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Herniation or coning is said to be occurring when part of the brain is forced through a rigid hole.Herniation


Types of cerebral herniation. (A) uncal; (B) central; (C) transfalcial; (D) foraminal.

Fig. Types of cerebral herniation (Ref. Hari. 18th ed., Fig 274-1, Pg -2248)  


Figure - Major herniations of the brain: subfalcine, transtentorial, and tonsillar.

  1. Uncal herniation
    The uncus and the temporal lobe are forced through the cerebellar tentorium (tentorium that separates the cerebrum from the cerebellum)
    1. It causes
      Sequential compression occurs of the
      1. Ipsilateral third nerve  
      2. Contralateral brainstem (later)            
      3. Whole brainstem (eventually)
    2. Physical signs
      1. Early
        1. I/L dilated pupils
        2. Signs of supratentorial mass lesions
      2. Later
        1. I/L hemiplegia
        2. Progressive ptosis & third n palsy
        3. Cheyne- stokes respiration
      3. Still Later
        1. Tetraparesis
        2. B/L fixed dilated pupils
        3. Erratic respiration
        4. Death
  2. Central herniation
    The diencephalon i.e. the thalamus and related structures that lie between upper brainstem and cerebral hemispheres are forced through the tentorium
    1. It causes
      Sequential compression occurs of the
      1. Upper midbrain (first)           
      2. Pons (later)          
      3. Medulla (finally)
    2. Physical signs
      1. Early
        1. Erratic respiration
        2. Small reactive pupils
        3. Increased limb tone
        4. Bilateral extensor plantar
      2. Later:
        1. Cheyne stokes respiration
        2. Decorticate rigidity
      3. Still Later:
        1. Fixed dilated pupils
        2. Decerebrate posturing
  3. Cingulate Herniation –
    It occurs by frontal mass cingulate gyrus. (medial frontal lobe) is forced down under falx cerebri, later on ACA obstruction causing stroke and abulia (lack of decision).

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