Magnetic resonance imaging characteristics of renal tumors after radiofrequency ablation

doi:10.1016/j.urology.2005.09.046

Urology

Volume 67, Issue 3, March 2006, Pages 508-512

https://doi.org/10.1016/j.urology.2005.09.046 Get rights and content

Abstract

Objectives

The interpretation of radiographic findings in renal tumors treated with minimally invasive modalities, such as radiofrequency ablation (RFA), is critical for assessing treatment adequacy. Magnetic resonance imaging (MRI) is commonly used for patients with renal insufficiency or contrast allergy. Because the MRI experience with renal RFA is limited, we reviewed our experience and report the unique MRI characteristics of RFA-treated renal tumors.

Methods

A single-institution database of renal RFA was reviewed to identify patients followed up with MRI. A radiologist and urologist retrospectively reviewed all MRI scans to identify the characteristic lesion findings after RFA.

Results

Eleven patients (12 tumors) treated by RFA were followed up with MRI examinations. The mean follow-up was 10 months. The mean tumor size at ablation was 2.4 cm, with minimal reduction over time. Ablated lesions were characterized by high signal intensity on T₁-weighted images, low signal intensity on T₂-weighted images, and an absence of contrast enhancement. Of the patients treated by percutaneous RFA, 71% developed a characteristic peritumor halo, seen as a rim of low signal intensity on T₁-weighted and T₂-weighted images, surrounding a zone of perinephric fat just external to the ablated area. Two lesions demonstrated enhancement on the initial postablation MRI scan, indicating incomplete ablation.

Conclusions

The MRI characteristics of successfully ablated renal tumors include the absence of enhancement, minimal size reduction over time, and high and low signal intensity on T₁-weighted and T₂-weighted imaging, respectively. Knowledge of these findings can aid radiologists and urologists in correctly assessing the success of RFA for kidney lesions.

Section snippets

Material and methods

The local institutional review board approved the data collection for this analysis. Between August 2000 and September 2004, 92 patients underwent RFA for renal lesions at our institution. Of these 92, patients, 11 (12 tumors) were followed up with serial MRI scans (total 34 examinations) after the initial treatment. All renal lesions were suspicious for renal cell carcinoma on initial CT or MRI. No patients had metastatic disease. The option of RFA as one of several therapeutic modalities was

Results

The baseline patient characteristics and biopsy results are shown in Table I. Seven tumors were treated with percutaneous CT guidance and five with a laparoscopic approach. The median follow-up was 10 months (range 6 to 30).

Preoperatively, the tumors were generally nearly isointense to normal renal parenchyma on T₁-WIs and slightly hyperintense but heterogeneous on T₂-WIs. All lesions demonstrated preoperative gadolinium contrast enhancement.

As shown in FIGURE 1, FIGURE 2, completely ablated

Comment

RFA is increasingly being used for the treatment of small lesions, especially in patients with considerable comorbidities. After treatment, imaging with CT has been used as a surrogate of successful ablation, given the potential sampling errors and morbidity associated with serial biopsies.⁹ The radiographic progression of ablated renal lesions by CT has been reported,¹ but, to our knowledge, experience with MRI has not been extensively described.

In our analysis, we found distinct MRI

Conclusions

The MRI characteristics of successfully ablated renal tumors include the absence of gadolinium contrast-enhancement, minimal size reduction over time, high SI on T₁-WIs, and low SI on T₂-WIs. Ablated areas may develop areas of heterogeneous intensity on T₁-WIs and T₂-WIs, but thick or nodular enhancing tissue in the region of the ablation zone should raise concern of incomplete ablation or tumor recurrence.

