Chapter 13: Anatomy of the Ear

Introduction

1. The temporal bone forms part of the side and base of the skull. It constitutes two-thirds of the floor of the middle cranial fossa and one-third of the floor of the posterior fossa. There are four parts to the temporal bone:

   1. Squamosa

   2. Mastoid

   3. Petrous

   4. Tympanic

2. The following muscles are attached to the mastoid process:

   1. Sternocleidomastoid

   2. Splenius capitis

   3. Longissimus capitis

   4. Digastric

   5. Anterior, superior, posterior, auricular (The temporalis muscle attaches to the squamosa portion of the temporal bone and not to the mastoid process.)

3. The auricle (Figure 13-1) is made of elastic cartilage, the cartilaginous canal of fibro-cartilage. The cartilaginous canal constitutes one-third of the external auditory canal (whereas the eustachian tube is two-thirds cartilaginous), the remaining two-thirds is osseous. Innervation of auricle is outlined in Figure 13-2.

4. The skin over the cartilaginous canal has sebaceous glands, ceruminous glands, and hair follicles. The skin over the bony canal is tight and has no subcutaneous tissue except periosteum.

5. Boundaries of the external auditory canal are:

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   Anterior	Mandibular fossa
   	Parotid
   Posterior	Mastoid
   Superior	Epitympanic recess (medially)
   	Cranial cavity (laterally)
   Inferior	Parotid

   The anterior portion, floor, and part of the posterior portion of the bony canal are formed by the tympanic part of the temporal bone. The rest of the posterior canal and the roof are formed by the squamosa.

6. Boundaries of the epitympanum are:

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   Medial	Lateral semicircular canal and VII nerve
   Superior	Tegmen
   Anterior	Zygomatic arch
   Lateral	Squamosa (scutum)
   Inferior	Fossa incudis
   Posterior	Aditus

7. Boundaries of the tympanic cavity are:

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   Roof	Tegmen
   Floor	Jugular wall and styloid prominence
   Posterior	Mastoid, stapedius, pyramidal prominence
   Anterior	Carotid wall, eustachian tube, tensor tympani
   Medial	Labyrinthine wall
   Lateral	Tympanic membrane, scutum (laterosuperior)

8. The auricle is attached to the head by

   1. Skin

   2. An extension of cartilage to the external auditory canal cartilage

   3. Ligaments

      1. Anterior ligament (zygoma to helix and tragus)

      2. Superior ligament (external auditory canal to the spine of the helix)

      3. Posterior ligament (mastoid to concha)

   4. Muscles

      1. Anterior auricular muscle

      2. Superior auricular muscle

      3. Posterior auricular muscle

9. Notch of Rivinus is the notch on the squamosa, medial to which lies Shrapnell membrane. The tympanic ring is not a complete ring, with the dehiscence superiorly.

10. Meckel cave is the concavity on the superior portion of the temporal bone in which the gasserian ganglion (V) is located.

11. Dorello canal is between the petrous tip and the sphenoid bone. It is the groove for the VI nerve. Gradenigo syndrome, which is secondary to petrositis with involvement of the VI nerve, is characterized by:

    1. Pain behind the eye

    2. Diplopia

    3. Aural discharge

12. The suprameatal triangle of Macewen triangle is posterior and superior to the external auditory canal. It is bound at the meatus by the spine of Henle, otherwise called the suprameatal spine. This triangle approximates the position of the antrum medially. Tegmen mastoideum is the ...