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J. Magnan et al.
als, it is adherent to the vestibulocochlear
nerve for 14mm or more. As the vestibulocochlear and facial nerve reaches the porus
acusticus (medial opening of the internal
auditory canal), they pass together with the
nervus intermedius and sometimes a loop of
AICA.
4. Lower cranial nerves includethe glossopha-
ryngeal (IX), vagus (X), spinal accessory
nerves(XI). Inferior and a bit anterior to the
foramen of Luschka is the olive, and just posterior to the olive lie the rootlets of origin for
cranial nerves IX, X, and XI.They cross inferiorly in a fan-shaped pattern the CPA towards
the jugular foramen.
5. The hypoglossal nerve exits the brain stem
through a series of small rootlets anterior to
the olive.
16.2.3 Internal Auditory Canal
The internal auditory canal is approximately
8.5 mm in length (range 5.5–10.5 mm), lined
with dura, and lled with spinal uid surrounding
the acousticofacial nerve bundle. Its medial end
is oval in shape and is referred to as the porus
acusticus. Its lateral end is a complicated structure referred to as the fundus or lamina cribrosa.
The fundus is divided into a superior and inferior
half by the transverse crest.
The upper half is further subdivided into an
anterior and posterior segment by a vertical crest
(Bill’s Bar). The vertical crest separates the macula cribrosa superior, which allows passage of
the superior vestibular nerve posteriorly, from
the meatal foramen, which allows the entry of
the facial nerve anteriorly into the fallopian
canal.
The inferior half of the fundus is a single
oval- shaped space, the anterior portion of which
is occupied by a rounded depression (tractus
spiralis foraminosus) lled with small openings
to accommodate the terminal branches of the
cochlear nerve. The posterior portion is lled
with a macula crista inferior through which
pass the terminal ends of the inferior vestibular
nerve.
16.2.4 Surgical Endoscopical
Anatomy oftheCPA (Fig.16.4)
The surgical CPA can then be divided into three
zones comprising each one a nerve, vessels and
its distinct pathologies:
1. Inferior zone: inferior external occupied by
the lower cranial nerves and the PICA born
from the ipsilateral vertebral artery.
2. Middle zone: more medial than the inferior
zone, consists of the acousticofacial bundle
which crosses this space in a straight line. It
is the zone of the AICA which may form
several loops there and engage itself
towards the porus and sometimes deep in
the meatus.
3. Superior zone: is located more medially at
the anterior tip of the CPA, well inside of
the middle zone. It contains the trigeminal
nerve. The other occupying permanent
structure of this space is the vein of Dandy,
a very bulky vein joining the higher petrous
sinus. The artery of this territory is the
SCA.
Fig. 16.4 Panoramic view of left cerebellopontine angle
in surgical position showing the three zones; inferior zone
in red containing the lower cranial nerves (IX, X, XI) and
postero-inferior cerebellar artery (PICA) and vertebral
artery (VA), middle zone in blue containing the acousticfacial bundle (VII, VIII) and antero-inferior cerebellar
artery (AICA), superior zone in yellow containing trigeminal nerve, Dandy vein, and superior cerebellar artery
(SCA). TB: posterior surface of temporal bone; IV: fourth
cranial nerve
16 Cerebellopontine Angle Pathologies
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167
16.3 Cerebellopontine Angle
(CPA) Tumors
Lesions of the cerebellopontine angle (CPA)
comprise 10% of all intracranial tumors.
The differential diagnosis of cerebellopontine
angle (CPA) includes vestibular schwannoma
(85%), meningioma (3–15%), epidermoid cyst
(2–6%), facial and lower cranial nerve schwannomas (2–3%), arachnoid cyst (1%), and other rare
tumors (include lipomas, dermoid tumors, paraganglioma, chordoma, trigeminal schwannoma,
malignancies, and metastatic lesions (primaries
from glial tumors, breast, lung, prostate)).
