Elective neurosurgery

ELECTIVE NEUROSURGERY

Dr Tridip Dutta BaruahAsst Prof, Dept Of Surgery

MGMCRI

Objectives

To understand and know:

The physiology of CSF production and understand the sign and symptoms of raised ICP

The pathophysiology of hydrocephalus and its treatment

Intracranial Pressure Intracranial pressure is the pressure inside the skull and thus

in the brain tissue and cerebrospinal fluid.

Normal ICP varies from 5 to 15 mmHg in the adult at rest.

ICP varies with venous pressure and is thus affected by factors such as gravitational drainage an manoeuvres that raise intrathoracic pressure .

Normal values in small children and infants are lower than for adults.

Raised intracranial pressure

Results in reduced cerebral perfusion and brain herniation

The major causes of raised ICP are haematomas, tumours and hydrocephalus

Pathophysiology Of Raised ICPThe Monroe Kellie Hypothesis: It is the pressure volume relationship between ICP, volume of CSF, brain tissue and Cerebral Perfusion Pressure. The hypothesis states that cranium is incompressible and

the volume inside the cranium is fixed. The addition of a new mass lesion can initially be

compensated for by the egress of CSF and venous blood from the skull. During this compensation phase, there is only a small increase in ICP.

When compensation is maximal, there is then a rapid rise in ICP. This increased pressure causes compression and herniation of the brain

Raised ICP and Cerebrovascular Physiology

The brain does not store much energy and is unable to utilise anaerobic metabolism.

Cerebral Perfusion Pressure=MAP – ICP In normal circumstances, cerebral blood flow is

maintained at a constant rate despite fluctuations in mean arterial pressure (MAP) of between 50 and 150 mmHg via mechanisms termed cerebral autoregulation.

In the injured brain, cerebral autoregulation may be impaired either locally or globally.

Cerebral HerniationSub-falcine herniation refers to shift of the cingulate gyrus of one hemisphere under the falx cerebri .Uncal herniation refers to shift of the medial temporal lobe(uncus) medially towards the tentorial hiatus.Tentorial herniation refers to a downwards shift of midbrain structures through the tentorial hiatus. Tonsillar herniation refers to a downwards shift of the cerebellar tonsils and medulla through the foramen magnum. This type of herniation is associated with death.

Cerebral Herniation

Symptoms Of Raised ICP

Headache Early morning: Worse on lying down Nausea and vomiting Visual blurring or double vision Drowsiness

Signs Of Raised ICP

Pappiloedema

Sunsetting Sign

Copper Beating Skull

Treatment Of Raised ICPAppropriate treatment depends on identifying the cause.

Medicali) Mannitol : osmotic diuretic ii) High-dose steroids. Steroids reduce the permeability of the blood–brain barrier.iii) carbonic anhydrase inhibitor such as Acetazolamide.

Surgicali) Craniotomy: in trauma, acute extraduraland subdural haematomas, intracerebral contusions and chronicsubdural haematomas.ii) Occasionally, surgical control of ICP will involve a largebony decompression (craniectomy), such as in traumatic braininjury or extensive middle cerebral artery (MCA) infarction

Hydrocephalus

Hydrocephalus is a condition in which there is disequilibrium between CSF production and absorption, leading to raised ICP, and is often associated with dilated ventricles.

Not all patients with ventriculomegaly have hydrocephalus and not all patients with hydrocephalus necessarily have enlarged ventricles.

It can be Obstructive or comunicating.

Cerebrospinal Fluid Physiology

The total CSF volume in an adult is about 150 ml. CSF production occurs at a rate of approximately 0.33 ml per min

or 450 ml per day, resulting in a turnover of three volumes per day. CSF production is primarily by the choroid plexus of the ventricles

and is an active process independent of ICP. CSF flows from the lateral ventricles, through the foramen of

Munro, into the third ventricle and then into the cerebral aqueduct and fourth ventricle before exiting into the subarachnoid space via the midline foramen of Magendie and lateral foramina of Lushka.

