2º TEMPORAL BONE CBCT PROTOCOL

To ensure an accurate assessment of the temporal bone using CBCT, it is essential to follow a well-designed imaging protocol that includes appropriate reconstructions, which are particularly crucial given the complex anatomy and intricate structures of this region.

Key elements of this protocol include standard reconstructions such as the true axial and true coronal views, alongside specialized projections like the Stenver and Poschl views. These reconstructions are tailored to provide optimal visualization of the bony labyrinth and associated structures, including the vestibule, vestibular canal, and semicircular canals.

-True Axial and True Coronal Reconstructions

The true axial and true coronal reconstructions are fundamental in CBCT imaging of the temporal bone, offering high-resolution cross-sectional views essential for anatomical orientation and precise localization. The axial view, obtained perpendicular to the long axis of the petrous bone, allows for detailed assessment of the semicircular canals, the vestibule, and the cochlea. It is particularly effective in identifying bony abnormalities such as fractures or congenital malformations.

The coronal reconstruction, oriented perpendicular to the axial plane, provides complementary information by visualizing the superior semicircular canal and the ossicular chain in greater detail.

-Specialized Projections: Stenver and Poschl Views

The Stenver and Poschl views, unique to temporal bone imaging, are angulated projections designed to enhance the visualization of structures that are often challenging to assess in standard views. The Stenver view, angled along the long axis of the petrous ridge, provides an unparalleled perspective of the inner ear structures, particularly the cochlea and vestibular system. This projection is highly effective for evaluating conditions such as otosclerosis or cochlear implant placement.

The Poschl view, oriented along the plane of the superior semicircular canal, offers a detailed depiction of the bony labyrinth, making it indispensable for detecting dehiscence or structural abnormalities in the semicircular canals. These projections are crucial for a complete assessment of the temporal bone.

By utilizing these tailored reconstructions, radiologists can achieve a more accurate understanding of the temporal bone's complex anatomy, ensuring that critical features are not overlooked.

3º COMPARATION WITH OTHER IMAGING MODALITIES

It is important to emphasize that while CBCT provides an impressive evaluation of bone structures, it should be noted that it is often compared to other imaging techniques such as magnetic resonance imaging (MRI). MRI offers a much more advanced anatomical assessment of soft tissues and is the preferred technique for evaluating nerve structures.

4º EAR ANATOMY

However, as already mentioned, it is extraordinary in the study of the bony anatomy of the petrous bone.

Temporal Bone Anatomy:

The temporal bone, located at the base of the skull, houses several critical structures related to hearing and balance. Understanding its anatomy is essential for accurate diagnosis and treatment planning in otology.

Parts of the Temporal Bone:

• Squamous: The thin, flat portion of the temporal bone.
• Mastoid: Contains the air-filled mastoid cells and is involved in the transmission of sound vibrations.
• Petrous: Houses the inner ear structures such as the cochlea, vestibule and semicircular canals.
• Tympanic: Forms the wall of the external auditory canal.
• Styloid process: A slender bone that projects down from the temporal bone, serving as an attachment point for muscles and ligaments.
  

1. External Ear:

• Auricle: The visible outer part of the ear that helps in sound collection.
• External Auditory Canal (EAC): The EAC extends to the tympanic membrane (TM) and plays a key role in channeling sound toward the eardrum. The anterior wall of the EAC forms the posterior wall of the glenoid cavity, while the posterior wall contributes to the anterior portion of the mastoid part of the temporal bone.

• Tympanic Membrane:

• Pars tensa: The larger part of the eardrum, consisting of three layers—external, intermediate, and internal. The malleus handle is embedded here.
• Pars flaccida: Lacking the intermediate layer, making it more susceptible to retraction and cholesteatoma formation.
  

2. Middle Ear: The middle ear is an air-filled cavity housing the ossicular chain, which transmits sound vibrations from the tympanic membrane to the inner ear.

Walls:

• Lateral: Tympanic membrane.
• Medial: Inner ear structures.
• Superior: Tegmen tympani and mastoideum.
• Inferior: Jugular foramen.
• Posterior: Includes the facial recess, pyramidal eminence, sinus tympani, and round window.

Divisions:

• Epitympanum (attic): The upper portion of the middle ear, which connects to the mastoid air cells through the aditus ad antrum.
• Mesotympanum: Contains the ossicular chain, which consists of:
  • Malleus: Includes the head, neck, anterior process, lateral process, and manubrium.
  • Incus: Composed of the body, short process, and long process.
  • Stapes: Includes the head, neck, anterior and posterior crura, and the base.
• Hypotympanum: Contains the opening of the Eustachian tube.
  
  

3. Inner Ear:

• Cochlea: A bony spiral duct wound around the central modiolus, making 2.75 turns. The cochlea is divided by the spiral lamina into distinct chambers.
• Vestibular Aqueduct: Contains the endolymphatic duct and sac, which are crucial for maintaining fluid regulation within the inner ear.
  
• Vestibule: The largest labyrinthine cavity, it connects the cochlea to the semicircular canals.
• Semicircular Canals: Three orthogonal canals (superior, lateral, and posterior) equipped with ampullae that detect movement.
  
• Facial Nerve Pathway: The facial nerve traverses the temporal bone through distinct segments: Cisternal > Canalicular >Labyrinthine>Tympanic>Mastoid>Extracranial
  
• External auditory canal
  

This detailed anatomy of the temporal bone, enhanced by CBCT imaging, allows radiologists to achieve precise evaluations and accurate diagnoses of temporal bone-related pathologies.

5º CLINICAL CASES AND PATHOLOGIES

In the same way that CBCT perfectly evaluates ear anatomy, it also provides a detailed assessment of both prevalent and less common conditions  affecting the external, middle, and inner ear.

Outer Ear Pathologies: Exostoses, benign bony outgrowths in the external auditory canal, are clearly defined in terms of size, location, and canal impact.

Middle Ear Pathologies: Otosclerosis, affecting stapes fixation at the oval window, appears as altered bone density around the annular ligament and otic capsule, aiding procedural planning.

Inner Ear Pathologies: CHARGE syndrome-associated malformations, such as cochlear hypoplasia and semicircular canal dysplasia, are comprehensively analyzed, while labyrinthitis, advancing to membranous labyrinth ossification, is reliably detected.