16.3.1 Vestibular Schwannoma (VS)
It is a benign tumor of the Schwann cell that
most commonly arises from the Schwann cells
of the inferior vestibular nerve (Fig.16.5). It is
misnomer as acoustic neuroma since it is not a
neuroma and typically does not originate from
the cochlear nerve. They comprise about 6% of
all intracranial tumors, about 30% of posterior
fossa tumors, and about 85% (most common) of
tumors in the region of the cerebellopontine
angle. The incidence is increasing, 20 new cases
per million population, per year. There are no
Fig. 16.5 Left CPA with medium-size vestibular
schwannoma
causative risk factors or exposures. Bilateral vestibular schwannomas are associated with autosomal dominant neurobromatosis type 2 (NF2).
The histology of vestibular schwannoma composed of Antoni A tissue (uniform compact spindle cells with parallel palisading nuclei and
verocay bodies), and Antoni B tissue (less cellular, fatty, and less uniform). Vestibular schwannomas stain positive with S-100 and vimentin. It
is a benign condition with a very rare malignant
degeneration (<1%).
16.3.1.1 Clinical Presentation
1. Most of the asymptomatic patients are diagnosed incidentally on imaging studies performed for separate indications. The symptom
of vestibular schwannomas depends upon the
size and location of the tumor. Although most
vestibular schwannomas grow slowly, the
growth rate of schwannoma is variable and
difcult to predict. Tumor size either remains
static, increases or rarely regresses. Usually, it
is a slow increment, 1–2mm/year. Three separate growth patterns can be distinguished
within acoustic tumors, as follows:
(a) No growth or very slow growth.
(b) Slow growth (i.e., ≥2mm/year on imag-
ing studies).
(c) Fast growth (i.e., ≥1.0cm/year on imag-
ing studies).
Tumors that arise within the internal auditory canal may produce earlier symptoms in
the form of hearing loss or vestibular disturbance by compressing the adjacent nerves and
vascular structure. While if it grows medially
in the CPA, the tumors can continue to grow
until they reach 2–3 cm in size before any
symptoms appear.
2. Most vestibular schwannoma (VS) cases
prove at the otological stage with unilateral
auditory or vestibular dysfunction. The most
common presenting symptom is a unilateral,
progressive, high frequency sensorineural
hearing loss that develops in approximately
95%. From 5% to 25% of patients with VS
present with sudden sensorineural hearing
loss. The hearing loss occurs through direct
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168
injury to the cochlear nerve or interruption of
the cochlear blood supply. For this reason, any
patient with unilateral sensorineural hearing
loss needs further investigation to rule out
VS. There is a poor correlation between the
tumor size and the hearing status as patients
with large tumors may have normal hearing
and patients with small tumors may be severe
hearing loss in the affected ear.
The second most common symptom is unilateral tinnitus (75%) of patients with VS.The
presence of unilateral tinnitus alone is enough
reason to evaluate the patient for VS tumor.
Vertigo and disequilibrium are uncommon
presenting symptoms among patients with
VS.Vertigo attacks are correlated with smaller
tumors, whereas chronic disequilibrium is
correlated with larger tumors.
Other reported symptoms include decreased
sensation of the ear canal and concha bowl
(Hitselberger sign) and it is due to injury of
the sensory bers of the facial nerve.
3. Expansion of the tumor within the CPA may
lead to the neurological stage which is becoming less and common. Increased intracranial
pressures, brainstem compression, and cranial
nerve dysfunction induce headache, facial
weakness, unilateral facial numbness, visual
loss, dysphagia, hoarseness, and hydrocephalus. Facial weakness is sufciently uncommon (<1%) that facial weakness associated
with a small- or medium-size tumor should
raise suspicion that it is not a vestibular
schwannoma.
