Mural repair following obliteration of aneurysms. Part III: Pathomorphological effects of Nd:YAG laser on aneurysm obliteration

Twenty-four experimental aneurysms were created in rat carotid arteries using the venous pouch technique. Four to twelve weeks later, these aneurysms were totally obliterated by the external application of Nd:YAG laser. The aneurysmal dome and neck were both exposed to the laser using low amplitude (1-2 W) at continuous or repeat intervals (0.3 sec on/0.1 sec off). Small aneurysms were easily obliterated without external signs of necrosis, whereas aneurysms larger than 2 mm required complete coagulation resulting in a charcoal-like appearance. At varying intervals (30 min, 7 days, 3 weeks, 6 weeks), the obliterated aneurysms were harvested and evaluated using the scanning electron microscope and standard histological techniques. The results indicate that the effects of the laser on the aneurysm and parent vessel are similar to those encountered following the application of bipolar coagulation with massive coagulation necrosis of the aneurysmal neck and dome. Notably, however, the extension of this process onto the parent vessel involving especially the endothelium surrounding the aneurysm orifice (commonly seen with bipolar coagulation) is minimal following laser coagulation. There appears to be a protective effect on the parent vessel endothelium by blood flow through the vessel. On this basis, it appears that the laser may be an alternative method of aneurysmal coagulation; the use of laser entails less manipulation of the aneurysm. The Nd:YAG laser may be a useful adjunct in the surgical obliteration of clinical cerebral artery aneurysms, especially small ones.     

Haemodynamic stress in lateral saccular aneurysms

Summary The flow velocities in lateral glass and silastic aneurysm models were quantitatively measured with the non-invasive laser Doppler method. The influences of the elasticity of the wall, the pulse wave and the properties of the perfusion medium on the intra-aneurysmal circulation were investigated. As shown previously, the inflow into the aneurysm arose from the downstream lip and was directed toward the centre of the fundus. Backflow to the parent vessel took place along the walls of the fundus. With non-pulsatile perfusion, flow velocities in the centre of the standardized aneurysms varied between 0.4 and 2% of the maximum velocity in the parent vessel. With pulsatile perfusion, flow velocities in the centre of the fundus ranged between 8 and 13% of the flow velocity in the axis of the parent vessel. Flow velocities in the aneurysms were slower with a macromolecular perfusion medium with blood like properties compared to a glycerol/water solution. Flow velocity measurements near the aneurysmal wall allowed the estimation of the shear stresses at critical locations. The maximum shear stresses at the downstream lip of the aneurysm were in the range of the stresses measured at the flow divider of an arterial bifurcation. The present results suggest that in human saccular aneurysms intra-aneurysmal flow and shear stress on the wall are directly related to the pulsatility of perfusion,i.e. the systolic/diastolic pressure difference and that the tendency to spontaneous thrombosis depends on the viscoelastic properties of the blood, namely the haematocrit.     

A proposed parent vessel geometry-based categorization of saccular intracranial aneurysms: computational flow dynamics analysis of the risk factors for lesion rupture

OBJECT: The authors created a simple, broadly applicable classification of saccular intracranial aneurysms into three categories: sidewall (SW), sidewall with branching vessel (SWBV), and endwall (EW) according to the angiographically documented patterns of their parent arteries. Using computational flow dynamics analysis (CFDA) of simple models representing the three aneurysm categories, the authors analyzed geometry-related risk factors such as neck width, parent artery curvature, and angulation of the branching vessels. METHODS: The authors performed CFDAs of 68 aneurysmal geometric formations documented on angiograms that had been obtained in patients with 45 ruptured and 23 unruptured lesions. In successfully studied CFDA cases, the wall shear stress, blood velocity, and pressure maps were examined and correlated with aneurysm rupture points. Statistical analysis of the cases involving aneurysm rupture revealed a statistically significant correlation between aneurysm depth and both neck size (p < 0.0001) and caliber of draining arteries (p < 0.0001). Wider-necked aneurysms or those with wider-caliber draining vessels were found to be high-flow lesions that tended to rupture at larger sizes. Smaller-necked aneurysms or those with smaller-caliber draining vessels were found to be low-flow lesions that tended to rupture at smaller sizes. The incidence of ruptured aneurysms with an aspect ratio (depth/neck) exceeding 1.6 was 100% in the SW and SWBV categories, whereas the incidence was only 28.75% for the EW aneurysms. CONCLUSIONS: The application of standardized categories enables the comparison of results for various aneurysms' geometric formations, thus assisting in their management. The proposed classification system may provide a promising means of understanding the natural history of saccular intracranial aneurysms.     

