2. Hydrocephalus, raise intracranial pressure & cerebral herniation

Question 1

Definition of hydrocephalus

Answer 1

Accumulation of excessive cerebrospinal fluid in the ventricular system

Question 2

Types of hydrocephalus

Answer 2

1. Obstructive (Non-communicating) Hydrocephalus

2. Non-obstructive (Communicating) Hydrocephalus

Question 3

Defintion of Obstructive (Non-communicating) Hydrocephalus

Answer 3

Only a portion of the ventricular system enlarged due to an obstructive lesion preventing the normal flow of CSF into the subarachnoid space
- Especially in the cerebral aqueduct of Sylvius (in the midbrain, connection between 3rd & 4th ventricles) which is the narrowest portion of ventricular system

Question 4

Causes of Obstructive (Non-communicating) Hydrocephalus

Answer 4

1. Tumours within the ventricular system
2. Scarring involving foramina of Luschka or Magendie at base of brain (e.g. tuberculous meningitis)
3. Haemorrhage (intracerebral or subarachnoid)

Question 5

Definition of Non-obstructive (Communicating) Hydrocephalus

Answer 5

Enlargement of entire ventricular system in the absence of an obstruction to CSF flow

Question 6

Causes of Non-obstructive (Communicating) Hydrocephalus

Answer 6

1. Loss of arachnoid granulations (congenital absence, subarachnoid scarring)
2. Normal pressure hydrocephalus (enlarged ventricles with only intermittently elevated CSF pressure due to decreased compliance of ventricular walls & increased viscosity of CSF)
3. Hydrocephalus ex vacuo (dilation of ventricles with compensatory increase in CSF volume following loss of brain parenchyma)

Question 7

Definition of raised intracranial pressure

Answer 7

An increase in mean cerebrospinal fluid pressure (normal in a supine adult = 7-15mmHg)

Question 8

Cause of raised intracranial pressure

Answer 8

1. Diffused conditions
   - Cerebral edema (infection, infarction or head injury leading to a disruption of the blood-brain barrier, resulting in increased vascular permeability)
   - Hydrocephalus
2. Localized conditions (space-occupying lesions)
   - Tumours
   - Haemorrhage/infarct
   - Cerebral abscess

Question 9

Pathological effects & complications of raised intracranial pressure

Answer 9

1. Clinical Features:
   - Vomiting, nausea, headache
   - Papilledema (swelling of optic disc)
2. Complications:
   - Decreased cerebral perfusion (vascular compression)
   - Cerebral herniation
   - Loss of consciousness, bradycardia, hypertension, neurogenic pulmonary edema

Question 10

Definition of cerebral herniation

Answer 10

Displacement of brain tissue in relation to rigid partitions (dural folds) & encasement (skull) of brain

Question 11

Types of cerebral herniation

Answer 11

1. Diencephalic Herniation
2. Subfalcine (Cingulate) Herniation
3. Transtentorial (Uncal) Herniation
4. Tonsillar herniation

Question 12

Diencephalic herniation

Answer 12

1. Descent of thalamus & midbrain through tentorial hiatus
2. Due to generalized swelling of both hemispheres with
   compression of ventricles

Question 13

Pathological effects & complications of diencephalic herniation

Answer 13

Tearing of branches of basilar artery

Question 14

Definition of Subfalcine (Cingulate) Herniation

Answer 14

1. Displacement of cingulate gyrus under the falx cerebri

2. Due to asymmetrical expansion of a cerebral hemisphere

Question 15

Pathological effects & complications of Subfalcine (Cingulate) Herniation

Answer 15

1. Often clinically silent
2. Hemorrhage & necrosis of affected segments
3. Compression of branches of anterior cerebral artery

Question 16

Definition of Transtentorial (Uncal) Herniation

Answer 16

Displacement of medial aspect of temporal lobe (uncus)

through tentorial cerebelli

Question 17

Pathological effects & complications of Transtentorial (Uncal) Herniation

Answer 17

1. Loss of consciousness
2. Oculomotor nerve palsy (papillary dilation, down-
   and-out gaze)
3. Cortical blindness (due to compression of posterior
   cerebral artery which supplies the primary visual
   cortex)
4. Hemiparesis ipsilateral to side of lesion (due to
   compression of contralateral cerebral peduncle, produces a cerebral peduncle indentation known as ‘Kernohan’s notch’)
5. Duret hemorrhages (hemorrhagic midline & paramedian lesions in midbrain & pons due to tearing of penetrating vessels)

Question 18

Definition of Tonsillar herniation

Answer 18

1. Displacement of cerebellar tonsils through the foramen magnum
2. Due to a space-occupying lesion in the posterior fossa

Question 19

Pathological effects & complications of Tonsillar herniation

Answer 19

1. Neck stiffness
2. Coning (fatal compression of pons & medulla with
   accompanying impairment of vital respiratory & cardiac centres)