Magnetic Resonance Imaging to Evaluate Neoadjuvant Therapy Effects on Rectal Carcinoma.

Although total mesorectal excision reduces the local recurrence rate in comparison to other surgical approaches, the occurrence of local relapse is still common, especially in cases when there is malignant infiltration of the circumferential resection margin. Mesorectal fascia is an important prognostic and diagnostic factor and it may be argued that mesorectal fascia represents the circumferential resection margin if total mesorectal excision is used as a surgical approach. Tumor infiltration of mesorectal fascia warrants preoperative neoadjuvant therapy in order to reduce the risk of tumor relapse. The aim of this study was to show the importance of high-resolution phased-array magnetic resonance imaging (MRI) as a modality of choice in preoperative evaluation of the effects of neoadjuvant therapy on locally advanced rectal carcinoma. This prospective comparative study included 51 patients with locally advanced rectal carcinoma that infiltrated mesorectal fascia. All study patients underwent MRI scanning twice, i.e. before and after neoadjuvant chemoradiotherapy. MRI results before and after neoadjuvant chemoradiotherapy were compared to evaluate regression of tumor length and regression of tumor infiltration of mesorectal fascia. Gender distribution of 51 patients with rectal carcinoma subjected to neoadjuvant therapy was equal, and their average age was 51 (32-81) years. MRI results showed tumor regression from mesorectal fascia following chemoradiotherapy in 36 (70.5%) cases, and Wilcoxon test showed significant differences between pretherapeutic and post-treatment MRI findings (Z=-3.162, p=0.002) in the sense of regression of tumor infiltration of mesorectal fascia. In 41 (80.3%) cases there was a reduction of tumor length, where Wilcoxon test showed differences between pretherapeutic and post-treatment MRI findings (Z=-2.754, p=0.006) in the sense of tumor length reduction. The mean pretherapeutic tumor length was 5.4 (2.3-15) cm. The mean reduction of tumor length following chemoradiotherapy was 3.56 (0.3-4.1) cm. In all 36 patients that had tumor-free mesorectal fascia following surgical treatment, the post-treatment MRI results were confirmed by histopathology. In conclusion, MRI is important for evaluation of tumor infiltration of mesorectal fascia, and is useful on patient selection for appropriate treatment for rectal carcinoma. MRI reliably evaluates the effects of neoadjuvant therapy, which contributes to better outcome of treatment for this disease.