Thermal ablation in adrenal disorders: a discussion of the technology, the clinical evidence and the future

Abstract

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.

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FIGURE 1

Ablation probe components; (a) General ablation probe components. All ablation probes have the same general setup which includes cables/wires leading from a generator, along with cooling inflow and outflow tubes from a peristaltic pump. The applicator shaft consists of an insulated portion and ends at the radiation tip from where hyperthermia is induced. The cross section of the ablation probes (b), (c), and (d) show while probes look similar externally, their internal components vary considerably.

FIGURE 2

Ablation probe heating patterns; (a) This illustration depicts the general heating pattern demonstrated by each modality and the effects of proximal vasculature. (b) Mathematical models can be used to predict heating patterns for each modality and device in adrenal tissue. The simulations illustrate thermal profiles following ablation with a 15 G monopolar RF applicator with a 10 mm active electrode following 2 and 10 min heating. The applied RF power was adjusted to constraint temperature at the electrode - tissue interface within the range 90–97°C. MWA simulations are for a 14 G water-cooled directional applicator and a 15 G water-cooled omni-directional MWA applicator [39]. Both MWA applicators operate at 2.45 GHz and simulations are shown for 30 W power delivered to the applicator for 5 min. Simulation figures courtesy Faraz Chamani, Austin Pfannenstiel, Punit Prakash. MWA, microwave ablation.