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Citation Excerpt :
After a successful ablation, the zone of ablation should appear as a region of increased attenuation (>40 HU) on the unenhanced studies surrounded by a rim of fat attenuation.99 On MR imaging, the ablation zone often shows heterogeneous hyperintense signal on T1-weighted and hypointense signal on T2-weighted images.100 A thin, smooth rim of enhancement surrounding the ablation may be encountered and should be considered a benign finding.
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Remer et al (21) reported thin peripheral rim enhancement in 30%–50% of lesions between 1 and 3 months postoperatively. This peripheral rim enhancement after treatment bas been reported to be a common MR finding in the first few months after laparoscopic cryoablation or RF ablation in hepatic and renal lesions (13,22–24). Bolte et al (24) reported 10 cases (42%) of peripheral rim enhancement within 3 months on MR images.
To assess the diagnostic value of gadoxetic acid–enhanced magnetic resonance (MR) imaging in follow-up of patients with hepatocellular carcinomas (HCCs) who were treated with radiofrequency (RF) ablation and to compare it with that of four-phase multi–detector row computed tomography (CT).
From July 2007 to May 2008, 36 patients (43 HCCs) were enrolled who were treated with RF ablation (tumor size, 20–47 mm; mean, 24.5 mm) and underwent gadoxetic acid–enhanced MR imaging and four-phase (precontrast, arterial, portal venous, and equilibrium) multidetector CT for follow-up. Two radiologists independently reviewed these images, and conspicuity of tumor margins and detection of residual or recurrent tumor were assessed on a five-point scale with receiver operating characteristic (ROC) curve analysis. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were evaluated.
The mean conspicuity value of tumor margins was significantly higher on MR imaging than on multidetector CT (P < .001). The degree of differentiation between residual/recurrent tumor and hyperemia was significantly greater on MR imaging (P < .001). The mean area under the ROC curve was significantly higher with MR imaging (P = .015), as were sensitivity, specificity, PPV, NPV, and accuracy of detection rate (mean, 100%, 96.2%, 82.4%, 100%, and 96.7%, respectively, vs 41.7%, 56.8%, 13.5%, 85.7%, and 54.7% for multidetector CT). The interobserver agreement rate for MR imaging was higher (0.919) than for multidetector CT (0.672; P < .05).
Diagnostic accuracy, conspicuity of tumor margins, and detection rate of residual or recurrent tumor were found to be better with gadoxetic acid–enhanced MR imaging than with four-phase multidetector CT.
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Citation Excerpt :
Therefore, the zone of ablation seen as an area of nonenhancement on early post ablation CT or MR imaging is generally larger than the original tumor25 (Fig. 1). On MR imaging, the zone of ablation appears generally hypointense at T2-weighted MR imaging and iso- to hyperintense at T1-weighted imaging relative to renal parenchyma33-36 (Fig. 2). Shortly after thermal ablation, a thin rim enhancement has been occasionally demonstrated peripheral to the zone of ablated renal parenchyma on CT27 and MR imaging17,33 and this finding resolves gradually over time and is barely detectable after 3 months.33
Thermal ablation procedures including radiofrequency ablation and cryoablation have been increasingly used for treatment for small renal cell carcinoma. Currently, computed tomography and magnetic resonance imaging are usually used to assess residual or recurrent disease after thermal ablation of renal tumor. After thermal ablation, the zone of ablation is usually seen as an area of hypoattenuation on computed tomography and is generally hypointense at T2-weighted magnetic resonance imaging and iso- to hyperintense at T1-weighted imaging relative to renal parenchyma. The ablation zone frequently involutes over time. Residual tumor after thermal ablation is most common at the margin of the ablation zone and often seen as nodular or crescent-shaped areas of contrast enhancement. Accurate assessment of ablated tumors at postprocedural imaging is essential for evaluating the adequacy of treatment and guiding further management. Complications are uncommon and usually minor but should be detected on postprocedural imaging studies.
Current treatment of small renal masses
