in the name of god chapter 165 extra-axial neoplasm of the posterior fossa department of...
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IN THE NAME OF GOD
Chapter 165 EXTRA-AXIAL NEOPLASM OF THE POSTERIOR FOSSA
Department Of Oto-rhino-Laryngology Of Isfahan Medical Science
DDX OF SKULL BASE NEOPLASMS
POSTERIOR FOSSA:
1) Common Cerebellopontine Lesions: Acoustic neuroma- Meningioma - Epidermoid- Nonacoustic
neuroma -Paraganglioma -Arachnoid cyst- Hemangiom
2) Petrous Apex Lesions : Cholesterol granuloma -Epidermoid - Asymmetric
pneumatization -Retained mucus or mucocele - Petrous carotid artery aneurysm
3) Uncommon Cerebellopontine Lesions : Metastatic tumor -Lipoma –Dermoid-
Teratoma - Chordoma - Chondrosarcoma- Giant cell tumor
4) Intra-Axial Tumors :
Hemangioblastoma- Medulloblastoma - Astrocytoma - Glioma - Fourth ventricle tumor
ANs most common tumors more than 90%
Secondary tumors paragangliomas 10% of CPA neoplasms
Acoustic Neuroma :benign schwannoma vestibular eighth nerve. 8% -10% of all intracranial tumors.
slowly growing- circumscribed-grossly displacing neural structures-firm and dense to soft with large cystic spaces.
pressure neurovascular structures,-auditory and vestibular symptoms earlier in IAC than CPA.
>95% unilateral -nonhereditary lesions
(NF) type 1 (von Recklinghausen's disease) :
AD - gene : 17, arising both intracranially -extracranially Schwann cells of any nerve; <5% ANs
bilateral AN is not a part of the syndrome.
NF type 2 :bilateral AN in > 96% of patients. Schwannomas of the other cranial nerves,
meningiomas and epandymomas are more in NF 2. gene : 22
ANs in NF 2 are onset early in life(often < 21 y)
AN s < 30y close evaluation of the contralateral ear.
technically more challenging to remove because of tendency to adhere to nearby structures.
Malignant schwannomas rarely occur,often in:
1) NF2) solitary schwannomas3) pigmented schwannoma growth rate : variable, slow growing(0.2
cm/y) ANs that are not treated are potentially
lethalGradual enlargement leading to indentation
of brainstem, ICP ,death during of 5-15y
Growth of ANs in three phases:1) IAC growth : 7-8 nerve compression and
Displacement 7,8 nerve and (AICA)
2) cisternal portion : Fourth ventricle shift often (2 to 3 cm ) -total ventricle obstruction - hydrocephalus - Trigeminal compression occurs at about the 3-cm
3) brainstem compression : cerebellar
tonsil herniation -death
Signs and Symptoms: Most: (SNHL progressive unilateral)-
tinnitus, dysequilibrium, facial hypesthesia loss SDSlarge tumors : facial sensation or corneal
reflex (compression 5 (CN)) -compress the fourth ventricle and brainstem, ataxia, Increased ICP (headaches, nausea)
Rotatory vertigo is far less common
>20% of AN with SSNHL may totally recoveronly 1% SSNHL have AN> 5% of AN have normal hearingany patient with asymmetric or sudden
hearing loss (even after total recovery) should be R/O retrocochlear lesion.
