What is the Mastoid Process?
The mastoid process is present in the temporal bone of the skull and is a conical projection. Externally, one can feel it behind the earlobe as its location is below and behind the auditory meatus. It consists of sinuses or air cells that form a link with the middle ear.
Mucoperitoneum covers these air cells and is also present in the squamous part of the temporal bone and the tympanic cavity. The presence of the mastoid process is one of the primary characteristics of the lateral cranium. Medial to the mastoid process is the mastoid notch.
The stylomastoid foramen pierces it from the front and the mastoid foramen is present at the back. It is not present in individuals at birth but develops over time. When a person starts to move his/her head, there is pulling of the sternocleidomastoid muscles of the neck. Thus, the projection appears only when the child turns two years old.
Location of Mastoid Process
The parietal bones are a pair of bones found on the lateral walls of the skull. The mastoid process arises from the posterior ends of the parietal bones comprising of the inner and middle ear. The anterior portion of the mastoid process merges indistinctly to the descending portion of the flat section of the temporal bone and there is an attachment of the occipital bone with the posterior border.
Absence of the Mastoid Process in Newborns
As mentioned before, the mastoid process is absent in newborns. This leaves the facial nerve or cranial nerve VII. It is a vital nerve that controls facial expressions, conveyance of taste sensations, etc. In the absence of the mastoid process, the nerve develops close to the surface when it arises from the stylomastoid foramina.
Its proximity to the surface makes it prone to damage during surgeries to treat problems of the middle ear or forceps delivery. Pull on the petromastoid parts of the temporal bone by the sternocleidomastoid muscles causes the development of the mastoid process after the individual becomes one year old and develops entirely by the age of 2 years.
Mastoid Process Functions
- Occipitofrontalis muscles cover the skull from the cheekbone to the process. The rough outer surface of the mastoid process provides the occipitofrontalis muscles a suitable place to lodge itself. The facial nerve gives rise to the posterior auricular branch which supplies the nerves to the muscle covering.
- The mastoid process gives rise to the following muscles that perform various functions in the body:
1). Splenius capitis muscle: rotatory flexes of the head
2). Longissimus capitis muscle: one side rotatory flexes of the head
3). Sternocleidomastoid muscle: contralateral rotation of the head
4). Posterior belly of gastric muscles: opening of jaw
- Protects the occipital artery by allowing it to lodge in the shallow occipital groove present in the mastoid process
- Digastrics fossa is a deep groove that will enable the anchoring of digastric muscles and is present in the medial portion of the process
- Helps to find out the gender of an unidentified body by examination of the mastoid process, because the mastoid process in human males is more prominent than females
At the back of the petrous part of the temporal bone, a small cavity known as the mastoid antrum is present. The aditus serves as a connection between the mastoid air cell, posterior wall of the middle ear, the sigmoid sinus and cerebellum in the brain. Thus, the infection spreads from the ears to the brain via the mastoid antrum.
Following are the medical ailments that can affect the mastoid process:
- Mastoiditis: It refers to inflammation or infection of the mastoid bone. Due to the difficulty of the medications to reach their target, the mastoid process is a common cause of mortality among children. In severe cases, the infection can spread to the brain. Some ear infections, especially otitis media which is an inflammatory disease of the middle ear, or cholesteatoma can cause mastoiditis. The symptoms include enlarged ears, hearing impairment, swelling and redness of the ear, fever, headache, ear pain, ear drainage, etc.
Use of antibiotics, cleaning of the ears and the use of ear drops can be useful in treating such a condition. If the situation is severe, the individual may have to undergo a myringotomy; i.e., drainage of the fluid from the middle ear or mastoidectomy; i.e., removal of the mastoid bone that is infected. If the correct treatment is not given for mastoiditis, it may result in meningitis, loss of hearing, brain abscess or even death.
- Cholesteatoma: It is a condition in which a benign skin cyst is present on the mastoid process and the middle ear. Usually, it is the function of the Eustachian tube to equalize ear pressure. If the tube does not open enough to perform its function, it can cause perforation and retraction of the eardrum that forms a pocket and allows the skin cyst to develop. A history of chronic ear infections, gradual loss of hearing and discharge from the ears are signs of this condition. Surgeries such as ossiculoplasty, tympanoplasty or mastoidectomy are some of the procedures that people may have to undergo to treat cholesteatoma.
- Mastoid cancer: Abnormal growth of squamous cells (often squamous cell carcinoma) can result in the formation of malignant lumps and tumors on the mastoid process. Mastoid cancer is a form of skin cancer that may develop in individuals having a family history of skin cancer or are regularly exposed to coal, tar, arsenic, etc.
- Parotiditis and mumps: One may experience severe pain, especially while chewing due to inflammation and infection of the parotid gland which is a condition known as parotitis. The pain is a result of the action of the parotid sheath that is tough and tries to limit the swelling of the gland. When the individual opens his/her mouth, the downward and backward movement of the mandibular ramus compresses the mastoid process. Thus, pain occurs while opening the mouth or chewing.