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Review: Posterior Fossa Anatomy and Tumors David Halevi.

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1 Review: Posterior Fossa Anatomy and Tumors David Halevi

2 Anatomy: Osseus Borders Superior: Tentorium cerebelli Inferior: Foramen magnum Anterior: apex of the petrous temporal. Posterior: enclosed by the occipital bone. Lateral: portions of the squamous temporal and mastoid part of the temporal bone

3 Anatomy: Internal Structures

4 Foramen magnum Transmits the medulla, the ascending portions of the spinal accessory nerve (XI), and the vertebral arteries. Internal acoustic meatus Lies in the anterior wall of the posterior cranial fossa. It transmits the facial (VII) and vestibocochlear (VIII) nerves into a canal in the petrous temporal. Jugular foramen Lies between the inferior edge of the petrous temporal bone and the adjacent occipital bone and transmits the internal jugular vein (actually begins here), the glossopharyngeal (IX), the vagus (X) and the spinal accessory (XI) nerves. Anterior condylar (hypoglossal) canal Lies at the anterolateral margins of the f. magnum and transmits the hypoglossal (XII) nerve

5 Tumors

6 Cerebellar astrocytoma 33% of all posterior fossa tumors in children 25% of all pediatric tumors Average age at presentation is 9 years Frequently a benign, slowly growing cystic tumor Most favorable of all intracranial neoplasms May arise in the hemisphere or vermis

7 Medulloblastoma Malignant Midline from the cerebellar vermis Cerebellar hemisphere in older patients Large tumours completely fill the 4th ventricle Presentation: Hydrocephalus & cerebellar dysfunction

8 Ependymoma & Ependymoblastoma Arises from the floor of the 4th ventricle May infiltrate, the underlying brainstem 50% present < 3 years Anaplastic ependymoma (ependymoblastoma) Hydrocephalus, Facial weakness (dorsal brainstem)

9 Choroid plexus papilloma & carcinoma 0.4 - 0.6% of all intracranial tumors More frequent in children than in adults 60% occur in the lateral ventricle 30% in the fourth ventricle CSF overproduction may occur

10 Hemangioblastoma 7-12% of all posterior fossa tumors Age of presentation is 30-40 years old More common in males

11 Brainstem glioma 15% of all brain tumors 25-30% of all brain tumors in children Most are low-grade astrocytoma Predominantly in the Pons Less frequently in the medulla May infiltrate extensively throughout the brainstem

12 Metastatic tumors 3% occur in the brainstem 18% occur in the cerebellum 1°: breast, lung, skin, and kidney

13 Clinical presentation Depends on: Location Aggressiveness Due to: Compression on cerebellum or midbrain Raised intracranial pressure

14 Clinical presentation ↑ICP Headache Vomiting Strabismus Blurring of vision due to papilledema Meningismus Macrocephaly in children Hydrocephalus

15 Clinical presentation Brain stem compression: Ocular palsy Diplopia Hemiparesis

16 Clinical presentation Cerebellar compression: Truncal or limb ataxia Nystagmus Dysmetria

17 Surgery Anaesthesia Sitting or prone position Vertical midline incision Posterior fossa craniotomy Excision

18 Treatment Surgery Radiotherapy Chemotherapy Anticonvulsant therapy CSF shunt (risk of tumour spread!) Steroid medication

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