Diagnostic Studies 1) Audiometry 2) (MRI) (MRI) – audiometry are not sensitive to
detect small ANs3) ABR: most sensitive even small tumors
AN (95% -100%)4) Stacked ABR :modified ABR -improved
sensitivity for intracanalicular ANs
IMAGING DDX OF CPA LESIONS: 1) Extra-axial : Most common (AN) -
Common (Meningioma- Epidermoid)
2) Extradural: Common (Paraganglioma : glomus jugulare, vagale)
3) Intra-axial: (Rare) Astrocytoma, ependymoma, papilloma, hemangioblastoma, metastasis
Acoustic Neuroma:*Centered *on IAC- enlarge IAC -Spherical
or ovoid- acute bone-tumor angle-in CT scan : Mostly isodense- often
inhomogeneous – in MRI T1,T2 : Isointense or hypointense
MRI : lesions as small as 3 mmcontrast CT can fail to detect ANs smaller
than 1.5 cm
CT primary imaging modality in patients ;
1) who cannot undergo MRI because of medical reasons (e.g., cardiac pacemaker or cochlear implant)
2) unmanageable phobic reactionsOxygen cisternography : used to diagnose
small, mainly intracanalicular lesions
MENINGIOMAS18% of intracranial tumors and 3% of CPA
tumorsarachnoid villae are the cells of origin benign but locally aggressive tumors globular mass firmly adherent to dura materpsammoma bodiesthin investing capsulebone without destructionhyperostotic in 25%
The signs and symptoms ; similar ANsSmall tumors: HL , tinnitus, imbalanceLarger tumors : other cranial nerve
involvement and hydrocephalusDiagnostic Studies Audiovestibular Testing75% abnormal ABRImaging: Unlike ANs, meningiomas are usually
eccentric to the porous. 60% extend to the middle fossa
CT, 2/3 meningiomas ; hyperintense - homogeneous and calcified
Hyperostosis (characteristic of meningiomas )
Eccentric IAC -Hemispherical,rarely plaquelike
obtuse bone tumor anglein MRI T1 : Isointense or hypointense in
T2 :Variable
PRIMARY CHOLESTEATOMAS: originates from epithelial rests within the
temporal bone or CPA.slow growing, and symptoms often do not
become apparent until the second to fourth decade of life.
expand, compression of surrounding structures variable shapes with irregular surfaces. They may burrow into crevices on the surface
of the brain or dumbbell into the middle fossa.
Diagnostic Studies :Auditory Testing,SDS; is poorer than degree
of pure-tone loss. ABR abnormalCT and MRIEpidermoids CPA should be DDX from arachnoid
cysts-arachnoid cysts have smoother surfaces than primary cholesteatomas.
epidermoids petrous apex should be DDX from the much more common cholesterol granulomas.
primary cholesteatoma requires excision, whereas drainage is sufficient for cholesterol granulomas and arachnoid cysts
CT: less dense than brain + no enhancement,
irregular margins-Anterolateral or posterolateral to brainstem-erosion- dumbbell into middle fossa or contralateral CPA –hypodense-peripheral calcium
MRI: inhomogeneous and hypointense (on T1) homogeneous and isointense or hyperintense on
T2.
special MRI (diffusion-weighted images) (DWI) may differentiate
Facial nerve neuroma: Signs and Symptoms depend portion of the
nerve affected. Peripheral involvement; parotid mass, ME
involvement (CHL )- IAC or CPA involvement (SNHL)
Unlike hemangiomas of the facial nerve, schwannomas do not produce facial weakness until the tumors are very large
Diagnostic Studies Auditory Testing : Impedance testing may
reflect motor fiber impairment on ipsilateral reflex testing or CN VIII involvement on contralateral reflex testing.
ABR : tumors arising in the IAC shows abnormalities
Electroneurography (ENOG) may be reduced in facial nerve
neuromas even when no facial weakness or tic is present,whereas ENOG remains normal in AN until the tumor becomes very large.
Imaging: Intratemporal facial nerve lesions( bone destruction )
facial nerve neuromas and Ans usually impossible to distinguish with CT.
Anterosuperior erosion of the IAC or erosion of the labyrinthine facial nerve canal if present may be the only diagnostic clue
More distal tumors enlarge the geniculate ganglion and fallopian canal.
Patients CPA neuromas should be warned preoperatively of a 1% risk of facial nerve neuroma,if preoperative ENOG is abnormal on the tumor side.
OTHER CRANIAL NERVE NEUROMAS ANs 95% of intracranial schwannomas
1) trigeminal neuromas are the next most common;
arise intradurally, from the nerve root in the CPA and Meckel's cave, and extradurally, from the gasserian ganglion in the middle cranial fossa.
Typically these lesions enlarge Meckel's cave and produce hypesthesia of the face
The tumor is nearly of CSF intensity because of the predominance of the intratumoral cystic components
2) Neuromas of CNs IX, X, and XI : smooth enlargement jugular foramen and
hypesthesia and weakness of the palate, vocal cord,shoulder
3) Hypoglossal neuromas ; motor hemiatrophy of the tongue and
enlargement hypoglossal canal on radiography.