4. Bilateral vestibular schwannomas strongly
suggest the presence of neurobromatosis
type 2 (NF-2), an autosomal dominant neurocutaneous disorder associated with a mutation
on the long arm of chromosome 22 that code
for the protein merlin. It is characterized by
the development of multiple schwannomas,
meningiomas, and ependymomas. The occurrence of bilateral vestibular schwannomas is
almost considered the pathognomonic of this
disorder. Such patients typically with family
history present clinically in the second and
third decades of life, much earlier than those
with the sporadic intracranial schwannoma.
J. Magnan et al.
Neurobromatosis Type 2
• Autosomal dominant
• Mutation in NF2 gene (22q12.2) which
codes for the protein neurobromin 2
(or merlin): regulation of contactdependent inhibition of cellular
proliferation
• Diagnosis requires one of the
following:
– Bilateral VS, or
– Unilateral VS with a family history
of NF2, or
– Multiple brain tumors with a family
history of NF2
16.3.1.2 Diagnosis
Different evaluation tools can be used to diagnose VS including audiologic and electrophysiologic evaluations, vestibular tests, but the key
assessment is the imaging study.
Pure-tone audiometry and word discrimination evaluation in VS patients typically present
with asymmetric sensorineural hearing loss with
disproportionately poorer than expected word
discrimination test. Rollover phenomenon is seen
in VS cases as increased sound intensity results in
decreased word discrimination ability.
Electrophysiologic testing by auditory brainstem response (ABR) represents the most
sensitive and specic audiologic test with sensitivity reach up to 85–90% in medium and large
tumors, but it is not as sensitive as MRI as it may
miss tumors <1cm in size. ABR ndings suggestive of retro-cochlear lesion are prolonged interaural wave V latency, interaural wave I–III, and
interaural I–V latencies.
Vestibular assessment is mainly done by
caloric test and vestibular evoked myogenic
potential (VEMP), which can help to determine
the nerve of origin (superior vs. inferior vestibular nerve) of VS that may add prognostic
information. The prognosis for hearing preservation with surgical resection is more difcult
with a tumor in inferior vestibular nerve due to
proximity to the cochlear nerve and possible
16 Cerebellopontine Angle Pathologies
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169
shared blood supply. The caloric test in VS
identies a unilateral vestibular weakness in
the tumor side, which indicates that the tumor
has affected or originates from the superior
vestibular nerve. Myogenic potential (VEMP)
testing that shows an absent or reduced VEMP
response with normal caloric testing indicates
VS originating from the inferior vestibular
nerve.
Magnetic resonance imaging (MRI) is the
gold standard in the evaluation of patients with
unilateral auditory and vestibular dysfunction. It
appears in MRI with contrast as isointense T1
with contrast shows intense enhancement that
can appear as “ice cream cone” or “mushroom”
shape (Figs.16.6, 16.7, and 16.8). MRI imaging
can detect down to a 1–2mm sized tumor with
contrast administration. CT with contrast indicated if MRI is unavailable or contraindicated,
may miss tumors <1 cm. Table16.1 shows the
differential diagnosis of CPA tumors along with
their MRI ndings.
16.3.1.3 Management
Vestibular schwannoma management goal is to
preserve life with avoidance of any serious neurologic sequelae as facial paralysis, optimally
achieved with complete tumor removal and preserving the facial and hearing functions. VS management includes one of the following three
primary treatment options: (1) surgical excision
of the tumor, (2) arresting tumor growth using
stereotactic radiation therapy, or (3) careful serial
observation.
The selection of treatment options depends on
multiple factors including mainly the tumor size
and the age, but also medical status of the patient,
tumor progression, hearing status, and patient
preference (see Fig.16.9).
Observation
Although VS most often is a slow growing tumor
the growth rate of schwannoma is variable and difcult to predict. A tumor is considered to be growing
when its size is superior to 2mm per year. Simple
observation without any therapeutic intervention has
been used in the following groups of patients:
• Elderly patients (>65years).
• Patients with small tumors (<1.5 cm), espe-
cially if their hearing is good.
• Patients with medical conditions that signi-
cantly increase the risk of the operation.
