Interventional Neurology

Interventional neurology refers to endovascular, catheter-based techniques using fluoroscopy and angiography to diagnose and treat vascular disease of the central nervous system. Interventional Neurology has evolved (and still evolving ) into a complex field, with a set of techniques and a knowledge base that are distinct from other fields of medicine. Rapid advances in the field of interventional neurology and the development of minimally invasive techniques have resulted in a great expansion of potential therapeutic applications.

Here is a brief view of current endovascular treatments available for various vascular disorders of brain and spine and also future of Interventional neurology.

DIAGNOSTIC CEREBRAL CATHETER ANGIOGRAPHY

Also called as Digital subtraction angiography ( DSA). Typical indications include the diagnosis of cerebral aneurysms, arteriovenous malformations, cerebral vasospasm, intracranial stenosis, arteriovenous fistula or small vessel vasculopathy including vasculitis. It is often performed just prior to a planned neurosurgical or neurointerventional procedure, as well as immediately after a neurosurgical case. Despite alternative imaging modalities and safety concerns, the actual indications for catheter angiography have not significantly decreased because of the increasing numbers of suspicious vascular findings seen on the very studies (CTA and MRA) thought to supplant it. Furthermore, since minimally invasive endovascular techniques have gained prominence and sometimes replaced open surgical techniques, catheter angiography remains an indispensable modern imaging modality. Spinal DSA is useful tool in diagnosis and treatment planning of spinal AVM, spinal Dural AV fistula.

3D rotational angiography allows evaluation of the opacified artery and its branches from any angle. The technique facilitates understanding of complex vascular anatomy and is a frequently used application in modern diagnostic as well as therapeutic neurovascular care especially in aneurysm and AVM treatment planning.

Cerebral DSA is gold standard for diagnosis of various vascular disorders like intracranial stenosis, posterior circulation stenosis, Dural AV fistulas etc. DSA is indicated when distinctions affecting treatment are unclear; for example, angiography can assist in cases in which differentiation between carotid and vertebrobasilar TIA or evolving stroke is uncertain on clinical grounds and noninvasive imaging only.

Although the risks associated with cerebral angiography have been gradually decreasing, the risk for any complication is approximately 1% to 5%, of which half are minor groin hematomas. Renal function should be normal as iodinated contrast dye used for DSA is nephrotoxic.

ENDOVASCULAR TREATMENT OF ACUTE ISCHEMIC STROKE

The corner stone of the treatment in acute ischemic stroke (AIS) is revascularization. It was only in 1995 when National Institute of Neurological Disorders and Stroke rtPA Stroke Trial (NINDS Study Group) revolutionalized the management of AIS using recombinant tissue plasminogen activator (rtPA) within 3hrs reducing the stroke morbidity by 30%. Eventually the window period was increased to 4.5 hrs after ECASS III. Inj rtPA ( Actilyse ) and Tenectaplase ( Tenectase) are the IV thrombolytic agents approved for acute Ischemic Stroke and both are available in India. Dose of Inj Actilyse is 0.9 mg/kg (10 % as bolus and remaining as IV infusion over 60 mins ). It can be given upto 4.5 hrs from symptom onset. Inj Tenectaplase is approved by DGCA ,India. It can be given upto 3 hrs from symptom onset and its dose is 0.25 mg/kg ( given as bolus dose). Unfortunately, intravenous thrombolysis (IVT) has higher failure rate in large vessel occlusion (LVO).

Intra-arterial urokinase achieved 66% recanalization in LVO and also prolonged the window period for acute stroke intervention upto 6 hours. In this procedure , drug (urokinase or rtPA) is administered through microcatheter at the site of occlusion. This targeted delivery of drug also minimises systemic side effects of drug. But there is minimal increase of risk of hemorrhagic complications. Though FDA has not approved intraarterial rtPA , it can be used in selected cases within 6 hrs of Stroke onset. American Stroke Association (ASA) has given Class 2 recommendation for this treatment. Thus, while both these therapies improved stroke outcomes, a proportion of patients having large vessel occlusions were not amenable to these measures.

