) is a Schwann cell–derived
, usually arising from the vestibular branch of CN VIII during
fth or sixth decade of life. Risk factors include prolonged expo-
sure to loud noise, childhood exposure to low-dose radiation, and
possible links to parathyroid adenoma. Symptoms include
. The tumor is usually
unilateral. It appears as a well-circumscribed, encapsulated mass. The
tumor attaches to the nerve but can usually be separated from the
nerve. Histologically, schwannomas arise from perineural elements
of Schwann cells. Areas of alternately dense and sparse cellularity,
Antoni B regions
, are characteristic of the tumor.
Treatment options include surgical removal of the tumor, stereotactic
radiosurgery, stereotactic radiotherapy, and proton beam therapy.
CT and MRI of Inner Ear Structures.
Recent developments in imaging resolution have made it possible
to distinguish many of the anatomical features of the inner ear
in human subjects.
Computed tomography (CT) imaging
temporal bones is helpful for evaluating bony anatomy, such as the
middle ear ossicles and bony labyrinthine structures. CT is useful
in cases of
to look for fractures and dislocations,
and inﬂ ammatory processes to evaluate for bone erosion, and
to explain hearing dysfunction.
resonance imaging (MRI)
is most often performed to evaluate a
sensorineural hearing loss
. It is used to exclude a
and, occasionally, to evaluate for infection.
The brainstem, internal auditory canals, cranial nerves, and mem-
branous labyrinthine structures (perilymph-F lled cochlea, vesti-
bule, and semicircular canals) are well evaluated on MRI. In the
CT scan (
), bone is light and perilymph dark; these relations are
reversed in the T2-weighted MRI (
Pathological and Clinical Terms for the Ear
Sensorineural hearing loss
: Hearing loss that involves the loss of hair cells or neurons; accounts for about 90% of all hear-
ing loss. Can occur after sound- or drug-induced damage to hair cells, disease-induced damage to neurons in the auditory
system, and loss of hair cells with advancing age (±ig. 21-7C).
: Excessive accumulation of clear, watery ﬂ uid in a tissue or cavity;
refers to an accumula-
tion of endolymph within the membranous labyrinth (±ig. 21-9C).
: Abnormal noise in the ear (e.g., ringing, whistling, hissing, roaring, chirping), ranging from “mild” to “extremely
annoying”; inner ear trauma produced by loud noise is the leading cause; also occurs in Ménière disease. Advancing age
is frequently accompanied by gradual loss of hair cells, producing sensorineural hearing impairment and tinnitus (±igs.
21-9C and 21-12A).
: The illusory sensation of spinning or tilting most frequently caused by inner ear disturbances. Can last for minutes,
days, or weeks and can be incapacitating; often accompanied by severe nausea (±igs. 21-9C, 21-10C, and 21-12A).
Conductive hearing loss
: Decrease in sound conduction to the inner ear. Possible causes include buildup of ﬂ
in the middle ear because of infection, blockage of external auditory meatus by wax, and disorders or traumatic damage
of the ossicles (±ig. 21-11C).
: Redness of a tissue as a result of inﬂ
ammation (±ig. 21-11C).
: Earache (±ig. 21-11C).
: Description of a tumor that is nonmalignant, that is, does not invade surrounding tissues and does not metastasize
to other locations in the body (±ig. 21-12A).
Axial MRI scan
CT scan of temporal
bone in horizontal plane
Ventral (anterior) surface of the brain