First of all,
we are going to explain the most important temporal bone anatomy in order to better understand the patological findings (Fig 1).
The anatomy of this reagion include the:
- external ear that contains the external auditory canal and auricle (outer ear).
- Middle ear and eardrum wich is call the tympanic membrane that contains three ear bones or ossicles: Malleus,
incus and stapes.
- The inner ear contains the cochlea,
a snail-shaped bone which transforms sounds into nerve impulses.
The vestibule,
contains the utricle and saccule which sense motion in relation to gravity and three semicircular canals which sense rotational motion.
The mastoid air cells,
are air cells which are behind the external auditory canal and the middle ear.
The anatomy of the temporal bone is complex and is further complicated by the small size and three-dimensional orientation of associated structures.
Computed tomography (CT) has revolutionized imaging of the temporal bone.
Recent advances in multisection CT scanners allow acquisition of high-resolution volumetric data that enable image reformation in any plane (Fig 5).
Middle ear cholesteatomas have an erosive potential along the ossicles and bony walls of the middle ear cavity,
mostly by means of an inflammatory response that activates osteoclastic activity.
Because serious intracranial and labyrinthine complications may arise,
surgery is the elective treatment,
with the goal of eradicating disease while simultaneously trying to preserve anatomy and function.
TYPES OF CHOLESTEATOMAS
Most middle ear cholesteatomas (98%) are acquired.
These are usually related to chronic inflammatory middle ear disease combined with disturbed ventilation of the middle ear.
The most accepted pathogenic mechanism is invagination of tympanic membrane retraction pockets owing to eustachian tube dysfunction,
although other theories have been proposed.
According to its origin there are two types:
- Congenital(2%): intact eardrum.
- Location in the temporal bone variable.
Otoscopic diagnosis may be difficult.
- Acquired(98%): tympanic membrane perforation.
- Pars tensa: also called sinus cholesteatomas (less commnon)
- Pars flaccida: attic cholesteatoma,
the most common.
In an attic cholesteatoma,
the most common form of acquired cholesteatoma,
the pars flaccida,
posteriorly and superiorly located,
invaginates toward the Prussak space.
Erosion of the scutum and medial ossicular displacement by the growing cholesteatoma are specific findings at computed tomography (CT).
Less common pars tensa cholesteatomas,
also called sinus cholesteatomas,
extend toward the posterior tympanic recesses (sinus tympani and facial recess) and from there to the medial epitympanic space,
producing lateral ossicular displacement.
Congenital middle ear cholesteatomas are less frequent (2% of cases),
and their location in the temporal bone is more variable.
When located in the middle ear cavity,
a whitish retrotympanic mass is seen at otoscopy behind an intact eardrum and otoscopic diagnosis may be difficult (Fig 5a).
Histologically,
they are identical to congenital epidermoid cysts located elsewhere (meninges,
skull base,
spinal canal,
brain) and are also produced by trapping of ectoderm during fetal development.