Vascular Neurosurgery

William Harvey Cushing, Walter Dandy, Krayenbuhl, Yasargil, William Spence, Rhoton
Drake, Fredric B. Meyer, Michael T Lawton: Author of 'Seven Aneurysms-Tenets & Techniques for Clipping', Spetzler, Sugita, Dolenc, van Loveren, Hunt and Hess, Laligam Shekhar, etc have made important contributions.

Austrian physicist Christian Doppler (1842): described Doppler effect which led to  Doppler Ultrasound. The use of Doppler ultrasound to measure cerebral blood flow was initially reported by Satomara in 1959. Aslid & colleagues first reported the ability to record blood flow velocity in the intracranial arteries with Doppler ultrasound in 1982 and introduced TCD (Trans Cranial Doppler ) ultrasonography. The lower 2-MHz frequency allowed penetration through the cranium in the thin portions of the skull.

Kety and Schmidt ( 1948) applied Fick's principle ( Latter half of 19th Century) to  determine  Cerebral blood flow ( 54 ml/100 g per minute). Sundt noted that a minimal CBF of 18 mL/100 g per minute is needed to maintain a normal EEG parameters during carotid endarterectomy ( CEA).
Irreversible cellular damage occurs when CBF is below 10 mL/100 g per minute.

For treating carotid occlusive disease, the options include CEA, carotid artery angioplasty & stenting. William Spence performed the first successful performed Carotid endarterectomy (CEA) in 1951.


The most common cause of SAH is trauma.
Spontaneous subarachnoid hemorrhage due to ruture of intracranial aneurysm commonly occurs in the age group of 40-60 years with a peak incidence in the fifties.
Aneurysm bleed is the commonest cause of spontaneous SAH ( about 85%).
Other common causes of spontaneous SAH are:  artriovenous malformations ( AVM), hemorrhage from tumor, pituitary apoplexy, vasculopathy ( like collagen vascular disease, amyloid angiopathy , arterial dissection) , haematological ( anticoagulant therapy, leukaemia, hepatic or renal disease induced coagulopathy ) and drugs like cocaine, amphetamine and ephedrine.

Subarachnoid hemorrhage (SAH) is a neurological emergency  characterized by hemorrhage into the subarachnoid space, and may present as sudden, severe headache ( as bolt from blue ) which patient may state that he or she may have never experienced before. Sentinel hemorrhage occurs in about 40% of patients with SAH. This is also known as " warning leak". Nuchal rigidity or meningismus is noted in 50% of patients due to meningeal irritation following SAH. Hemiparesis, focal neurological deficits including cranial nerve deficits are other common features. Fundus examination may reveal papilloedema and subhyaloid hemorrhage.

On the basis of GCS and Focal deficit, the severity of the clinical presentation of the patients may be graded into 5 grades , according to the World Federation of Neurological Surgeons  (WFNS).
In WFNS Grade 1 the patients are of GCS 15/15 and have no focal deficit. And, if patient's GCS is 13 or 14 then it is Grade 2. And patient has a focal deficit with a GCS of 13 or 14, his grade becomes Grade 3.   poor GCS of 7-12 makes a patient of grade 4 and if patients GCS is 6 or less then his garde becomes 5, irrespective of the presence or absence of focal deficit.

NCCT ( NECT) , i.e., Noncontrast or nonenhanced CT scan of the barin is the first investigation of choice. It shows hyperdensity in the subarachnoid space and may indicate the site of bleed. or example, anterior communicationg artery aneurysm bleed shows blood or hyperdensity in the anterior interhemispheric cisterm. the ruture of the Middle cerebral artery may present with hematoma in the temporal lobe or in the sylvian fissure of that side.

Fischer's grading of SAH on the basis of CT findings:
In Grade 1: there is no detectable blood on CT scan
Grade 2 : Diffuse thin  SAH  less than 1 mm thickness, & if thickness of clot is more than 1mm then it is labeled as Grade 3.
Grade 4: Intraventricular or intracerebral clot with diffuse or no subarachnoid hemorrhage

If  CT scan is normal and still there is strong suspicion of SAH, then the next  investigation is Lumbar Puncture, which reveals xanthochromia.

Common locations of intracranial aneurysms include Anterior communicating artery ( 30%), the junction of the ICA and Pcom ( 25% ), MCA bifurcation ( 20% ), ICA bifurcation ( 7.5%). Around 7% arise from the basilar bifurcation and 3% arise from the PICA, a branch of vertebral artery.

Digital Substraction Angiography ( DSA) or CT Angiography ( CTA) is the investigation of choice. MR angiography ( MRA) does not use any contrast and it is a good non invasive screening investigation.
Trans cranial Doppler ( TCD) detects vasospasm.
Rebleeding is the major concern during the initial treatment of patients who are admitted with rupture of intraqcranial aneurysmal rupture. Hydrocephalus, seizure, neurological deficit due to vasospasm and ischemia are other common problems.
Vasospasm is treated by triple H therapy ( induced hypertension, hypervolemia and Hemodilution) to improve cerebral perfusion. Calcium channel blocker- Nimodipine in the dose of 60 mg four times a day is neuro protective. Intraarterial papaverine is also used as vasodilator for spastic arteries after SAH.
Clipping of the aneurysm and coiling of the aneurysm are the two options for treating intracranial aneurysms. Subarachnoid space is the arena of aneurysm surgery because it houses the brain's arteries & provides a navigable labyrinth to deep targets that can be dissected without violating or harming the brain. Subarachnoid dissection, therefore, is a foundation of vascular neurosurgery.
Posterior circulation aneurysms, multiple aneurysms, Poor grade patients or surgically unfit patients, aneurysms with AVM are indications for endovascular treatment with coiling.

Every intracranial saccular aneurysm is associated with a cistern:

    Middle cerebral artery ( MCA) aneurysm is in sylvian cistern
    Posterior communicating artery ( PCoA) & ophthalmic artery ( Oph A) aneurysm in carotid cistern
    Anterior communicating artery (ACoA) in lamina terminalis cistern
    Pericallosal artery (Pca A)  in callosal cistern
    Basilar bifurcation in interpeduncular cistern
    Posterior inferior cerebellar artery ( PICA ) in lateral cerebellomedullary cistern

The pathway to some aneurysm traverses several cisterns:

    For example, the pathway to Anterior communicating artery aneurysms progresses from carotid to chiasmatic to lamina terminalis cistern, & the pathway to basilar bifurcation aneurysms progresses from Slvian to carotid to lamina terminalis to crural to interpeduncular cistern.

So, arteries define a trail through the center of the subarachnoid space ( SAS). Every artery has a safe surface to follow during subarachnoid dissection. Safe surface means smooth contours and few branches. For example, the superior surface of the M1 MCA segment gives off lenticulostriate arteries, & dissection along this surface can injure them. In contrast, the inferior surface gives rise to anterior temporal artery which is easily seen and less vulnerable.

Careful subarachnoid dissection does not require division or sacrifice of even a small arterial branch. It can be mobilized if required.

Subarachnoid dissection remains " outside " of the brain so respect & preserve the pial boundaries outside of the vessel.

Skull base approaches minimize the brain retraction.

Pterional approach involves fronto-temporal craniotomy. Orbitozygomatic approach enhances the surgical exposure of standard pterional craniotomy.

Anteror interhmispheric approach is used to clip aneurysms of the pericallosal artery.

Far- Lateral approach or lateral suboccipital approach is needed for aneurysms of posterior fossa.

Sources;
Excerpts from
Seven Aneurysms Tenets and Techniques for clipping. Author : Michael T. Lawton ( Thieme) , 2012