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Mastoid Process

Contents

Introduction

The skull is composed of multiple small bones held together by a fibrous joints. Its inferior surface gives rise to a number of projections, and these allow for the attachment of many structures of the neck and face. In this article we will discuss the gross and functional anatomy, together with the clinical relevance of one of the projections, the mastoid process.

Mastoid process - lateral-left view

Mastoid process - lateral-left view

Anatomy

Borders & Relations

The mastoid process is a pyramidal bony projection from the posterior section of the temporal bone. The superior border of the mastoid portion of the temporal bone articulates with the parietal bone. The posterior border articulates with the occipital bone, and the anterior border is merged with the descending portion of the squamous section of the temporal bone. The petrosquamous suture runs vertically from the superior border of the mastoid process.

Recommended video: Temporal bone
Anatomy and landmarks of the temporal bone.

Muscles

The mastoid part has a rough outer surface that gives rise to the occipital belly of occipitofrontalis muscle, which covers the skull from the superior nuchal line to the mastoid process. This muscle is innervated by the posterior auricular branch of the facial nerve  (cranial nerve VII).

Occipitofrontalis muscle - axial view

Occipitofrontalis muscle - axial view

It also gives rise to auricularis posterior muscle that attaches to the lower part of the cranial surface of the concha (outer ear).

The mastoid process itself (the pointed projection) gives rise to:

Sternocleidomastoid muscle - lateral-right view

Sternocleidomastoid muscle - lateral-right view

  • the splenius capitis muscle (extends rotates and laterally flexes the head)

Splenius capitis muscle - dorsal view

Splenius capitis muscle - dorsal view

  • the posterior belly of the digastric muscle (opens the jaw when the masseter and temporalis muscles are relaxed)

Posterior belly of digastric muscle - lateral-right view

Posterior belly of digastric muscle - lateral-right view

  • the longissimus capitis muscle (laterally flexes and rotates the head and neck if one side alone contracts, extends the head if both contract)

Longissimus capitis muscle - dorsal view

Longissimus capitis muscle - dorsal view

Fossae, Grooves & Features

Stylomastoid foramen - caudal view

Stylomastoid foramen - caudal view

The medial surface of the mastoid portion has a deep groove called the digastric fossa, which allows the digastric muscle to attach. Further medial to this groove is the occipital groove, which the occipital artery passes over. The sigmoid sulcus also lies on the inner portion of the mastoid bone and is there the transverse venous sinus of the brain lodges.

The styloid process lies anterior and medial to the mastoid process, and in between them is the stylomastoid foramen. This foramen allows the muscular branch of the facial nerve to leave the skull and go onto innervate the muscles of facial expression. The mastoid bone is normally pneumatised or air filled by the mastoid air cells.

Mastoiditis

This is a condition caused by infection of the mastoid air cells. Symptoms include tenderness over the area, fever and swelling. The area may be red, and the patient may have earaches. It is commonly caused by untreated otitis media, where the infection tracks from the middle ear into the mastoid section of the temporal bone. The mastoid process is underdeveloped at birth which leaves the posterior auricular branch of the facial nerve (which ascends anterior to the mastoid process) superficial and unprotected.

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Show references

References:

  • Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders.
  • Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
  • Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.
  • Ariyasinghe C. MD and Knipe H. MD et al: Mastoid part of temporal bone. Radiopaedia.org (accessed 18/03/2016).
  • Knipe H. MD et al: Mastoid air cells. Radiopaedia.org (accessed 18/03/2016).

Author, Review and Layout:

  • Shahab Shahid
  • Uruj Zehra
  • Catarina Chaves

Illustrators:

  • Mastoid process - lateral-left view - Yousun Koh
  • Sternocleidomastoid muscle - lateral-right view - Paul Kim
  • Splenius capitis muscle - dorsal view - Yousun Koh
  • Posterior belly of digastric muscle - lateral-right view - Paul Kim
  • Longissimus capitis muscle - dorsal view - Yousun Koh
  • Stylomastoid foramen - caudal view - Yousun Koh
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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