Temporal Bone Imaging Made Easy

This book presents standard imaging techniques, basic anatomy and an approach to common pathology encountered in temporal bone imaging. Intended as a survival guide for residents and general radiologists, it covers all topics comprehensively, and provides intuitive point-by-point summaries, similar to those of popular radiology reference sites, for easy comprehension at a glance. The book also offers guidance on the pertinent points that need to be included in a report and how to answer basic questions that are likely to be asked by the referring clinician or supervising radiologist.

This book will be a valuable resource for general radiologists, radiology residents, ENT residents, otology surgeons and anyone involved in the occasional temporal bone study.

• Language: English
• Publisher: Springer
• Release date: May 12, 2021
• ISBN: 9783030706357

Book preview

Part IBasic Anatomy and Approach to Common Symptoms; Making Sense of History

© Springer Nature Switzerland AG 2021

G. G. Pulickal et al. (eds.)Temporal Bone Imaging Made EasyMedical Radiologyhttps://doi.org/10.1007/978-3-030-70635-7_1

Basic Temporal Bone Imaging Anatomy: External, Middle and Inner Ear

Kabilan Chokkappan¹  

(1)

Department of Diagnostic Radiology, Khoo Teck Puat Hospital, Singapore, Singapore

Kabilan Chokkappan

Email: [e-mail]

1 Temporal Bone Overview

2 External Ear

2.1 External Ear Canal

2.2 Tympanic Membrane

3 Middle Ear

3.1 Divisions

3.2 Important Structures and Landmarks (Table 4)

3.3 Ossicles

3.4 Suspensory Ligaments and Muscles

4 Inner Ear

4.1 Cochlea

4.2 Vestibule

4.3 Semi-circular Canals

4.4 Internal Acoustic Meatus

5 Facial Nerve

Further Reading

Abstract

An understanding of the normal temporal bone anatomy is half the battle; in this chapter, a practical and relevant description of the anatomy is provided to enable the reader to better understand the subsequent pathology. The anatomy is broken down into various sub-sections, i.e. external, middle, inner ear and facial nerve. Simple illustrations and tables are provided that enable a more intuitive understanding of the complex anatomy and relationship between different anatomical structures. A glossary of various popular anatomical terms is provided for quick reference.

Keywords

Temporal bone segmentsExternal ear canalEACTympanic membraneMiddle earOssiclesSuspensory ligamentsTensor tympaniStapediusCochleaVestibuleSemi-circular canalsCochlea aqueductVestibular aqueductFacial nerve

1 Temporal Bone Overview

Temporal bones are a pair of skull bones that form the lateral skull base (Fig. 1 and Table 1). They contain several channels, intrinsic fissures and extrinsic sutures. Anatomically, the temporal bone consists of five distinct segments detailed below.

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Fig. 1

(a and b) Gross anatomy of the temporal bone segments. (1) Squamous, (2) Mastoid, (3) Styloid, (4) Tympanic and (5) Petrous

Table 1

Segments of temporal bone

2 External Ear

The external ear consists of the pinna and the external auditory canal (EAC). The pinna is readily examined clinically and usually does not warrant any imaging.

2.1 External Ear Canal

The EAC is of more radiological concern, and it extends from the auricle to the tympanic membrane medially. The lateral one-third is fibrocartilaginous and medial is two-third osseous, formed by the tympanic portion of temporal bone (Fig. 2). The junction of the fibrocartilaginous and osseous segments forms a natural narrowing called the ‘isthmus’ (Fig. 3), and foreign bodies located medial to it are difficult to extract.

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Fig. 2

(a and b) Coronal and sagittal illustrations of EAC. (1) Cartilaginous segment of the EAC, (2) Bony segment of the EAC, (3) Temporomandibular joint, (4) EAC, (5) Tympanic segment of the temporal bone and (6) Mastoid temporal bone

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Fig. 3

Axial CT image just above the floor of the EAC. The isthmus of the EAC (white line) and the barely perceptible normal tympanic membrane (white arrow) are shown. The mastoid segment of the facial nerve (dashed arrow) surrounded by pneumatized mastoid air cells

The anterior wall of the EAC forms the posterior aspect of the glenoid fossa (Fig. 3); hence, fractures of the EAC may extend to the temporomandibular joint. The posterior wall makes the anterior margin of the mastoid temporal bone and is removed during canal wall-down mastoidectomy (Fig. 3).

2.2 Tympanic Membrane

The tympanic membrane (TM) is located at the medial end of the EAC and separates the external ear from the middle ear. Under normal conditions, it is a translucent cone-like structure that points into the middle ear (refer Sect. 1 in chapter "Common Otoscopic Signs, Imaging of Common Surgeries and Implants") and is barely perceptible on CT (Fig. 3). The tip of the handle and lateral (short) process of the malleus are embedded upon it (Fig. 4). The anterior and posterior malleal folds divide the TM into the smaller pars flaccida superiorly and a larger pars tensa inferiorly. The TM attaches to the scutum superiorly (Fig. 5) and to the bony annulus elsewhere.

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Fig. 4

Axial CT image showing the manubrium of the malleus (long white arrow) lying parallel to the long process of the incus (short white arrow). The round window (short-dashed arrow) lies immediately lateral to the basal turn of the cochlea (long dashed arrow). The belly of the tensor tympani muscle (short thick arrow) and part of the cochlear aqueduct (red arrow) are also seen at this level

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Fig. 5

(a and b) Unmarked and marked coronal CT images of the temporal bone through the level of the cochlea (thick red arrow) shows the labyrinthine segment of the facial nerve (thin red arrow) lying just above it and the tympanic segment lateral to it (dashed red arrow). The malleoincudal joint (thick white arrow) lies medial to the scutum (red outline) in the epitympanum, and the tensor tympani muscle (thin white arrow) inserts itself into the manubrium (dashed white arrow) of the malleus

3 Middle Ear

The middle ear or tympanic cavity is an air-filled space in the petrous temporal bone containing the ossicles and suspensory structures. It mainly functions as a means of impedance between the air-filled external ear and the fluid-filled inner ear in conducting the sound waves (Fig. 6). Its boundaries are described in Table 2.

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Fig. 6

The middle ear cavity as seen through the roof to demonstrate its relationship with the external and inner ear. Prominent structures in the anterior, posterior, medial and lateral walls are as follows, (1) Eustachian tube, (2) Canal for tensor tympani, (3) Tensor tympani tendon, (4) Sinus tympani, (5) Pyramidal eminence, (6) Facial recess, (7) Aditus ad antrum, (8) Cochlear promontory, (9) Oval window, (10) Stapedius and (11) Tympanic membrane

Table 2

Boundaries of the middle ear

3.1 Divisions

Middle ear is divided into three parts by its relationship with the tympanic membrane (Fig. 7 and Table 3), i.e. hypo, meso and epitympanum (below, at the level of and above the tympanic membrane).

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Fig. 7

(a and b) Divisions of the middle ear illustrated coronal right ear (a) and corresponding coronal CT image of the left ear (b) with dotted lines representing the superior and inferior margins of the TM

Table 3

Divisions of the middle ear

3.2 Important Structures and Landmarks (Table 4)

Table 4

Middle ear - important landmarks

3.3 Ossicles

The ossicles form a chain of three small inter-articulating bones extending from the tympanic membrane to the oval window, conducting sound vibrations to the inner ear (Fig. 18 and Table 5). Knowledge on various parts of