The role of magnetic resonance imaging in determining the proximal extension of early stage cervical cancer to the internal os

Purpose: To study the interobserver variability of MRI for visualization of the internal os and measuring the distance between tumor and the internal os in patients with early cervical carcinoma and to compare the distance between tumor and the internal os measured on MRI with invasion of the internal os determined by histopathology. Materials and methods: All T2-weighed MRI examinations between January 2003 and December 2007 of patients who underwent hysterectomy, of ≤40 years, with clinical stage IB1 cervix carcinoma and tumor size ≤2 cm were retrieved. 27 patients fulfilled these criteria. Two radiologists retrospectively reviewed the images for visualization of the internal os and the distance between tumor and the internal os; agreement and intraclass correlation coefficients (ICCs) were calculated to determine interobserver variability. The distance between tumor and the internal os measured on MRI was compared with invasion of the internal os determined by histopathology. Results: In 26 patients, visualization of the internal was rated as good or moderate by both radiologists (agreement 96%). In 15 patients, both radiologists observed a tumor and the ICC for the distance between tumor and the internal os was 0.752 (95%CI: 0.406-0.909). Assuming 5 mm distance between tumor and the internal os on MRI as criterion for invasion of the internal os, 1 true-positive, 2 false-positives and none false-negatives were observed. Assuming 1 cm as criterion increases the number of false-positives, respectively 3 and 5 by radiologist 1 and radiologist 2. Conclusion: MRI has high interobserver values for visualization of the internal os and no false-negatives for involvement of the internal os.