Department of Neurosurgery, Russian Military-Medical Academy, St.Petersburg
Continuous development of microneurosurgery, neuroradiology and interventional radiology has led to full-value diagnosis and surgical treatment of diseases and injuries of veins and sinuses of the brain and dura mater. Today a combination of direct neurosurgical and intravascular interventions is a standard in rendering medical care to patients with this threatening pathology.
The system of cerebral veins as a whole is divided conditionally into deep and superficial venous networks and a complex of the dura mater sinuses. Large veins (Halen’s vein, Rosenthal’s vein, internal and thalamostriatal veins, etc.) carrying blood from structures of the middle line in the direction of the tentorial sinus are referred to the system of deep veins. The system of superficial veins with rather changeable anatomy provides drainage into sagittal, transverse, sigmoid and cavernous sinuses. Trolard’s vein, Labbe’s vein, the vein of the cerebral lateral fissure (Sylvian) are almost invariable. The system of venous sinuses ensures carrying blood out of the skull cavity along conjugate jugular veins.
The majority of sinuses is formed by duplication of the dura mater. Their wall is strengthened by fibers; it allows to preserve permanency of a lumen irrespective of a level of intrasinusal pressure. Superficial cerebral veins fall into lumens of sinuses; a posterior venous wall, protruding into a lumen, forms something similar to a valve to some extent. An intrasinusal apparatus located in a lumen of sagittal and lateral sinuses consists of septa, trabeculae, promontories, regulating flows of venous blood. Such parasinusal structures as lateral lacunae join a cavity of the superior sagittal sinus. They serve a damper and protect the brain from venous plethora in case of an increase of venous pressure. Lacunae are connected with the brain liquor system. Emissaria connect a lumen of sinuses with venous collectors of bones of the skull fornix and base, veins of soft tissues of the head, accessory nasal sinuses. There is a great number of nerve endings in sinus walls. Thus, they are considered to be a peculiar reflexogenic zone, participating in regulation of cerebral circulation.
The cavernous venous sinus is of special interest from the anatomic-physiologic point of view. The internal carotid artery with periarterial nervous plexuses, surrounding it, goes inside the sinus cavity. The sinus walls contain the IIIrd, IVth, Vth (the 1st and 2nd branches) and VIth pairs of cranial nerves. Hypophysis and external walls of the sphenoid sinus are adjacent to the inner wall of the cavernous sinus. Thus, it differs greatly from other venous sinuses due to its localization and structure.
For the first time the cavernous venous sinus was mentioned in the manual by G. Fallopius (1562). It was described by G. Ridley as “sinus circularis” (1695) and by R. Viessens as “receptacula sellar equinae lateralis apposita” (1715) at the end of the XVII and beginning of the XVIIIth centuries. J. Winslow was the first to introduce the term “sinus cavernosus” (1732).
The cavernous sinus is an anatomic complex, consisting of elements which differ both in their structure and origin. It has:
The structure of the sinus is characterized by two extreme forms, reflecting individual mutability and transformations conditioned by age. If to take one extreme form (typical of children’s age), then the venous sinus proper is a simple interlacing of small thin-walled veins which surround the slightly curved ICA. Both the artery and interlaced veins are located in loose connective “stroma”. A borderline between the venous sinus proper and cavernous capsule is vague. This form reflects incomplete reduction and a continuing process of consolidation of a primary venous network.
As for the second extreme form, the venous sinus is represented by a wide lacuna whose walls are adjacent to the ICA on one side and to a cavernous capsule and a nerve trunk, passing by its external wall, on the other side. The carotid artery is curved to a great extent. Intrasinusal connective tissue is absent. This form is more characteristic of adults. Consolidation of small veins into a common lacuna appears to take place in a postnatal period. It is promoted by a process of redistribution and hardening of intasinusal connective tissue.
