The introduction of Guglielmi detachable coils (GDCs) in 1991 has revolutionized the endovascular treatment of intracranial aneurysms and is rapidly gaining popularity as an alternative approach to surgical clipping in selected cases. 

Requirements: 

The success of endovascular procedures depends on the catheter, guide wire and embolization material; technical equipment of the endovascular angiography suite; pre-, intra-, and post-procedural management of patients; and most importantly the experitise  of the physician. 

Microcatheters require  materials which increase control of the catheter tip, improve movement and torque .  The proximal segment (thick wall, stiff) transmits both torque and longitudinal movement almost without any deficit. The middle segment of the catheter is more flexible and has a thinner wall but still features high torque and control stability. The distal segment of the catheter is characterized by a high degree of softness and reduced wall thickness. Depending on the type of catheter used, the distal section is soft, providing little control stability and increased flow catheter qualities or has more torque stability and less flow dependability. Besides new wall properties, the newest generations of microcatheters have hydrophilic surface coatings, allowing for better performance. 

Guide-wire supported microcatheters permit flow-independent movements of the catheter tip, making possible advancement along fine vessels that branch off large-lumen main vessels, such as perforating arteries that feed AVM’s. Guidewires feature extremely floppy tips of different lengths that can be shaped at the tip, which makes passing them along curved vascular formations easier. The latest generation of wires is made from nickel-titanium and has a hydrophilic surface coating to reduce friction between catheter and guidewire. Seeker, QuickSilver, Sorcer  and Terumo Glidewire are some of the popular ones. 

Embolization materials-The choice depends on the  type of  vascular lesion, goal, and the vascular anatomy. None is ideal.

The following materials are in use.

Cyanoacylates can be injected through the finest catheters because of their low viscosity and feature the best time stablity of all embolizing media. 

NBCA (N-Butyl-2-cyanoacrylate) hardens immediately upon contacting free hydrogen ions of the blood and is mixed with low-viscosity oily contrast media, or tantalum powder for radiological visualization. It is liquid at the time of injection but should solidify at the desired pathological target and should produce an endovascular cast without migrating into the venous system. It has low viscosity even when mixed with Lipiodol, can be injected through microcatheters. Fluoroscopic monitoring  is mandatary to see the progress of material on injection. 

PVA( Polyvinyl alcohol)  particles of defined sizes – 150-500micro m – may be used, but because of the limited stability of the occlusion effect, they should be used only as preoperative embolizing media.

Microcoils ( GDC )are available in different lengths and with different helix diameters. They are advanced through microcatheters and can occlude a high flow fistula or small arteries. In contrary to previously available ‘free coils’ modern coils with electrolytic detachment mechanisms allow safe and precise placement of the coil before detachment. Coils mounted with thrombogenic hairs or additional glue injections may help to improve the results.

Silastic or latex balloons, Gelfoam in powder form, Fibrin glue, Silicone spheres, Silk, and Ethibloc are other agents occasionally  used these days. 

Radiography equipment- the preferential standard in radiography equipment is biplane digital subtraction angiography with high-resolution live roadmapping capability. Developments like rotational angiography with the option of three-dimensional reconstruction may increase the information on AVM architecture.

Anesthesia-Management by a highly qualified specialist reduces risks. The necessity of stable blood pressure is one reason to perform endovascular procedures under general anesthesia. Another reason is the need for optimal imaging, especially roadmapping. 

Intra-procedural monitoring and tests-This includes anesthesiologic monitoring and if available, neurophysiologic monitoring, such as SSEP and EEG – and transcranial doppler . Intra-operative functional monitoring by short acting barbiturates (amobarbital sodium – 75-100mg) injected into microcatheters causes transient deficits and tests the eloquence of the brain – but due to the AVM, the amount of drug reaching the target brain is uncertain, a negative test does not offer safety – the patient should be conscious and co-operative. 

Technique: 

The standard approach is by the trans-femoral route using Seldinger’s technique. The guiding catheter(5F to 8F), which is located in the carotid or vertebral artery is continuously flushed with heparinized saline.