Haemodynamic stress in terminal aneurysms

Summary The flow velocities in glass and silastic aneurysm models located at bifurcations were quantitatively determined using the non-invasive laser-Doppler method. The geometrical relation between aneurysm and parent vessels was found to be the primary factor governing the intra-aneurysmal flow pattern. Flow was stagnant in straight terminal models, with the aneurysm forming an extension of the afferent vessel, as long as the outflow through the branches of the bifurcation was balanced. Average flow velocities in the fundus were small but turbulent flow fluctuations of high amplitudes were observed. Asymmetric outflow through the branches of the bifurcation induced a rotatory intra-aneurysmal circulation from the dominant to the subordinate branch. The circulation in angled terminal aneurysms with the aneurysmal axis at a 45 degree angle to the plane of the bifurcation was a vortex, which was a natural consequence of the excentric inflow from the afferent vessel. Maximum flow velocities measured in the centre plane of the angled terminal aneurysms were in the range of 50 to 80% of the axial velocity in the afferent vessel. The elasticity of the models did not affect the global turnover rates but it damped the intra-aneurysmal pulse wave. On the basis of the measured velocity gradients near the walls maximum shear stresses on the wall of human terminal aneurysms were estimated to be in the order of 50 dynes/cm² (5 Pascal), a value that is similar to the maximum wall shear stresses estimated for lateral aneurysms.     

Transluminal imaging with perspective volume rendering of computed tomographic angiography for the delineation of cerebral aneurysms

Transluminal imaging with perspective volume rendering of computed tomographic angiography was used to investigate three patients with unruptured cerebral aneurysms. Selective changes in the opacity chart of computed tomography values, based on a spiked peak curve, represented the contour of the vessel and aneurysmal walls as a series of rings, and allowed a transluminal view from outside or inside the vessel lumen through the spaces between the rings. This imaging technique provided direct visualization of the underlying structures and an extensive perspective view of the cerebral aneurysms, including the parent arteries and surrounding bony structures, through the overlying vessel and aneurysmal walls. Transluminal imaging may be a useful method for the extra- and intraluminal diagnosis of a cerebral aneurysm, and for simulation of the interventional and surgical procedures considered for cerebral aneurysms.     

Rupture mechanism of a thrombosed slow-growing giant aneurysm of the vertebral artery--case report

A 76-year-old male developed left hemiparesis in July 1991. The diagnosis was thrombosed giant vertebral artery aneurysm. He showed progressive symptoms and signs of brainstem compression, but refused surgery and was followed up without treatment. He died of rupture of the aneurysm and underwent autopsy in March 1995. Histological examination of the aneurysm revealed fresh clot in the aneurysmal lumen, old thrombus surrounding the aneurysmal lumen, and more recent hemorrhage between the old thrombus and the inner aneurysmal wall. The most important histological feature was the many clefts containing fresh blood clots in the old thrombus near the wall of the distal neck. These clefts were not lined with endothelial cells, and seemed to connect the lumen of the parent artery with the most peripheral fresh hemorrhage. However, the diameter of each of these clefts is apparently not large enough to transmit the blood pressure of the parent artery. Simple dissection of the aneurysmal wall by blood flow in the lumen through many clefts in the old thrombus of the distal neck may be involved in the growth and rupture of thrombosed giant aneurysms of the vertebral artery.     

Characterization of the volume data of three-dimensional CT and MR angiograms for the delineation of cerebral aneurysms

