posterior cranial fossa-decamber2009

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POSTEIOR CRANIALFOSSA

Mohammed issa al-oqaily

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CRANIAL



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POSTEIOR CRANIAL3



The inside view of cranium is known as

cranial cavityThe cranial cavity containsthe brain and its surroundingmeninges, portions of thecranial nerves, arteries,veins, and venous sinuses.

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Cranial cavity is contained by thefrontal, parietal, sphenoid,

temporal and occipital bones, and

in part the ethmoid, all covered by

endosteal layer of dura mater

Bones that make up the cranial cavity




Anatomy of the lateral aspects of the skull

(b)

Parietal boneCoronal suture

Frontal bone

Frontal sinus

Sphenoid bone(greater wing)

Crista galli

Nasal bone

Sphenoid sinus

Ethmoid bone(perpendicular plate)

Vomer bone

Maxilla

Mandible

Alveolar margins

Incisive fossa

Lambdoid suture

Occipitalbone

Occipitomastoidsuture

External occipitalprotuberance

Internal acousticmeatus

Sella turcicaof sphenoid

bone

Pterygoidprocess of sphenoid

bone

Mandibularforamen

Palatinebone

Squamoussuture

Temporalbone

Palatineprocess of

maxilla



1. Anterior cranial fossa which accommodates the

anterior lobe of brain.

2. Middle cranial fossa, much wider than the anterior

cranial fossa contain the 2 temporal lobes of brain.

3. Posterior cranial fossa is much shallower and wider

than the middle cranial fossa and it accommodates the

occipital lobes of the brain.

The cranial cavity is divided into three

cranial fossa




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Posterior cranial fossa

•It is the deepest and most capacious of the 3

cranial fossae.

•It contains the cerebellum, pons, and medulla

oblongata.




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Continue . . .

a The foramen magnum is located centrally

and inferiorly in the posterior fossa. The

posterior fossa is surrounded by deep

grooves containing the transverse sinuses

and sigmoid sinuses





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Boundaries:

AnteriorlySuperior border of the petrous part of temporal bone

and dorsum sallae.

PosteriorlyInternal surface of squamous part of the occipital bone.

Floor Basilar, squamous & condylor parts of the occipital

bone & mastoid part

foramen magnum forms the central part of the floor.1312/21/09 Mohammed issa al-oqaily

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Tumors of theposterior cranial

fossa

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a Tumors in the posterior fossa are

considered critical brain lesions. This is, primarily, because of the limited space

within the posterior fossa and the potential

involvement of vital brain stem nuclei.




Frequency

a Posterior fossa tumors are more common

in children than the adults.a Between 54% and 70% of all childhood

brain tumors originate in the posterior

fossa.a About 15-20% of brain tumors in adults

occur in the posterior fossa




Continue . . .

a Certain types of posterior fossa tumors,

such as medulloblastoma, pineoblastoma,

ependymomas, primitive neuroectodermaltumors (PNETs), and astrocytomas of the

cerebellum and brain stem, occur more

frequently in children.




Continue . . .

a Some glial tumors, such as mixed gliomas,

are unique to children. They are located

more frequently in the cerebellum (67%)

and are usually benign.




Etiology

a No specific causes for posterior fossa tumors

exist. However, genetic factors, such as

dysfunction of some tumor suppressor genes(p53 gene) and activation of some

oncogenes, may play a role in their

development.2

Environmental factors such asirradiation and toxins may also play a role.




Common

types of posterior

fossa tumors

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Cerebellar astrocytoma

a

Cystic cerebellar astrocytoma comprisesabout 33% of all posterior fossa tumors in

children. It represents 25% of all pediatric

tumors. Average age at presentation is 9

years.





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a

Typically, cerebellar astrocytoma presents as alaterally located cyst with a well-defined solid

component. The tumor may be solid or cystic

and may be located medially in the vermis or

laterally in the cerebellar hemisp.




Primary neuroectodermal tumors

a PNETs include medulloblastomas,

medulloepitheliomas, pigmented

medulloblastomas, ependymoblastomas, pineoblastomas, and cerebral neuroblastomas.

a These tumors originate from undifferentiated cells

in the subependymal region in the fetal brain.

PNETs are second to the cerebellar astrocytoma in

frequency




Medulloblastoma

a Medulloblastoma initially arises in the

inferior medullary velum and grow to fill

the fourth ventricle, infiltrating the

surrounding structures. Some erroneously

thought it arose from medulloblast cells,

which do not exist.





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Ependymoma and ependymoblastoma

a Ependymomas are derived from ependymal

cells. They occur more frequently in females,with 50% presenting in children younger than 3

years.




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Choroid plexus papilloma and carcinoma

a Choroid plexus papilloma and carcinoma

represent 0.4-0.6% of all intracranial tumors.

a They are more frequent in children than in

adults (3% of childhood brain tumors).

a Sixty percent occur in the lateral ventricle

and 30% in the fourth ventricle. The third

ventricle and cerebellopontine angle are rare

locations for this tumor.




a Cerebrospinal fluid (CSF) overproduction

may occur, sometimes reaching more than 4

times normal volumes.a In most of cases, CSF analysis demonstrates

increased protein, xanthochromia, or both.


Continue . . .




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Dermoid tumors

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Hemangioblastoma



Metastatic tumors

a Three percent of all

cranial metastatic lesions

occur in the brainstemand 18% occur in the

cerebellum.

a Originating sites include breast, lung, skin, and

kidney.




a Symptoms may be caused by focal

compression of the cerebellum or brain

stem centers and increased intracranial

pressure.


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Continue . . .

a Symptoms due to focal compression of the

cerebellum include characteristic eye

findings and vermian syndrome.




Outcome and Prognosis

a The 5-year survival rates exceed 60% for

all patients and 80% for certain good-risk

individuals with posterior fossa tumors.


posterior cranial fossa-decamber2009

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