6. CSF and Cerebral Blood Supply

What is CSF?

Cerebrospinal fluid that cushions and circulates around the brain and spinal cord

What secretes CSF?

Choroid plexus

What is CSF made from?

A modified filtrate of plasma

What is the full flow path of CSF?

Lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → median and lateral apertures → subarachnoid space → arachnoid granulations → dural venous sinuses

Where does CSF flow first after the lateral ventricles?

Interventricular foramina

Where does CSF go after the interventricular foramina?

Third ventricle

Where does CSF go after the third ventricle?

Cerebral aqueduct

Where does CSF go after the cerebral aqueduct?

Fourth ventricle

How does CSF exit the fourth ventricle?

Through the median and lateral apertures

Where does CSF go after leaving the fourth ventricle?

Into the subarachnoid space and cisterns

Where does CSF circulate?

Around the brain and spinal cord

How is CSF reabsorbed into venous blood?

Through arachnoid granulations into dural venous sinuses

What are arachnoid granulations responsible for?

Reabsorbing CSF into venous blood

What is the Circle of Willis?

A collateral arterial ring at the base of the brain linking anterior and posterior circulation

Why is the Circle of Willis important?

It provides collateral blood flow between major cerebral arteries

What are the key components of the Circle of Willis?

ACA, anterior communicating artery, internal carotid arteries, posterior communicating arteries, PCA, vertebral arteries, and basilar artery

What does ACA stand for?

Anterior cerebral artery

What does MCA stand for?

Middle cerebral artery

What does PCA stand for?

Posterior cerebral artery

What does the anterior communicating artery connect?

The left and right anterior cerebral arteries

What arteries form the basilar artery?

Vertebral arteries

What circulation does the basilar artery help supply?

Posterior circulation

What brain areas does the ACA supply?

Medial frontal and parietal cortex

What body region is represented in the ACA motor and sensory territory?

Contralateral lower limb

What deficits can occur with an ACA stroke?

Contralateral lower limb motor and sensory deficits

What brain areas does the MCA supply?

Lateral cerebral hemisphere

What body regions are represented in the MCA motor and sensory territory?

Contralateral face, lips, and upper extremity

What important cognitive area can the MCA supply in the dominant hemisphere?

Language areas

What deficits can occur with an MCA stroke in the dominant hemisphere?

Contralateral face and upper extremity deficits with possible aphasia

What does the PCA supply?

Occipital lobe, visual cortex, parts of the temporal lobe, thalamus, brainstem, and cerebellum

What visual area is supplied by the PCA?

Visual cortex

What visual deficit can occur with PCA involvement?

Contralateral visual field loss

What areas are supplied by posterior circulation?

Occipital lobe, visual cortex, parts of temporal lobe, thalamus, brainstem, and cerebellum

What is a watershed area?

A border zone between major cerebral artery territories

Where are common watershed areas found?

Between ACA-MCA territories and MCA-PCA territories

Why are watershed areas vulnerable?

They are supplied by terminal branches farthest from the strongest blood supply

What type of blood flow problem commonly affects watershed areas?

Global hypoperfusion or drops in blood pressure

What is a watershed infarct?

A stroke in a border zone between major cerebral artery territories

Why are watershed infarcts clinically important?

They can produce mixed cortical and subcortical deficits

What conditions are watershed infarcts associated with?

Hypoxic-ischemic injury and low-flow states

What is the easiest way to remember ACA supply?

ACA supplies the medial cortex and contralateral leg

What is the easiest way to remember MCA supply?

MCA supplies the lateral cortex and contralateral face and arm

What is the easiest way to remember PCA supply?

PCA supplies posterior brain regions, especially vision

What is the easiest way to remember watershed areas?

They are weak border zones between artery territories that are vulnerable when blood pressure drops