How to orient it on a skull image

1. Find the external auditory canal
   • The inner ear lies medial and slightly posterior to it.
   • Move inward through the middle-ear region to reach the bony labyrinth.
2. Identify the cochlea
   • It is the small snail-shaped structure.
   • It lies anterior and inferior to the vestibule.
   • Its base faces toward the internal auditory canal and its apex points anterolaterally.
3. Identify the vestibule
   • This is the central chamber between cochlea and semicircular canals.
   • It lies posterior to the cochlea and anterior to the semicircular canals.
4. Identify the semicircular canals
   • They are posterior and superior to the vestibule.
   • Superior (anterior) canal: vertical, arches upward.
   • Posterior canal: vertical, more posterior.
   • Lateral (horizontal) canal: roughly horizontal, but tilted about 30 degrees upward anteriorly.
5. Internal auditory canal
   • Lies medial to the cochlea and vestibule.
   • This is where CN VII and CN VIII enter the temporal bone.

Simple mental map

Lateral  ← external ear / middle ear

           Semicircular canals
                ↑ posterior-superior
                |
Cochlea  →  Vestibule  ← Internal auditory canal (medial)
anterior-inferior

• Cochlea = anterior and inferior
• Semicircular canals = posterior and superior
• Internal auditory canal (IAC) = medial
• Middle ear and mastoid = lateral

Coronal view

Anterior → posterior slice progression

Cochlea  →  Vestibule  →  Semicircular canals / mastoid

What you should see

• Cochlea: lower and more anterior. It appears as a compact spiral or “snail-like” bony structure.
• Vestibule: just posterior and superior to the cochlea, central in position.
• Superior semicircular canal: above the vestibule. It can appear as an arch or ring on more posterior coronal images.
• Lateral semicircular canal: posterior-lateral to the vestibule, near the epitympanum/aditus.
• Posterior semicircular canal: more posterior, often nearer the posterior temporal bone and mastoid.

Coronal shortcut

        Superior semicircular canal
                  ↑
            Vestibule
                  \
                   Cochlea
              anterior-inferior

Sagittal view

Anterior                                      Posterior

Cochlea  →  Vestibule  →  Semicircular canals → Mastoid

What you should see

• Cochlea: the most anterior inner-ear structure. It is also relatively inferior.
• Vestibule: immediately posterior to the cochlea, acting as the hub connecting cochlea and canals.
• Superior semicircular canal: rises above the vestibule, making a vertical loop.
• Posterior semicircular canal: lies posterior to the vestibule and is vertically oriented.
• Lateral semicircular canal: runs roughly horizontally, but its anterior end tilts upward, so it may not look perfectly horizontal on routine sagittal images.
• IAC: medial to the cochlea/vestibule. It carries CN VII and VIII toward the cerebellopontine-angle cistern.

Sagittal shortcut

             Superior canal
                 ∩
Cochlea → Vestibule → Posterior canal
  🐌         ○            ∩
 anterior                 posterior

Important imaging caveat

Labeled multiplanar inner-ear MRI

• Panel b, sagittal: cochlea is anterior, vestibule is central, and the superior semicircular canal arches above and posterior to the vestibule.
• Panel c, coronal: the superior semicircular canal is at the top, the vestibule is below it, and the cochlea is inferoanterior.
• IAM/IAC = internal auditory meatus/canal, medial route for the facial and vestibulocochlear nerves.

Labeled anatomic diagram

Posterior wall of the middle ear

Main landmarks from superior to inferior

1. Aditus ad antrum
   • A superior opening from the epitympanic recess into the mastoid antrum.
   • This is why middle-ear infection can spread into mastoid air cells.
2. Fossa incudis
   • A small depression in the upper posterior wall.
   • Receives the short process of the incus.
3. Facial canal
   • The descending or mastoid segment of the facial nerve lies in this region.
   • It is a major surgical landmark.
4. Facial recess
   • A recess lateral to the facial nerve, often used as a surgical route to the middle ear.
   • Boundaries:
     • Medial: facial nerve
     • Lateral: chorda tympani
     • Superior: fossa incudis / incus buttress
5. Pyramidal eminence
   • A cone-shaped projection on the posterior wall.
   • Contains the stapedius muscle.
   • The stapedius tendon emerges from its apex to attach to the stapes neck.
6. Sinus tympani
   • A deep recess medial to the pyramidal eminence.
   • Lies between the posterior wall and medial wall and can hide cholesteatoma during surgery.
   • Its superior boundary is the ponticulus and inferior boundary is the subiculum.
7. Posterior canaliculus for chorda tympani
   • The chorda tympani enters the middle ear through the posterior wall, then runs forward between malleus and incus.

Easy diagram

              Superior
                 ↑
      Aditus ad antrum
           Fossa incudis
                 |
          Facial recess
     Chorda tympani | Facial nerve
                 |
       Pyramidal eminence
       (stapedius emerges)
                 |
          Sinus tympani
                 ↓
              Inferior

Posterior wall / retrotympanum of the middle ear

• Facial recess: lateral to the vertical (mastoid) segment of the facial nerve and medial to the chorda tympani. It is the route used for a posterior tympanotomy.
• Pyramidal eminence: bony projection containing stapedius muscle. The stapedius tendon emerges at its tip and attaches to the neck of stapes.
• Sinus tympani: deep recess medial to the pyramidal eminence, behind the oval-window region. It is a common hidden site for residual cholesteatoma.
• Ponticulus: ridge forming the superior border of the sinus tympani.
• Subiculum: ridge forming its inferior border.
• Facial nerve canal: runs in the posterior wall and is the key surgical landmark.
• Chorda tympani: crosses near the lateral aspect of the facial recess.

Lateral                          Medial
Chorda tympani → Facial recess → Facial nerve / pyramidal eminence → Sinus tympani