Neurosurgeon

Vascular neurosurgery

I work in close association with the Department of Neuroradiology at Royal Perth Hospital, a world class unit greatly experienced in the diagnosis and treatment of neurovascular problems.

Vascular neurosurgery involves aneurysms, AVMs and carotid endarterectomy.

These days, many vascular lesions can be fixed without surgery... e.g. coiling of aneurysms. Sometimes a combination of neuroradiological and surgical techniques are used... e.g. particularly treatment of arteriovenous malformations that can be partly occluded by a neuroradiologist prior to surgery.

If a vascular problem is complex it will be operated at Sir Charles Gairdner Hospital rather than at the Mount Hospital because SCGH has certain equipment that may be needed for a complex vascular case... e.g. intraoperative angiography involves obtaining an angiogram (picture of the brain blood vessels) during surgery.

Aneurysms An aneurysm is a blister that has developed in the wall of a blood vessel. In neurosurgery this means a blister in the wall of an artery within the skull, situated in the subarachnoid space over the surface of the brain. This means that rupture will be into the subarachnoid space, called a subarachnoid haemorrhage. Children rarely have aneurysms but about 1% of the adult population has an aneurysm. The risk of rupture is about 1% per year but this very much depends on the size and position of the aneurysm (see below). The annual risk of aneurysm rupture is: Size Most aneurysms Posterior circulation aneurysms (rare) <7mm 0.1% 2.5% 7-12mm 2.6% 14.5% 13-24mm 14.5% 18.4% >25mm 40% 50%

The significance of an aneurysm is that once it ruptures, it tends to rerupture again and again. Each rupture carries a high risk of death or neurological deficit. About 15% of ruptures result in sudden death. About half of survivors either die or have a poor outcome if left untreated.

Aneurysms are usually asymptomatic until they rupture. Occasionally they may cause headache or press on a nerve to draw attention to them but usually they are discovered after they have burst. It is not uncommon for them to be discovered in the course of investigation by CT or MRI for an unrelated problem.

Once ruptured, an aneurysm must be fixed to prevent another rupture.

There are two types of treatment:

1. coiling, which means insertion of extremely fine metal wires into the aneurysm at the time of angiography, done entirely through a fine tube (catheter) inserted into a groin artery.

2. clipping, involving a craniotomy (skull opening) and direct placement of a small clip (like a peg) on the aneurysm to obliterate it under a microscope.

It is preferable to coil an aneurysm because this avoids a brain operation and recovery is quicker. Nowadays, about three-quarters of aneurysms are amenable to coiling. In Perth, coiling is only done at Sir Charles Gairdner and Royal Perth hospitals but the surgery can be done at The Mount, Royal Perth or Sir Charles Gairdner hospitals.

Regardless of how the aneurysm is treated, certain complications of rupture can develop:

1. vasospasm is contraction or spasm of arteries after they have been surrounded by blood. This can cause a blockage of blood flow to the brain to cause a stroke or even death. There are various ways to prevent and treat vasospasm including increasing the blood pressure with drugs and intravenous fluids or angiography to directly expand the contracted artery (called angioplasty) or inject drugs to dilate the artery.

2. hydrocephalus means excess water in the brain due to blood in the subarachnoid space blocking the circulation of cerebrospinal fluid (CSF). This is treated by a tube placed directly into the ventricles (fluid chambers of the brain) draining to an external bag, or a shunt, which involves tubing kept entirely within the body to drain CSF into the peritoneal cavity of the abdomen.

3. epilepsy is a fit or seizure which can occur any time - from the time of rupture, usually in the first few days, to many months later. This is treated with drugs.

Top

Arteriovenous Malformations (AVMs)

The problems that an AVM nidus can cause are: 1) rupture, causing bleeding into the brain and/or over its surface 2) epilepsy (seizures or fits) 3) progressive neurological deficit - e.g. weakness 4) headache, particularly migraine - please note that the vast majority of migraine is not due to an AVM The most serious complication is rupture. The risk of this is about 4% per year. Treatment 1) Surgery (removal) remains the gold standard treatment, but not all AVMs are best suited for this. 2) Radiotherapy specifically called stereotactic radiosurgery. This involves the placement of a frame on the head followed by a CT and/or MRI (and sometimes an angiogram). A computer works out the best way to deliver a single shot of high intensity x-rays to destroy the AVM. The advantage of this treatment is that it is done over one day as an outpatient procedure. About 80% of AVMs treated in this manner will be destroyed within two years. This treatment is only suitable for AVMs about 3cm or smaller.

3) Embolization meaning cerebral angiography, with the introduction of various materials into the AVM to block it. In Western Australia this is performed only at Royal Perth Hospital. Embolization is usually done prior to surgery and rarely is a cure by itself.

4) If the AVM is considered too great a risk to be treated by any of the above measures, it is simply observed and treated symptomatically - e.g. medication for seizures or for migraine.

