The mastoid cells (also called air cells of Lenoir or mastoid cells of Lenoir) are air-filled cavities within the

mastoid process The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, t ...

of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

of the

cranium The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

. The mastoid cells are a form of

skeletal pneumaticity Skeletal pneumaticity is the presence of air spaces within bones. It is generally produced during development by excavation of bone by pneumatic diverticula (air sacs) from an air-filled space, such as the lungs or nasal cavity. Pneumatization is h ...

. Infection in these cells is called

mastoiditis Mastoiditis is the result of an infection that extends to the air cells of the skull behind the ear. Specifically, it is an inflammation of the mucosal lining of the mastoid antrum and mastoid air cell system inside the mastoid process. The ma ...

. The term ''cells'' here refers to enclosed spaces, not

cell Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a de ...

s as living, biological units.

Anatomy

The mastoid air cells vary greatly in number, shape, and size; they may be extensive or minimal or even absent. The cells are typically interconnected and their walls lined by mucosa that is continuous with that of the mastoid antrum and tympanic cavity.

Extent

They may excavate the mastoid process to its tip, and be separated from the

posterior cranial fossa The posterior cranial fossa is the part of the cranial cavity located between the foramen magnum, and tentorium cerebelli. It is formed by the sphenoid bones, temporal bones, and occipital bone. It lodges the cerebellum, and parts of the brai ...

and

sigmoid sinus The sigmoid sinuses (sigma- or s-shaped hollow curve), also known as the , are paired dural venous sinuses within the skull that receive blood from posterior transverse sinuses. Structure The sigmoid sinus is a dural venous sinus situated withi ...

by a mere slip of bone or not at all. They may extend into the

squamous part of temporal bone The squamous part of temporal bone, or temporal squama, forms the front and upper part of the temporal bone, and is scale-like, thin, and translucent. Surfaces Its outer surface is smooth and convex; it affords attachment to the temporal muscle ...

petrous part of the temporal bone The petrous part of the temporal bone is pyramid-shaped and is wedged in at the base of the skull between the sphenoid and occipital bones. Directed medially, forward, and a little upward, it presents a base, an apex, three surfaces, and three ...

zygomatic process of temporal bone The zygomatic processes (aka. malar) are three processes (protrusions) from other bones of the skull which each articulate with the zygomatic bone. The three processes are: * Zygomatic process of frontal bone from the frontal bone * Zygomatic ...

, and - rarely - the jugular process of occipital bone; they may thus come to adjoin many important structures (including the bony labyrinth, tympanic cavity, external acoustic meatus, pharyngotympanic tube, superior jugular bulb, posterior cranial fossa, middle cranial fossa, carotid canal, abducens nerve, sigmoid sinus) to which they may disseminate infection in case of infective mastoiditis.

Innervation

The cells receive from the posterior branch of the meningeal branch of the mandibular nerve (nervus spinosus), and branches of the

tympanic plexus The tympanic plexus is a nerve plexus within the tympanic cavity formed upon the promontory of tympanic cavity by the tympanic nerve (branch of the inferior ganglion of glossopharyngeal nerve (CN IX)), and the superior and inferior caroticotympan ...

Vasculature

The cells receive arterial supply from the stylomastoid branch of the

occipital artery The occipital artery is a branch of the external carotid artery that provides arterial supply to the back of the scalp, sternocleidomastoid muscles, and deep muscles of the back and neck. Structure Origin The occipital artery arises from (the ...

posterior auricular artery The posterior auricular artery is a small artery that arises from the external carotid artery. It ascends along the side of the head. It supplies several muscles of the neck and several structures of the head. Structure Origin The artery ar ...

, and (sometimes) a mastoid branch of the

. The

superior petrosal sinus The superior petrosal sinus is one of the dural venous sinuses located beneath the brain. It receives blood from the cavernous sinus and passes backward and laterally to drain into the transverse sinus. The sinus receives superior petrosal veins, ...

receives venous drainage from the mastoid air cells (mastoid infection may thus lead to a cerebellar abscess).

Development

At birth, the mastoid is not pneumatized, but becomes aerated before age six. At birth, the mastoid antrum is well developed but the air cells are represented only by small diverticula from the antrum. The air cells then gradually extend into the bone of the mastoid during the first years of life. Their most significant enlargements takes place during puberty.

Function

The air cells are hypothesised to protect the temporal bone and the inner and middle ear against trauma and to regulate air pressure.

Clinical significance

Infections in the middle ear easily spread into the mastoid air cells through the

aditus ad antrum The aditus to mastoid antrum (otomastoid foramen) is a large, irregular opening upon the posterior wall of the tympanic cavity by which the mastoid antrum (situated posteriorly) communicates with the epitympanic recess of the tympanic cavity (situa ...

, resulting in

, a potentially dangerous and life-threatening condition. Infection may then further spread into the middle cranial fossa or posterior cranial fossa, causing meningitis or abscess of adjacent brain tissue. Infection may also spread to muscles of the neck, causing pain and

torticollis Torticollis, also known as wry neck, is an extremely painful, dystonic condition defined by an abnormal, asymmetrical head or neck position, which may be due to a variety of causes. The term ''torticollis'' is derived . The most common case ha ...

References

External links

* {{Authority control Bones of the head and neck Ear Otorhinolaryngology Human head and neck Otology Skull