Head and Neck Imaging

Inner ear

1. Anatomy

The inner ear is surrounded by a dense bony capsule, known as the bony labyrinth. The anterior part of the inner ear is the cochlea, while the posterior part is made up of the vestibule and the semicircular canals. Three semicircular canals arise from the vestibule, orientated perpendicularly to each other. Within the bony labyrinth the membranous labyrinth is found. The membranous labyrinth contains endolymph, and is surrounded by the perilymphatic fluid space. The perilymphatic space communicates to some extent with the subarachnoidal space via the bony cochlear aqueduct (see also cochlear aqueduct wide). The vestibular aqueduct contains a canal-like extension of the endolymphatic space, the endolymphatic duct, which has a terminal enlargement known as the endolymphatic sac. The vestibular aqueduct has a wide opening on the posterolateral surface of the petrous bone, containing the proximal part of the endolymphatic sac; the remainder of the sac extends between the dural folds. Also, see inner ear.

2. Pathology

Congenital malformations

According to Jackler, inner ear malformations can be divided into a group with and a group without cochlear malformations. For those with cochlear malformations, see cochlea. Those with a normal cochlea are classified as:

  • dysplasia of vestibule and semicircular canals

  • enlarged vestibular aqueduct

    However, recent detailed studies have revealed that patients with an enlarged vestibular aqueduct often have other inner ear malformations (see large vestibular aqueduct syndrome).

    Inflammation

    The inner ear may be affected by several types of inflammation: viral or bacterial infection, and autoimmune disease. See labyrinthitis.

    Otodystrophies

    The otodystrophies that may affect the inner ear are: otosclerosis, Pagets disease, fibrous dysplasia head and neck, osteopetrosis and osteogenesis imperfecta.

    Tumour

    Tumours may arise from within the membranous labyrinth (inner ear schwannoma). Intracanalicular acoustic schwannoma may extend into the inner ear along the cochlear nerve (see also hook shape sign in acoustic schwannoma). Tumours originating in the vicinity of the cochlea may encroach on its bony capsule.

    Trauma

    The inner ear may be involved in a transverse fracture temporal bone. Hearing loss may be due to labyrinthine concussion, without a fracture visible on CT. Post-traumatic serous labyrintitis or inner ear haematoma may be revealed on MRI.

    RH