What structures are affected with transtentorial herniation?
Herniation of uncus of temporal lobe through tentorial hiatus causing compression of:
- CN3 (ipsilateral mydriasis)
- Midbrain (hemiparesis, Cushing's reflex, resp failure)
- Posterior cerebral artery (hemianopia)
Signs and sxs of increased ICP
Drowsiness (most important!)
AM nausea relieved by vomiting
Papilledema (blurred disc margins)
Most common causes of communicating hydrocephalus
Infection and subarachnoid hemorrhage
Uncommon: carcinomatosis, increased CSF viscosity, choroid plexus papilloma
Most common causes of pediatric hydrocephalus
Congenital: stenosis of aqueduct of Sylvius (esp. children with spina bifida)
Acquired: intracranial bleeding (e.g. IVH) in premature infants, meningitis, tumors
Common complication after resolution of hydrocephalus
Subdural hematoma 2/2 tears in bridging veins after brain parenchyma falls aways from cranial vault
10-15 mmHg (measured at position equal to level of foramen of Monro) with variation of 3-5 mmHg 2/2 cardiac and respiratory variation
If craniospinal intradural space is nearly constant in volume and its contents are nearly incompressible, an increase in the volume of one of the constituents will lead to a rise in ICP
Why does small increase in volume of intracranial contents cause no rise in pressure?
Small amount of CSF can move into spinal subarachnoid space
Define compliance and elastance of intracranial space
Compliance - amount of 'give'
Elastance - inverse of compliance; resistance offered
What is 'autoregulation' of cerebral blood flow?
Brain maintains constant cerebral blood flow between physiological ranges in BP by adjusting intracranial vascular resistance
What is normal cerebral blood flow?
800 mL/min or 20% of cardiac output
Cerebral blood flow and cerebral perfusion pressure equations; what is the implication?
CBP = CPP / CVR
CPP = MAP - ICP
To maintain cerebral perfusion in setting of raised ICP, systemic BP needs to be elevated
Signs/sxs of herniation of cerebellar tonsils into foramen magnum
Compression of medulla causes neck stiffness (2/2 irritation of dura around foramen), rapid respiratory failure, abrupt limb paresis and sensory disturbance
'Coning' of brainstem leads to shearing of vessels supplying the brainstem
'Coning' of brainstem
Herniation of brainstem into foramen magnum; can cause traction damage to pituitary stalk leading to DI and often death
What is subfalcine herniation?
Cingulate gyrus herniates below falx cerebri
Common causes of raised ICP
Space-occupying lesion (e.g. tumor, abscess, hematoma), hydrocephalus, benign intracranial HTN
Cushing's reflex or response
HTN with bradycardia
'False localizing' sign of increased ICP
Stretching of CN6 by caudal displacement of brainstem causing diplopia
Major complication from ICP monitoring
Infection; directly proportional to duration of monitoring
2 major types of ICP abnormalities
1. Elevation of baseline ICP
2. Development of pressure waves
Tx of raised ICP
Definitive - removing the cause
Temporary - maintain ventilatory state, hyperventilate, diuretics (mannitol or furosemide)
Abnormal enlargement of ventricles 2/2 excessive accumulation of CSF from disturbance of flow, absorption, or secretion (uncommon)
Lateral ventricles > foramen of Monro > 3rd ventricle > aqueduct of Sylvius > 4th ventricle > foramina of Magendie and Luschka > subarachnoid space (including spinal) and basal cisterns > through tentorial hiatus > over cerebral hemispheres
Where is CSF produced? Reabsorbed?
Produced by choroid plexus of lateral ventricles; absorbed by arachnoid villi of dural sinuses
Obstructive vs. communicating hydrocephalus
Obstructive - obstruction of flow through ventricular system
Communicating - either obstruction of flow outside ventricular system (e.g. through basal cisterns) or failure of absorption by arachnoid granulations
Congenital atresia of foramen of Luschka and Magendie causing hydrocephalus
Clinical features of hydrocephalus in infants
Failure to thrive, increased skull circumference, tense anterior fontanelle, 'cracked pot' sound on skull percussion, transillumination of cranial cavity with strong light, thin scalp with dilated veins, 'setting sun' appearance
What is meant by 'setting sun' appearance in infants with hydrocephalus?
3rd ventricular pressure on superior colliculus of midbrain tectum causes lid retraction and impaired upward gaze
Why do patients with gradual-onset hydrocephalus develop visual failure?
Papilledema causing optic nerve atrophy