Page 72 - Read Online

Page 2 of 19 Deivasigamani et al. Mini-invasive Surg 2023;7:9 https://dx.doi.org/10.20517/2574-1225.2022.99

With the advent of cross-sectional imaging, there has been a stage migration of kidney cancer with
increased diagnosis of renal cancer at an earlier stage and coinciding increased 5-year survival rate, 93% for
[2]
tumors localized to the kidney but 70% for local spread and 12% for distant spread . Thus, there is interest
in treating RCC at an early stage before it spreads, but the discovery of small renal masses (SRMs), defined
as a contrast-enhancing solid or cystic renal lesion measuring 4 cm, requires a diagnostic and management
decision because some SRMs represent benign lesions and others an indolent malignancy with a low risk of
metastasis that can be managed with a surveillance strategy . For small renal tumors, surgical extirpation
[3]
(partial or radical nephrectomy) and active surveillance are frequently considered the best management
options. Even if active surveillance is initially used, if the SRM grows at a significant rate, intervention is
merited, and not all patients with SRMs are good candidates for surgical resection. For these patients,
minimally invasive ablative therapies, particularly thermal ablation (TA) techniques such as cryoablation
(CA), radiofrequency ablation (RFA) and microwave ablation (MWA), provide an alternative management
strategy.

CA, which has been used for many tissue types for over 30 years, involves cooling targeted tissue while
using image guidance to a temperature sufficient to induce cellular death. Rapid cooling within targeted
tissue by CA causes coagulative necrosis of cells via direct cellular membrane damage as well as changes in
the cellular microenvironment. The use of CA for urologic applications has increased due to the relative
benefits of CA, including real-time image monitoring during treatment, decreased anesthetic requirement,
and excellent safety profile in patients at increased risk for surgery. This article provides a narrative review
of the mechanisms of action and techniques implemented for CA, as well as the selection criteria,
complications, renal function outcomes, and oncologic outcomes of CA for the management of SRMs.

METHOD OF EVIDENCE ACQUISITION
A literature search of Medline, Embase, and Scopus databases was conducted in August 2022 using Medical
Subject Headings (Mesh) and a free-text approach. In the free-text protocol, the following Mesh terms were
used: Small Renal Masses, Renal Cryosurgery/Cryotherapy, Renal Cryoablation and Percutaneous/
Laparoscopic Cryoablation/therapy. Only articles in English were considered. Conference abstracts and case
reports were excluded. When the findings of multiple series from the same institution overlapped, the most
recent series was assessed.

Additionally, references within articles obtained through the initial query were examined further. All writers
evaluated and approved the papers that were selected. The reporting of the type of CA method used
(percutaneous, laparoscopic, or open), patient selection criteria and reporting of complications with
oncologic and functional outcomes were all considered for review.

CRYOABLATION
Cryogenics - mechanism of action
Cooper was the first to document the necrotic impact of CA in 1964 ; however, its applications in urology
[4]
and the use of percutaneous probes for treatment are relatively new. CA is characterized by intense and
rapid cooling that causes ice ball formation encompassing the target tissue. The temperature nadir of the
target tissue and duration of the tissue at the nadir temperature was the initial basis of cryoablative
[5]
dosimetry . Based on multiple in-vitro and in-vivo experiments, a temperature nadir of -40 °C has been
established as the optimal target temperature to establish cell kill in renal tumors . In addition to
[6]
temperature nadir, additional factors that modulate the effectiveness of CA in causing cancer cell death
include the time of exposure, rate of cooling, rate of thawing, and the number of freeze-thaw cycles . CA
[5-7]
results in cell death through a variety of mechanisms, including physical damage to the cell membrane