• Patients with a tumor on the side of an only
hearing ear.
The observation should be followed with
serial MRIs every 6months for the rst year, and
yearly thereafter if no growth is detected then
resume on observation. Individuals who are
being observed ultimately require therapeutic
intervention in between 15% and 40%. In young
patients, the growing tumor potential is higher. It
is the reason why they are better served by tumor
removal as the hearing-preservation approach
may be lost. The management and observation
strategy of vestibular schwannomas is summarized in Fig.
16.9.
Fig. 16.6 Axial T2 CISS and coronal T1 WI MRI before
and after IV contrast administration showing a small right
intracanalicular soft tissue signal intensity lesion that
shows homogenous post-contrast enhancement representing right-sided intracanalicular vestibular schwannoma
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J. Magnan et al.
Stereotactic Radiation Therapy
It aims to prevent tumor growth and does not
eliminate it. Stereotactic radiotherapy is indicated for tumors less than 2.5 cm (including
CAI), elderly, and poor surgical candidates with
asymptomatic growing tumors. It is contraindicated for cystic tumors, big tumor, or small no
growing tumor.
Fig. 16.7 Axial post-contrast T1 WI MRI showing large
left cerebellopontine mass lesion extending to the middle
line and distorting the brainstem and widening the left
internal auditory canal with rather homogenous enhancement representing large left vestibular schwannoma
Current modalities for radiation for vestibular
schwannoma include (1)single fraction Gammaknife given using rigid frame xed to patient’s
head, (2) hypofractionated linear accelerator
photon radiation therapy (cyber-knife) with
image- guided system, and (3) proton beam.
Advantages of radiation therapy include the
benet of no hospitalization and the rapid return
to normal activity, lower immediate posttreatment morbidity, and mortality, i.e., lower risk of
facial nerve injury and stroke. Overall long-term
outcomes are similar to surgery.
Disadvantages of radiation therapy include
delayed sensorineural hearing loss due to blood
vessel brosis and treatment failure with a high risk
of facial paralysis after required salvage surgery
and a rare risk of malignant degeneration (<0.1%).
Surgery
Surgical removal remains the treatment of choice
for tumor eradication. Surgery considered a better choice for younger healthy patients and larger
tumors (the distance between the porus acusticus
and the middle line is 2.5–3cm). The goal of surgical intervention is to have a complete resection
of the tumor while preserving facial nerve and
auditory function. Tumor size and location play a
major role in determining the complications rate;
larger tumors have more risk for facial nerve dysfunction and hearing loss.
Different surgical approaches were described
for resection of vestibular schwannoma
(Fig. 16.10). The surgical approach is selected
based on tumor size, location, and auditory function
Fig. 16.8 Axial T2 CISS, axial T1 WI MR before and
after IV contrast administration showing bilateral intracanalicular soft tissue lesions extending into the CP angle
cisterns and showing homogenous enhancement pattern
representing bilateral vestibular schwannomas in a known
patient with NF type 2
16 Cerebellopontine Angle Pathologies
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Table 16.1 Differential diagnosis of cerebellopontine angle lesions with their CT and MRI ndings
Tumor CT MRI T1 MRI T2
Schwannoma
(vestibular 85%,
facial 1%)
Meningioma
(3–15%)
Paraganglioma Erosion of
Epidermoid (2–6%) Hypointense Hypointense Hyperintense Non-enhancing Restricted diffusion
Cholesterol
granuloma
Mucocele Hypodense Hypointense Hyperintense Rim-enhancing
Lipoma Hyperdense Hyperintense Hypointense Non-enhancing Suppresses with fat
Arachnoid cyst Hypodense Hypointense Hyperintense Non-enhancing Dark on T2 FLAIR
Isodense,
heterogeneous
enhancement
Hypodense,
homogeneous
Enhancement,
calcications
caroticojugular spine
Isodense, with
smooth expansion of
bone
Isointense Iso/
hyperintense
Isointense Isointense Strong
Isointense Isointense Strong
Hyperintense Hyperintense Non-enhancing
MRI T1 with
contrast Notes
Strong
enhancement, with
cystic areas
enhancement
enhancement
Usually centered
into IAC
Dural tail, often
eccentric to IAC
Salt and pepper
appearance
on DWI, cause
bone erosion
saturation
171
Fig. 16.9 Management
strategy of vestibular
schwannoma
Non growing
Observation
(MRI yearly)
in the operated side (Fig.16.11). Each approach is
discussed and compared in detail in Table 16.2.
