Non-invasive MR assessment of macroscopic and microscopic vascular abnormalities in the rectal tumour-surrounding mesorectum

Objectives To evaluate the MRI macroscopic and microscopic parameters of mesorectal vasculature in rectal cancer patients. Methods Thirteen patients with rectal adenocarcinoma underwent a dynamic contrast-enhanced MRI at 1.5 T using a blood pool agent at the primary staging. Mesorectal macrovascular features, i.e., the number of vascular branches, average diameter and length, were assessed from baseline-subtracted post-contrast images by two independent readers. Mesorectal microvascular function was investigated by means of area under the enhancement-time curve (AUC). Histopathology served as reference standard of the tumour response to CRT. Results The average vessel branching in the mesorectum around the tumour and normal rectal wall was 8.2 +/- 3.8 and 1.7 +/- 1.3, respectively (reader1: p = 0.001, reader2: p = 0.002). Similarly, the tumour-surrounding mesorectum displayed circa tenfold elevated AUC (p = 0.01). Interestingly, patients with primary node involvement had a twofold higher number of macrovascular branches compared to those with healthy nodes (reader1: p = 0.005 and reader2: p = 0.03). A similar difference was observed between good and poor responders to CRT, whose tumour-surrounding mesorectum displayed 10.7 +/- 3.4 and 5.6 +/- 1.5 vessels, respectively (reader1/reader2: p = 0.02). Conclusions We showed at baseline MRI of rectal tumours a significantly enhanced macrovascular structure and microvascular function in rectal tumour-surrounding mesorectum, and the association of primary mesorectal macrovascular parameters with node involvement and therapy response.