Temporal bone pneumatization
Pneumatization of temporal bone is divided in to 5 compartments:
1. Middle ear
4. Petrous apex
5 Accessory: This region include Squamous, zygomatic, occipital and styloid cells.
Penumatization of temporal bone follows definite cell tracts. These tracts are:
1. Posterosuperior cell tract
2. Posteromedial cell tract
3. Subarcuate cell tract
4. Perilabyrinthine cell tract
5. Peritubal cell tract
These tracts communicate with each other.
Posterosuperior and posteromedial cell tract:
These tracts extend medially through the antrum to pneumatize the medial pyramid. The posterosuperior tract lies at the level of above the level of Internal acoustic meatus.
This tract arises more medially from the mastoid antrum, extending anteromedially passing below the superior semicircular canal. This tract often participates in the formation of posterosuperior tract and may pneumatize the petrous apex.
Perilabyrinthine cell tract:
This tract pneumatizes the labyrinthine area. It divides into supralabyrinthine and infra labyrinthine tracts.
Peritubal cell tract:
This tract pneumatizes the tubal and peritubal area.
Functions of temporal bone air cells:
1. Sound reception
4. Supplementary air reservoir
5. Sound dissipation
6. Lightening the weight of skull
7. Protection against injury
Pneumatization of mastoid region is of three types:
1. Sclerotic mastoid - Absent pneumatization. The non pneumatized portion is covered with dense bone.
2. Diploic mastoid - Partial pneumatization. The non pneumatized area is filled with bone marrow.
3. Pneumatic mastoid - Complete pneumatization
The process of pneumatization begin between 22-24 weeks of fetal life, and continues till the child reach the age of 8. The development of air cavities begin with the formation of bony cavities. This process is dependent on the normal periosteal activity. This cavity is known to contain primitive bone marrow. This bone marrow gets transformed into loose mesenchymal connective tissue. This cavity gets invaded by mucosa from the middle ear cavity.
Areas of temporal bone that are normally pneumatized:
1. Middle ear: Epitympanum, mesotympanum and hypotympanum
2. Squamomastoid: Antrum, central mastoid tract, and peripheral cells
3. Perilabyrinthine: Supralabyrinthine and infralabyrinthine
4. Petrous apex: Petrosal cells and apical cells
5. Accessory cells: Zygomatic cells, occipital cells, squamous cells and styloid cells
Temporal bone pneumatization can be best studied by High resolution CT scan. This procedure shows clearly the complete pneumatization with excellent resolution.
Temporal bone pneumatization is symmetrical in 75% of normal individuals. Any asymmetrical penumatization indicates middle ear disease.
Mastoid pneumatization can fail due to various causes leading to the formation of sclerosed mastoid. Various theories have been proposed to account for this failure of pneumatization process. These theories include:
Wittmaack theory: This theory is otherwise known as endodermal theory. This was first proposed by Wittmaack, who believed normal middle ear mucosa is a must for normal pneumatization to proceed. In the presence of infantile otitis media the pneumatization of temporal bone may get arrested causing a failure of the process of pneumatization. Infantile otitis media is common in premature infants due to meconium soiling of the middle ear cavity.
Tumarkin's theory: This theory proposed by Tumarkin states that failure of pneumatization occur due to failure of middle ear aeration due to eustachean tube dysfunction.
Diamant and Dahlberg: Suggested that dense bone is congential and is a normal anatomical variant.
Ikarashi proved that long lasting inflammation increases bone mass thereby preventing normal pneumatization.
Factors determining the middle ear pressure:
1. Ventilation from eustachean tube
2. Passing of gases into circulation by diffusion
3. Thickness of middle ear mucosa
4. Elasticity of tympanic membrane
5. Size of mastoid pneumatization