CSF absorption is a pressure-dependent passive process involving filtration across the arachnoid villi, which are abundant along the superior sagittal sinus into which the CSF is absorbed.

CSF Pathway

Aetiology

Hydrocephalus

Hydrocephalus

Hydrocephalus

Hydrocephalus

Investigations Lumbar puncture is contraindicated in obstructive hydrocephalus

because of the risk of causing tonsillar herniation and death. Ventricular size can be assessed with a computerised tomography

(CT) scan of the brain. The ventricles may be enlarged as a result of generalised cerebral atrophy or localised neuronal cell loss (ex vacuo dilatation) as well as by hydrocephalus.

In children, chronic raised ICP can result in copperbeating of the skull.

A magnetic resonance imaging (MRI) scan of the brain can provide better anatomical detail of lesions causing hydrocephalus and is particularly useful in the diagnosis of aqueduct stenosis.

Investigations ICP monitoring with a parenchymal probe placed into the frontal

lobe via a twist drill burrhole is a useful diagnostic tool for patients in whom hydrocephalus or CSF shunt dysfunction is suspected.

In communicating hydrocephalus, a lumbar puncture may be both diagnostic, by measurement of opening pressure, and therapeutic, by draining a volume of CSF that allows the closing pressure to be within normal limits.

In the diagnosis of normal pressure hydrocephalus, other diagnostic procedures include the CSF tap test and CSF infusion studies.

Management

Management of hydrocephalus will depend on the underlying cause. Options include Removing a causative mass lesion Ventricular shunting or third ventriculostomy. Removing a causative mass lesion

External Drains

External drains can be placed within the ventricle (EVD) or the lumbar thecal sac (lumbar drain).

These are useful for temporary CSF drainage and can be used to administer intrathecal antibiotics to treat CSF infection.

Removing Causative Mass Lesion Intracranial mass lesions may present with

obstructive hydrocephalus.In some circumstances it may be appropriate to treat the hydrocephalus by tumour removal and decompression of the CSF pathways.

In other cases, such as a patient who presents with an impaired conscious level secondary to obstructive hydrocephalus, it may be appropriate to treat the hydrocephalus with an EVD or ventriculoperitoneal shunt and allow the patient to recover before undertaking tumour surgery.

Ventriculoperitoneal shunt

A ventriculoperitoneal shunt involves the insertion of a catheter into the lateral ventricle (usually right frontal or occipital).

The catheter is then connected to a shunt valve under the scalp and finally to a distal catheter, which is tunnelled subcutaneously down to the abdomen and inserted into the peritoneal cavity.

If the CSF pressure exceeds the shunt valve pressure, then CSF will flow out of the distal catheter and be absorbed by the peritoneal lining.




Complications Of VP Shunt Most common complications include shunt blockage and

infection. Approximately 15–20% of shunts are revised withinthe first 3 yrs.

Shunt blockage may affect the ventricular catheter, shunt valve or distal catheter. Causes of blockage are choroid plexus adhesion, blood, cellular debris or misplacement of the distal catheter in the pre-peritoneal space.

Shunt infection affects between 1% and 7% of shunt insertions and is usually caused by skin commensals, such as Staphylococcus epidermidis. Most infections become apparent clinically by 6 weeks and over 90% are apparent within 6 months. Treatment is by removal of the shunt, external CSF drainage and treatment of infection prior to re-insertion of the shunt at a different site

Endoscopic Third Ventriculostomy ETV involves the insertion of a neuroendoscope into the frontal horn

of the lateral ventricle and then into the third ventricle through the foramen of Munro. A stoma can be created in the floor of the third ventricle in between the mamillary bodies and infundibular (pituitary)recess.

CSF can then communicate freely between the ventricular system and interpeduncular subarachnoid space. It is useful when there is obstruction of the CSF pathways below the third ventricle such aqueduct stenosis or posterior fossa mass lesions.

Advantage over shunting in that no tubing is left in the patient and so infection rates are lower. ETVs may block off, however, with about one-half of these patients ending up with a shunt. Rare, but serious, complications include basilar artery rupture or memory impairment from injury to the fornix.

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Elective neurosurgery