MASTOID PROCESS: MUSCLES, FUNCTIONS AND DISEASES - ANATOMY AND PHYSIOLOGY - 2024

The mastoid process, also known as Mouret's mastoid block, is located in the posteroinferior part of the temporal bone, in the skull. The temporal bone is a paired bone of the skull, it has an irregular shape and in its constitution three portions or parts can be described: a squamous portion, a petrous portion and a mastoid portion.

Regarding the mastoid portion, three edges are anatomically described: an upper one, which corresponds to the temporal line and its parieto-mastoid suture; an anterior border, delimited by the external auditory meatus and the parietal mastoid fissure; and a posterior border, which coincides with the occipito-mastoid suture.

The mastoid portion of the temporal bone contains in its structures the mastoid process a structure of great anatomical-clinical importance. The mastoid process is constituted as follows: 2/3 postero-inferior that form the base of the peñasco and an antero superior third that is formed by the scale of the same bone.

It groups in its content a large number of air cavities attached to the middle ear; this is why it is involved in its infectious processes. Therefore, the detailed study of this structure is of vital importance due to the surgical interest of the area.

Muscles that attach to the mastoid process

The mastoid process or Mouret's mastoid block has an external face and an internal face, which provide insertion or origin for various muscles. These include:

Sternocleidomastoid muscle

Neck muscle that originates from the outer aspect of the mastoid process. It inserts on the upper border of the sternal manubrium and on the upper part of the middle third of the clavicle.

Among its functions, it bilaterally flexes the cervical spine and unilaterally handles the extension of the skull.

Minor complex muscle

Muscle considered portion of the dorsal longus, since it is itself an extension of said muscle. It has its origin in the posterior tubercles of the transverse processes of the last 5 cervical vertebrae and in the first two dorsal vertebrae; it inserts on the external face of the mastoid process.

Its functions include the following: unilaterally, it is responsible for the rotation of the head towards the same side and the ipsilateral inclination of the same; bilaterally, it participates in the extension or hyperextension of the head.

Posterior belly of digastric muscle

The muscle fibers of the posterior belly of the digastric muscle originate in the digastric groove, which is located on the inner side of the mastoid process. These fibers insert into the intermediate tendon, in the hyoid bone.

Among the functions it performs as part of the digastric muscle is the ascent of the hyoid bone, as well as bringing the jaw down and back.

Diseases

The pathology associated with the mastoid process is known as mastoiditis. This is generally due to contiguous spread of infections at the level of the middle ear; that is, to ill-treated or untreated acute otitis media that, for this reason, could infect neighboring mastoid tissue.

At present it is considered an infection of the temporal bone related to acute otitis media; in fact it is considered a serious complication of this disease. Regarding the frequency, the pediatric age is the most affected.

Among the risk factors associated with the development of mastoiditis are:

- Pictures of acute otitis media.

- Previous antibiotic treatment.

- Age less than 4 years.

- Immunodeficiency.

Etiology

The germs most commonly associated with acute mastoiditis are: Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Haemophilus influenzae and Moraxella catarrhalis.

Other organisms rarely associated with this pathology are Pseudomonas aeuroginosa and other gram negative bacilli.

In the case of chronic mastoiditis, the most common germs are Pseudomona aeuroginosa, Enterobacteriaceae, Staphylococcus aureus, and anaerobic bacteria.

Clinical picture

Signs and symptoms of mastoiditis include pain, redness, and tenderness in the mastoid region.

It should be taken into account that, as mastoiditis is generally associated with acute otitis media, other signs and symptoms such as earache, vertigo, hearing loss, fever and headache, as well as nonspecific symptoms, including anorexia, adenopathy, diarrhea or irritability. In severe cases there may even be otorrhea.

Diagnosis

Regarding the diagnosis, this is based on the findings corresponding to the anamnesis and the physical examination of the signs and symptoms described above with a history, as well as a history of infection of the middle ear. This information guides the practitioner.

Imaging studies provide additional information, including magnetic resonance imaging and computerized axial tomography, the latter being the gold standard in terms of imaging studies for the diagnosis of this disease.

Exploratory surgery is an option used as a last resort in the diagnosis of this pathology.

Treatment

It is suggested to administer intravenous antibiotic treatment in view of the fact that mastoiditis can bring complications such as infection of the central nervous system.

The treatment of choice is a third-generation cephalosporin in combination with metronidazole or amoxicillin, plus clavulanic acid or clindamycin.

Treatment with antibiotics alone or associated with myringotomy (incision in the tympanic membrane currently used for the aspiration of exudates or non-suppurative transudates at the level of the middle ear) and ventilation tubes is effective only in the less severe forms.

In turn, medical treatment is considered to have failed when the patient continues with fever and earache after 48 hours.

In the case of surgical treatment, mastoidectomy is indicated in case of exteriorized mastoid abscess, intracranial complications, cholesteatoma or purulent otorrhea, as well as if there is presence of granulation tissue for more than two weeks.

References

1. Latarjet Ruiz Liard, Human Anatomy Edition. Editorial Panamericana. Volume 1.
2. Anatomy of the mastoid process. Otorrinoweb. Recovered from: otorrinoweb.com
3. Larrú Martínez. Mastoiditis (v.2 / 2008). Guide_ABE. Infections in Pediatrics. Quick guide to the selection of empirical antimicrobial therapy. (Online). Updated 04/15/2008, consulted 03/31/2018 Retrieved from: infodoctor.org/gipi
4. Del Castillo Martìn F, Sanchez Purificación M, et al. Acute mastoiditis in childhood. Study of 15 cases. Vol. 44 No. 4, 1996. (Online). Consulted on 03/31/2018 Retrieved from: www.aeped.es
5. Richard L. Drake (2006). Gray's Anatomy for Students. Elsevier.