Labyrinth: Definition, Types, Anatomy and Associated Injuries

The inner ear lies within the petrous part of the temporal bone, between the middle ear and the internal acoustic meatus.

These are laterally and medially, respectively.

The cavity of the inner ear has two main components: the bony labyrinth and the membranous labyrinth.


Bone labyrinth:

It consists of a series of bony cavities within the petrous part of the temporal bone. It consists of the vestibule, the cochlea and three semicircular canals. All these structures are internally lined with periosteum and contain a liquid called perilymph.

The bony labyrinth is aligned with the longitudinal axis of the temporal crag.

Membranous labyrinth:

It is located within the bony labyrinth in the inner ear and has the same general shape, however, it is considerably smaller and is partially separated from the bony walls by a quantity of fluid, the fluid called endolymph .

It contains the sensory end organs, the cochlear duct, the semicircular canals, the utricle and the saccule. It is a collection of tubes filled with liquid and cameras that contain receivers for the senses of balance and hearing. In certain places, it is fixed to the walls of the cavity.

The walls of the membranous labyrinth are aligned with distributions of the cochlear nerve, one of the two branches of the vestibulocochlear nerve. The other branch is the vestibular nerve.

Inside the vestibule, the membranous labyrinth does not preserve the shape of the bony labyrinth, but consists of two membranous sacs, the utricle and the saccule. The membranous labyrinth is also the location of the receptor cells that are found in the inner ear.



Central part of the bony labyrinth in the inner ear. It is separated from the middle ear by the oval window, and is medial to the eardrum (tympanic cavity), communicates previously with the cochlea and then with the semicircular canals.

Two parts of the membranous labyrinth; The saccule and utricle are found inside the vestibule.


The cochlea houses the cochlea duct of the membranous labyrinth, the auditory part of the inner ear. The cochlear duct can be described as having a triangular shape:

Lateral wall : formed by thickened periosteum, known as spiral ligament.

Ceiling : formed by a membrane that separates the cochlear duct from the scala vestibuli, known as Reissner’s membrane.

Soil : formed by a membrane that separates the cochlear duct from the scala tympani, known as the basilar membrane.

It revolves around itself around a central portion of bone called modiolo, producing a cone shape that points in an anterolateral direction.

Extending outward from the modiolus is a shelf of bone known as the spiral lamina, which adheres to the cochlear duct, holding it in place. The presence of the cochlear duct creates two chambers filled with superior and inferior perilinfa:

Scala vestibuli : located superiorly to the cochlear duct. As its name suggests, it is continuous with the lobby.

Scala tympani : located inferiorly to the cochlear duct. It ends in the round window.

Semicircular channels:

There are three semicircular canals: anterior, lateral and posterior. They contain semicircular canals, which are responsible for balance (along with the utricle and saccule).

Canal semicircular lateral:

It is the shortest of the three channels. The movement of the fluid within this channel corresponds to the rotation of the head around a vertical axis (the neck), or in other words, rotation in the transverse plane.

This happens, for example, when you turn your head to the left and right sides before crossing a road.

It measures from 12 to 15 mm, and its arch is directed horizontally backwards and laterally. Therefore, each semicircular channel is at right angles to the other two.

Its ampullar end corresponds to the upper and lateral angle of the vestibule, just above the oval window, where it opens near the ampullary end of the upper channel; its opposite end opens at the top and rear of the lobby.

The lateral channel of one ear is almost in the same plane as that of the other; while the upper channel of one ear is almost parallel to the posterior channel of the other.

Canal semicircular superior:

The upper or anterior semicircular canal is a part of the vestibular system and detects rotations of the head around the lateral axis, or in other words, rotation in the sagittal plane. This happens, for example, by nodding.

It has a length of 15 to 20 mm, is of vertical direction and is placed transversely to the longitudinal axis of the petrous part of the temporal bone, on whose anterior surface its arch forms a round projection.

It describes approximately two thirds of a circle. Its lateral extremity is amputated and opens to the upper part of the vestibule; the opposite end joins the upper part of the posterior channel to form the commune of the crus, which opens towards the upper and middle part of the vestibule.

Canal semicircular posterior:

The posterior semicircular canal is a part of the vestibular system that detects the rotation of the head around the left-right (frontal) axis, or in other words, rotation in the coronal plane.

This happens, for example, when you move your head to touch your shoulders or when you do a side flip.

It goes upwards, according to its nomenclature, and later, almost parallel to the back surface of the cliff. The vestibular aqueduct is immediately medial to it.

The posterior canal is part of the bony labyrinth and is used by the vestibular system to detect rotations of the head in the coronal plane. It is the longest of the three channels, measuring between 18 and 22 mm.

Its lower or ampuped end opens towards the lower and rear part of the vestibule, its upper part towards the commune of crus.

Injuries in the labyrinth

Unnoticed rape in or through the osseous and membranous labyrinth of the inner ear during mastoid surgery can cause hearing loss and vestibular symptoms.

The unnoticed entry into the labyrinth should be repaired by placing fascia on the defect immediately. Bone or bone wax can be placed over the fascia to secure its position. Care is taken not to apply direct suction at the fistulous site to preserve the labyrinthine fluids.

It has been found that a fracture classification system in which temporal fractures are delineated in computed tomography based on the disruption of the otic capsule is predictive of complications of temporal bone trauma such as facial nerve injury, sensorineural deafness and otorrhea. cerebrospinal fluid.

In radiographic images, the otic capsule is the densest portion of the temporal bone.

In otospongiosis, one of the main causes of adult onset hearing loss, the otic capsule is exclusively affected. This area is not usually remodeled in adult life, and is extremely dense.

With otospongiosis, normally dense endochondral bone is replaced by haversian bone, a spongy, vascular matrix that produces sensorineural hearing loss due to compromised conductive capacity of the inner ear ossicles.

This results in a hypodensity in the computed tomography scan, with the affected portion for the first time, usually the fissula before fenestram.