CNS

Imaging in CNS
Pathology in CNS tumours
Primary IntraCranial Neoplasm
Pituitary
Spine

Epidemiology

  • CNS tumors —> 2% of Cancers
  • 15-34yr and 75-85yr

Clinical Anatomy

Central sulcus —> separates frontal lobe from parietal lobe
Sylvian fissure —> separates frontal and parietal lobes inferiorly from temporal lobe

Brain

  • Supratentorial
  • Infratentorial
  • Tentorium cerebelli:
    • An extension of the dura mater that covers the top of the cerebellum.
      • The top portion is called the supratentorium.
      • That below is known as the infratentorium.
  • Supratentorial location is frequent in adults.
  • Infratentorial location is frequent in children

Embryologically, the brain consists of

  • Prosencephalon (forebrain)—> will make (during the later stages of embryonic life):
    • Telencephalon(Two hemispheres)
      • Gives rise to olfactory bulb
      • Shell of grey matter = Cerebral Cortex.
      • White matter solely had neuronal pathways
    • Diencephalon (interbrain)
      • Situated between the cerebrum and the mesencephalon, adjacent to the third ventricle
      • Thalamus & the pineal region
        • Thalamus
          • Involved in integration of sensory functions
      • Lateral to the thalamus —> internal capsule
        • Carries the motor fibers (upper motor neurons) from the cortex en route to the brainstem and spinal cord
      • The thalamic structures surrounding the third ventricle
      • This is the part that links the two hemispheres of the brain.
  • Mesencephalon(midbrain)
    • Smallest part of the brain
    • A connection between the spinal cord and the neuronal pathways
    • Interior of mesencephalon
        • Tectum
          • Occupied by cranial nerve nuclei:
            • Oculomotor(CN III)
            • Trochlear(CN IV)
              • The only CN that exits from dorsal location
            • Proprioceptive portions of the trigeminal nerves(CN V)
        • Dorsal plate houses the superior and inferior colliculi
          • Regulate eye movements and hearing impulses, respectively. The trochlear nerve is the only cranial nerve that exits from this dorsal location.
    • Also contains important and vital functional cranial nerves
      • Oculomotor nerve(CN III)
      • Trochlear nerve(CN IV)
    • Nuclei
      • Nucleus ruber
      • Substantia nigra
  • Rhombencephalon (hind brain)
    • The pons
      • Bolbous midportion of brainstem
        • Between misbrain(sup) and medulla(inf)
      • The pons relays information between the two cerebellar hemispheres and from the spinal cord to the cerebellum
      • Carries the major ascending and descending pathways between the mesencephalon and the medulla oblongata
      • Contains the major motor and tactile sensory nuclei for the trigeminal nerve, which emerges from its lateral surface
      • Border between the pons and the medulla oblongata —> emergence following cranial nerves:
        • Abducens(CN VI)
        • Facial(CN VII)
        • Vestibulocochlear(acoustic-CN VIII)
      • Dorsal surface of the pons:
        • Forms rostral half of rhomboid fossa of 4th ventricle
      • Adjucent CSF cisterns:
        • Ant to pons
          • CN V & VI
        • Lat to pons
          • CN VII & VIII
    • Bulbus
      • The pons and the bulbus (also known as the medulla oblongata or simply “medulla”) contain important start and end nuclei for some cranial nerves.
    • Cerebellum
    • Fourth ventricle, is located between these three parts.

There are anatomically defined regions that have clearly associated neurological functions:

  • Primary motor : front of Central Sulcus
  • Primary sensory: behind Central Sulcus

=Rolandic cortex
Remember the homunculus? :)

  • Face Lateral
  • Legs Mesial
  • Speech and language in the frontal and temporal
    • Broca ( just above Sylvian Fissure )—> This fissure separates Frontal and Temporal
      • In Frontal lobe —> Motor Speech Area
    • Wernicke ( posterior end of Sylvian Fissure )
      • Superior Temporal Gyrus
    • Short Term Memory
      • Mesial part of temporal lobe(hippocampus and fornix)
    • Primary visual cortex
      • Medial and inferior surface at the occipital pole.

The medulla oblongata forms the link between the pons, the spinal cord, and the cerebellum. It houses the majority of the cranial nerve nuclei (abducens, facial, vestibulocochlear, glossopharyngeal, vagal, accessory, and hypoglossal).

Several anastomotic vessels (one anterior communicating artery and two posterior communicating arteries) produce communication between the anterior and posterior circulations and form the so-called circle of Willis. Although the degree of formation of a complete circle of Willis varies among individuals, this anatomic ring allows for bilaterally uninterrupted oxygen supply in case of local vascular obstruction.


Ventricular System

  • Develops by ballooning from the primitive neural canal
  • Lined with a specialized form of glia
    • Ependyma
  • CSF is produced by the choroid plexus
    • Choroid Plexus; lies in:
      • Roofs of 4th & 3rd ventricles
      • Medial walls of the central body
      • Inferior horns of the lateral ventricles
  • Foramina of Munro
    • Transmit CSF between 3rd and lateral ventricles at the superolateral corners of the third ventricle
  • Aqueduct of Sylvius
    • In the midbrain
    • Transmits CSF from 3rd to 4th ventricles
    • Narrowest canal of CNS
    • Most common location of obstruction of flow by compression or tumor deposits ==>Noncommunicating hydrocephalus
  • Foramen of Megndie
    • Midline
    • CSF in 4th ventricle flows out through this formane and formans of Luschka
  • Foramens of Luschka
    • Two formens
    • Lateral
    • CSF in 4th ventricle flows out through this and the midline foramen of Magendie

All three foramina are located in the roof and lateral corners of the fourth ventricle at the level of the medulla oblongata.

The subarachnoid space widens into several cisterns, the largest of which are the cisterna magna (posterior to the medulla oblongata at the foramen magnum), the cistern of the lateral sulcus bilaterally at the base of the brain, and the ambient cistern posterior to the midbrain. CSF resorption back into the venous system occurs at arachnoid (or Pacconian) granulations, special outpouching structures from the arachnoid membrane that enhance fluid movement from the CSF space into the venous sinus system. Scarring from infection or inflammation or clogging of the arachnoid granulations causes increased pressure in the CSF space and communication hydrocephalus.

Three membrane covering Brain and Spinal Cord:

  • Dura Matter
  • Pia Matter
  • Arachnoid
    • Leptomeninges (literally thin meninges) = Pia mater and Arachnoid mater
    • Dura matter and Pia matter sensitive to pain.

Cranial Nerves