Head and Neck Imaging

Cochlea

1. Anatomy

anterior part of the labyrinth. The cochlea is a conical structure, its base bordering the internal auditory canal and its apex orientated anteriorly, laterally and slightly inferiorly. The bony cochlear canal makes approximately 2.5 turns around the modiolus. The bony capsule of the cochlea and the modiolus are connected by the interscalar septum. The osseous spiral lamina is an incomplete bony shelf projecting from the modiolus, separating by means of the basilar membrane the scala tympani from the scala vestibuli. The membranous cochlea (ductus cochlearis) is also situated within this bony spiral canal, and contains the spiral organ of Corti with the auditory receptor cells. Also, see ear and cochlea.

2. Pathology

Congenital malformation

According to Jackler, inner ear malformations can be divided into a group with and a group without cochlear malformations. Those with cochlear malformations can be categorized as follows:

  • congenital labyrinthine aplasia (Michel aplasia);

  • common cavity (cochlea and vestibule);

  • cochlear aplasia (normal vestibule and semicircular canals) (Fig.1);

  • cochlear hypoplasia; and

  • incomplete partition ('true' Mondinis malformation, no interscalar septum)

    Additionally, anomalies of the modiolus have been recognized (see modiolus anomalies).

    Inflammation

    Several types of inflammation can affect the cochlea: viral or bacterial infection and autoimmune disease, see labyrinthitis.

    Otodystrophies

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

    Tumour

    Cochlear tumours may arise from within the membranous labyrinth (vestibular or cochlear schwannoma). Intracanalicular acoustic schwannoma may extend into the cochlea along the cochlear nerve (see also hook shape sign in acoustic schwannoma). Tumours originating in the region of the cochlea may invade its bony capsule (e.g. glomus tumour).

    Trauma

    The cochlea may be involved in a transverse fracture temporal bone. Hearing loss may be due to cochlear concussion, without a fracture visible on CT. Post-traumatic serous labyrinthitis or cochlear haematoma (Fig.2) may be revealed on MRI.

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    Fig.2

    Plain axial T1-weighted spin-echo images of temporal bones, a 3 mm more caudal than b. Patient experienced right-sided sudden hearing loss during straining. Compared to the left side, the intensity of the right cochlea (arrowhead) is higher; also the vestibule and semicircular canals (arrows) show a higher intensity on the right side. Intralabyrinthine haemorrhage.
    Cochlea, Fig.1
    Cochlea, Fig.2 (a)
    Cochlea, Fig.2 (b)