SRMs form a distinct group of pathology where a number of treatment options are available that can be tailored to the individual patient. It is well understood that surgical extirpation of stage T1a renal tumors provides up to 97% 5-year cancer-specific survival rates.[13
] Open partial nephrectomy has been established as the gold standard for the treatment of SRMs, although excellent 5-year cancer-specific survival has also been achieved by laparoscopic partial nephrectomy (LPN) in certain centers.[14
] The main drawback with LPN is the demanding technical ability. The other drawbacks of LPN include higher morbidity and a possible impact on renal function secondary to warm ischemia.[16
] The option of minimally invasive thermal ablation, such as LCA, in place of LPN could be utilized by all laparoscopic surgeons who are familiar with radical nephrectomy.[10
] Furthermore, SRMs are often found in patients with significant comorbidities in whom LCA is often a suitable option. In the series by Gill et al
., the mean ASA score of the patients who underwent LCA was three, reiterating the value of minimally invasive surgery in this population.[17
Gill et al
., first described renal cryoablation in a series of 32 patients demonstrating the feasibility of LCA.[10
] More recently, the Cleveland group published their cryoablation series with a minimum of 5 years follow-up demonstrating a 5-year cancer disease specific survival rate of up to 92% and disease-free survival up to 81%.[18
] Similarly, a promising recurrence-free survival rate of 97% has been quoted by Cestari et al
., in the short- term follow-up.[19
In our institution, renal cryoablation has been offered to patients with peripherally situated renal tumors that are less than 40 mm in size and who are thought to be at higher risk for open partial nephrectomy or have expressed their preference for cryoablation. Considering the lack of long-term data, patients younger than 60 years were actively discouraged from undergoing renal cryoablation. LCA was only performed on two patients under the age of 60 years, one who was a diabetic and had expressed his preference to be considered for LCA and the other had Von-Hippel-Landau disease which necessitates maximum preservation of renal function. The three patients with tumor sizes greater than 40 mm were older than 75 years. All the alternative treatment options had been discussed both with the patients and at the multidisciplinary meeting and LCA was thought to be the safest option in these patients. Although Lehman et al
., have shown that LCA of larger tumors (> 30 mm) increases the risk of both operative complications and the recurrence rates, in our series the larger tumors (>40 mm) have not shown any progression at a mean of 22 months follow-up.[20
In our series, a 18G Trucut®
needle was used to biopsy the tumor under laparoscopic ultrasound guidance prior to cryoablation. An adequate histological sample was obtained in 20 patients (91%) from the biopsies taken immediately prior to LCA. Although a final, complete surgical specimen for pathological analysis could not be obtained due to the nature of cryoablation, reports from the literature have shown concordance rates of up to 100% between the histology of preoperative biopsies and the excised tumor.[21
] The majority of SRMs in our study were confirmed to be RCCs; however, two SRMs were confirmed to be oncocytomas and one lesion a TCC. It has been reported that some oncocytic tumors identified on core biopsy prior to extirpative surgery can be associated with tumor heterogeneity and can harbor RCC.[22
] Hence we applied the same follow-up protocol for RCCs as well as oncocytomas in this study. We recognize that TCC is an unusual diagnosis in a renal cryoablation series. The preoperative CT scan in this patient had shown a peripherally situated, well-circumscribed, enhancing tumor that measured 29 mm in maximum diameter, consistent with an RCC. Even on retrospective review, it was difficult to identify the tumor as a TCC.
In our series, three tumors demonstrated central enhancement on postcryoablation CT. The preoperative sizes of these tumors were 40 mm or less and the abnormal enhancement appeared on early CT follow-up (3–14 months). One of these three patients developed inferior vena cava thrombus with a 20-mm increase in tumor size on the follow-up CT scan; this patient was subsequently treated with open radical nephrectomy. In this case, retrospective review of the precryoablation CT revealed that the tumor had actually invaded renal segmental veins which would have precluded renal cryoablation as a treatment option. Although our LCA failure rate as demonstrated on CT follow-up is 14% (3/21) if we exclude the patient with segmental vein invasion who would not have been a suitable candidate for cryoablation, our failure rate of 10% (2/20) is comparable to other studies.[17
] In addition, in a study of the longest available renal LCA follow-up (8 years), a local recurrence rate of 14% has been reported.[18
The mean (range) postablation cryolesion size was 23 mm (0–58), which includes three tumors that have undergone complete dissolution. Furthermore, two lesions initially increased in size following LCA at 3 months but subsequent CT scans demonstrated that these lesions are decreasing in size but have not yet returned to their pre-LCA size. This is a recognized phenomenon as reported in other series.[17
] In a series by Gill et al
., the mean cryolesion size at day one post-LCA was 36 mm compared to the preoperative mean tumor size of 21 mm. The cryolesions subsequently returned to their preoperative size at a mean of 6 months.[17
] Similarly, Cestari et al
., demonstrated that following an initial increase in cryolesion size post-LCA, a 85% reduction in cryolesion size was achievable by 24 months post-LCA.[19
] Interestingly, we had used five cryoprobes to achieve a peripheral tumoral temperature of at least –40°C in the two patients with cryolesions which initially increased in size post-LCA but are now slowly reducing in size. The number of cryoprobes used may have an influence on the post-LCA cryolesion size. The rationale behind using many cryoprobes was to ensure a wide margin (approximately 10 mm) of ice ball around the tumor.
The complications in our series include a case of serious bleeding requiring blood transfusion and another requiring embolization. We believe that these may have been caused by unnoticed movement of the cryoprobes during cryoablation. We have since ensured that the thermocouple and the cryoprobes are protected from movement during the freeze-thaw cycles.
The lack of significant deterioration in serum creatinine post-LCA is reassuring; however, we understand that a more formal measure of renal function in the form of glomerular filtration rate (GFR) would provide a more objective assessment of nephron loss secondary to cryoablation.
In our institution, we have reliably identified three recurrent tumors on CT follow-up, two of which were treated appropriately. If we exclude the patient with preoperative CT features of segmental vein invasion who would not have been a suitable candidate for cryoabation, our local recurrence rate is 10% (2/20). Apart from two bleeding-related complications and a postoperative pneumonia, we have observed that renal cryoablation is a safe procedure. Although size and enhancement characteristics on postcontrast CT scan are used as surrogate markers for recurrent/residual tumor, long-term follow-up studies are required to establish oncological outcome and also to consolidate the indications for renal cryoablation.