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Posterior bony ampulla

The posterior bony ampulla is the dilated bony enlargement at the anterior end of the posterior semicircular canal within the petrous temporal bone. It houses the posterior ampullary crest, a sensory ridge containing hair cells that detect angular acceleration of the head in the coronal (side-bending) plane.

This structure is part of the vestibular labyrinth and plays a crucial role in balance, postural control, and vestibulo-ocular reflexes. The posterior bony ampulla lies near the vestibule and adjacent osseous structures, making it a key landmark in temporal bone anatomy and a frequent subject of high-resolution CT and MRI evaluation.

Synonyms

  • Posterior semicircular canal ampulla

  • Bony ampulla of the posterior canal

  • Ampullary enlargement of posterior canal

Location and Structure

  • Situated at the anterior end of the posterior semicircular canal where it opens into the vestibule

  • Shape: Ovoid, bulbous bony cavity

  • Contents:

    • Posterior ampullary crest (crista ampullaris)

    • Sensory epithelium and supporting structures

    • Endolymph within the membranous labyrinth

  • Osseous boundaries: Formed by dense otic capsule bone

  • Adjacent spaces: Vestibule immediately anteromedial, posterior canal arch posteriorly

Relations

  • Anteriorly: Vestibule of the inner ear

  • Posteriorly: Arch of the posterior semicircular canal

  • Inferomedially: Proximity to the posterior fossa dura

  • Superiorly: Common crus junction with superior canal (nearby)

  • Laterally: Facial nerve labyrinthine segment located superior-anteriorly relative to the ampulla

Function

  • Detects angular acceleration in the coronal plane

  • Provides critical input for balance and spatial orientation

  • Contributes to the vestibulo-ocular reflex (VOR) for gaze stabilization

  • Houses the crista ampullaris, containing hair cells that transduce head motion into neural signals

Clinical Significance

  • Benign paroxysmal positional vertigo (BPPV): Posterior canal most commonly affected

  • Labyrinthitis or vestibular neuritis: May involve ampullary structures

  • Semicircular canal dehiscence: Rarely affects posterior canal but can alter vestibular response

  • Temporal bone fractures: Can disrupt the bony ampulla

  • Vestibular schwannomas or masses: Rarely compress nearby structures

  • Imaging importance: Essential in evaluating vertigo, temporal bone trauma, congenital anomalies

MRI Appearance

T1-weighted images (Pre-contrast)

  • Bony ampulla: Appears as very low signal (dark) due to dense otic capsule bone

  • Endolymph/membranous ampulla: Low-to-intermediate signal

  • Adjacent structures:

    • Vestibule: low-to-intermediate signal

    • Facial nerve: intermediate signal

T1-weighted images (Post-contrast)

  • Normal: No enhancement inside the bony ampulla; endolymphatic spaces remain non-enhancing

T2-weighted 3D High-Resolution (e.g., 3D T2 DRIVE, CISS, SPACE)

  • Endolymph within ampulla: Very bright hyperintense signal

  • Bony otic capsule: Dark hypointense rim sharply outlining the ampulla

  • Membranous crest: May appear as a thin low-signal ridge within bright fluid

CT Appearance

CT Temporal Bone (High-Resolution Non-Contrast)

  • Bony ampulla: Seen as a rounded, well-defined osseous enlargement of the posterior canal

  • Otic capsule: Thick, very dense bone surrounding the ampulla

  • Endolymph space: Not directly seen but inferred from contour of bony cavity

MRI image

Posterior bony ampulla MRI axial image