To evaluate the feasibility of magnetic resonance imaging in predicting unusual site ectopic pregnancy: a retrospective cohort study.

Objective: To evaluate the accuracy of pelvic MRI in the diagnosis of unusual ectopic pregnancy (EP), when ultrasound (US) examination is inconclusive.

Methods: We retrospectively reviewed the medical records of 150 patients with suspected EP. Clinical, US and MRI features of 15 unusual EPs were analysed. Two radiologists independently reviewed each case resolving by consensus any diagnostic discrepancy. Interobserver agreement was assessed using the Cohen κ test.

Results: MRI displayed a gestational sac-like structure surrounded by a thick wall in all cases. The thick wall displayed hyperintensity in 41 %, isointensity in 35 % and hypointensity in 24 % of cases on T1-weighted images. Diffusion- and fat saturation T1-weighted images were the most accurate sequences, as they enabled identification of 15/15 and 14/15 patients, respectively. Although US was false negative in detecting cervical and uterine infiltration underlying the caesarean scar, MRI was able to identify the invasion. Interobserver agreement was very good for all sequences (κ=0.892-1.0).

Conclusions: MRI plays an important role in the early diagnosis of unusual EP. It should be considered after negative US findings, providing accurate evaluation of the site and the possible infiltration of these lesions, which help in the management of these patients.

Key Points: • MRI is being increasingly used as a problem-solving modality in ectopic pregnancy. • MRI plays an important role in early diagnosis of unusual ectopic pregnancy. • Knowledge of MRI features in EP is essential to determinate appropriate management.