High-resolution MR imaging for nodal staging in rectal cancer: are there any criteria in addition to the size?

Abstract

Purpose: MR staging of nodal metastases in patients with rectal cancer using criteria based on size, shape and signal intensity can be difficult, because ≥50% of the nodes are less than 5mm in size. Therefore new MR criteria were evaluated to see whether it can improve the MR assessment of nodal metastases in rectal cancer patients. Materials and methods: Ninety-nine patients with primary rectal carcinoma underwent 1.5T high-resolution MRI with a quadrature phased array coil. Among them, 75 patients who had undergone total mesorectal excision were enrolled in this study. An MR radiologist, blinded for the histological results, randomly recorded the characteristics of each detectable node (LN); common criteria such as short-axis diameter, the ratio of long- to short-axis diameter, and signal intensity on each sequence; new criteria such as the margin (smooth, lobulated, spiculated, indistinct), a homogenous or mottled heterogeneous appearance, gross enhancement and its pattern, the venous encasement, and the dirty perirectal fat signal. Results: Among 75 patients, 22 (29%) were node-positive. All patients who did not have detectable LN on MR were node-free (n=15). Presence of LNs>4mm was significantly higher in the node-positive group. Presence of LNs>8mm was seen only in the node-positive group. Presence of a spiculated border and an indistinct border shows sensitivities of 45 and 36%, and specificities of 100 and 100%, respectively. Presence of a mottled heterogeneic pattern shows a sensitivity of 50%, a specificity of 95%. The presence of these three features were strongly correlated with LN positivity (P<0.001, respectively). Presence of a venous encasement (n=4) and dirty perirectal fat signal (n=3) were also significantly (P<0.05, respectively) correlated with LN positivity. Conclusion: In addition to size, new criteria such as a spiculated or indistinct border and a mottled heterogeneous appearance could be useful to predict regional lymph node involvement in patients with rectal cancer.