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

Abstract 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.