Three-dimensional CT angiography and MR angiography with perspective volume rendering were used to investigate two patients with cerebral aneurysms. Compared with the intraoperative photographs, volume data from CT angiogram and MR angiogram were characterized on simulated virtual 3D images with virtual neuro-endoscopic and transluminal imaging techniques. In a case of an unruptured double internal carotid (C2) blister aneurysm, CT angiogram showed a configuration of the distal aneurysm similar to that in the intraoperative photograph, but failed to show the margin of the proximal aneurysm adjacent to the anterior clinoid process bone due to a partial volume effect. The MR angiogram represented both aneurysms and the parent artery, including the C3-C2 internal carotid artery. The whole shape of the aneurysm, however, differed from that in the intraoperative photograph, showing instead an elongation of the aneurysmal dome. In a case of a ruptured tiny middle cerebral artery aneurysm, CT angiogram failed to show the subtle bulging of the aneurysm. In contrast, MR angiogram clearly demonstrated the bulging of the walls at the beginning of the ascending and descending branches of the M2, which is consistent with the aneurysmal convolution observed in the intraoperative photograph. In both cases, transluminal images of the 3D-CT and MR angiograms represented the intraluminal contour of the vessel and aneurysmal walls as a series of rings, and allowed a transluminal view from outside the vessel lumen through the spaces between the rings of the vessel wall. The orifices of the aneurysm and parent arteries were shown through the vessel and aneurysmal walls, providing an extensive perspective view of the angio-architecture of the aneurysm. Morphological configuration of the inner space of the vessel and aneurysm was well visualized on CT angiogram, which was consistent with the operative view. Due to a partial volume effect, the surrounding bony and venous structures overlapped with the aneurysm made them indistinguishable from each other. In contrast, the MR angiogram provided the flow-related volume information, so that dynamics of the flow in the vessel lumen visualized the elongation of the aneurysmal dome and subtle bulging of the tiny aneurysm.     

Multiple peripheral aneurysms of the posterior inferior cerebellar artery

Peripheral aneurysms of the posterior inferior cerebellar artery (PICA) are rare. The authors describe a case in which five distinct peripheral aneurysms of the PICA were diagnosed and microsurgically clipped while preserving the parent vessel. One of the aneurysmal sacs was excised and examined pathologically, and no evidence of an infectious etiology was found. The surgical approach to peripheral PICA aneurysms is discussed and the literature concerning these unusual aneurysms is reviewed.     

Treatment of giant intracranial aneurysms with saphenous vein extracranial-to-intracranial bypass grafting: indications,operative technique,and results in 29 patients

OBJECTIVE: The treatment of giant intracranial aneurysms is a challenge because of the limitations and difficulty of direct surgical clipping and endovascular coiling. We describe the indications, surgical technique, and complications of saphenous vein extracranial-to-intracranial bypass grafting followed by acute parent vessel occlusion in the management of these difficult lesions. METHODS: Between January 1990 and December 1999, 29 patients with giant intracranial aneurysms underwent 30 saphenous vein bypass grafts followed by immediate parent vessel occlusion. There were 11 men and 18 women with a mean follow-up period of 62 months. Twenty-five patients harbored aneurysms involving the internal carotid artery, 2 had middle cerebral artery aneurysms, and 2 had aneurysms in the basilar artery. Serial cerebral or magnetic resonance angiograms were obtained to assess graft patency and aneurysm obliteration. RESULTS: All 30 aneurysms were excluded from the cerebral circulation, with 28 vein grafts remaining patent. Two patients had graft occlusions: one because of poor runoff and the other because of misplacement of a cranial pin during a bypass procedure on the contralateral side. Other surgical complications included one death from a large cerebral infarction, homonymous hemianopsia from thrombosis of an anterior choroidal artery after internal carotid artery occlusion, and temporary hemiparesis from a presumed perforator thrombosis adjacent to a basilar aneurysm. CONCLUSION: With appropriate attention to surgical technique, a saphenous vein extracranial-to-intracranial bypass followed by acute parent vessel occlusion is a safe and effective method of treating giant intracranial aneurysms. A high rate of graft patency and adequate cerebral blood flow can be achieved. Thrombosis of perforating arteries caused by altered blood flow hemodynamics after parent vessel occlusion may be a continuing source of complications.     

Delineation of cerebral aneurysms with transluminal imaging of three-dimensional MRA]

We used transluminal imaging with perspective volume rendering of magnetic resonance angiography in patients with unruptured cerebral aneurysms. Selective changes in the opacity chart of signal intensity values, based on using a spiked peak curve, represented the contour of vessels and aneurysmal walls as a series of rings, which provided a transluminal view inside and/or outside the vessel lumen through the spaces between the rings. This imaging technique allowed direct visualization of the underlying objects and offered an extensive perspective view of the architecture of an aneurysm, including an aneurysm and its parent arteries through the overlying vessel or aneurysmal walls, or through both in a single view. Transluminal imaging may be a useful adjunct modality for the intra- and extraluminal diagnosis of a cerebral aneurysm, and for simulation of the interventional and surgical procedures for cerebral aneurysms.     