The relationship between the venous sinus proper and ICA is of peculiar importance. The venous sinus proper cannot change a lumen width as it is limited by a dense cavernous capsule. Thus, pulse increase of the ICA volume is possible only at the expense of reduction of the cavernous sinus volume. The cavernous sinus is the most important regulator of cerebral circulation. This “venous heart” has a great impact on intracranial venous circulation. Exclusion of the intrasinusal part of ICA results in ceasing pulsation of venous blood inside the sinus and deceleration of venous circulation in the skull cavity.
The cavernous sinus, being a powerful reflexogenic zone, participates in regulation of arterial cerebral circulation too. A close contact with the cavernous nervous plexus and the main arterial trunk, supplying the brain, pituitary body, sensory organs with blood, a great number of nerve receptors and slow blood flow indicate that the cavernous sinus is more than a simple collector. Reception peculiarities in the sinus confirm that it is an internal reflexogenic zone, regulating blood circulation in the brain and sensory organs.
Veins connected with the cavernous sinus are divided into 4 groups:
There are various trabeculae (vessels, connective trabeculae proper and nerve fibers) in places where the cavernous sinus joins the above-mentioned vessels. They interlace and form valves, participating in directing flows of venous blood and eliminating quick growth or fall of intrasinusal pressure .
The cavernous sinus has a length of 1.2-2.8 cm. Its width is equal to 0.7-1.6 cm. Short sinuses are watched in brachycephaly and long sinuses in dolichocephaly and mesencephaly. A height of the cavernous sinus in its middle segment is 0.7-1.9 cm. Brachycephaly is characterized by a short and wide sinus with a small height. A long and narrow sinus with a small height is typical of dolichocephaly. An upper wall of the cavernous sinus consists of a leaf of the dura mater, forming a diaphragm of petrosal sella with a thickness of 0.4-1.0 mm. An internal wall consists of a fibrous leaf of the dura mater which covers surfaces of the Turkish saddle and forms a capsule of hypophysis. A thickness of a bone adjacent to this internal wall and forming a wall of a pneumatic sinus of the sphenoid bone is equal to some centimeters in children and varies from 1 mm up to 1 cm in adults.
The cavernous sinus reaches oval, round and spinous foramens on the outside. As for the width, the sinus projection on the skull base goes from the crest between middle clinoid processes and a base of the wall of the Turkish saddle up to openings of the middle cranial fossa. A length of this projection is described by a distance between an internal segment of the superior orbital fissure and a posterior edge of the internal foramen of canalis caroticus.
The cavernous sinus has the properties of baroreception. Growth of intrasinusal pressure leads to reduction of systemic arterial pressure, stimulates breathing and accelerates cerebral blood flow.
A cavernous segment of ICA is curved. At first the artery ascends, going round posterolateral parts of the Turkish saddle. Then it turns to the front, running along a lateral wall of the saddle, and enters the carotid sulcus. After reaching anterior segments of the Turkish saddle, the artery goes medially and upward and leaves the sinus in the area of inferiomedial parts of the anterior clinoid process. There are several permanent branches in the cavernous segment of ICA:
A cavernous segment of ICA has two flexures: posterior with a convexity directed backwards and anterior with a convexity directed to the front. These posterior and anterior flexures vary with people from 15 up to 120o and 15 up to 90o respectively. In brachycephaly both siphons bend at an angle of 15o in the majority of cases. As for dolichocephaly, usually the posterior siphon bends at an angle of 90-120o; this angle is equal to 60-90o for the anterior siphon. Depending on values of angles of ICA flexures there are (fig.1):
|Fig. 1. Types of ICA siphon according to its anatomic structure.|
Nerve trunks (oculomotor, trochlear, abducent and the 1st branch of the trigeminal nerves) are localized in a layer of connective tissue between a lateral wall of the cavernous capsule and a wall of the venous sinus proper. The higher the ordinal number of a nerve the greater the length at which it contacts the sinus (the smallest and biggest numbers belong to the IIIrd and VIth nerves respectively). It does not depend on the sinus anatomic form.
