CSF Analysis and Other Body Fluids

CSF Analysis and Other Body Fluids

Formation of Cerebrospinal Fluid (CSF)

Functions of CSF

Collecting CSF

Possible complications of lumbar puncture,

Indications for CSF examination

Composition of CSF

ROUTINE LABORATORY EXAMINATION OF CSF

CEREBROSPINAL FLUID (CSF)--The investigation of clinical disorder of the central nervous system (CNS) is partly based on the examination of cerebrospinal fluid (CSF). The central nervous system consists of the brain, spinal cord and peripheral nerves.

The brain is encased within the cranial cavity and weighs about one-fifth of the body weight. Structurally it is partitioned into the cerebrum (greater brain), the brain stem (midbrain, pons varolii and medulla oblongata) and the cerebellum (lesser brain)

CEREBROSPINAL FLUID (CSF)

 The brain is protected by the cranium, and the spinal cord by the vertebral column. The brain and the spinal cord are covered by three membranes collectively called the meninges. The meninges consist of

 1. An outer protective membrane called the duraa mater;

 2. A middle membrane called the arachnoidmater; and

3. An inner membrane called the pia mater (Fig. 10.1b).

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The arachnoid mater and the pia mater are separated from each other by the subarachnoid space which is filled with the cerebrospinal fluid. Thare are subdural space Between the duraa mater and the arachnoid mater.

Formation of Cerebrospinal Fluid (CSF)- 

Formation of Cerebrospinal Fluid (CSF)

The lateral ventricle is a large irregularly shaped chamber that lies deep within each cerebral hemisphere. Within these lateral ventricles are vascular structures called choroid plexuses where the CSF is formed. The cells of choroid plexus actively secrete CSF. The fluid passes into the third ventricle via the interventricular foramen of Monro before flowing down to the cerebral aquaduct into a fourth ventricle.

The fourth ventricle lies between the pons and cerebellum of the brain. The CSF then flows from the fourth ventricle down the small central canal of the spinal cord and through openings (foramina) into the subarachnoid space to completely surround the brain and the spinal cord. Small blood vessels in the arachnoid mater constantly reabsorb CSF in circulation so that the production is balanced by an equal reabsorption of fluid.

Functions of CSF (Cerebrospinal Fluid)

1. Cerebrospinal Fluid provide a "fluid cushion" to support and protect the brain and the spinal cord.

2. It acts as a shock absorber for the brain and the spinal cord.

3. It carries nutrients to the brain and spinal cord and removes waste products.

4. It helps to maintain a constant pressureinside the head and around the spinal cord.

5. It keeps the brain and spinal cord moist.

Collecting CSF (Cerebrospinal Fluid)

 A specimen of CSF is collected by a lumbar puncture, using a long needle with a stylette inside. The needle is introduced between the third and fourth lumbar vertebrae into the spinal sub-arachnoid space with the patients back well flexed for good separation of the vertebrae. It is a very critical operation and damage to the spinal cord can easily occur.

The cord stops at the level of the first lumbar vertebra and cannot be damaged by the needle entering the subarachnoid space a few centimetres lower.

The CSF is usually collected into 2 or 3 sterile containers, numbered according to the order of collection, each containing about 1-3ml of CSF.

The brain, spinal cord and the site of lumber puncture

Possible complications of lumbar puncture

1. Production of cerebellar pressure cone in patients with increased intracranial pre ssure.

2. In the case of spinal cord tumour, paresis may progress to paralysis as a result of lumbar puncture.

3. During the whole process of lumbar puncture, infection can inadvertently be introduced by

(a) the use of unsterile equipment; (b) by passing the needle through a septic spot in the lumbar region,(c) by not observing aseptic precautions.

4. After-puncture headache as a result of leakage of CSF. This condition can be minimised by using a small bore needle. 

Indications for CSF examination

1. Diagnosis and detection of suspected meningitis, subarachnoid haemorrhage, encephalitis, central nervous system syphilis, spinal cord tumour or multiple sclerosis.

2. Differential diagnosis of cerebral infarction from intracerebral haemorrhage (about 80 % of the latter show xanthochromia or bloody appearance of CSF).

Composition of CSF(Cerebrospinal Fluid):-

 The CSF is mainly composed of water, dissolved oxygen and solids. The average volume is between 100 ml and 150 ml which is produced at the rate of 430 ml/day. It is similar to plasma in composition, but the concentrations of sodium, chloride, magnesium and glutamine are greater in CSF than in plasma; while concentrations of glucose, potassium, calcium, cholesterol, uric acid and iron are higher in plasma. Table 10.1 shows the composition of normal CSF.

Compostion of normal  Cerebrospinal Fluid (CSF)
Volume	100-150ml
Total protirn	0.15-0.45g/dl
Glucose	3-4.5 mmol/l (50-80mg%)
chloride	118-134 mmol/l
Sodium	144-154 mmol/l
PH	7.3-7.4
CELLS	0-5 Lymphocytes/cu.mm

ROUTINE LABORATORY EXAMINATION OF CSF(Cerebrospinal Fluid)
  

Macroscopic(gross) Examination of CSF

Chemical Examination of CSF