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Aneurysm treatment

ENDOVASCULAR TREATMENT OF CEREBRAL ANEURYSMS

An aneurysm in an abnormal bulging of the wall of artery in outward direction. It can be either fusiform (where wall bulges in all direction giving a spindle shape) or saccular (where only one wall bulges outward). Aneurysm can occur from any blood vessel in the body. In this section we will discuss about the aneurysms arising from blood vessels of the brain.

Since the wall of the artery is weak where aneurysm has formed, they have tendency to rupture.When the aneurysm in the brain ruptures, it results in bleeding in the brain especially in the subarachnoid space in the brain. Smaller the aneurysm, more the chances of rupture. Once the aneurysm ruptures, bleeding in the brain presents as sudden acute headache in the patient which he/she describes as the “worst headache of life”. Headache could be associated with vomiting, neck stiffness and loss of consciousness also.

Rupture of brain aneurysm is a medical emergency. 10-15% patients die before reaching hospital. About 40-50% may die within first month of haemorrhage. Survivors may suffer a stroke after a week or so as bleeding in the subarachnoid space causes narrowing of the blood vessels in that region (known as vasospasm) which reduces the blood supply to the brain.

Aneurysm of the brain once ruptured has high tendency to rupture again in the next few days. Every subsequent rupture is worse than before. Hence urgent treatment is mandatory for ruptured aneurysms.

Treatment of ruptured brain aneurysm has two goals. One path of treatment is aimed at taking care of the effects of bleeding which has already occurred in the brain, mainly to prevent vasospasm. Other aim of the treatment is to prevent repeat rupture of the aneurysm by blocking the blood flow into aneurysm . This has to be done as early as possible. And can be achieved in two ways namely surgical clipping and endovascular treatment.

For surgical clipping, skull is opened and by going through the brain, surgeon reaches the site of aneurysm and places a clip across the neck of the aneurysm from outside, so that no blood flows inside the aneurysm.

Endovascular treatment is performed without opening a skull. The blood vessel in the groin is punctured and through that opening, using multiple plastic tubes (called as catheters) endovascular treatment is performed. Using a small catheter, aneurysm sac is entered and multiple platinum springs (called as coils) are used to pack the aneurysm sac so that no blood enters it.

Sometimes, when the mouth (called as neck) of the aneurysm is wide, the platinum springs will not stay inside the sac of aneurysm and will tend to fall in the artery from which it is arising. In such circumstances a balloon is used temporarily to block the mouth of aneurysm and retain the coils inside and then balloon is removed at the end of the procedure.

When the mouth of the aneurysm is very wide, a metal tube called stent is placed across the mouth of aneurysm so that coils stay within the sac of aneurysm and flow through the artery is preserved.

The procedure of endovascular coiling of aneurysm is minimally invasive and doesn’t need any stitches. It is performed under general anesthesia in angiography suite called as ‘cath lab’.

Sometimes, brain aneurysms do not rupture, but present with pressure effects on adjacent nerves. This can cause diminution of vision, closure of eye (not able to open the eye), headache etc. depending on which nerve is being compressed by the aneurysm.

Some aneurysms can be giant in size that is more than 2.5cm in diameter. Such aneurysms are best treated by blocking the aneurysm sac and parent artery with coils. Before occluding an artery, a preliminary test is performed to see if brain can tolerate the occlusion of the artery without any problem by occluding the artery temporarily. But when circumstances do not allow occlusion of parent artery, the technique used to reduce the blood flow in these aneurysm is by placing metallic stents across the neck of aneurysm called as flow diversion technique.

Fusiform aneurysms are also treated by this flow diversion technique using metal stents.

Sometimes the arterial wall gets slit open and aneurysm forms which is called as dissecting aneurysm. Such aneurysms are treated ideally by occluding the aneurysm and dissected segment of the artery.

After the procedure of endovascular treatment in completed, which may take few hours, patient is kept in intensive care unit for observation.

It is important to understand that the embolization procedure doesnot repair areas of brain already damaged due to subarachnoid hemorrhage and vasospasm. It prevents repeated rupture of aneurysm or induces thrombosis in the aneurysm which is not ruptured.

Patients who undergo endovascular coiling of brain aneurysm are frequently advised to come for a follow up angiogram to see statusof the aneurysm after few months.