Glomus Tumors first symptom : pulsatile tinnitus, after CHL
develops. Involvement of the nerves of the jugular foramen and the hypoglossal nerve (progressive neurologic deficits)
CT with bone review: irregular destruction of the jugular foramen.
biopsy is not indicated in these lesions.If surgical resection requires manipulation of the
artery, preoperative assessment of the adequacy of collateral flow via the circle of Willis is necessary-preoperative embolization when surgical resection is planned.
MRI : salt and pepper mixturelimitations of MRI in evaluating
paragangliomas:1) bone changes not visualized 2) distinguishing tumor intensity from bone
marrow is difficultMRI : information about infralabyrinthine
and intracranial tumor extensions
Arachnoid Cysts : thin-walled sacs: contain yellow, entrapped CSF.theory : congenital developmental anomaliesSymptoms : mass effect on surrounding
structures similar ANs(retrocochlear pattern) similar to epidermoids (Enlargement of IAC )
CT : smooth-surface lesion, approximates CSFMRI : nonenhancing +isointensity or
hypointensity T1 and hyperintensity T2
management of these lesions:1) not total resection.surgical drainage via
retrosigmoid 2) diuretic therapy
Hemangiomas; symptoms : compression of adjacent
structures. **Capillary hemangiomas: arise of the
geniculate ganglion. progressive facial weakness . pulsatile tinnitus.
CT : smooth enlargement of the geniculate ganglion and enlargement of the labyrinthine portion of the fallopian canal by a soft-tissue mass.
Enhancing, honeycomb bone, irregular -intratumoral bone spicules
Intratemporal vascular tumor in the region of the geniculate ganglion
***Cavernous hemangiomas: in the IAC symptoms typical of an AN. symptoms more rapidly than an AN
CT and MRI; slightly more hyperintense than AN.
PETROUS APEX LESIONS ; Cholesterol Granulomas 1) occlusion + 2) Hemorrhage into the air cells
results 3) foreign body reaction+ 4) granuloma
formation.expansile lesion with extension into CPA and
signs and symptoms of CN VIII dysfunction.
CT: punched-out lesion - isodense mass -does not enhance-rim enhancement
MRI, T1 and T2 : hyperintense Cholesterol granulomas ; more common than
epidermoids.
CT, epidermoids ( rim enhancement) MRI: hyperintense on T1 and T2; whereas epidermoids are hyperintense only on T2. Total excision of cholesterol granulomas: unnecessary. Drainage
Asymmetric Petrous Apex Pneumatization
should be distinguished from true neoplasms.lack of bone destruction or expansion on CT,
absence of contrast enhancement with gadolinium
hypointensity on T2-weighted distinguish this finding from a neoplasm
Petrous Carotid Artery Aneurysms rare, appear as expansile, well-defined
masses preoperative identification is critical Carotid aneurysms may be confused with the
radiologic appearance of chondrosarcomas.
Giant Cell Tumors extremely rare. originate from
undifferentiated cells of the supporting connective tissue
consist of multinucleated giant cells in a background of spindle-shaped stromal cells.
Patients with this unusual condition have retrocochlear signs and symptoms.
CT : diffuse lesion of the temporal bone compressing the contents of the IAC.
Metastatic Tumors ; metastasize to the CPA from ; lung, breast,
prostate, oropharynx, and cutaneous melanomas
suggest especially in a patient with a history of another malignancy
rapid progression of symptoms and associated neurologic signs in addition to hearing loss and dizziness.
lytic lesions in the petrous apex.other cranial neuropathiesbrainstem dysfunction
Chordomas arise in remnants of the embryonic notochord.1/2 arise in the sacrococcygeal regions, 1/3 at the
skull base in the region of the clivus or less commonly, the upper cervical vertebrae
extensive bone destruction and progressive cranial nerve palsies.
not unusual. frontoorbital headache and vision complaints
(e.g., limited visual fields, diplopia, loss of acuity) are more common, occasionally the initial symptoms (extension into the CPA)
CT: bone destruction, masses are homogeneous with moderate enhancement and a greater density than bone
MRI : isointense T1 image and hyperintense T2 image
Chondrosarcomas ;clinically indistinguishable from chordomas
except that they are centered more laterally.
