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

To determine if the menstrual cycle affects MR interpretation in patients with pelvic endometriosis.

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.

Interobserver agreement for image quality was moderate for T2 weighted imaging (k=0.475, p-value <0.001) and substantial for T1 fat saturated imaging (k=0.733, p-value<0.001), with no significant difference in image quality between menstrual and non-menstrual scans (all p-values>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).

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.