Role of MRI in rectal carcinoma after chemo irradiation therapy with pathological correlation

Abstract

Rectal cancer is associated with a high risk of metastases and local recurrence; local recurrence rates after surgical treatment being up to 32% (1). Local recurrence is directly related to incomplete tumor resection (2, 3) and also related to the circumferential safety of resection (4, 5). An accurate local staging at the time of initial diagnosis is therefore very important.

Aim: The aim of this study is to use MRI in comparing the morphologic features of rectal cancer before and after 6 weeks of chemo irradiation treatment and to correlate the post treatment MRI appearances with the histological findings in resected tumors.

Material and methods: 68 patients with histopathologically proven rectal adenocarcinoma received standardized 5-week chemo radiation therapy and subjected to MRI before and after treatment for clinical staging. A correlation between pathological response and MRI findings was done.

Result: Sixty-eight patients with adenocarcinoma rectal cancer were included in the study. Preoperative MRI examination was performed. All patients subsequently underwent operation. The mean time lag between the MRI study and operation was 16.8 days. After preoperative chemo-radiotherapy, MRI findings showed that, there is a significant shift toward downstaging. 16/59 (23.5%) patients achieved down-staging from clinical stage III (before therapy) to stage II after therapy (P = 0.001) by achieving both tumor (T) downsizing and lymph node downstaging. MR images obtained after radiation therapy with concomitant chemotherapy have (100%) sensitivity, (78.7%) specificity, (100%) NPV in the differentiation of T1–2/T3–4 tumors with MRI, accuracy 80.9% with agreement 70.58% and 100% accuracy for node staging.

Conclusion: High resolution pre treatment MRI of the rectum has a high predictive value of treatment outcome either for neoadjuvant treatment or surgery.

Keywords: MRI; Rectal carcinoma; Chemo irradiation therapy