CT ; bone destruction and invasiveness.
MRI ; hyperintense on T2 in the area of bone destruction in the skull base
The mass is markedly but inhomogeneously enhancing, with components containing small, poorly enhancing or nonenhancing foci in Meckel's cave (arrow in A) and in petrous apex (arrows in B), as well as involvement of the
longus colli muscle and jugular fossa (arrows in C).
Lipomas ;thinly encapsulated -soft, multilobular masses of
typical adult adipose tissue.Lipomas within the IAC : symptoms typical of an
AN. on CT : less dense than neuromas MRI is diagnostic; hyperintense on T1,
nonenhancing with gadolinium, and hypointense on T2 .
Dermoid Tumors ;skin-lined cystic tumor containing dermal and
adnexal structures. The lining of the cyst : mature, stratified squamous epithelium.
slowly expanding (symptoms similar to a primary cholesteatoma)
CT ; non homogeneous cystic mass that
contains calcium but less dense than brain
Teratomas ; arise from multipotential cells various tissues,
representing more than one germ layer. Contain: ectodermal, mesodermal,
endodermalCarcinomatous or sarcomatous : 10% -35% When malignant degeneration occurs,
symptoms progress rapidlyotherwise symptoms progress slowly like
benign CPA tumors.
CT : non homogeneous lesion of less density than brain without enhancing
INTRA-AXIAL TUMORS 1) arise from the brainstem (gliomas)2) cerebellum :(medulloblastomas from the
vermis or astrocytomas from the peduncles)3) the fourth ventricle (choroid plexus
papillomas and ependymomas). highly unusualIn children, brainstem gliomas ; most
common source of CPA neoplasms.Intra-axial tumors are usually isointense on
T1 MRI and hyperintense on T2 images
Hemangioblastomas ;tumors of blood vessel origin in the
cerebellum. They may also occur in the cerebral
hemispheres and in association with a similar retinal tumor and may be multicentric.
Histologically: benign, may produce major neurologic
dysfunction by compression of the brainstem.Rapidly progressing signs and symptoms of
cerebellar dysfunction Hearing and balance are likely to remain
normal.
Imaging studies : intrinsic to the cerebellum that may extend into the CPA.
Medulloblastomas ;arise from the cells of the external granular
layer of the cerebellar folia. exophytic masses on the cerebellum with
extension into the CPA. Symptoms : destruction of cerebellar tissue
and mass effect of the tumor on the CPA's adjacent structures.
rapid development of symptoms + hearing loss and dizziness
neurologic findings include facial weakness, dysmetria of speech and hand motion, perverted nystagmus ,abnormal peripheral reflexes.
Temporal bone imaging : normal, CT and MRI show a lesion intrinsic to the cerebellum.
Brainstem Gliomas; Exophytic gliomas may arise on the surface of
the pons and grow into the CPA. intrinsic to the brainstem.
signs and symptoms similar to those of ANs, predominantly long tract signs.
Patients with exophytic lesions may be diagnosed preoperatively to have ANs.
Long tract signs in association with characteristic brainstem distortion on imaging make preoperative diagnosis possible in the patients with intrinsic lesions.
TUMORS OF THE FOURTH VENTRICLE Malignant Choroid Plexus Papillomas
and Ependymomas arise from the fourth ventricle cause CPA symptoms by growing through the
foramen of Luschka. early signs of CN VIII dysfunction.
Ependymomas may calcifyMRI: isointense with brain on T1 -mildly
hyperintense to brain on T2 images
CPA ependymoma. A and B, Pre- and post-gadolinium images. The mass protruding into the right CPA from the foramen of Luschka shows clear demarcation and strong enhancement. C, T2-weighted image. The tumor is hyperintense and does not extend into the IAC
In malignant ; CT shows a mass with enhancing characteristics of a schwannoma
Malignant ependymomas require multimodality therapy:
1) role of surgery is biopsy 2) brainstem decompression3) management of hydrocephalus.
SELECTION OF SURGICAL APPROACH The principal goal : tumor removal with minimal
postoperative morbidity. surgical approach should be tailored to patient's
pathology and functional status. In cases without serviceable hearing, the
translabyrinthine; 1) provides wide exposure 2) maximal facial nerve safety3) minimal cerebellar retraction4) low incidence of severe postoperative
headache.