All procedures are performed with the patients under general anesthesia (propofol or halothane) and with systemic heparinization, including those procedures that are performed to treat recently ruptured aneurysms. A 5000-unit bolus of heparin and then 1000 units of heparin per hour are administered until the end of the procedure. The patient is  reversed at the end of the procedure with protamine sulfate (8-9 mg/1000 units of total heparin administered) unless an embolic complication occurred.

Complications:

The complications most frequently reported in the literature include rupture of  AVM or  aneurysm either by the coil, microcatheter, or wire used to guide the microcatheter, thromboembolic events, and thrombosis of the parent artery ,accidental migration of embolic material to normal vessels causing neurodeficits.

Cranial nerve palsies due to occlusion of the ECA branches supplying the transcranial course of the cranial nerves is a possibility. Scalp necrosis due to occlusion of branches of  ECA, premature balloon detachment, pulmonary embolism, and infection are other possible, but rare complications.

Post-operative monitoring of vital parameters is necessary because fluctuating blood pressure poses particular dangers as a result of the changed hemodynamics of the brain. Multiple neurologic examinations and neuropsychological tests are important follow-ups in addition to MR imaging studies and angiograms. 

Cerebral AVMs:

Curative embolization: To achieve definite treatment the complete obliteration of the AVM nidus must be the goal of intervention. Only small AVMs with easily accessible feeders can be occluded in a permanent way without increasing the risk of the procedure, so most of the reported  endovascular series have only a ew completely occluded AVMs. More than one intervention is often necessary to achieve permanent, complete obliteration of a nidus, because, occluding all compartments of a large AVM would last too long and second the sudden reduction of large shunt volumes might cause too much change in hemodynamic conditions. But commonly, feeding branches for which a sufficiently selective catheter position could not be achieved in a first or second session remain un-occluded. But commonly, feeding branches for whicha sufficiently selective catheter position could not be achieved in a first or second session remain un-occluded. The stability of the occlusion is the second prerequisite for a successful endovascular therapy of cerebral AVMs for which the types of occlusion and the embolizing material used are considered.   The stability of the occlusion, that is the prevention of the formation of collaterals into the nidus is best achieved if the nidus is filled with the embolizing medium. For this, a correct assessment of the flow condition in the respective compartment and select the proper quantity and mixture ratio of glue and dye.

Occipital AVM         ... post embolization           High flow temporal AVM    ....post embolization residue             Parieto occipital AVM        ...post embolization

Pre-radiosurgical embolization:

The goal of pre-radiosurgical embolization is to make radiosurgery feasible and to minimize the bleeding risk in the latency period. The aim is to reduce the nidus diameter to a volume of less than 10ml, embolization of weak elements in the angio-architecture of the nidus (eg: flow related or non flow related aneurysms, venous pouches or high flow fistulas) and minimization of dural supply to the AVM nidus. The occlusion must remain unchanged over time despite the fact that it is only a partial occlusion. The resulting size and shape of the parts of the AVM remaining open for radiosurgery is important – the more irregular, the lower the feasibility of radiosurgery. In addition to size and shape is the relationship to eloquent areas of the brain influencing dosimetric planning.

Deep spherical AVM remnants are treatable by radiosurgery, whereas large, spotted, superficial remnants in eloquent areas represent an endovascular result untreatable by subsequent radiosurgery. 

Palliative embolization:

Large and giant AVMs cause primary seizures, headache and other focal symptoms. Surgery is not possible because of multiplicity of feeders, complex angio-architecture & large size. For these patients palliative embolization may be offered with goals of reducing the shunt volume in the nidus to obtain seizure control or to reduce focal hypoxia. Another goal is to embolize feeding artery aneurysms.

Care should be taken to prevent obliteration of venous outflow. These patients should have regular clinical and angiographic examinations. 

DURAL AVMs/F ISTULAE:

Caroticocavernous fistulas:  CCFs can be fast-flow (type A) and slow-flow (type B, C, D). Type A is found in ruptured aneurysm and traumatic ones and ECA is not involved; ICA contributes through small meningeal branches not usually accessible to detachable balloons.  Inflatable balloon via the endarterial route is used, reportedly with 80% success. In failed cases, the venous approach through the inferior petrous sinus or the superior orbital vein (which may have to be exposed surgically) may be tried. In some ICA has to be sacrificed.   Type B is a dural shunt/AVM, between meningeal branches of ICA and the cavernous sinus;embolization is not possible usually.

