Purpose of review
To summarise the emerging role of thermal ablation as a therapeutic modality in the management of functioning adrenal tumours and metastases to the adrenal gland.
Recent findings
Observational evidence has demonstrated the benefit of thermal ablation in (i) resolving adrenal endocrinopathy arising from benign adenomas, (ii) treating solitary metastases to the adrenal and (iii) controlling metastatic adrenocortical carcinoma and phaeochromocytoma/paraganglioma.
Summary
Microwave thermal ablation offers a promising, minimally invasive therapeutic modality for the management of functioning adrenocortical adenomas and adrenal metastases. Appropriate technological design, treatment planning and choice of imaging modality are necessary to overcome technical challenges associated with this emerging therapeutic approach.
Objective: To investigate the feasibility and efficacy of localized, subtotal, cortical-sparing microwave thermal ablation (MTA) as a potential curative management for primary aldosteronism. The study investigated with equal importance the selected ablation of small volumes of adrenal cortex while sparing adjacent cortex. Method: An in-vivo study was carried out in swine (n ¼ 8) where MTA was applied under direct visualization, to the adrenal glands at 45 W or 70 W for 60 s, using a lateral, side-firing probe and a nonpenetrative approach. Animals were survived for 48 h post-procedurally. Animals were investigated for markers of histological, immunohistochemical and biochemical evidence of adrenal function and adrenal damage by assessing samples drawn intra-operatively and at the time of euthanasia. Results: Selected MTA (70 W for 60 s) successfully ablated small adrenocortical volumes ($0.8 cm 3 ) characterized by coagulative necrosis and abnormal expression of functional markers (CYP11B1 and CYP17). Non-ablated, adjacent cortex was not affected and preserved normal expression of functional markers, without increased expression of markers of heat damage (HSP-70 and HMGB-1). Limited adrenal medullary damage was demonstrated histologically, clinically and biochemically. Conclusion: MTA offers potential as an efficient methodology for delivering targeted subtotal corticalsparing adrenal ablation. Image-guided targeted MTA may also represent a safe future modality for curative management of PA, in the setting of both unilateral and bilateral disease.
A graphical representation of the variability of relative permittivity and effective conductivity (S/m) of the functional tissues composing the adrenal gland and related diseases in the frequency range of the microwave thermal ablation techniques. The operating frequencies generally adopted to excite the electromagnetic field by an interstitial antenna are: 915 MHz, 2.45 GHz and 5.8 GHz.
Take-Home Messages• Ovine dielectric data are collected, distinguishing between the two functional tissues composing the adrenal gland (cortex and medulla): a sizable difference between the dielectric properties of the two tissues is observed. • Optimized Cole-Cole model of the ovine dielectric properties are presented to allow integration of the data into numerical electromagnetic models. • Human data are collected considering both healthy and diseased adrenal tissues. For the first time, dielectric properties of ex vivo human adrenal glands are measured, presented and compared with data of ex vivo animal models. • The ovine adrenal gland is a feasible model for the optimization of electromagnetic based devices tackling Primary Aldosteronism, such as microwave thermal ablation devices. The ovine model electromagnetically resembles the composition of the human adrenal gland. The ovine model can potentially be adopted in preclinical studies to test the safety and performances of MWA.
Some of the authors of this publication are also working on these related projects: Non-invasive measurement View project Urinary Bladder Monitoring using Electrical Impedance View project
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