There is no development of the cochlea anteriorly hence this developmental anomaly can be classified as a cochlear aplasia. On the left, axial ( b, c) and coronal ( d) CT shows an IAC bending posteriorly towards a cystic dilated vestibular system. The internal auditory canal (IAC) is also absent. On the right ( a) axial CT shows a small cyst in place of the cochleovestibular system, corresponding to labyrinthine aplasia. a- d Patient 1: a 6-month-old girl presenting with congenital deafness has bilateral congenital malformations of the labyrinth on CT. after a gestational viral infection such as by rubella or cytomegalovirus, due to a genetic cause or the result of a combination of both, as in aminoglucoside-induced deafness with underlying mitochondrial DNA mutations. Congenital malformations may be acquired, e.g. Both ears may be affected to a different degree. Ībnormal development may cause a myriad of variations, ranging from complete absence of the labyrinth to a minor dysplasia of one semicircular canal (Fig. The mesenchyme surrounding the otocyst becomes condensed and forms the otic capsule. The otocyst divides into dorsal and ventral segments that will become vestibular and auditory parts the endolymphatic appendage appears dorsally. The otic disc becomes invaginated and gives rise to the otic vesicle or otocyst. 1 and 2).įull size image Imaging patterns of disease Abnormal developmentįormation of the labyrinth starts at about 3.5 weeks of gestation by formation of the otic disc and is complete at about 26 weeks of gestation. The endolymphatic duct is connected to the saccule and courses through a bony canal-the vestibular aqueduct-to form the endolymphatic sac in the posterior fossa (Figs. The vestibule harbours the oval window the stapes footplate is attached to the oval window. The vestibular system is located posterior to the cochlea and contains the vestibule with the saccule and utricle and three semicircular canals which are oriented perpendicular to each other. The cochlea is connected to the middle ear by the round window. The modiolus containing the spiral ganglion can, however, be visualised in the centre of the cochlea. The scala media, containing the organ of Corti and filled with endolymph, cannot be visualised separately with current imaging systems. These scalae are connected to each other at the apical tip of the cochlea (helicotrema) and they contain perilymph. Within each turn the cochlea is divided into the scala tympani and scala vestibuli by the osseous spiral lamina. The normal cochlea consists of two-and-a-half turns separated by interscalar septae. The inner ear comprises the cochlea, the vestibular system and the endolymphatic duct and sac. The display slice thickness should not exceed 1.5 mm. Contiguous or overlapping sections from the superior most mastoid air cells to the stylomastoid foramen should be obtained with the gantry angle parallel to the infraorbital-meatal line. With multidetector CT, images can be reconstructed in any desired plane, obviating the need for direct coronal scanning. Temporal bone CT should consist of both axial and coronal images. MRI will render supplementary information on the fine intralabyrinthine structures. CT forms an ideal means to evaluate the bony details of the otic capsule and labyrinth and will also allow evaluating the course of the facial nerve canal and eventual associated anomalies of middle ear structures and the external auditory canal. In patients requiring anaesthesia, these exams should be planned in one session. These techniques render complementary information. Imaging of the inner ear is performed with computed tomography (CT) and/or magnetic resonance imaging (MRI).
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