Mechanical thrombectomy (MT) with newer thrombectomy devices have many advantages compared to thrombolysis in LVO stroke. A recent review of literature of five randomized control trials (RCT) proved superiority of MT using stent retrievers over best medical management using IVT. Recently published study of Mechanical Thrombectomy in Acute Ischemic Stroke due to large vessel occlusion by Singh et al showed results comparable with Published RCTs and shows feasibility of this procedure in real world scenario like India. The Merci Retrieval system was the first FDA approved treatment option for embolectomy in cerebral arteries. The Penumbra Stroke System (Penumbra, Alameda) was also approved by FDA in 2008 and is the most widely used thromboaspiration device in the US. Newer generation stent retrievers available give more success rate with fewer complications. Solitaire, Trevo, Eric etc are the stentrivers available in India. With the use of ballon guide catheters ( Merci, Cello, Flowgate) with stentrivers , recanalization rate is over 80%. Recanalization rates with thromboaspiration or stentrivers are comparable and both techniques are equally efficacious. Sometimes both techniques has to be used ( Solumbra technique).

Mechanical Thrombectomy is recommended upto 6 hours of symptom onset. But according to new ASA/AHA 2018 guidelines, in selected cases it can be done in patients with 6-24 hours of symptom onset ! Patients with large vessel occlusion requiring mechanical Thrombectomy should also receive IV thrombolysis and then shifted to Cathlab for mechanical Thrombectomy ( Bridging Thrombolysis ). Procedure of mechanical Thrombectomy : Procedure is performed through femoral artery access. 8F balloon guide catheter is navigated over Guide wire and placed in the ipsilateral cervical internal carotid artery. The microcatheter is navigated distal to the clot over microwire. Solitaire stentriver is then delivered through the microcatheter and deployed over the thrombus. Solitaire serves dual function, namely, immediate flow restoration by creating temporary bypass through the thrombus and also acts as a clot retriever, trapping thrombus into its cells The balloon of guide catheter is inflated with contrast to provide proximal ICA occlusion and flow arrest during the recovery of the stent retriever. Subsequently, the Solitaire and microcatheter are slowly recovered as a unit under constant aspiration with 50-mL syringe through the balloon guide catheter.

ENDOVASCULAR ASPECTS OF SECONDARY STROKE PREVENTION

Carotid Angioplasty-Stenting ( CAS ) Current surgical interventions to lower the risk of stroke among people with carotid artery stenosis include carotid endarterectomy (CEA) as well as carotid angioplasty and stent placement (CAS). Carotid angioplasty with stent placement (CAS) was resurrected as an alternative treatment for revascularization of carotid artery stenosis in high-risk surgical candidates. Several Randomized control studies and comparisons with CEA have increased the popularity of CAS. These studies have focused on the safety and effectiveness of CAS. With improving devices and techniques, CAS has become safer than and as effective as surgical treatment. Patients undergoing CAS have small embolic showers occurring frequently during the procedure. These microemboli are composed of thrombotic and plaque substances. This underlies the importance of using a distal protection device to prevent the microemboli from being released into cerebral circulation during carotid angioplasty and stenting. Distal protection devices include occlusive balloons, filter devices, and flow reversal devices.

Procedure of CAS : Procedure is performed through femoral artery access. 8F guide catheter or 6 F long sheath is navigated over Guide wire and placed in the common carotid artery. Stenosis is crossed with microwire. Over microwire distal embolization protection device ( Spider ) is placed into ICA. Angioplasty is done using noncompliant Balloon at desired pressure. Inj atropine is given to counteract bradycardia due to carotid body stimulation during angioplasty.Then stent is deployed across the stenosis. This procedure is done generally under local anaesthesia.

Vertebral artery stenting :Most common site of stenosis is at origin of vertebral arteries , also called as osteal stenosis. In some cases traumatic / spontaneous dissection of vertebral artery results in flow-limiting narrowing necessitating stenting. Stenting is generally required in patients with severe stenosis causing symptoms of Vertebro-Basilar insufficiency. Procedure of vertebral artery stenting is generally done under local anaesthesia and stents used are balloon mounted drug eluting stents.

