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Posterior semicircular canal

The posterior semicircular canal (PSCC) is one of the three semicircular canals of the inner ear and plays a critical role in detecting rotational head movements in the coronal plane (ear-to-shoulder tilt). It forms part of the vestibular apparatus located within the petrous temporal bone.

The canal forms a vertically oriented loop with an ampullated end (containing sensory epithelium) and a non-ampullated end that joins with the non-ampullated end of the superior semicircular canal to form the common crus. It contains endolymph, and angular acceleration causes movement of the cupula and activation of vestibular hair cells.

The posterior semicircular canal is the most commonly affected site in benign paroxysmal positional vertigo (BPPV) due to canalith migration. It is routinely evaluated on high-resolution MRI and CT in the assessment of vertigo, dehiscence, fractures, congenital abnormalities, and labyrinthitis.

Synonyms

  • PSCC

  • Posterior vertical canal

  • Inferior semicircular canal (less common)

Location and Structure

  • Position: Posterior aspect of the bony labyrinth, oriented vertically and nearly perpendicular to the petrous ridge

  • Shape: Curved bony tube containing membranous canal filled with endolymph

  • Components:

    • Ampulla: Expanded sensory end containing crista ampullaris

    • Non-ampullated limb: Joins superior canal to form common crus

  • Orientation: Detects rotation of the head in the coronal plane (tilt left/right)

  • Relation to other labyrinthine structures: Lies closest to the sigmoid sinus, posterior fossa dura, and vestibule

Relations

  • Medially: Vestibule

  • Laterally: Sigmoid sinus and mastoid air cells

  • Superiorly: Common crus and superior semicircular canal

  • Inferiorly: Proximity to jugular bulb (high-riding jugular bulb may abut canal)

  • Anteriorly: Facial nerve mastoid segment and pyramidal eminence

Function

  • Detects rotational acceleration in the coronal plane (tilting movements)

  • Contains the crista ampullaris, which converts mechanical endolymph flow into neural signals

  • Works in coordination with the superior semicircular canal of the opposite ear for paired vestibular balance

  • Provides essential input for postural equilibrium, ocular reflexes, and spatial orientation

Clinical Significance

  • BPPV (Posterior Canal Variant): Most common variant; otolith debris accumulates in this canal

  • Labyrinthitis: Causes inflammation and T2 fluid signal abnormalities

  • Dehiscence: Rare; may cause sound/pressure-induced vertigo

  • Temporal bone fractures: May disrupt canal function and cause vertigo or sensorineural hearing loss

  • Congenital abnormalities: Dysplasia or aplasia seen in inner ear malformations

  • Imaging importance: High-resolution MRI and CT essential for evaluating vestibular pathology

MRI Appearance

T1-weighted images (pre-contrast)

  • Bony wall: Low signal

  • Endolymph and perilymph: Low-to-intermediate signal

  • Ampulla: Low signal; subtle contour differentiates it from vestibule

T1-weighted Fat-Saturated Post-Contrast

  • Normal canal: No enhancement of endolymph or perilymph

T2-weighted 3D High-Resolution Sequences (3D T2 DRIVE / CISS / FIESTA)

  • Endolymph/perilymph: Very bright fluid signal, sharply outlining canal lumen

  • Bony walls: Dark low-signal ring

  • Common crus: Clearly visualized joining superior canal

  • Ampulla: Rounded, fluid-bright expansion

CT Appearance

Temporal Bone CT (Non-Contrast)

  • Bony canal: Thin, dense, well-defined osseous ring

  • Orientation: Vertical plane, posterior to vestibule

MRI images

Posterior semicircular canal image 1

MRI images

Posterior semicircular canal image 2