What structures are contained within the petrous part of the temporal bone aside from the internal carotid artery (ICA)?

Structures Contained Within the Petrous Part of the Temporal Bone

The petrous portion of the temporal bone contains the middle and inner ear structures (cochlea, vestibule, semicircular canals), the facial nerve canal (CN VII), the internal auditory canal with CN VII and CN VIII, and the jugular bulb/foramen, in addition to the internal carotid artery. 1

Key Anatomical Components

Vascular Structures

• Internal carotid artery (ICA): Traverses the carotid canal through the petrous bone before entering the subarachnoid space near the ophthalmic artery level 2
• Jugular bulb: Located within the jugular foramen at the posterior aspect of the petrous bone 2
  • High-riding jugular bulb is a common anatomical variant that can be identified on temporal bone CT 2
  • The jugular bulb's highest level (P1) is positioned approximately 12.03 mm from the cochleariform process and 10.98 mm from the chorda-facial junction 3

Neural Structures

• Facial nerve (CN VII): Runs through the facial nerve canal within the petrous bone 1

  • The canal includes the geniculate ganglion, tympanic segment, and mastoid segment
  • Ossification of the facial canal is incomplete at birth and continues postnatally 4
  • Facial canal dehiscence occurs in >10% of adults, primarily in the tympanic segment 4

• Internal auditory canal (IAC): Contains both CN VII and CN VIII (vestibulocochlear nerve) 1

  • The posterior wall of the ascending petrous IAC at the Eustachian tube level serves as an important surgical landmark 3

Inner Ear Structures

• Cochlea: The auditory organ housed within the petrous bone 1, 4
• Vestibule and semicircular canals: The balance organs including anterior, posterior, and superior semicircular canals 1, 4
  • Superior semicircular canal dehiscence (SSCD) is a pathologic condition detectable on high-resolution temporal bone CT 2

Middle Ear Components

• Ossicles and middle ear cavity: Contained within the petrous temporal bone structure 1
• Eustachian tube: Courses through the petrous bone 1

Clinical Relevance for Surgical Planning

Critical Anatomical Relationships

The petrous bone's complex anatomy requires precise understanding for surgical approaches 5:

• Carotid canal dimensions: Mean external opening measures 7.52 mm medio-laterally and 5.41 mm antero-posteriorly 6
• Distance between carotid canals: Approximately 50.03 mm between medial margins and 62.73 mm between lateral margins 6
• Carotid-foramen lacerum distance: Averages 15.6 mm 6

Imaging Considerations

When evaluating the petrous temporal bone, high-resolution CT without contrast effectively demonstrates 2:

• Bony canal anatomy and dehiscences
• Vascular variants (aberrant ICA, persistent stapedial artery)
• Jugular bulb position and diverticula
• Semicircular canal integrity
• Facial nerve canal course

Important caveat: The intrinsic sloping of the petrous temporal bone requires oblique reformats (Stenver and Pöschl planes) to avoid overestimating superior semicircular canal dehiscence 2