The phrase “aerated mastoid air cells” is commonly found on medical imaging reports, such as CT scans. This term describes a normal and expected physiological state within the temporal bone of the skull. It confirms that these small cavities are properly filled with air, which is the healthy condition. This finding indicates a functioning connection between the ear and these bone spaces.
Understanding the Mastoid Bone Structure
The mastoid process is a pyramidal projection of the temporal bone located directly behind the ear. This structure is not solid bone; instead, it contains a complex system of interconnected, small, hollow spaces known as the mastoid air cells. These cells vary widely in size and shape, giving the bone an appearance similar to a honeycomb structure on imaging.
These cavities are lined with a mucous membrane continuous with the middle ear cavity. The mastoid air cells communicate with the middle ear through a passage called the mastoid antrum. This anatomical connection allows air to flow freely between the middle ear and the mastoid spaces, a process called pneumatization.
The air cells serve several functions, primarily acting as a buffer against pressure changes in the middle ear. By increasing the total volume of the middle ear system, they help moderate pressure fluctuations that affect the eardrum and hearing. They may also help protect the delicate inner ear structures from trauma and contribute to reducing the overall weight of the skull.
Interpreting Aerated Mastoid Air Cells
Aerated mastoid air cells means the cavities are open and filled with gas, as they should be. Since air appears dark on CT scans, an aerated mastoid displays a healthy, honeycomb pattern of dark spaces separated by thin bony walls. This confirms that the passage connecting the middle ear to the mastoid is open, allowing for normal ventilation and pressure equalization.
Aerated status confirms there is no significant accumulation of fluid, pus, or abnormal tissue within the mastoid spaces at the time of the scan. Finding well-aerated mastoid cells is the normal and desired outcome in a person without an active ear infection or chronic ear disease. This suggests a healthy functioning middle ear and mastoid system, free from blockages commonly associated with ear pathology.
The extent of this aeration, or pneumatization, develops after birth, accelerating between the ages of two and five and typically completing by age six. A well-developed and aerated mastoid acts as a reservoir of air that helps the middle ear system handle pressure changes more effectively. The presence of clear aeration indicates that the body’s natural pressure-regulating mechanism is currently unimpaired.
What Happens When Air Cells Are Not Aerated
When a report states that the mastoid air cells are not aerated, or are “opacified,” it means the air has been replaced by something else, typically fluid, thickened mucous, or inflammatory tissue. This replacement material appears gray or white on a CT scan, filling the spaces that should normally be dark with air. This non-aerated state indicates a blockage or disease process that has spread from the middle ear into the mastoid system.
The most common cause of opacification is an infection of the middle ear, or otitis media. Bacteria travel from the middle ear into the connected mastoid air cells, leading to mastoiditis, which is the inflammation or infection of the mastoid bone. In such cases, opacification is caused by the accumulation of pus and inflammatory fluid.
A long-standing lack of ventilation, often due to chronic Eustachian tube dysfunction, can cause the mastoid bone to undergo a process called sclerosis. Sclerosis involves the deposition of new bone, which reduces the air spaces and makes the mastoid appear dense and solid on imaging. Other conditions, such as a cholesteatoma—a non-cancerous growth of skin cells—can also block the drainage pathway and lead to mastoid opacification.
While the finding of non-aeration is significant, only a medical professional can interpret the specific imaging results in the context of a patient’s symptoms and medical history.