Angioplasty-stenting of intracranial Stenosis :Intracranial stenosis is responsible for 8–10% of all ischemic strokes. There is a high yearly rate of recurrent strokes in patients with intracranial stenosis that has been estimated at approximately 8–12% and in those not taking antithrombotic treatment, the rate of recurrent ischemic stroke events can be even higher and has been estimated at 52%. Percutaneous transluminal angioplasty with possible stent placement has been recommended for treatment of intracranial stenosis especially for patients not responding to medical treatment. The long-term follow-up has suggested ipsilateral stroke prevention of up to 96% for the first year and approximately 87% for up to the third year after interventional treatment. For symptomatic patients with >50% intracranial stenosis who have failed medical therapy, balloon angioplasty with or without stenting should be considered. Patients who have an asymptomatic intracranial arterial stenosis should first be counseled regarding optimizing medical therapy. There is insufficient evidence to make definite recommendations regarding endovascular therapy in asymptomatic patients with severe intracranial atherosclerosis. Contraindications for intracranial stenting are inability to have antiplatelet therapy and/or anticoagulation and highly calcified lesions or anatomy that prevents endovascular access. In India balloon mounted drug eluting stents are available and widely used for intracranial stenosis. Advantage of these stents are lower rate of restenosis.

Procedure of Intracranial stenting :Procedure is performed through femoral artery access. 6F guide catheter is navigated over Guide wire and placed in the internal carotid artery / vertebral artery. Stenosis is crossed with microwire. Angioplasty is done using noncompliant ballloon slowly and carefully at desired pressure. Then stent is placed across the stenosis under fluoroscopic guidance.

ENDOVASCULAR TREATMENT OF CEREBRAL VENOUS THROMBOSIS ( CVT )

Cerebral venous thrombosis (CVT) can occur in the form of cortical venous thrombosis, venous sinus thrombosis, deep venous thrombosis, jugular venous thrombosis, or various combinations of the above. CVT has high mortality rate ranging from 5–30%. The interruption of outflow in the brain circulation leads to augmentation in the pressure of the entire system with venous hypertension, intracranial hypertension, and hemorrhagic events.

The main goal of the treatment of CVT should be the recanalization of venous drainage system with complete reestablishment of normal brain circulation. The treatment of choice is IV anticoagulation followed by local thrombolysis where indicated. Endovascular treatment is indicated for patients unable to receive antico-agulation and for those who deteriorate despite anticoagulation heparin. Endovascular therapy is also indicated in high-risk categories including those with seizures, coma, disturbed consciousness, deep cerebral vein thrombosis, posterior fossa involvement, and/or pro-gressive focal deficits.

The endovascular route used is transvenous through the femoral vein, navigating the catheter into the venous circulation and final placement in the matrix of thrombus. The thrombolytics are given as bolus dose followed by infusion over a period of hours for a better recanalization. The rate of recanalization (partial and total) ranges from 70–95%. Drugs used are urokinase and rtPA.

ENDOVASCULAR TREATMENT OF ANEURYSMS

Intracranial aneurysms (IAs) are localized dilations of the cerebral arteries wall and are prone to rupture, resulting in bleeding. The overall prevalence of unruptured IAs is between 2% and 3.2% in the general population with a male to female ratio of 1:2.1 It is the leading cause of hemorrhagic stroke, responsible for 85% of subarachnoid hemorrhages (SAH).

the outcome for patients with SAH remains poor, with overall mortality rates of 25% and significant morbidity among approximately 50% of survivors.

Long-term follow-up in the International subarachnoid aneurysm (ISAT) trial evaluating exclusively ruptured aneurysm, with a mean follow-up of nine years, has demonstrated the effectiveness of coil embolization in essentially eliminating the risk of future subarachnoid hemorrhage.

Considerable advances have been made in the ability to use coils for endovascular treatment of intracranial aneurysms in situations that might have appeared unsuitable a few years ago. The new designs of coils, including the three-and two-dimensional configurations, have improved results. Focusing on the anatomy of the aneurysm and on the neck and dome ratio, as well as its packing with coils in a step-wise manner, has led to remarkable success in coiling of aneurysms previously considered to be difficult.

Simple Coiling Detachable coils were invented by Guglielmi in the 1990s, and transluminal embolization techniques were gradually developed since then.Simple coiling refers to transluminal navigation of a microcatheter into the aneurysmal dome with the help of microguidewires and the delivery and packing of detachable coils within the aneurysmal sac. The goal in coiling is to achieve dense packing and induce rapid blood clot formation within the aneurysmal sac, hence isolating it from active circulation.