Raised ICP

RAISED INTRACRANIAL PRESSURE

Pathophysiology

·         Normal intracranial pressure 5 to 15 mmHg in the adult at rest.

·         ICP varies with venous pressure and gravitational drainage and manoeuvres that raise intrathoracic pressure (coughing, Valsalva, positive pressure ventilation) or lower it (normal inspiration).

Aetiology of raised intracranial pressure

The principle causes of raised ICP are

·         Mass lesions,

·         Hydrocephalus and

·         Cerebral oedema.

The Monro–Kellie doctrine - the skull as a rigid container that encloses the brain, CSF and arterial/venous blood.

·         The addition of a new mass lesion initially be compensated for by the egress of CSF and venous blood from the skull.

·         During this compensation phase, there is only a small ↑ in ICP.

·         When compensation is maximal, there is then a rapid ↑ in ICP for relatively small ↑ in volume > compression and herniation of the brain

Cerebral oedema

·         Cytotoxic oedema - cerebral swelling as a result of cellular engorgement and can occur in both neurones and glia in response to insults such as ischaemia.

·         Vasogenic oedema - results from an accumulation of extracellular cerebral fluid, usually as a result of breakdown of the BBB and leakage of fluid through ‘leaky’ capillaries (commonly seen with tumours such as metastases, malignant gliomas and meningiomas)

Raised intracranial pressure and cerebrovascular physiology

·         Brain does not store much energy - unable to utilize anaerobic metabolism.

·         Dependent on a constant flow of O2 and glucose

·         In the absence of arterial blood flow, brain tissue will be viable for only a few minutes.

·         Cerebral autoregulation - In normal circumstances, is maintained CBF at a constant rate despite fluctuations in mean arterial pressure (MAP) of between 50 and 150 mmHg.

·         These mechanisms include neural regulation (via aortic and carotid baroreceptors) and local factors ( arteriolar responsiveness to O2 and CO2).

·         MAP ↑ > ICP ↑, MAP ↓ > ICP ↑

·         Cerebral perfusion pressure (CPP)=MAP – ICP.

·         An poor prognostic factors = ICP of >20–25 mmHg or a CPP of < 60 mmHg.

Cerebral herniation

·         Sub-falcine herniation - shift of the cingulate gyrus of one hemisphere under the falx cerebri and across to the contralateral side.

·         Uncal herniation - shift of the medial temporal lobe (uncus) medially towards the tentorial hiatus > 3^rd  nerve is stretched > dilatation and fixation of the ipsilateral pupil ± a rapidly progressive contralateral hemiparesis as pressure is exerted on the ipsilateral cerebral peduncle.

·         Tentorial herniation - downwards shift of midbrain structures through the tentorial hiatus.

·         Tonsillar herniation - downwards shift of the cerebellar tonsils and medulla through the foramen magnum - death due to compression and/or ischaemia of the cardiorespiratory centres.

Clinical features

·         Headaches (to be worse in the early morning or on lying down)

·         may be exacerbated by coughing, straining or bending

·         Associated symptoms - nausea, vomiting or visual disturbance (double vision or blurred vision).

·         Symptoms relevant to the location of the pathology- eg: cognitive and personality change, unsteadiness of gait and incontinence of urine in frontal lobe pathology

·         As ICP ↑ further > lethargy or drowsiness f/b unconsciousness and coma

·         Raised ICP may be associated with papilloedema on fundoscopy

·         Diplopia due to a 6^th  nerve palsy

·         There may be abnormalities of conjugate gaze. In particular, impaired upgaze or sun-setting may be seen as part of Parinaud’s syndrome, caused by pressure on the dorsal midbrain.

Treatment

Medical

·         Mannitol is an osmotic diuretic that can be used in emergency settings to reduce ICP: the dose is 0.5–1.0 g kg-1.

·         Vasogenic oedema - high-dose steroids in the form of dexamethasone ( example 8 mg Bd)

·         Steroids ↓ the permeability of the BBB and are useful in reducing cerebral swelling prior to definitive treatment

·         A carbonic anhydrase inhibitor ( acetazolamide )↓ ICP by ↓ CSF production.

