| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
EDUCATION EXHIBIT |
Department of Radiology, Mayo Clinic Rochester, Minnesota
The incidental detection of a renal mass during the course of imaging is an increasingly recognized phenomenon in the radiology community. In fact, reports indicate that renal carcinoma was incidentally detected in only 7%–13% of patients prior to 1973 (1,2) but in 48%–61% in the 1990s (3,4), an increase due in part to increased use of radiologic imaging (5). Compared with symptomatic tumors, these incidental tumors often are smaller in size, are of lower nuclear grade, and present at an earlier stage (6).
Although surgical extirpation is the established standard of treatment for solid renal masses, medical professionals involved in the management of small incidental tumors have struggled with such aggressive intervention. Particularly in elderly patients or in patients with conditions that render them poor risks for surgery, careful observation has been proposed as a reasonable option in the management of small (< 3-cm) renal tumors, while recognizing surgery as an option in the event of rapid growth (6–8).
In the midst of this dilemma, needle ablation technologies such as RF ablation and cryoablation have emerged as minimally invasive alternatives in the treatment of small renal masses (usually < 3–4 cm). Such techniques can be performed laparoscopically or percutaneously using imaging guidance. Success in tumor treatment is based on follow-up imaging.
Limited data are available regarding the long-term efficacy of renal RF ablation and cryoablation. Allowing for multiple initial treatment sessions, long-term (mean, 2.3–4.6 years) outcomes from percutaneous renal RF ablation have shown 90%–95% local tumor control (9–11). Three-year outcomes following laparoscopic cryoablation have also been published, with local tumor control being achieved in 88%–97% of cases and local tumor progression occurring 3–30 months after ablation (12,13). Long-term outcomes following percutaneous cryoablation have not been published.
We appreciate the opportunity to comment on this excellent review by Wile et al (14) of imaging following imaging-guided ablation of renal neoplasms. The authors clearly describe the CT and MR imaging appearances of renal neoplasms following both RF ablation and cryoablation. Of particular interest are the authors’ descriptions of histologic changes in the ablated tissue that account for the typical imaging findings. Wile et al also appropriately emphasize the value of contrast enhancement in assessing ablation success and determining tumor recurrence. In addition, the authors explain the peripheral and frequently enhancing rim that surrounds the ablation defect on follow-up images, an important finding that can cause concern for those not familiar with these ablation-related changes.
From our experience in treating renal tumors with RF ablation and cryoablation, we can add only a few more observations related to follow-up imaging. First, with cryoablation, MR imaging will occasionally demonstrate intratumoral arterial gadolinium enhancement within 24 hours of ablation. Remer et al (15) reported a similar finding in two of 22 patients, in whom patchy internal gadolinium enhancement was seen the day following renal cryoablation. We suspect that this enhancement represents an early glimpse of protracted tissue injury due to microvascular damage and thrombosis, which are known to occur during the hours and days following cryoablation (16). In our experience, this enhancement resolves within 3–6 months.
We have also chosen to be somewhat flexible in the timing of follow-up imaging. This timing is largely dependent on our confidence in treatment; we frequently choose to follow up small tumors at 6 months following ablation and larger or more challenging tumors at 3 months. In contrast, proposed guidelines for imaging following nephron-sparing surgery include no follow-up for T1 tumors and abdominal CT every 2 years for T2 tumors (17).
This review by Wile et al (14) begins to "close the loop" in the minimally invasive or ablative management of renal masses (ie, in defining treatment success or failure on the basis of imaging findings). However, there is an important caveat that can only be appreciated with a full understanding of the tumors typically treated with ablative techniques.
We know that small renal tumors are more frequently lower in nuclear grade, if not benign, compared with larger tumors. In 2003, Frank et al (18) published a very important paper detailing the pathologic features of solid renal tumors relative to tumor size. In this retrospective review of 2935 surgically resected renal tumors, 25% of tumors smaller than 3 cm were benign. The authors also found that smaller tumors were of lower nuclear grade than larger tumors.
Second, small renal masses typically treated with ablation usually have a very slow rate of growth. In a recent meta-analysis, 234 observed renal masses with a mean diameter of 2.6 cm demonstrated a mean annual growth rate of 0.28 cm (19). When one excludes the few rapidly growing small tumors, the mean annual growth rate falls to 1 mm (8).
In the absence of gross residual tumor following ablation, we are left to concern ourselves with radiologically occult microscopic tumor at the ablation margin. But to expect detectable growth of such slow-growing microscopic benign or malignant tumors over the course of 1, 2, or even 3 years is unrealistic. We must accept the fact that residual foci of malignancy may take many years to manifest at imaging. This fact is clearly demonstrated by the evidence of local tumor progression 14–31 months after cryoablation and RF ablation in studies with 2 or more years of follow-up (10–12).
RF ablation and cryoablation play a well-de-fined role in the treatment of renal tumors in elderly patients with comorbidity and in patients who are otherwise poor surgical risks. Although current short-term follow-up is promising, imaging has yet to validate the long-term efficacy of ablation in the treatment of renal tumors.
 |
References |
|---|
 Top References |
|---|
Related Article
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| RADIOGRAPHICS | RADIOLOGY | RSNA JOURNALS ONLINE |