Top

Trigeminal neuralgia Trigeminal neuralgia is also known as tic douloureux. It affects the trigeminal (fifth cranial) nerve, which supplies feeling to one side of the face (figure 1). It tends to come on in later years, occurring in episodes which become more frequent and severe with time, with intervals of no pain. The pain is typically described as an electric shock and most often affects the lower or upper jaw, occasionally the forehead. It can be precipitated by touching these areas, chewing, talking, etc. Causes In most cases the cause is a loop of an artery, less often a vein, contacting the trigeminal nerve. In a few percent of cases the cause is a tumour (usually benign), which is why all patients should have an MRI scan. If a tumour is found, surgery is usually advised.

1) Medications usually help. The most effective is carbamazepine (Tegretol), which almost always gives some relief. Patients can be well maintained on this drug for many years. The most common reason to cease this medication is because of a rash or because of excessive sedation and unsteadiness. Other medications include phenytoin, gabapentin, pregabalin, lamotrigine and clonazepam.

2) Injections - there are four types:

(i) alcohol injection into a branch of the trigeminal nerve in the face. This is rarely done and is reserved for frail patients.

(ii) radiofrequency (RF) injection involves a general anaesthetic but the patient is woken up in the middle of the procedure to see that the needle is in the correct position. This involves passing a long needle through a hole in the base of the skull and into the trigeminal ganglion, which is where the three branches of the trigeminal nerve join before the nerve enters the brain stem. The needle position is varied until the patient reports that tingling on the face is in the area of the pain. Subsequently, the patient goes back to sleep and the trigeminal ganglion is heated. This procedure lasts for several months but usually has to be repeated. A very rare complication is called anaesthesia dolorosa where the entire side of the face becomes number and painful. This condition is very difficult to treat.

(iii) balloon compression is done completely under general anaesthesia. A needle is passed as for a RF injection. A small balloon is passed through the needle into the trigeminal ganglion and then blown up to compress the ganglion. This "stuns" the ganglion and can give several months of pain relief. Again, this procedure often has to be repeated. (iv) glycerol injection can also be done without the patient being awake. I do not perform this procedure but it is about as effective as (ii) and (iii). It involves an injection of glycerol around the trigeminal ganglion. This also usually has to be repeated in a year or two. 3) Microvascular Decompression involves a small craniotomy (see craniotomy) behind the ear. There is only a minimal hair shave. Under a microscope the offending blood vessel is separated from the trigeminal nerve and kept permanently away by a pad of cotton wool.

The main risks of the procedure are:

(i) deafness on that side, which is why the procedure is not recommended if there is poor hearing in the opposite ear. This can occur because the hearing nerve (cranial nerve 8) is very close to the trigeminal nerve.

(ii) double vision can occur because the 4th cranial nerve is close by. It controls movement of the eye inward and downward and therefore damage to it results in difficulty reading or looking while going down stairs.

(iii) cerebrospinal fluid (CSF) leak can occur through the wound or, surprisingly, through the nose via a communication through the middle ear. This usually requires repeat surgery to close the leak.

(iv) stroke (paralysis down one side of the body) is rare and occurs in about 1% of cases.

(v) infection occurs in 1-2%.

(vi) facial numbness is usually not a problem.

(vii) facial weakness is rare.

(viii) recurrence of pain can occur in up to about 20% over the next 5 to 10 years.

Trigeminal Neuralgia Support Group (WA Inc)

Trigeminal Neuralgia Association

Hemifacial spasm

Hemifacial spasm is the same condition as trigeminal neuralgia but affects the facial (7th cranial) nerve, which supplies movement of half of the face. The irritated facial nerve produces painless twitches of the face, usually commencing around the eye and later affecting the lower face. Although seemingly minor, patients find the condition very annoying and embarrassing.

Tablets are of little use but botox (botulinum toxin) is the standard first line treatment involving injection of this drug into the facial muscles by a neurologist. These injections need to be repeated every three to six months and are expensive. If the injections are unsatisfactory, surgery is very effective, again separating the offending blood vessel from the nerve.

Hemifacial Spasm Association

Top

Hydrocephalus

Hydrocephalus means "water on the brain". Cerebrospinal fluid (CSF) is the fluid made within the brain from small, cauliflower-looking organs called the choroid plexus.

The choroid plexus is contained in each of the four cavities of the brain called ventricles. CSF leaves the ventricles through holes in the 4th ventricle to circulate out onto the surface of the brain and around the spinal cord (in the subarachnoid space) to eventually drain into a large vein under the skull called the superior sagittal sinus (SSS).

Hydrocephalus develops if there is an obstruction anywhere between the site of production in the ventricles and the SSS. Broadly speaking, hydrocephalus develops because of obstruction: 1. within the brain causing obstruction of the ventricles, usually due to tumours; or 2. over the surface of the brain within the thin space called the subarachnoid space, due to trauma, infection and spontaneous subarachnoid haemorrhage (e.g. from a ruptured aneurysm).