Many times, patients have multiple aneurysms in brain. In such case, the aneurysm which has ruptured is treated first and then remaining aneurysms are tackled later.

Thus through minimally invasive procedure, aneurysms in the brain can be treated without opening the skull by endovascular treatment.

 

 

 INTRACRANIAL ANEURYSMS:

 

Small intracranial aneurysms usually present with subarachnoid haemorrhage but giant (more than 2.5cm in size) aneurysms present with mass effect in more than 65-70% cases and  symptoms are dependent on aneurysmal location.

 

All anterior circulation giant intracranial aneurysms are near the visual pathways and can thus have symptoms related to sight .

 

Giant aneurysms of cavernous segment of ICA present with opthalmoplegia, retro orbital headache, facial sensory loss and sometimes massive epistaxis.(Figure 7 a)

 

Paraopthalmic (paraclinoid) ICA aneurysms also present with retro orbital headache, visual field defects, decreased vision secondary to optic nerve / chiasm compression.(Figure 7 b)

 

Carotid bifurcation aneurysms cause visual field defects, frequently homonymous hemianopia.(Figure 7 c)

 

Giant aneurysms of anterior communicating artery can cause bitemporal hemianopia.(Figure 7 d)

 

Posterior communicating artery aneurysms can present with ptosis due to compression of III nerve even when they are small in size.(Figure 8)

 

 

RADIOLOGICAL INVESTIGATION FOR INTRACRANIAL ANEURYSMS:

 

1.C.T. Scan – Presence of subarachnoid haemorrhage can be seen on CT scan .In giant aneurysms, their size, wall calcification and thrombus can be depicted well with C.T.Scan. C.T. angiogram with 3D reconstructions shows aneurysms extremely well  noninvasively.

 

2.MRI and MR angiogram – Aneurysms as small as 3 to 4 mm can be seen but visualization is flow dependent, If the blood flow in the aneurysm is poor, the visualization is suboptimal.

 

 

3.Digital subtraction angiogram – It is the gold standard.  It shows presence, number, location, size, shape, neck and fundus of the aneurysm.  It shows associated vasospasm.  And it is the only imaging modality which shows cross circulation through circle of Willis.

 

 

 

 

 

TREATMENT:

 

1.Surgery.

 

2.Endovascular therapy using coils to occlude aneurysm sac.

 

3.In giant aneurysms, parent vessel occlusion using balloon or coils produces subsequent thrombosis of the aneurysm.  Parent vessel can be occluded only proximally or trapped .  Most of the times, occlusion distal to the aneurysm is not necessary, However,  presence of good cross circulation through circle of willis is a prerequisite   to perform parent vessel occlusion. About 90% of petrous or intracavernous aneurysms eventually thrombose with parent vessel occlusion. ( Figure 9, 10)  75% of paraopthalmic aneurysms thrombose (25% donot thrombose due to retrograde flow from ophthalmic artery).  If the giant aneurysms are paraclinoid or supraclinoid in location, only 50% will thrombose due to retrograde flow from posterior communicating artery.

4.When cross circulation through circle of Willis is inadequate, parent vessel can not be occluded for the treatment of giant aneurysm. In such cases , stent assisted coiling of the aneurysm is performed, wherein stent helps to seal the mouth of aneurysm preventing the coils in the sac from prolapsing into the parent artery(Figure 11)

5.Few giant aneurysms can be treated just by placing stents across their neck . These stents divert the flow from aneurysm sac causing progressive thrombosis of the aneurysm. (Figure 12)

 

If the aneurysm does not thrombose completely, the incidence of bleeding and continued growth is about the same as for an untreated aneurysm.

 

Parent vessel occlusion of the ICA for the treatment of an giant intracavernous aneurysm is a safe and effective therapy provided there is good adequate cross circulation through circle of Willis, yielding a cure in the vast majority of cases.

 

COMPLICATIONS:

 

Complications of parent vessel occlusion  are essentially limited to  the ischemic events and are mostly temporary occurring in 5 to 10% of patients .  Permanent deficits, that too late, can occur in about 1 to 3% of patients.

 

Complications of coil embolization of aneurysmal sac are aneurysm rupture during procedure, coil malposition, guide cathether complications, distal embolization and  intra cranial vascular damage.

 

 

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