The combined approach typically involves an
enlarged retrosigmoid (suboccipital) and translabyrinthine approaches. This combined appraoch is
used in resection of CPA tumors that are greater
than 4–3cm which needs wide exposure.
Different considerations go into deciding
which approach should be used, which summarized in the following:
Vestibular
schwannoma
MRI after 6 months
Growing
Elderly
tumors ≤ 2.5 cm
and poor surgical
candidate
Stereotatactic
radiation
Young, healthy
patient,and
applicable to all
tumor sizes
Surgery
1. Preoperative auditory function: Translabyrinthine approach is preferred if no serviceable hearing. For patients that have a
serviceable hearing (discrimination score
>50%), the common approaches include the
retrosigmoid alone or combined with retrolabyrinthine approach and the middle cranial
fossa approach. Normal preoperative ABR
and abnormal caloric test ndings favor hearing conservation.
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172
fossa
J. Magnan et al.
ab c
Fig. 16.10 (a) Retrolabyrinthine approach; (b) Translabyrinthine approach, notice that the sigmoid sinus posterior
retraction provides wider view of the CPA; (c) retrosigmoid approach
Fig. 16.11 The surgical
approach in vestibular
schwannoma is selected
Vestibular
schwannoma
based on tumor size,
location, and auditory
function in the operated
side
Intracanalicular
≤1 cm or
Middle cranial
Ye s
Medial to IAC
Restrosigmoid
≤2.5 cm
Hearing preservation
No
Translabyrinthine
or >1cm
>2.5 cm
Translabyrinthine
or suboccipital or
combined
Table 16.2 Different surgical approaches for reresection of vestibular schwannoma: indications, advantages, and
disadvantages
Approach Indications Advantages Disadvantages
Translabyrinthine Approach of choice for
non-serviceable hearing; can
be used for all tumor sizes;
preferred with any vestibular
schwannomas over 2cm
Excellent exposure with
most direct access to CPA;
consistent facial nerve
identication distally with
lowest risk of injury; no
Sacrices hearing; needs
abdominal fat to close;
contraindicated in acute or
chronic otitis media
cerebellar retraction
Retrosigmoid Serviceable hearing with
tumor medially located to
IAC
Potential for hearing
preservation; remove tumors
of all sizes; direct and
quicker exposure of the
brainstem
Suboccipital (with
large craniotomy and
sitting position)
Serviceable hearing with
tumor medially located to
IAC/large tumors
Middle cranial fossa Serviceable hearing with
small intracanalicular
(intra-IAC)
Large exposure; no need
suction
Potential for hearing
preservation possible;
exposure of entire IAC; no
intradural drilling; low
postoperative headache rates
Retrolabyrinthine Serviceable hearing Combined with retrosigmoid
offers the best conditions for
Limited access to lateral IAC;
recurrence of tumor;
headache; intradural drilling
of IAC; and need for
endoscope
Cerebellar retraction; higher
incidence of headache;
potential of air embolism
Higher risk of facial nerve
injury; Requires retraction of
temporal lobe (small risk of
aphasia or seizure); poor
exposure to posterior fossa
Limited exposure to the CPA;
needs abdominal fat to close
preservation of hearing and
facial nerve function; less
cerebellar retraction
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173
2. Tumor size: Hearing conservation surgery is
more achievable with smaller tumors (<1.5cm)
and the use of cochlear monitoring.
