Mastoid antrum

The mastoid antrum is a spacious and irregularly shaped cavity located above the mastoid air cells within the mastoid process. Though connected, it is distinctly separate from the mastoid cells. Like the mastoid cells, the mastoid antrum is air-filled and lined with a mucous membrane that continues from the tympanic cavity.

Inside the tympanic cavity, on the inner wall, you can find two significant protrusions. One is due to the lateral semicircular canal and the other is because of the facial nerve canal. Positioned close together, these bulges are situated medially and anteroinferiorly in relation to the mastoid antrum. Above both the mastoid antrum and the middle ear cavity is a thin bone plate called the tegmen tympani. This appears as a shallow indentation on the anterior part of the petrous section of the temporal bone. The lateral wall of the mastoid antrum is made up of a part of the squamous temporal bone known as the suprameatal triangle.

From an embryological standpoint, the mastoid antrum is well-formed at birth. The mastoid air cells begin to develop at this time as outgrowths from the antrum and keep maturing until they fully form around puberty. Medically, understanding the mastoid antrum's location is significant because it forms a passage for infections to spread from the middle ear to the mastoid cells, a condition known as mastoiditis.