CT Scan of the Temporal Bone

This gallery of images presents the anatomy of the temporal bone by means of CT-scan (reconstructions).

Computed tomography or CT scan of the temporal bone uses X-ray technology and advanced computer software to generate detailed images of the head. The temporal bones are situated at the skull’s base and sides.

CT scan allows the radiologist to view the different levels or slices of the skull bone’s temples or side. The cross-sectional images produced by the rotating X-ray beam help the radiologist determine any injury or bone abnormalities(1).

Imaging data provided by CT scans of the temporal bone are fundamental to the diagnosis and treatment of chronic ear infections, temporal bone fractures, middle or inner ear disease, or conductive hearing loss(2).

How Does a CT Scan of the Temporal Bone Work?

A CT scan of the temporal bone is performed at a high-resolution and small field of view with thin imaging slices (0.5 mm)(3). This imaging method can visualize the temporal bone’s small and fine structures to the maximal detail.

Images produced by the CT scan highlighting bone details are most useful for assessing and diagnosing conditions. Using intravenous contrast (iodine-based dye) to enhance the images is unnecessary for the indications(4).

Three-dimensional (3D) multiplanar reformatted or 3D volume-rendered CT images have recently become available to help demonstrate the temporal bone’s anatomy and pathology(5).

These tools provide a better demonstration of the intricate and minute temporal bone structures’ morphology, orientation, and inter-relationships in 3D space.

Temporal Bone Anatomy on CT Imaging

There are several structures and disease entities in the temporal bone that one must be familiar with to interpret a CT imaging study. It is helpful to examine the region and go through key structures in an organized and systematic fashion.

The temporal bone consists of the lateral skull base, forming portions of the middle and posterior fossa (a hollow space in the skull, near the brainstem and cerebellum).

The five osseous components of the temporal bone are the squamous, mastoid, petrous, tympanic, and styloid portions(6).

Several intrinsic fissures, intrinsic channels, and extrinsic sutures are often visible on CT images and can mimic fractures (pseudofractures)(7).

External Ear

The external ear includes the external auditory canal (EAC) and auricle. The EAC extends medially from the auricle to the tympanic membrane.

This membrane attaches to the tympanic annulus (fibrocartilage ligament) and measures approximately 10 mm in diameter(8). The normal tympanic membrane is often faintly discernible on CT images.

If the membrane appears well-defined, it is likely thickened. An increased density suggests myringosclerosis (calcification within the tympanic membrane)(9).

A focal lobulated soft tissue opacity in the EAC (usually the inferior wall) with an erosion of the adjacent bony wall may represent an EAC cholesteatoma (a rare ear condition)(10).

Middle Ear and Mastoid

The middle ear is an air-filled cavity situated within the petrous portion of the temporal bone.

This cavity contains the ossicular chain and is bounded by the tympanic membrane laterally, the inner ear structures medially, the tegmen tympani superiorly, and the jugular wall (floor) inferiorly(11).

The tympanic membrane attaches superiorly to the scutum, a sharp bony projection. The tegmen refers to a thin bone plate that separates the middle cranial fossa’s dura from the middle ear and the mastoid cavity.

The tegmen tympani is the middle ear’s roof, while the tegmen mastoideum is the roof of the mastoid. High-resolution CT is useful for the assessment of tegmen defects or fractures(12).

If the tegmen exhibits abnormal downward bowing and contacts the malleus, there may be a resultant limitation of ossicular chain movement leading to conductive hearing loss(13).

Inner Ear

The inner ear within the petrous portion comprises the osseous labyrinth, including the cochlea, vestibule, and semicircular canals.

The cochlea contains the end-organ for hearing, while the vestibule and semicircular canals are responsible for equilibrium. These structures are well-delineated on CT images due to their sharp bony margins bordering on low fluid density within(14).

The otic capsule is the densest part of the temporal bone that surrounds the osseous labyrinth. However, the membranous labyrinth structures are not distinguishable on CT images(15).

The osseous spiral lamina is a microanatomic structure that is faintly discernible on thin-section temporal CT images(16).

Internal Auditory Canal and Facial Nerve

The internal auditory canal (IAC) is a channel in the petrous bone located between the porus acousticus (medial) and the fundus (lateral)(17).

The facial nerve passes through the IAC’s anterosuperior compartment and into the temporal bone’s facial nerve canal.

Meanwhile, the cochlear nerve courses along the IAC’s anteroinferior compartment, then through the cochlear fossette into the modiolus (central axis in the cochlea).

It is challenging to visualize soft tissue masses within the IAC on CT images. However, if the IAC is dilated and smoothly scalloped with a focally expansile appearance, an underlying mass may be suspected (vestibular schwannoma)(18).


  1. Fatterpekar, G. M., Doshi, A. H., Dugar, M., Delman, B. N., Naidich, T. P., & Som, P. M. (2006). Role of 3D CT in the evaluation of the temporal bone. Radiographics, 26(suppl_1), S117-S132.
  2. Casselman J. W. (1996). Temporal bone imaging. Neuroimaging clinics of North America, 6(2), 265–289.
  3. Juliano A. F. (2018). Cross Sectional Imaging of the Ear and Temporal Bone. Head and neck pathology, 12(3), 302–320. https://doi.org/10.1007/s12105-018-0901-y
  4. Ibid.
  5. Fatterpekar, G. et al. op. cit.
  6. Juliano, A. F., Ginat, D. T., & Moonis, G. (2013). Imaging review of the temporal bone: part I. Anatomy and inflammatory and neoplastic processes. Radiology, 269(1), 17-33.
  7. Collins, J. M., Krishnamoorthy, A. K., Kubal, W. S., Johnson, M. H., & Poon, C. S. (2012, October). Multidetector CT of temporal bone fractures. In Seminars in Ultrasound, CT and MRI (Vol. 33, No. 5, pp. 418-431). WB Saunders.
  8. Juliano, A. F., Ginat, D. T., & Moonis, G. op. cit.
  9. Juliano, A. F. op. cit.
  10. Baráth, K., Huber, A. M., Stämpfli, P., Varga, Z., & Kollias, S. (2011). Neuroradiology of cholesteatomas. American Journal of Neuroradiology, 32(2), 221-229.
  11. Juliano, A. F., Ginat, D. T., & Moonis, G. op. cit.
  12. Juliano, A. F. op. cit.
  13. Ibid.
  14. Ibid.
  15. Ibid.
  16. Juliano, A. F., Ginat, D. T., & Moonis, G. op. cit.
  17. Ibid.
  18. Juliano, A. F. op. cit.

Bibliographie:

• Harnsberger HR, Osborn AG, Ross JS, Moore KR, Salzman KL, Carrasco CR, Halmiton BE, Davidson HC, Wiggins RH. Diagnostic and Surgical Imaging Anatomy: Brain, Head and Neck, Spine. 3rd ed. Salt Lake City, Utah. Amirsys. 2007. • Bourjat P, Veillon F. Imagerie radiologique tête et cou. Paris, Vigot. 1995. • Gouazé A, Baumann JA, Dhem A. Sobota. Atlas d’Anatomie humaine. Tome 3. Système nerveux central, système nerveux autonome, organe des sens et peau, vaisseaux et nerfs périphériques. 1er éd. Paris, Maloine. 1977. • Kahle W, Cabrol C. Anatomie. Tome 3: Système nerveux et organe des sens. 1er éd. Paris, Flammarion. 1979.

References

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