Prediction of nodal involvement in primary rectal carcinoma without invasion to pelvic structures: accuracy of preoperative CT, MR, and DWIBS assessments relative to histopathologic findings

Abstract

Objective: To investigate the accuracy of preoperative computed tomography (CT), magnetic resonance (MR) imaging and diffusion-weighted imaging with background body signal suppression (DWIBS) in the prediction of nodal involvement in primary rectal carcinoma patients in the absence of tumor invasion into pelvic structures.

Methods and materials: Fifty-two subjects with primary rectal cancer were preoperatively assessed by CT and MRI at 1.5 T with a phased-array coil. Preoperative lymph node staging with imaging modalities (CT, MRI, and DWIBS) were compared with the final histological findings.

Results: The accuracy of CT, MRI, and DWIBS were 57.7%, 63.5%, and 40.4%. The accuracy of DWIBS with higher sensitivity and negative predictive value for evaluating primary rectal cancer patients was lower than that of CT and MRI. Nodal staging agreement between imaging and pathology was fairly strong for CT and MRI (Kappa value = 0.331 and 0.348, P<0.01) but was relatively weaker for DWIBS (Kappa value = 0.174, P<0.05). The accuracy was 57.7% and 59.6%, respectively, for CT and MRI when the lymph node border information was used as the criteria, and was 57.7% and 61.5%, respectively, for enhanced CT and MRI when the lymph node enhancement pattern was used as the criteria.

Conclusion: MRI is more accurate than CT in predicting nodal involvement in primary rectal carcinoma patients in the absence of tumor invasion into pelvic structures. DWIBS has a great diagnostic value in differentiating small malignant from benign lymph nodes.

Figure 1. Imaging and histological assessments of partial signet ring cell carcinoma in a 67-year old male patient.

(a) An enhanced CT scan image, showing an enhancing lymph node at the arterial phase with an irregular border in right mesorectum. (b) A high-resolution MR T2WI scan image, showing an irregular edge of a lymph node. (c) An enhanced T1WI (slice thickness 1 mm) scan image, showing a significant high signal intensity of lymph node. (d) A DWIBS scan image, showing a high signal intensity node. (e) Photomicrograph (×40) of HE stained specimen, confirming histologically invasion of the nodal capsule by tumor cells, proliferation of fibrotic tissue, and irregular marginal zone of the node.

Figure 2. Imaging and histological assessments of partial mucinous adenocarcinoma and signet ring cell carcinoma in a 61-year old female patient.

(a) An enhanced CT scan image at the arterial phase, showing an enhancing lymph node with a smooth border in left mesorectum. (b) A high-resolution MR T2WI scan image, showing a smooth-edge of a node. (c) An enhanced T1WI (slice thickness 1 mm) scan image, showing a significant high signal intensity of a lymph node. (d) A DWIBS scan image, showing a high signal intensity of a lymph node. (e) Image of a HE stained specimen (×40), showing the smooth-edge of a lymph node, metastatic tumor tissues in cortex and medulla of lymph node, irregular glandular configuration, and highly heterogeneity cells.

Figure 3. Imaging and histological assessments of rectal carcinoma in a 78-year old female patient.

(a) An enhanced CT scan image at the arterial phase, showing a rim-enhancing lymph node with an irregular border in right mesorectum. (b) A high-resolution MR T2WI scan image, showing an appearance of irregular edge in a node. (c) An enhanced T1WI (slice thickness 1 mm) scan image, showing a significant enhancement of the lymph node edge. (d) A DWIBS scan image, showing a high signal intensity node. (e) Photograph (×100) of a HE stained specimen, showing the presence of tumor tissues in various shapes and sizes coagulative necrosis in the lymph node.