Magnetic resonance imaging in preoperative assessment of the mesorectal nodal status of patients with rectal cancer – Can it be trusted?

•MRI prediction of mesorectal lymph nodes status has very poor accuracy.•Sensitivity of MRI for assessing nodal involvement was 51.2%, specificity 93.4%.•New MRI criteria for nodal assessment are not associated with acceptable outcomes. Magnetic resonance imaging (MRI) is a fundamental diagnostic modality for the evaluation of primary rectal cancer, but MRI assessment of nodal involvement remains a confounding factor. This prospective cohort study was conducted to investigate the accuracy of preoperative MRI in the assessment of nodal status by comparing histopathology reports to MRI findings on a node-by-node basis in 69 patients with rectal cancer. Primary surgery was performed in 40 (58.0%) patients; 29 (42.0%) study patients underwent neoadjuvant chemoradiotherapy (CRT). Histopathological examination revealed T1 tumour in 8 (11.6%) patients, T2 tumour in 30 (43.5%), and T3 tumour in 25 (36.2%). In total, 897 lymph nodes (LNs) have been harvested (13.1 ± 5.4 LNs per specimen). There were 77 MRI-suspicious LNs, 21 (27.3%) of which were histologically proven malignant. The sensitivity of MRI for assessing nodal involvement was 51.2% and specificity 93.4%. Of the 28 patients with MRI-suspicious LNs the diagnosis was correct in 42.8%. The MRI accuracy was 33.3% in “primary surgery” subgroup (n = 18, malignant LNs found in 6 patients). Diagnosis of MRI-negative LNs was correct in 90.2% of study patients; malignant nodes were found in 9.8% of patients initially classified as cN0. MRI prediction of nodal status in patients with rectal cancer has very low accuracy. Decisions regarding neoadjuvant CRT should not be based on MRI assessment of nodal status, but on the MRI evaluation of tumour depth invasion (T stage and relationship between the tumour and mesorectal fascia).