3. Tumor location: The tumor lies within the lat-
eral portions of the internal auditory canal cannot be reached by the retrosigmoid approach
without endoscope-assisted procedure.
4. Relevant anatomical variations: Translabyrinthine approach is much more difcult
with high-riding jugular bulb, anteriorly
placed sigmoid sinus, and contracted sclerotic
mastoid.
5. Surgeon preference.
Both ablative and hearing-preservation surgical approaches have complications, including the
following:
1. Abdominal subcutaneous hematoma: from the
site of fat harvest, with a rate of 3.2%.
2. Hemorrhage into the posterior fossa in the
immediate postoperative period can produce
brainstem compression and death. The mortality rate for surgical excision of vestibular
schwannoma has declined to less than 1%.
3. Cerebellar injuries (rare).
4. Facial nerve: surgical approaches must offer
preservation of facial nerve function (House
Brackmann grade I or II) in over 95% of
patients with tumors less than 1.5cm; however, this rate decreases as tumor size
increases. Consequently, partial resection
with complementary radiotherapy on the
residual piece is questionable in large tumors
to preserve the facial function. Incidence of
delayed facial palsy varies from 10% to
30%, the vast majority have complete
recoveries.
5. Lower cranial nerve injury is rare but can be a
risk in large tumor.
6. Cerebrospinal uid leak: the incidence has
been reported from 1% to 10% of cases.
7. Aseptic meningitis and meningitis: the
reported rate is between 1% and 8% of cases.
8. Postoperative headache: It is more common
with suboccipital approach, found in more
than 30% of patients and very rare in minimally retrosigmoid approach.
9. The ventriculoperitoneal shunt: It is becom-
ing rare. The resection of the tumor restores
the CSF system. But it can be required facing
a resistant postoperative CSF leak.
NF-2 management is more complex and
required a multidisciplinary center since the
patient is young with great risk of deafness along
with the loss of other special senses and locomotion. Radiotherapy requires higher doses to avoid
growing which is harmful for hearing preservation or rehabilitation. Generally, remove the
larger tumor with less hearing rst. If able to preserve the cochlear nerve at the time of surgery,
consider a cochlear implant. Consider the placement of auditory brainstem implant at the time of
initial surgery if the cochlear nerve sacriced.
Observe the only hearing ear with serial MRI or
CT if the patient is bearing auditory implant.
In conclusion,It is important to discuss with
the patient and the family the outcome and the
prognosis of the surgical removal of the tumor,
hence the patient would have a realistic expectation. The key point is not the hearing (except in
cases of only one hearing side) but the facial
nerve functioning. Hearing-preservation rates
and long-term facial nerve outcome are largely
tied to the size of the tumor. Regarding tinnitus,
in 25–60% of patients, it is improved or abolished; on the other hand, it can get worse in only
6–20%. Recurrence of the tumor is variable but
is generally reported at less than 1%, except in
cases of voluntary partial removal. Even in such
cases the tumor is still growing in 10–25%. MRI
Surveillance for postoperative tumor recurrence
should persist every year for 5 years then at
10years postoperatively.
16.3.2 Other Cerebellopontine Angle
Tumors
16.3.2.1 Meningiomas
Meningioma represents the second most common CPA tumor (3–15%). It arises from cap
(endothelial) cells from the arachnoid layer
(arachnoid villi) of the meninges. Histopathology
examination usually shows calcied psammoma
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Fig. 16.12 Axial view T1 WI MR after IV contrast
administration showing right CPA lesion with a dural tail
(sessile and broad-based) and showing homogenous
enhancement pattern representing right CPA meningioma
J. Magnan et al.
denser, contain calcications and hyperostosis,
and have dural tail appearance (sessile and broadbased) (see Fig.16.12).
Management options are the same as vestibular schwannoma and include surgical excision,
stereotactic radiation therapy, and external beam
radiation. Microsurgical resection is considered
the gold standard of treatment.
