The mastoid process is a bony prominence located behind the ear. It is a key component of the temporal bone, which forms the side of the skull. It has a number of important functions and is clinically significant in a number of ways.
Structure
The mastoid process is a triangular-shaped bony prominence that protrudes from the posterior aspect of the temporal bone. It is composed of spongy bone, which is a type of bone tissue that is more porous and less dense than compact bone. It is covered by a thin layer of connective tissue called the periosteum, which helps to nourish and protect the bone.
It is composed of a number of different parts, including the following:
- The mastoid antrum: This is a small, air-filled cavity located within the mastoid process. It is connected to the middle ear via the aditus ad antrum, which is a small opening that allows air to flow between the middle ear and the mastoid antrum.
- The mastoid cells: These are small, air-filled spaces within the mastoid process that are lined with thin layers of epithelial tissue. They are interconnected and communicate with the mastoid antrum.
- The mastoid notch: This is a small indentation located on the superior aspect of the mastoid process. It is important for the attachment of the sternocleidomastoid muscle, which is a muscle that runs from the clavicle to the base of the skull and is responsible for moving the head and neck.
- The styloid process: This is a bony protrusion located just below the mastoid process. It is important for the attachment of several muscles and ligaments that help to support the head and neck.
Location
The mastoid process is located behind the ear on the posterior aspect of the temporal bone. It is easily palpable (able to be felt) through the skin and is located just below the external auditory meatus (ear canal).
Function
The mastoid process has a number of important functions, including the following:
- Structural support: The mastoid process helps to support the head and neck by providing attachment points for muscles and ligaments. It also helps to protect the inner ear and other structures within the skull.
- Air circulation: The mastoid antrum and cells help to circulate air within the middle ear, which is important for maintaining proper hearing function.
- Sound transmission: The mastoid process and surrounding bone structures help to transmit sound waves to the inner ear, which is important for hearing.
Clinical Significance
The mastoid process is clinically significant in a number of ways, including the following:
- Mastoiditis: This is an infection of the mastoid process that can occur if bacteria or other microorganisms enter the mastoid cells or antrum. Mastoiditis can cause swelling and redness behind the ear, as well as fever and pain. It can be treated with antibiotics and, in severe cases, may require surgical drainage.
- Mastoid surgery: The mastoid process may need to be surgically removed (mastoidectomy) in cases of chronic or recurrent mastoiditis or other conditions that affect the bone, such as cholesteatoma (a benign growth in the middle ear). Mastoidectomy can be done through an incision behind the ear or through a less invasive procedure called a transcranial or endaural approach, which involves making a small incision in the ear canal or skull.
- Temporal bone fractures: The temporal bone, which includes the mastoid process, is susceptible to fractures due to its location on the side of the skull. These fractures can be caused by trauma, such as a blow to the head or a car accident. In some cases, temporal bone fractures can cause damage to the inner ear or other structures within the skull, leading to hearing loss or other complications.
- Acoustic neuroma: This is a rare type of benign tumor that can grow on the auditory nerve, which runs from the inner ear to the brain. Acoustic neuromas can press on the mastoid process and other surrounding structures, causing hearing loss and other symptoms. Treatment may involve surgery to remove the tumor or radiation therapy.