Surgical

·         Trauma - acute EDH,SDH, intracerebral contusions and chronic subdural haematomas;

·         CVS - Haematomas associated with ruptured aneurysms;

·         Neuro-oncology -   a variety of primary and secondary tumours.

·         Surgical control by a large bony decompression (craniectomy), such as in traumatic brain injury or extensive middle cerebral artery (MCA) infarction.

Hydrocephalus

Discuss about aetiology , investigation and management of hydrocephalus.

Definition An increase in the volume of cerebrospinal fluid (CSF) occupying the cerebral ventricles secondary to either impaired absorption or, less commonly, increased production of fluid.

Types of Hydrocephalus

Communicating This implies communication between the ventricles and the subarachnoid space. Usually due to ↑CSF production, occasionally due to ↓absorption or ↓drainage

Non-communicating CSF flow obstructed within the ventricles or between the ventricles and the subarachnoid space.

Normal pressure hydrocephalus The CSF pressure remains normal or is only intermittently raised. Failure to reabsorb the CSF is compensated by ↓ production. The condition may be congenital (+ myelomeningocoele or –myelomeningocoele [infantile hydrocephalus]) or acquired.

Hydrocephalus ex vacuo This is seen in conditions associated with cerebral atrophy and shrinkage, such as Alzheimer's Disease and Pick's Disease. The ventricles expand and there is no increase in CSF pressure.

Aetiology

·         Congenital hydrocephalus prevalence 82 per 100,000 live births

·         Acquired hydrocephalus incidence is unknown.

Causes

Congenital causes in infants and children

·         Stenosis of the aqueduct of Sylvius

·         Dandy-Walker malformation/Arnold-Chiari malformation type 1 and type 2

·         Agenesis of the foramen of Monro

·         Congenital toxoplasmosis

·         Bickers-Adams syndrome (stenosis of the aqueduct of Sylvius, severe mental retardation, and in 50% by an adduction-flexion deformity of the thumb)

Acquired causes in infants and children

·         Mass lesions (20% of all cases in children, e.g. medulloblastoma, astrocytoma)

·         Intraventricular haemorrhage (e.g.prematurity, head injury, or rupture of an AVM)

·         Infections - meningitis, cysticercosis in some areas

·         ↑Venous sinus pressure - related to achondroplasia, craniostenoses, venous thrombosis

·         Iatrogenic - e.g. hypervitaminosis A

·         Idiopathic

Causes of hydrocephalus in adults

·         Subarachnoid haemorrhage

·         Idiopathic (one third of cases)

·         Head injury

·         Tumours

·         Iatrogenic - posterior fossa surgery

·         Congenital aqueductal stenosis (may not be symptomatic until adulthood)

·         Meningitis, especially bacterial

·         Normal pressure hydrocephalus

·         All causes of hydrocephalus described in infants and children

Investigation

(1)   CT scan  - may be detected ventricular size, generalized cerebral atrophy or localized neuronal cell loss

(2)   MRI scan of brain can provide better anatomical detail of lesions and useful in diagnosis of aqueduct stenosis 

(3)   ICP monitoring with parenchymal probe if shunt dysfunction is suspected

(4)   Lumbar puncture may be both diagnosis and therapeutic in communication hydrocephalus

Management

(a)   Medical treatment

·         Drugs - Temporizing measure: Frusemide and acetazolamide ↓secretion of CSF. Isosorbide ↑absorption.

(b)   Surgical

·         Treat the underlying cause The cure rate is 80% if a tumour can be identified.

·         Repeated lumbar punctures is only valid in communicating hydrocephalus.

·         Insertion of a ventriculoperitoneal shunt – may be done by insertion of catheter into lateral ventricle ( usually right frontal or occipital )and then connected to a shunt valve under scalp,which is tunneled subcutaneously down to peritoneal cavity.

Credit to – Dr Win Htet Ko

·         Other surgical procedures Choroid plexectomy, choroid plexus coagulation, and endoscopic

·         Cerebral aquaductoplasty. Endoscopic fenestration of the 3rd ventricle floor in non-communicating hydrocephalus.