16.3.2.2 Epidermoid Cysts
Epidermoid cysts are congenital intradural
lesions developed from sequestered ectodermal
epithelial cell rests; it is also called congenital
cholesteatoma of the CPA.It represents approximately 5% of all masses in the CPA region (third
most common).
Symptoms are similar to other tumors of the
CPA; however, they may cause earlier hemifacial
spasm and progressive facial paralysis compared
with the other CPA lesions.
The diagnosis is mainly intraoperative (see
Fig.16.13). MRI imaging features include dark
on T1, extremely bright T2 signal, non- enhancing
on contrast, and restricted diffusion on diffusion
weighted image (DWI) (see Fig.16.6). The primary and only treatment of these lesions is surgical excision (see Fig.16.14).
Fig. 16.13 Intraoperative image of epidermoid cyst dur-
ing translabyrinthine approach showing cholesteatoma
surrounding the acoustic-facial bundle
bodies. It is more common among middle-aged
women. Meningiomas associated with hereditary
tumor syndromes such as NF2, where patients
develop multiple meningiomas. Around 2–5%
has a malignant nature.
Presentation depends upon their size and location; it is similar to vestibular schwannoma, generally larger than VS before causing hearing loss
or vestibular symptoms.
Imaging can often distinguish meningioma
from VS; meningiomas are homogeneous,
16.3.2.3 Facial andLower Cranial
Nerve Schwannomas
Schwannomas can develop on the 5th through the
12th cranial nerves; however, they are far less
common than VS. They account for 2–3% of
tumors within the CPA.
Facial nerve schwannoma usually involves
geniculate ganglion, and facial nerve function
generally not impaired until the tumor is quite
large. MRI is themethod of choice to diagnose
facial nerve schwannoma, characterized by
enhancing dumbbell-shaped expansion of the
intratemporal facial nerve and/or enhanced
enlargement of the geniculate ganglion region
(see Fig.16.15).
Management Plan
Preoperative facial nerve function is the most
important factor determining the treatment
approach (see algorithm Fig.16.16):
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Fig. 16.14 Axial view MRI T1, T2, DWI respectively, showing extensive left epidermoid cyst involving all CPA
16.3.2.4 Arachnoid Cysts (1%)
Arachnoid cysts are congenital malformation of
the arachnoid that results in a thin-walled sac
lled with CSF, and these lesions comprise less
than 1% of CPA tumors. It is typically asymptomatic but can cause compression symptoms.
The relationships between the image of the cyst
and the symptoms are often questionable.
The diagnosis is based on MRI, characterized
by non-enhancing lesion that is hypointense on
T1 and hyperintense on T2.
Management generally is through observation
or minimally invasive surgery for symptomatic
lesions via incision and drainage using a retrosigmoid approach.
175
Fig. 16.15 Post-contrast T1 MRI showing right-sided
enhancing lesion with cystic change suggestive of facial
nerve schwannoma involving the cerebellopontine angle,
meatus, labyrinthine segment, and geniculate ganglion
16.3.2.5 Others
Other rare tumors include lipomas, paraganglioma, chordoma, malignancies, and metastatic
lesions with primaries from glial tumors, breast,
lung, and prostate.
• Normal nerve function or weakness HB III or
less → Clinical and radiological follow-up
• Growing facial nerve tumors → decompression of the facial nerve in the temporal bone to
16.4 Neurovascular Conicts
ofCPA
delay facial palsy and/or radiotherapy to
reduce growing potential and prevent facial
palsy
• Facial palsy HB grade IV or more → Surgical
excision+reconstruction
• Symptomatic facial nerve tumors → surgical
excision
The complex and changing vascular system of
the CPA can come in contact with cranial nerves
passing in the CPA and cause vascular compression and irritation of the nerve (neurovascular
conict). Usually, it is caused by an abnormal
course of a vascular loop, vertebrobasilar doli-
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