Type A CCF .post embolization-ICA preserved                     Type C CCF            ...post embolization

Type C is a dural shunt between meningeal branches of ECA and cavernous sinus; successful embolization is possibleType D is dural shunt between meningeal branches of ICA and ECA with cavernous sinus; embolization through ECA feeders can be attempted. ICA feeders cannot be embolized usually.

Type D is dural shunt between meningeal branches of ICA and ECA with cavernous sinus; embolization through ECA feeders can be attempted. ICA feeders cannot be embolized usually.

In other Dural fistulas cure is achieved in 50% with endarterial embolization of the ECA  Embolization with particles has low morbidity rate but recanalization chances are high. Liquid materials have high cure rates and high morbidity rate. Coils are not used.

Dural AVMs of the spinal cord  are often treated by selective embolization

Vein of Galen malformations are treated by transarterial or the transvenous-transtorcular route.

The primary aim is total occlusion. Partial occlusion helps in controlling the congestive cardiac failure  in neonates till the optimal time for definitive treatment.

CEREBRAL ANEURYSMS: 

Surgical clipping has been the accepted treatment of choice for intracranial aneurysms during the last several decades. However, the management of intracranial aneurysms has become controversial with the recent advent of endovascular techniques.

The endovascular treatment of intracranial aneurysms has evolved rapidly. Initially, treatment of aneurysms using the endovascular approach was limited to occlusion of the parent vessel. Subsequently, detachable balloons were placed within the sac of the aneurysm, preserving the parent artery, and this technique is still used extensively in the Ukraine by Victor Scheglov.

More recently, Hilal in 1988, first reported aneurysm occlusions with nonretrievable coils. The introduction of Guglielmi detachable coils (GDCs) has revolutionized the endovascular treatment of intracranial aneurysms.  Indications: Many physicians consider surgical clipping to be the treatment of choice, reserving endovascular therapy using GDCs for aneurysms that cannot be treated surgically or for patients who are considered to be nonsurgical candidates because of the severity of their medical condition.

GDC Coil 3 D  &      Regular

Conversely, several physicians in Europe have adopted an opposite position and consider the endovascular approach with coils to be the treatment of first choice, reserving surgical  clipping for those aneurysms for which coiling has failed or those that are incompletely occluded after coiling.

Selection criteria:

The criteria for selecting patients to be treated using GDCs are continually being redefined.

The so called ‘unclippable ‘ aneurysm is  difficult  for the interventionist as well. The decision to treat using GDCs is based on the presenting medical condition, location of the aneurysm, and, in part, aneurysm shape. 

Aneurysm shape and size- spherical aneurysms with small necks have a greater chance of complete occlusion using GDCs than do large aneurysms with broad necks of 5 mm or greater in diameter.
The dome-to-neck ratio is not the only measurement criterion to be considered when treating aneurysms using GDCs.  The neck diameter will affect the morphological occlusion outcome.  Despite the favorable dome-to-neck ratio, the width of the neck allows prolapse of the coil into the parent artery, preventing complete occlusion^.

Aneurysms with an unfavorable dome-to-neck ratio and aneurysms with a favorable dome-to-neck ratio but with wide necks are not totally excluded from treatment using GDCs. These aneurysms may be amenable to coiling with the adjunctive use of a balloon positioned across the neck of the aneurysm, which was coined the remodelling technique by Moret. The  remodelling technique can fail secondary to vessel tortuousness, preventing placement of the balloon, or because of limited balloon sizes and available balloon inflation configurations, which prevent successful complete occlusion of the aneurysm. Over inflation also increases the risk of balloon failure,  either by rupture or by loss of the wire's ability to occlude the distal lumen, preventing inflation. Continual improvements in technique, balloon design, and size availability will provide improved outcomes. This technique shows promise in the treatment of surgically difficult aneurysms and aneurysms with unfavourable geometry using GDCs. Aneurysm location- Configurations unfavourable to successful coiling include locations where multiple branches arise, such as the MCA trifurcation. The branching  vessels can obscure visualization of the aneurysm neck, increasing the risk of coil protrusion into the parent artery or adjacent branch vessel.   A second unfavourable configuration is that of a branch vessel arising from the neck of the aneurysm, which commonly occurs with PComA aneurysms. AComA aneurysms are occasionally difficult to assess based on the pretherapeutic angiogram regarding whether the geometry is suitable for coiling.