Endovascular occlusion of intracranial vessels for curative treatment of unclippable aneurysms: report of 16 cases

Among 121 intracerebral aneurysms presenting at one institution between 1984 and 1989, 16 were treated by endovascular means. All 16 lesions were intradural and intracranial, and had failed either surgical or endovascular attempts at selective exclusion with parent vessel preservation. The lesions included four giant middle cerebral artery (MCA) aneurysms, one giant anterior communicating artery aneurysm, six giant posterior cerebral artery aneurysms, one posterior inferior cerebellar artery aneurysm, one giant mid-basilar artery aneurysm, two giant fusiform basilar artery aneurysms, and one dissecting vertebral artery aneurysm. One of the 16 patients failed an MCA test occlusion and was approached surgically after attempted endovascular selective occlusion. Treatment involved pretreatment evaluation of cerebral blood flow followed by a preliminary parent vessel test occlusion under neuroleptic analgesia with vigilant neurological monitoring. If the test occlusion was tolerated, it was immediately followed by permanent occlusion of the parent vessel with either detachable or nondetachable balloon or coils. The follow-up period ranged from 1 to 8 years. Excellent outcomes were obtained in 12 cases with complete angiographic obliteration of the aneurysm and no new neurological deficits and/or improvement of the preembolization symptoms. Four patients died: two related to the procedure, one secondary to rupture of another untreated aneurysm, and the fourth from a postoperative MCA thrombosis after having failed endovascular test occlusion. The angiographic, clinical, and cerebral blood flow criteria for occlusion tolerance are discussed.     

Evaluation of relation among aneurysmal neck, parent artery, and daughter arteries in middle cerebral artery aneurysms, by three-dimensional digital subtraction angiography

Intracranial aneurysms usually occur at arterial bifurcations. However, in middle cerebral artery (MCA) aneurysms, we often find that the aneurysmal neck does not necessarily exist just on the arterial bifurcation. In this study, we have evaluated the relation among aneurysmal neck, parent artery, and daughter arteries in middle cerebral artery aneurysms, by three-dimensional digital subtraction angiography. Twenty consecutive patients (9 men and 11 women) with MCA aneurysms were examined. The total number of aneurysms was 22, of which 10 aneurysms were unruptured and 12 were ruptured. Aneurysmal sizes and angles between the parent artery and each of the two daughter arteries were measured. Furthermore, aneurysms were classified into two types based on neck location. Thus, when the neck was located on the extension of the midline of the parent artery, it was defined as a classical neck type aneurysm, and when it was not, it was defined as a deviating neck type aneurysm. There were 15 cases of deviating and 7 cases of classical neck type. Interestingly, in the deviating neck type, all the aneurysms existed on the side of the daughter arteries of which the angles between parent arteries were narrower, and in 93%, the sizes of the daughter arteries in which the neck existed were smaller compared with other daughter arteries.     

Intraluminal thrombosis and growth-mechanism of giant intracranial aneurysms

12 giant intracranial aneurysms were studied by MRI. Intraluminal thrombosis was observed in 9 aneurysms. Thrombosis was found more frequently in larger aneurysms. Thrombi were formed posteriorly or inferiorly in the lumen of 4 among 5 IC-cavernous aneurysms. Location of the neck of the aneurysms and stagnation of blood flow influenced by gravity may be causative factors determining the location of thrombi. In 6 aneurysms intraluminal thrombi were inhomogeneous on MRI, suggesting that the thrombi had been formed at different times. New thrombi were formed between the aneurysmal wall and the old thrombus in 3 cases. Dissection of the aneurysmal wall by residual blood flow in the lumen or hemorrhage in the aneurysmal wall may be one of the growth mechanisms of giant intracranial aneurysms.     

Construction of experimental “giant” aneurysms

Giant aneurysms were produced in dogs by initially producing a fistula between the common carotid artery and the external jugular vein. One week later the vein was ligated above and below the fistula to create a blind aneurysmal pouch. This model has been found useful in testing experimental techniques of aneurysmal obliteration by direct injection into the sac while the lumen of the parent vessel is temporarily protected by an endovascular balloon inflated at the neck of the aneurysm.     

Transluminal visualization of intra-aneurysmal blood flow with transluminal flow imaging of three-dimensional MR angiography

As a preliminary investigation, we report transluminal flow imaging with perspective volume rendering of magnetic resonance angiography in patients with unruptured cerebral aneurysms. Selective change in signal intensities, based on using a square curve, was superimposed onto the transluminal image of the vessel and aneurysmal walls. This imaging technique provided direct visualization of flow-related information within the aneurysm in relation to its morphologic features. Transluminal flow imaging of three-dimensional magnetic resonance angiography may be a useful adjunct for the evaluation of intra-aneurysmal blood flow in clinical cases.     