In meningiomas and tumors that do not affect the IAC and have not affected hearing:
extended middle fossa approach is used if posterior and middle fossa exposure is necessary.
retrolabyrinthine approach is used for limited lesions of the CPA only
retrosigmoid approach : for more extensive lesions of the posterior fossa.
Extensive anteromedial exposure is needed for lesions of the clivus.
Translabyrinthine: 1) Large, medium, or small cerebellopontine
angle tumor2) Wide exposure3) facial nerve identified, immediate repair4) limited cerebellar retraction4) Total hearing loss
Retrosigmoid (suboccipital): 1) Cerebellopontine angle tumors without
extensive IAC 2) Hearing preservation possible3) wide exposure4) cerebellar retraction : hydrocephalus,
intradural drilling may result in severe headaches
Retrolabyrinthine: 1) CPA lesions without IAC 2) biopsy of cerebellopontine angle lesions3) Hearing preservation possible4) bone removal is extradural, no cerebellar
retraction5) Limited exposure
Transcochlear: 1) Extensive lesions of petrous apex and clivus2) Wide exposure of skull base with access to
clivus, vertebral, and basilar arteries and full exposure of petrous carotid artery
3) Temporary facial nerve paralysis4) total hearing loss
Transotic: Same as transcochlear
Middle fossa: 1) Intracanalicular tumors with minimal CPA
involvement 2) good hearing Hearing preservation possible3) Small tumors only4) temporal lobe retraction
Extended middle fossa :1) Petroclival lesions involving posterior and
middle fossa with good hearing2) Hearing preservation possible3) Extensive temporal lobe retraction
small tumors and good hearing have three options for surgical :
1) translabyrinthine approach that destroys hearing
2) the middle fossa approach in young patients with small, mainly intracanalicular tumors
3) the retrosigmoid approach in small tumors of the CPA that do not extend to the fundus of the IAC.
Hearing preservation is usually not feasible in
such lesions and the transcochlear or transotic approach may be used.
PATIENT MANAGEMENT AND SURGICAL COMPLICATIONS
Preoperative Management 1) Preoperative antibiotics are not routinely
used in uncomplicated cases.2) Osmotic agents and diuretics for brain
relaxation are usually not used in the translabyrinthine approach; however, the retrolabyrinthine, retrosigmoid, middle fossa, and extended middle fossa approaches require such techniques to minimize the need for retraction.
Intraoperative Monitoring 1) Facial nerve monitoring is used routinely
in all cases of posterior fossa
2) ABR monitoring is not routinely used.
Postoperative Care 1) The compression mastoid dressing until po
4th2) neurologic intensive care unit for 1 to 2
days and then transferred to the general ward.
3) Limited activity is begun on the first postoperative morning and ambulation usually begins po 3-4th
Complications1) Anteroinferior Cerebellar Artery changes in vital signs Atkinson's syndromeinfarction of the lateral tegmental pons2) Meningitis The mean time of onset of meningitis in
patients with AN is 8 days postoperatively.Aggressive medical management
3) Cerebrospinal Fluid Leaks
In translabyrinthine ; through the wound is rare(<10%)-usually
responds :mastoid dressing. obliteration of the eustachian tube In rare case of persistent leakage, lumbar CSF
drainage for 3 daysIn refractory cases, abdominal fat Hydroxyapatite cement
………..csf leakIn the retrosigmoid : mastoidectomy is also obliterated with fat. In
some institutions,fluid leakage through the eustachian tube.
Aggressive bone wax over mastoid air cells is necessary to avoid leaks
persistent leaks: fat obliteration of the mastoid and waxing of air cells are usually successful
4) Facial Nerve ideally managed ; immediate repair -
interposition graft
direct repair is impossible or intact nerve does not resume function within 1 year; facial hypoglossal anastomosis
Temporalis muscle transfer
5) Ophthalmologic facial paralysis and corneal insensitivity, in
large tumors. managed prolonged facial paralysis (6
months) ; a brow lift and eyelid spring. management partial facial weakness: 1- lubricating drops2- ointments3-contact lenses4- moisture chamber protection, and nightly
taping of the affected eye is undertaken5- gold weight implantation to the upper lid