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PATIENTS WITH A MASS LESION

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POSTERIOR FOSSA LESION

Intracranial mass lesions include:
-congenital
-neoplastic (benign, malignant)
-infectious (abscess, cyst)
-vascular (hematoma, AVM)

Common primary tumors include:
-glial cells astrocytoma, oligodendroglioma, glioblastoma
-ependymal cells ependymoma
-support tissues meningioma, schwanoma, choroidal papilloma

Intracranial mass lesions genrally present according to:
-growth rate:
-location:
-ICP

Growth rate
rapid growth rate: acute presentation (ex. headache, nausea, vomiting, papilledema, inc ICP)
slow growth rate: slow progressive presentation ex. weakness leading to focal neurological deficit

Location
supratentorial: associated with: seizures, hemiplegia, aphasia,
infratentorial: associated with: cerebellar dysfunctino (ex.ataxia, nystagmus, dysarthria)
brain stem: associated with: cranial nerve palsies, ΔMS, respiratory abnormalities

ICP
Increased ICP associated with: headache, nausea, vomiting, papilledema, focal neurological deficit, ΔMS

POSTERIOR FOSSA LESION

OBSTRUCTIVE HYDROCEPHALUS
-obstruction of the 4th ventricle or cerebral aqueduct by infratentorial masses which may obstruct CSF outflow
-resultant increase in ICP
-reduction of ICP is often performed by ventriculostomy prior to induction of general anesthesia

BRAINSTEM INJURY
-vital circulatory and respiratory centers within the brainstem are vulnerable to injury during operations in the posterior fossa
-injuries to the brain stem may occur due to:

Direct surgical Trauma

retraction
ischemia
Respiratory center injury often is associated with circulatory changes which involve:
-blood pressure
-heart rate
-rhythm
*neurosurgeon should be informed of circulatory changes suggestive of respiratory center injury

Monitoring
-evoked potential helps assess neural integrity during the surgical protection
ex. BAEP: allows for monitoring CN VIII during resection of acoustic neuromas
-EMG: allows for the monitoring of CN VII
Postioning of patients with posterior fossa surgery may be:
-modified lateral position
-prone position
-sitting position

*head should always be elevated above the level of the heart

Sitting position involved with increase chance of :
-pneumocephalus
-venous air embolus (VAE)