There are two types of treatment: 1. shunt surgery involving the insertion of a tube into a ventricle, draining off CSF into another body chamber, usually the abdomen but sometimes into the heart or pleural cavity around the lungs. The most common site of drainage is into the peritoneal cavity, which is within the abdomen, and is called a ventriculoperitoneal (or V-P) shunt; or, 2. third ventriculostomy which involves creation of a hole between the 3rd ventricle and the subarachnoid space to bypass an obstruction within the brain. This doesn't involve implantation of any foreign material and is preferable to shunt surgery if the patient is suitable, but only about 10-20% of hydrocephalus cases can respond to this type of surgery. 3rd ventriculostomy is a simpler form of surgery requiring only a small burrhole behind the hairline and it blocks much less often than shunts, rarely gets infected and rarely causes overdrainage.

Top

Chiari malformation

There are a number of types of Chiari malformation, which basically means that the cerebellum has descended (or herniated) down through the skull base into the spinal canal. This compresses the junction of the brain stem (within the skull) and the spinal cord (within the spinal canal). The most common type is called type I and is described below.

This image demonstrates the normal situation on the left, viewed from the patient's left. In the right diagram the cerebellum has descended into the spinal canal, viewed from the patient's right.

A Chiari I malformation may cause the following problems:

• Headache, particularly with coughing or straining.

• A syrinx within the spinal cord, meaning a cystic collection of fluid within the spinal cord. This can cause many types of symptoms in the arms or legs ... e.g. numbness, weakness, muscle wasting, pain, difficulty walking.

• Scoliosis (curvature) of the spine, which develops because of a syrinx.

• Difficulty swallowing, breathing or speaking due to direct pressure on the brain stem in front of the cerebellum.

The treatment is surgical and must be performed once the diagnosis is made. Otherwise, the condition can deteriorate irreversibly.

Surgery basically involves removal of the occipital bone from the back of the lower part of the cerebellum, plus laminectomies (see Spine section) of the upper cervical vertebrae, so that there is less pressure at the top of the spinal canal. The analogy is that of a cork in a bottle. The cork is not removed but the bottle neck is widened (pictured to right).

Top

Arachnoid cyst An arachnoid cyst is a collection of spinal fluid (cerebrospinal fluid or CSF) next to the brain or spinal cord (figure 1). Most are asymptomatic. The brain and spinal cord are surrounded by CSF and three layers, which are called the meninges. One would be aware of the condition called meningitis where the lining of the brain and spinal cord is inflamed. The outermost layer of meninges is called the dura (or dura mater), which is a thick, tough layer. Inside the dura is a delicate layer called the arachnoid, which is likened to a spider web. Inside the arachnoid is the pia, which intimately covers the brain and spinal cord. The CSF is between the arachnoid and pia, in a space called the subarachnoid space (figure 2).

An arachnoid cyst forms when there is a duplication of the arachnoid layer trapping CSF within. CSF is able to enter the cyst but has difficulty escaping, resulting in a slow enlargement of the cyst. If symptoms occur it is usually headache. Neurologic deficit is rare. Treatment is often not required. If symptoms are thought to be due to the cyst, there are two surgical options:

1) Fenestration involves directly puncturing the cyst and widely opening it into the adjacent subarachnoid space to allow the CSF to flow freely. This usually results in a cure.

2) Shunting involves inserting a tube into the cyst and tunneling the tube into the abdomen for drainage, as for hydrocephalus. I have never performed this procedure for an arachnoid cyst and do not recommend it.

Top

Subdural haemorrhage (SDH)

Subdural haemorrhage, or haematoma (meaning a lump of blood), means a collection of blood in the subdural space. The three layers of the brain, spinal cord and nerves are called the meninges.

Figure 1 to the left shows a subdural haematoma. The yellow arrows indicate blood (greyish white material) between the skull (white) and brain (grey). The outermost layer of meninges is called the dura (or dura mater), which is a thick, tough layer. Inside the dura is a delicate layer called the arachnoid, which is likened to a spider web. Inside the arachnoid is the pia, which intimately covers the brain and spinal cord. The CSF is between the arachnoid and pia, in a space called the subarachnoid space (figure 2). If the SDH is fresh it is called acute. An acute SDH is clotted blood and needs a craniotomy (or bone flap) to remove it because it cannot be sucked out through a simple burrhole (hole drilled into the skull, about 1cm wide). A chronic SDH is blood that has developed slowly and which liquefies. A chronic SDH can be drained through one or two burrholes.

An acute SDH usually occurs following serious head injury with bleeding from torn blood vessels and brain, but may be secondary to a torn artery or vein on the surface of the brain, and is the sort of bleeding that can occur after brain surgery. Chronic SDH usually occurs from a torn vein on the surface of the brain. The bleeding is slow and takes days or weeks to accumulate. It can result from a minor head knock and is particularly likely in people on blood thinning drugs such as warfarin. Chronic SDH results in headache, drowsiness, confusion, seizures or weakness down the opposite side of the body.

Top