed. Secondly, due to the retrospective approach of this study the duration of balloon interposition itself was only determinable in 2 patients. Even if a learning curve can be assumed balloon interposition will add further time exposure which should be taken into consideration when planning complex ablation procedures.

Conclusion
In summary, balloon interposition is a feasible, safe and effective second-line technique to protect the colon or stomach during percutaneous thermal ablation of subcapsular hepatic lesions.
Funding Open Access funding enabled and organized by Projekt DEAL. This study was not supported by any funding.

Declarations
Conflict of interest The authors declare that they have no conflict of interest.
Consent for Publication For this type of study, consent for publication is not required.
Informed Consent For this type of study, formal consent is not required. For this type of study, informed consent is not required.
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