Meninges of The Brain And Cerebrospinal Fluid Question And Answers

Cerebrospinal fluid

1. The CSF is modified tissue fluid. It is present in
   • Ventricles of brain,
   • Subarachnoid space around brain, and
   • Spinal cord.
2. Cerebrospinal fluid Formation
   

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   • The bulk of the CSF is formed by choroid plexus lining lateral ventricle.
   • Small amount is formed by choroid plexus of 3rd and 4th ventricles.
   • The total quantity: About 150 ml.
   • Rate of formation: 200 ml/hour and 5000 ml/day.
   • Normal pressure: 60 to 100 mm H2O.

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1. Cerebrospinal fluid Circulation

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1. Cerebrospinal fluid Absorption
   
   1. Chiefly absorbed through
      • Arachnoid villi, and
      • Arachnoid granulation.
   2. Partly by
      • Perineural lymphatics around the 1st, 2nd, 7th and 8th cranial nerves, and
      • Veins related to spinal nerves.
        
2. Cerebrospinal fluid Functions
   
   • Protection of brain,
   • Nutrition of brain and coverings, and
   • Removal of waste products from brain.
3. Applied anatomy
   

• CSF can be obtained by
  • Lumbar puncture,
  • Cisternal puncture, and
  • Ventricular puncture.
• Biochemical analysis of CSF is of diagnostic value in various diseases.
• Obstruction to the flow of CSF in the ventricular system leads to hydrocephalus in children and raised intracranial pressure in adult.

Choroid Plexus

Choroid Plexus Introduction: It is tuft of capillaries covered by pia mater and ependymal cells. They are lined simple, ciliated columnar epithelium present in the ventricles of brain

1. Gross anatomy
   
   • Site: Present at the site where pia mater and ependyma come close together.
   • Examples
     
     • CSF is mainly produced by choroid plexus of central part and inferior horn of lateral ventricle.
     • Roof of
       • 3rd ventricle.
       • 4th ventricle
   • Structure: It consists of minute tuft of capillaries covered by pia materependyma.
   • Age changes: Calcification of choroid plexus occurs in late age. It is present at the junction of body and inferior horn of lateral ventricle.
      
2. Choroid Plexus Blood supply
   Arterial supply:
   • Anterior choroidal artery, a branch of internal carotid artery.
   • Posterior choroidal artery, a branch of posterior cerebral artery.
   • Posterior inferior cerebellar artery (PICA), the largest branch of vertebral artery.
   • Venous drainage by choroid vein, combines with thalamostriate vein—to form internal cerebral vein > great cerebral vein > straight sinus > transverse sinus> sigmoid sinus.
3. Choroid Plexus Functions: Formation of cerebrospinal fluid by ultrafiltration.
4. Applied anatomy

• Hydrocephalus: It is caused by
  • Neural tube defect,
  • Meningitis,
  • Brain tumour, and
  • Choroid plexus tumour.
• Calcification of choroid plexus can be visualized by radiography, which is important in differentiating tumour of pineal gland.

Interpeduncular fossa

Interpeduncular fossa Introduction: It is a lozenge shaped space present between the cerebral peduncles of the midbrain.

1. Gross anatomy
   

• Shape: Rhomboid
• Boundaries

1. • Anteromedially: Optic chiasma shaped
   • Anterolaterally: Optic tract.
   • Posteriorly: Upper border of pons.
   • Posterolaterally: Crus cerebri.
   • Forms: Floor of IIIrd ventricle.
   • Contents: They are described from anterior to posterior.
     • Tuber cinerium: Slightly raised area of grey matter between mammillary body and optic chiasma.
       
     • Infundibulum: It suspends hypophysis cerebri.
     • Posterior perforated substance: It is grey matter perforated by
       • Posterior cerebral arteries, and
       • Inferior cerebellar arteries.
2. Interpeduncular fossa Relations
   
   • Anterolateral: Anterior cerebral artery.
     
   • Posterior: Posterior cerebral artery.
     
   • Posterolateral: Posterior communicating artery.
3. Applied anatomy

• Aneurysm of circle of Willis compresses optic chiasma and results into hemianopia.
• The pressure on hypophysis cerebri produces bitemporal hemianopia due to interruption of crossed nasal fibres.

Arachnoid granulations (pacchionian bodies)

Arachnoid granulations Introduction: These are finger-like projections, which project into dural venous sinuses. These are due to collection of arachnoid villi, which are the sites for the absorption of cerebrospinal fluid

1. Situation: They are situated along the sides of superior sagittal sinus, present on the medial border of parietal bone.
2. Arachnoid granulations Structures: These are small, granular bodies.
   Each arachnoid villus is a diverticulum in the subarachnoid space.
   It is covered by a thin cell layer which in turn is covered by endothelium of venous sinus.
   Age changes: It erodes the inner table of skull as the age advances.
3. Arachnoid granulations Functions
   • It is a main site for absorption of cerebrospinal fluid.
   • It allows cerebrospinal fluid to pass to the venous spaces.
   • It prevents reflux of blood.
4. Applied anatomy

• Clotting of blood in the superior sagittal sinus blocks these safety valves and causes rapid increase in cerebrospinal fluid.
• The granulations increase with the advance of age. The age of person can be roughly determined by presence of granulations.
• Congenital absence of the arachnoid granulations is observed in hydrocephalus.

Cisterna magna (cisterna medullaris) (Cisterna cavity, closed sac)

Cisterna magna Introduction: It is an enlarged subarachnoid space between the anteroinferior surface of cerebellum and posterior surface of medulla oblongata.

1. Shape: It is Relations lar in sagittal section
2. Cisterna magna Relations:
   • Anteriorly: Posterior surface of medulla oblongata.
   • Posteriorly: Anterior and inferior surface of cerebellum.
3. Cisterna magna Communications
   • It receives cerebrospinal fluid from
     • Roof of 4th ventricle (through foramen of Magendie).
     • Lateral recess of 4th ventricle (through foramina of Luschka).
   • It communicates
     • Inferiorly: With spinal subarachnoid space.
     • Anteriorly: With pontine cistern.
       
4. Applied anatomy

• Cisternal puncture: Cerebrospinal fluid can be tapped through the posterior atlanto-occipital membrane. It is rarely performed.
• Tumour in the space obstructs the circulation of CSF and results into hydrocephalus.