Anterior communicating artery aneurysms: an overview.

AComA aneurysms are most commonly found at the A1-A2 junction on the dominant side. The angle of the arteries at the bifurcation and the direction of blood flow are factors of hemodynamic stress in the apical region where these aneurysms often develop. They exist at the bifurcation of dominant A1, A2 and AComA and usually point in the direction away from the dominant A1. They are more prone to rupture and demonstrate the highest incidence of post-operative morbidity among anterior circulation aneurysms. Consideration of aneurysm morphology may be used to guide approaches in AComA aneurysms. Resection of the gyrus rectus in combination with a pterional approach was popularized by Yasargil and it became the standard for treatment or exposure of AComA aneurysms, although other skull base approaches are also widely used. Clip selection is of extreme importance and the preservation of blood flow to the perforators should be emphasized. Adequate dissection and exposure of the entire "H" complex prior to clipping is the key to a successful outcome. Separating the perforators from the neck or dome of the artery and preserving the parent vessel presents a substantial challenge to the surgeon when the aneurysm is behind the parent artery, making it difficult to achieve a good outcome.     

Surgical treatment of the middle cerebral artery aneurysm--from the experiences of 174 cases (author's transl)]

174 cases of middle cerebral artery aneurysm submitted to surgical operations without using microscope were reviewed. At operation, the head is set on the neutral and slightly chin up position, not turned to any directions. Small craniotomy, which is about half as much as the ordinary unifrontal craniotomy, is performed. The merit of our method is as follows; the M1 portion (Fisher) of the middle cerebral artery runs horizontally, so that we can keep the parent artery during the operation, and owing to the chin up position the strong retraction of the frontal lobe can be avoided. Of 174 cases, 9 were dead (mortality rate 5.2%) and 18 were poor (10.4%). Bad operative outcome is due to the obstruction of the middle cerebral artery around the aneurysmal neck. Therefore, we should always keep in mind to preserve the blood flow of the parent artery as well as that of its branches. Study was made mainly on this point of view such as the general technical process of the aneurysmal neck treatment, the treatment of the cases with severe arteriosclerosis and with large aneurysms having the blood coagula inside.     

Large kissing aneurysms of the middle cerebral artery: a case report--classification of kissing aneurysms

We report a rare case of kissing aneurysms located at the middle cerebral artery. A 69-year-old man had a severe subarachnoid hemorrhage associated with intracerebral hematoma (Hunt and Hess grade 5, WFNS grade V). Angiography revealed two large-sized aneurysms of the middle cerebral artery, and these aneurysms were seen as contacting each other. Both aneurysms were adherent, with fibrous tissue at each dome site. Neck clipping was performed. The difficulty of neck clipping with kissing aneurysms is dependent upon the relationship between the two aneurysmal necks. We classify kissing aneurysms into two groups based on the location of the aneurysmal neck (Type 1: each aneurysmal neck is located on the same parent artery. Type 2: each aneurysmal neck is located on different parent arteries.). In Type 1, preoperative diagnosis of kissing aneurysms is difficult and premature rupture during the application of a clip occurs frequently. Therefore, careful and meticulous dissection between the aneurysms is especially required. On the other hand, with Type 2 cases, large aneurysms (> 15 mm) are seen much more frequently than in cases of Type 1. Our classification of kissing aneurysms is useful to assess the difficulty of neck clipping for these aneurysms.     

Saccular aneurysm in the left main coronary artery

The patient was a 70-year-old male with a chief complaint of chest pain. Coronary angiography revealed a saccular aneurysm of 11 mm in diameter at the furcation of the left main coronary artery. Triple vessel disease was also seen. At surgery, it was judged that the risk to rupture of the aneurysm was high because the aneurysmal wall was very thin. Therefore, the blood flow into the aneurysm was blocked, and coronary artery bypass grafting was performed. In a pathological study on the aneurysmal wall, no atherosclerotic and no inflammatory changes were found, but acidic mucopolysaccharides were detected in the tunica media. Coronary aneurysms with coronary stenosis in the elderly have been reported to be arteriosclerotic without exception. Here we present this rare case of a left main coronary artery aneurysm with coronary stenosis in an old-aged patient, considered to be due to metabolic abnormalities in the smooth muscle cells.