2009, Actas Urologicas Espanolas
Cada día son diagnosticados con más frecuencia de manera incidental Carcinomas Renales (CR), debido al aumento del uso de las técnicas de Radiodiagnóstico para el estudio de otras patologías. Su incidencia en los países desarrollados es superior al 40%, siendo malignos el 80% de los tumores sólidos de riñón menores de 4cm. El tratamiento estándar de este tipo de tumores es la nefrectomía parcial con un índice de recidivas del 1-2%. El mayor incremento en el diagnostico de esta patología se ha producido en pacientes entre los 70 y 90 años, grupo de edad que se acompaña de gran numero de comorbilidades. En las dos ultimas décadas y acompañando al desarrollo de las técnicas radiológicas, se han establecido entre nosotros dos técnicas, ablativas, que a través del frío, la Crioterapia (CA), y a través del calor, la Radiofrecuencia (RFA), consiguen la necrosis del tumor. Los resultados oncológicos a corto y medio plazo alcanzan un 95% de remisiones en tumores menores de 4 cm. y al ser técnicas que se pueden realizar por vía percutánea, tanto las complicaciones como las estancias hospitalarias han disminuido. Ya en 1995 Bosniak basándose en la experiencia de la observación del crecimiento y conducta de los CR pequeños durante más de 8 años propugna la postura de “Esperar y Ver” o “Vigilancia Activa”(VA). Presentamos la CA, nuestra serie de RAF y revisamos la literatura de la VA.
En pacientes con edad avanzada, enfermedades concomitantes que desaconsejen la cirugía, monorrenos, con tumores renales múltiples o pacientes que rechacen la cirugía, las técnicas ablativas pueden ser utilizadas de manera segura y eficaz en manos expertas, alcanzando a medio plazo resultados oncológicos similares a la nefrectomía parcial, del mismo modo que en pacientes correctamente informados la vigilancia activa se ha demostrado como segura a medio plazo. Para mejorar las indicaciones, serán necesarias nuevas técnicas diagnósticas, que nos ayuden a diferenciar los tumores potencialmente más agresivos de los que no se van a desarrollar y series mayores y con más años de evolución para confirmar los resultados actuales.
Incidental diagnosis of renal carcinoma (RC) is increasingly common due to widespread use of radiodiagnostic techniques for other conditions. In developed countries, incidental tumor account for more than 40% of detected tumors, and 80% of solid kidney tumors less than 4 cm in size are malignant. Standard treatment for these tumors is partial nephrectomy, and their relapse rate is 1%-2% The higher increase in diagnosis of this disease has occurred in patients aged 70 to 90 years, a group where associated comorbidities are very common. In the past two decades, in parallel to development of radiographic techniques, two ablation procedures achieving tumor necrosis through cold, cryotherapy, and through heat, radiofrequency, have become established. These procedures achieve 95% short- and long-term remissions in tumors less than 4 cm in size. In addition, since these procedures may be performed percutaneously, both complications and hospital stay have decreased. As early as in 1995, Bosniak, based on observation of the growth and behavior of small RCs for longer than 8 years, advocated a watchful waiting or active surveillance attitude. This article reports cryotherapy, our radiofrequency series, and a literature review.
In the event of elderly patients, concomitant diseases advising against surgery, multiple renal tumors, a solitary kidney, or patients who reject surgery, ablation procedures may be safe and effective when performed by expert hands, achieving mid-term oncological results similar to partial nephrectomy. Active surveillance has also been shown to be safe in the mid-term in adequately informed patients. To improve indications, new diagnostic procedures that help us differentiate the potentially more aggressive tumors will be required. Larger series and longer follow-ups are neede to confirm current results.

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Adult urologyMagnetic resonance imaging characteristics of renal tumors after radiofrequency ablation

Abstract

Objectives

Methods

Results

Conclusions

Section snippets

Material and methods

Results

Comment

Conclusions

J Urol

Urology

Urology

Ultrasound Med Biol

Urology

Urology

Adult urology
Magnetic resonance imaging characteristics of renal tumors after radiofrequency ablation