Avaliação por ressonância magnética funcional da necrose coagulativa por ablação de radiofrequência nas metástases hepáticas colorretais

Abstract

The majority of patients who have colorectal liver metastases (CLM) are not eligible for resection. Therefore other techniques to achieve locoregional control of the disease have been used. Liver radiofrequency ablation (RFA) have been more frequently used for treatment of this condition due to good response rates, particularly when associated to modern chemotherapy. Although characterization of CLM pre ablation are well established, parameters post RFA require more objective standardization. Apparent water diffusion coefficient (ADC) have been used as a necrosis and ischemic parameters in MR analyzes. Even though it is not yet well defined its rule and the diffusion weighted images (DWI) in evaluation of RFA generated coagulative necrosis, specifically in patients with CLM. The objective of this study is to analyze the spectrum of changes in functional MR after CLM RFA. A retrospective study was done between 2001 and 2006, where 51 patients were submitted to CLM RFA in Johns Hopkins Hospital (Baltimore, USA) and 16 fulfilled inclusion criteria. The inclusion criteria were: (1) to have CLM treated with curative intention on surgery guided by intra-operative ultra-sound (IOUS), and (2) to have an MR immediately and after (until 10 days) the RFA procedure. MR images before and after RFA were identified and reviewed. Contrasted and DWI MR Images were done in 1.5 T unit. T1 and T2 images were done with and without venous contrast. All of exams had 4 to 6 mm thickness, 2mm gap and a flip angle of 150. ADC was determined with a b-value of 500 sec/mm2 (intensity of diffusion gradient). Pre and post RFA functional MR analyzes included the following parameters: (1) ADC value, (2) contrast enhancement, (3) diffusion and (4) change in tumor size. In addition, survival and time to local recurrence were calculated. The images were reviewed by two radiologist/surgeon consensus. A total of 65 lesions were evaluated, with 1,7cm mean size pre RFA. After RFA the mean size increased to 3,5 cm(p<0,001). Arterial and venous contrast enhancement diminished significantly post RFA (lowered to mean 10% and 17,5%, respectively, p = 0,002 and p<0,001). Mean ADC lesion pre RFA was 2.79 x 10-3 mm2/sec, and pré-ARF, after RFA lowered to mean 1.75 x 10-3 mm2/sec (p<0.001). Median overall survival was 34,7 months. Functional MR through diffusion and contrast enhancement can provide coagulative necrosis and cellular dehydration subjective and objective estimation in the ablated area. When associated with increase in tumor size can act as an additional marker of tumor response.