CSF CIRCULATION

CEREBROSPINAL FLUID (CSF) IS A CLEAR COLORLESS BODILY FLUID FOUND IN THE BRAIN AND SPINE WHICH ACTS AS A CUSHION OR BUFFER FOR THE BRAIN'S CORTEX, PROVIDES MECHANICAL AND IMMUNOLOGICAL PROTECTION TO THE BRAIN AND ALSO SERVES A VITAL FUNCTION IN AUTOREGULATION OF CEREBRAL BLOOD FLOW.

PRODUCTION

CSF IS PRODUCED IN THE BODY AT A RATE OF 0.35- 0.4 ML/MINACCOUNTING UPTO 500ML/ DAY

80% IS FORMED BY THE CHOROID PLEXUSES FOUND IN THE LATERAL, THIRD AND FOURTH VENTRICLES. ( MAXIMUM FROM LATERAL VENTRICLES)

20% BY EPENDYMA, BRAIN PARENCHYMA AND SPINAL CORD

DISTRIBUTION

TOTAL VOLUME OF CSF : 150MLCSF IN VENTRICLES : 25MLCSF IN CRANIAL SUB ARACHNOID SPACE : 100MLCSF IN SPINAL SUB ARACHNOID SPACE : 25 ML

CSF TURNOVER RATE IS 3 TO 4 TIMES PER DAY.

ABSORPTION

MOSTLY THROUGH THE ARACHNOID VILLI

CERVICAL LYMPHATICS VIA PERINEURAL SPACES OF CRANIAL NERVES.

PERIARTERIAL SPACES- VIRCHOW ROBIN SPACES

VIA THE SPINAL NERVES

CIRCULATION OF CSF

THE FLOW OF CSF IS OF TWO TYPES

BULK FLOW

THE CSF PRODUCED BY THE CHOROID PLEXUS, CIRCULATES THROUGH THE VENTRICLES, THE CISTERNS, AND THE SUBARACHNOID SPACE TO BE ABSORBED INTO THE BLOOD BY THE ARACHNOID VILLI. THIS COMPRISES THE BULK FLOW.

CUSHING DESCRIBED THIS AS “THE THIRD CIRCULATION”

PULSATILE FLOW

THE INTRACRANIAL VOLUME IS ASSUMED TO BE ALWAYS CONSTANT BY THE MONRO-KELLIE DOCTRINE.

THE INTRACRANIAL DYNAMICS CAN BE VIEWED AS AN INTERPLAY BETWEEN THE SPATIAL REQUIREMENTS OF FOUR MAIN COMPONENTS: ARTERIAL BLOOD, CAPILLARY BLOOD (BRAIN VOLUME), VENOUS BLOOD AND CSF.

CSF FLOW IS NEITHER LAMINAR NOR CONSTANTLY UNIDIRECTIONAL.

PULSATILE CSF MOVEMENT DURING EACH CARDIAC PUMPING CYCLE OCCURS AS ANTEROGRADE CAUDAL FLOW IS FOLLOWED BY RETROGRADE CRANIAL FLOW.

THIS CYCLIC FORWARD AND BACKWARD FLUID MOTION IS A RHYTHMIC PASSIVE RESPONSE TO ARTERIAL PULSATIONS AND BRAIN COMPLIANCE.

THIS MECHANISM, TRANSMISSION OF SYSTOLIC PULSATIONS WITH EACH HEARTBEAT FROM THE INTRACRANIAL CAVITY TO THE CENTRAL CANAL, WAS DESCRIBED AS THE PATHOPHYSIOLOGY FOR THE FORMATION OF SYRINX BY GARDNER – HYDRODYNAMIC OR “WATER– HAMMER” THEORY

VARIOUS PHASES OF PULSATILE FLOW:

PHASE NUMBER

FLOW PHENOMENA

1 ARTERIAL PEAK FLOW

2 CERVICAL CSF PEAK FLUSH

3 JUGULAR BLOOD PEAK FLUSH

4 VENTRICULAR CSF PEAK FLUSH

5 EQUALIZATION OF PRESSURES

PC CINE MR IS A USEFUL IMAGING TECHNIQUE IN EVALUATING CSF DYNAMICS THAT AFFECTS VARIOUS DISEASE PROCESSES

THE PARAMETERS MEASURED INCLUDE

1. PEAK CSF VELOCITY IN AQUEDUCT2. AVERAGE FLOW RATE3. STROKE VOLUME4. COMPLIANCE INDEX (CI)