Giant intracavernous aneurysm   post balloon occlusion of ICA             Ophthalmic aneurysm             ...post coiling          Basilar tip aneurysm              ...post coiling

Accurate measurement of the aneurysm neck and relationship to the parent artery of many aneurysms may be difficult to obtain from the pretherapeutic angiogram. In these situations, subselective injections with the microcatheter may provide better assessment of the aneurysm geometry, or 3D-CT angiography can define the aneurysm and in many cases, only placement of the initial coil will provide the true measurement of the aneurysm neck.  

Technique:

The technique is broadly the same as in AVMs.

The choice of microcatheter is dependent on the aneurysm size, with the Tracker  10 systems being used primarily for aneurysms measuring 8 mm or less in diameter and the Tracker 18 systems being reserved for larger aneurysms. The guidewires used with the microcatheters varies

GDC coils are used more commonly. GDCs are manufactured with two primary wire diameters (GDC 10 and GDC 18), corresponding in size to 10 and 18 . The advantage of the smaller system is that the coil itself is softer than that of the larger system and is of similar secondary helical diameter, reducing the risk of perforation. The primary disadvantage is the limitation in size of the secondary helix to 10 mm, and aneurysms larger than 1 cm need to be treated using the GDC 18 system, which has secondary helical radii up to 18 mm. Therefore, accurate measurements of the aneurysm size before coiling is essential to select the appropriately sized coiling system. The use of GDC 10 coils through a No. 18 microcatheter is not recommended because the coils may buckle and become damaged.

The development of GDC 10 and 18 soft coils further reduced the risk of aneurysm perforation over the initial standard GDC 10 and 18 coils. A second advantage of the soft coil is reduced configurational memory of the secondary helix, which allows the coil to better adapt to the remaining space within a partially coiled aneurysm, improving the ability to densely pack the aneurysm. Additionally, the reduced configurational memory of the soft coil allows improved results using the remodeling technique because the coil has less tendency to revert to its original shape and decreases the incidence of coil protrusion through the neck of the aneurysm.

The use of two-dimensional coils has also been found to be an advantage in the treatment of aneurysms. Deployment of the first loop of coil with a shorter radius into the aneurysmal sac decreases the risk of perforation and migration of the coil into the parent vessel.

Wide-necked aneurysms having an unfavourable neck-to-fundus ratio are difficult to embolize with conventional GDC coils without the use of balloon remodelling or other supplemental methods. A neck-to-fundus ratio close to 1.0 constitutes an aneurysm difficult to treat by using the conventional GDC coil without resorting to an adjunctive method. compared with smaller-necked aneurysms. 

The technical difficulty encountered in providing stable support for the conventional coil mass within a wide-necked aneurysm has prompted the suggestion of various methods, in addition to balloon remodelling, such as coiling through a stent or the use of two-catheter techniques. Use of an inherently complex-shaped GDC coil with a propensity to form a 3D cage spontaneously after deployment. The complex shape results in a lower tendency to prolapse into the parent vessel lumen. The 3D coil seems to provide an inherently stable framework in the wide-necked aneurysm, which enables the subsequent deployment of four conventional GDC coils without the use of additional microcatheters. During deployment, the 3D coil is stiffer compared with the conventional or two-dimensional GDC variant. This subjective stiffness is actually translated into greater local mechanical stress being applied to the aneurysm during 3D coil placement. Although the eventual role of this type of coil in aneurysm embolization will be defined only with longer-term experience, the 3D-shape GDC seems to provide a single-microcatheter solution for the endovascular treatment of aneurysms harbouring a wide neck or an unfavourable neck-to-fundus ratio.                                                             

When the remodelling technique is performed, latex balloons and silastic balloons may be used.

All coils are deployed with live simultaneous biplane roadmapping.

