Endometriosis: does the menstrual cycle affect magnetic resonance (MR) imaging evaluation?

Purpose To determine if the menstrual cycle affects MR interpretation in patients with pelvic endometriosis. Materials and methods Thirty-one patients with either laparoscopically proven endometriosis, or a high clinical suspicion of deep infiltrative endometriosis, were prospectively recruited from May 2008 to October 2009 and January to June 2012. Two pelvic MR scans were performed for pre-operative planning; during menses and the other mid-cycle. Two experienced radiologists independently assessed image quality and disease extent. Both were blinded to patient identity, previous imaging and menstrual status. Interobserver agreement was assessed using the Kappa (k) test. Descriptive statistics were prepared using chi-squared (or Fishers' exact) tests and Mann-Whitney (rank sum) tests to assess for significant differences between menstrual and non-menstrual imaging. Results Interobserver agreement for image quality was moderate for T2 weighted imaging (k = 0.475, p-value 0.255). Readers demonstrated at least moderate interobserver agreement for certainty level of endometriosis at site-specific locations, with median k 0.599 (IQR 0.488-0.807). No significant difference in disease extent was observed between menstruating and non-menstruating scans (all p-values > 0.05). Conclusion Findings suggest no significant differences in image quality, disease extent or disease severity between menstruating and non-menstruating MR; thus, timing of pelvic MR for assessment of endometriosis need not be influenced by the menstrual cycle