Prediction of rectal lymph node metastasis by pelvic computed tomography measurement

AimRectal cancer staging represents a crucial step to select the best treatment for this tumour. Particularly after neo-adjuvant chemoradiotherapy (CRT), it may influence the surgical procedure (e.g. radical resection vs. local excision). The aim of this study was to determine the best lymph node size cut-off at computed tomography (CT) to predict nodal metastasis in rectal cancer patients with and without preoperative CRT.MethodsA consecutive series of patients operated on for primary mid–low rectal adenocarcinoma, all staged with pelvic CT scan, were subdivided as follows: those who underwent surgery alone treatment without CRT (Group A) and those who underwent preoperative CRT (Group B). All CT scans were re-viewed by a single radiologist and, based on the lymph node size, findings were compared with pathologic lymph node status (pN). At each lymph node size cut-off value, the following were calculated: accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). The best cut-off value was defined as having an accuracy ≥70% with the highest NPV.ResultsThe study population consisted of 162 patients: Group A (n = 52) and Group B (n = 110). Patients classified as pN-positive (n = 45) had a higher number of and larger sized lymph nodes by CT scan than patients classified as pN-negative (n = 117). The cut-off values with an accuracy ≥70% ranged between 7 and 11 mm in Group A and between 9 and 14 mm in Group B. The cut-off with the best NPV was 7 mm for Group A and 10 mm for Group B.ConclusionsAcknowledging the limitations of the dimensional criterion, lymph node size cut-off values found in our study may be useful for planning rectal cancer treatment using CT scan.