The effects of the levonorgestrel intrauterine system (Mirena coil) on endometrial morphology.

AIMS The Mirena coil is a levonorgestrel releasing intrauterine device that is in widespread use. This study aims to document the endometrial morphology associated with this device. METHODS Endometrial specimens from 75 women with the Mirena coil were reviewed and the histological features detailed. RESULTS Morphological features found in most of the endometria were decidualisation of stroma (72 of 75 cases), atrophy of endometrial glands (65 of 75 cases), a surface papillary pattern (38 of 75 cases), and a stromal inflammatory cell infiltrate (59 of 75 cases). Additional common histological features were the presence of foci of stromal myxoid change (29 of 75 cases) and stromal haemosiderin pigment (24 of 75 cases). Reactive atypia of surface glands, glandular metaplastic changes, stromal necrosis, and stromal calcifications were found in small numbers of cases. CONCLUSION The endometrial features are characteristic and relatively constant and are in keeping with the effects of both a progestogenic compound and a mechanical device. Pathologists should be aware of these histological features because the Mirena coil is in widespread use.