Coiling is performed until no further coils could be placed within the aneurysm.

Heparin is reversed with protamine sulfate, and the patient is woken up from propofol sedation and is transferred to the Neuro Intensive Care Unit for observation.

Patients with unruptured aneurysms are usually discharged within 48 hours after uneventful coiling.

Patients with acutely ruptured aneurysms are monitored in the Neuro Intensive Care Unit. Endovascular balloon angioplasty and papaverine infusions are performed as necessary for patients who developed symptomatic vasospasm in some centres.

Follow-up angiography, are performed at 6 months, 1 year, and 2 years after treatment.  

 

Post procedural problems:

Ideally, treated aneurysms should have dense and tight coil packing, which requires experience and has been improved with the development of the soft GDC.  

The problem of residual neck & neck regrowth  in apparently completely occluded aneurysms after coiling using GDCs remains a potential concern. One explanation provided by the literature is that during coiling using GDCs, there is no mechanical apposition of the aneurysm neck endothelium, allowing for potential recanalization and regrowth. These neck regrowths tend to be small, less than 5% of the original aneurysm size, and can occur as early as 6 months or as late as 2 years after the procedure.    

The inherent tortuousness of the cavernous region at times can prevent stability of the microcatheter tip during placement of the last few coils into the aneurysm neck. Movement of the microcatheter during the final stages of the procedure can result in ejection of the microcatheter tip from the aneurysm neck, preventing complete packing, which results in neck remnants and possible neck regrowth.  

In basilar tip aneurysms, microcatheter stability is usually less of a problem; however, the relationship of the aneurysm neck to the origins of the posterior cerebral arteries becomes the limiting factor in preventing complete occlusion. Minimal coil protrusion at this location can cause partial stenosis of the PCA, resulting in the increased risk of thromboembolism or thrombosis.
Incomplete occlusion is not the desired outcome, and often, further treatment using the remodeling technique, parent vessel occlusion, or surgery can be performed.

The remaining incompletely occluded aneurysms should be followed, with one of three possible outcomes: 1) progression to complete occlusion, 2) the residual lumen remains stable, and 3) there is enlargement of the residual lumen.  

The literature reports about a 2.2% subsequent haemorrhage rate among ruptured aneurysms that are incompletely occluded with coils. It has been suggested that partial occlusion of an aneurysm treated in the acute phase protects the dome of the aneurysm from subsequent bleeding and allows a second treatment at a later date when the patient has clinically recovered from the SAH. 

Vasospasm occurs and is attributed to the SAH. Increased incidence of symptomatic vasospasm in acutely ruptured aneurysms treated using coils, because blood and hemoglobin degradation products are not removed from the subarachnoid space has not been reported.

Cerebral and vertebral tumors:  

The aim is to devascularise the tumor. This reduces the intraoperative blood loss, provides easier manipulation of the tumor at surgery, and shortens the operation time.  The embolization is carried out ideally 12- 24 hours before the planned definitive surgery to avoid the probable development of collateral circulation and revascularization of the tumor. Meningiomas, more commonly, are subjected to preoperative embolization procedures .They arise from the cap cells of the meninges and hence they are fed primarily  by the meningeal arteries. As they enlarge additional supply comes from the pial vessels; peripheral portion may be supplied by cerebral arteries.  The ultimate result is dependant on the percentage of dural supply, the ability to reach the different arterial feeders and the possibility to carry the embolization intratumorally. Hence basal tumors are usually inaccessible.

parietal meningioma          …post embolization            large skull base tumor       …post embolization

Surgery for Vertebral hemangiomas is made easy following embolization.

Specific complications include skin necrosis by extensive occlusion of the cutaneous branches of the ECA, and cranial nerve palsies due to occlusion of the ECA branches supplying the transcranial course of the cranial nerves.

Recanalization procedures:

It includes ‘local intra-arterial fibrinolysis ’ which is mostly carried out in thromboembolic occlusion of the middle cerebral artery and the basilar artery, and the ‘ percutaneous transluminal angioplasty in cases of ICA, the subclavian or vertebral artery.

Relatively new is the application of this procedure in the management of vasospasm, which is still in the experimental stage.