Describe the various types of brain herniation, including their radiological and clinical features.

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College answer

1. Subfalcine (cingulate or transfalcine) 
•    This occurs when the brain extends under the falx cerebri. Radiological features include 
•    a shift of the septum pellucidum,  
•    effacement of the anterior horn of the lateral ventricle. Clinical features may be mild or absent, including  
•    headache,  
•    drowsiness,  
•    contralateral leg weakness. 
 
 
2. Uncal (or temporal transtentorial) 
•    The uncinate process or medial portion of the temporal lobe is displaced downwards onto the tentorium cerebelli and suprasellar cistern. 
Radiological features 
•    Shift of brainstem and distortion of adjacent cisterns 
•    Dilation of contralateral temporal horn 
•    PCA territory infarct due to compression of posterior cerebral artery as it crosses tentorium 
Clinical features include  
•    ipsilateral pupillary dilation and lack of reactivity to light and  
•    deviation of eye to “down and out position” due to pressure on the third cranial nerve.  
•    Compression of ipsilateral posterior cerebral artery results in ischaemia of ipsilateral visual cortex and contralateral visual field deficits in both eyes (contralateral homonymous hemianopia) 
•    There is also a decreased conscious level and  
•    There may be a contralateral hemiparesis due to the primary lesion causing the uncal herniation 
•    There may also be ipsilateral hemiparesis and leg extension (referenced to the side of herniation). This is referred to as a false localising sign due to compression of contralateral cerebral peduncle with corticospinal and some corticobulbar fibres 
(Kernohan‟s notch) 
•    Progression will lead to decreased conscious state, bradycardia, decorticate posture, respiratory depression and death 
 
3. Central  
•    Symmetrical downward movement of thalamus through tentorium cerebelli Radiological appearance: 
•    Peri-mesencephalic cistern effacement 
•    May be diffuse loss of grey-white matter differentiation  
Clinically  
•    Loss of consciousness with small reactive pupils and  
•    Paralysis of upward eye movements („sunset eyes‟) 
•    May progress to decorticate posturing 
•    Diabetes insipidus may be present 
 
4. Transcalvarial 
Brain squeezes through a fracture or surgical site in the skull Clinical features relate to side and lobe involved 
 
5. Infratentorial herniation 
6. Cerebellar Tonsillar (downward cerebellar herniation, transforaminal herniation) Cerebellar tonsils move downwards through the foramen magnum.  
Clinically causes 
• cardiac and respiratory depression. 
 
7. Upward transtentorial herniation or reverse coning 
•    Increased pressure in posterior fossa causing upward movement of cerebellum through tentorial notch with compression of midbrain, e.g. when CSF is abruptly drained above the level of the tentorium Clinical features 
•    Coma, respiratory depression, haemodynamic instability and death 

Additional Examiners' Comments: 
Many candidates had large knowledge gaps and were factually incorrect with their answers. Division between supratentorial and infratentorial herniation was fundamental to the question. Many candidates mixed uncal and cerebellar tonsil herniation and there was little mention of lateralising signs and general impact on conscious state. 

Discussion

The discussion of brain herniation elsewhere has a lot more detail than this, including explanations.

Herniation Radiological features Clinical features
Falcine
  • Displacement of the cingulate gyrus under the falx cerebri
  • Leg weakness
Midline shift
  • Midline shift of the septum pellucidum
  • A decreased level of consciousness, proportional to the degree of shift.
Uncal
  • Uncus and medial temporal lobe displaced medially
  • Effacement of the suprasellar cistern
  • The hippocampus obliterates the quadrigeminal cistern
  • midbrain effaced and displaced laterally
  • Ipsilateral fixed dilated pupil (3rd nerve palsy)
  • Decreased level of consciousness
  • Hemiparesis
  • Cortical blindness
Central tentorial
  • Obliteration of basal subarachnoid cisterns
  • Increased brainstem sagittal diameter 
  • Inferior displacement of the basilar artery
  • Coma​
  • Parinaud's syndrome:
  • Diabetes insipidus
Tonsillar
  • Cerebellar tonsil below the foramen magnum
  • Coma
  • Apnea
  • Hypertension
Upward
  • Flattened quadrigeminal cistern
  • "Spinning top" midbrain
  • Hydrocephalus
  • Coma
  • Miosis (reactive)
  • Absent or assymmetric doll's eye
  • Decerebrate posuring
Transcalvarial
  • Depends where the defect is
  • Depends where the defect is
     
     

References

References

Caron, Guy, et al. "Submental endotracheal intubation: an alternative to tracheotomy in patients with midfacial and panfacial fractures." Journal of Trauma and Acute Care Surgery 48.2 (2000): 235-240.

Barriot, P. A. T. R. I. C. K., and B. R. U. N. O. Riou. "Retrograde technique for tracheal intubation in trauma patients." Critical care medicine 16.7 (1988): 712-713.

Mohan, Raja, Rajiv Iyer, and Seth Thaller. "Airway management in patients with facial trauma." Journal of Craniofacial Surgery 20.1 (2009): 21-23.