Fetal MRI has progressively become a major tool in prenatal imaging, and its complementary role towards ultrasound (US) is now widely accepted. Ultrasound is still the gold standard for prenatal imaging, but its capacity to rule out temporal bone pathology is limited. In contrast, MRI is capable of high spatial resolution, to study the development of the temporal bone structures during gestation. Indeed, it is possible to fully delineate the cochlea, vestibular apparatus (vestibule and semicircular canals), and the middle ear using MRI with T2-weighted sequences, as early as at gestation week (GW).

Review basic US anatomic views of the evaluation of the fetal ears (external, middle and inner ear). Summarize the MRI sequences allowing good anatomical study. To trace US and MRI anatomy of the fetal ear.

US anatomy of fetal ear: prenatal sonographic visualization of the fetal middle and inner ear is hampered by acoustic shadowing of the temporal bones.

The inner ear: the most important limitation of sonographic fetal cochlear imaging is ossification of the temporal bones, which causes acoustic shadowing.

We can see fetal cochlear using coronal head scanning through the mastoid fontanel or squamous suture.

Middle ear: ossicle (incus and malleus) are observed only in the second half of pregnancy. They appeared as a bright echo within the upper part of the tympanic ring in.

External ear: US can help auricular detection of two ears which is better in 20–24 weeks and can be considered as the best period to detect external ear abnormalities.

Prenatal tympanic ring imaging in US is more feasible in the second-trimester examinations. Tympanic rings appear as distinct, thin, circular structures lying on the infero-lateral surface of the fetal skull.

MRI anatomy of fetal ear:

– sequences: all fetal cerebral magnetic resonance imaging (MRI) examinations performed at 1.5 Tesla. We review T2-W axial, sagittal and coronal images. The external, middle and inner ears were respectively evaluated. Fetuses presenting with a facial and/or cerebral malformation were excluded;

– MRI anatomy: contrary to sonography, the contribution of MRI in the prenatal diagnosis of middle and inner ear abnormalities has been investigated in recent years;

– inner ear: the ability to identify the inner structure of the cochlea improved with gestational age, is related to a progressive gain of T2 contrast against the surrounding otic capsule as it ossifies, and not to the cochlear development itself that is supposed to be fully complete. The T2-weighted MRI images showed a high signal intensity of fluid in the membranous labyrinth, which, at 14 weeks, was the first recognizable fetal temporal bone structure;

– middle ear: visualization of the middle ear with fetal MRI can be visualized after 25 week. The ossicles are seen as a T2-hypointense area, never with enough detail to discriminate each ossicle. The tympanic cavity is always well-demonstrated on axial and coronal T2-W slices;

– external ear: the external ears (EA) are normally only patent after 28 gestation week, after the progressive involution of an ectodermal plug that occludes them until then.

MRI represents the most important tool for fetal ear exploration and the knowledge of its anatomy may lead to a better understanding of congenital ear disorders.