Arteriovenous malformations of the dura mater (dural AVM or DAVM) make 10-15% of all intracranial pathology of this type. Usually they are localized in the area of transverse and sigmoid sinuses, though they can involve any anatomic area or sinus of the dura mater. Pathogenesis of dural AVM is unknown. The majority of them develops spontaneously against a background of transformations of a vascular wall caused by age, hormonal changes, trauma or thrombosis of large vessels. The so-called posttraumatic arteriovenous fistulas are the most typical phenomenon. The first place among them is occupied by carotid-cavernous fistulas.
The main clinical manifestations of DAVM are as follows:
Peculiarities of clinical manifestation of DAVM and its threat to health of a patient are conditioned by such factors as a degree of arteriovenous shunting, direction of blood drainage from damaged vessels, a level of blood pressure in the venous system. Considerable escape into the latter, especially in the so-called “direct “ fistulas, drainage into the system of pial veins and marked venous hypertension result in an unfavorable course of the disease. Thus, intracranial hemorrhages are watched in 15-29% of patients with drainage into the system of cerebral veins.
DAVM is referred to a category of cerebral vascular lesions, whose full-value diagnosis is possible only in case of applying cerebral angiography, which demands separate catheterization and contrast study of territories of external and internal carotid arteries.
Indications for surgical treatment of DAVM include:
Arterio-sinusal fistulas in the area of the cavernous sinus are divided into direct (carotid-cavernous fistulas) and indirect (DAVM in the area of the cavernous sinus). For the first time a clinical picture of carotid-cavernnous fistula (CCF), manifesting itself as pulsating exophthalmos, was described by Travers in 1813. However, pathologic essence of the disease was unknown. The autopsy of a patient with pulsating exophthalmos, made by Henry in 1856, revealed fistula between the internal carotid artery and cavernous sinus.
The most frequent cause of CCF is craniocerebral trauma. Sometimes it can result from such diseases as atherosclerosis, aneurysms of the cavernous segment of the internal carotid artery. The ratio of traumatic and spontaneous CCF is 4:1. Traumatic CCF are most frequent in men aged 16-40. Nontraumatic CCF dominate in middle-aged and old women.
All symptoms of CCF are divided into three groups from the point of view of its pathogenesis (Samotokin B.A., Khilko V.A., 1973):
The first group (symptoms of fistulas) includes:
Symptoms of the second group (secondary signs, depending on disturbances of venous outflow and trophism) comprise:
Symptoms of the third group (depending on trauma or a disease, being the cause of fistula) are as follows:
The most typical manifestation of CCF is pulsating exophthalmos. Cases with absence of exophthalmos are extremely scanty in fistula. Sometimes due to thrombosis of the superior ophthalmic vein on the fistula side, exophthalmos develops only on the opposite side. A degree to which exophthalmos is marked can vary from 2 up to 20 mm (more often from 5 up to 7 mm). As a rule, exophthalmos, being the result of CCF, is accompanied by eyeball pulsation. According to our findings, mild exophthalmos was present in 75% of cases, moderate - in 21.4% of observations and severe - in 3.6% of patients.
A permanent symptom of CCF is vascular noise synchronous with a pulse. Auscultation shows that it is well-heard above the orbit (in case of marked exophthalmos) or in the mastoid area when outflow from the cavernous sinus is directed mainly into the inferior petrosal sinus, causing insignificant exophthalmos. Noise in a head disappears completely or to a considerable extent in compression of the common carotid artery on the fistula side.
Congestion in the orbit and eyeball is marked to the utmost in an acute period of CCF formation. It can be accompanied by lagophthalmos, chemosis, congestion in corneal and conjunctival vessels. Congestive phenomena in an eyeball are combined with an increase of intracranial pressure rather often; sometimes there can be acute glaucoma.
Impaired mobility of an eyeball in CCF is watched in more than a half of cases. It is conditioned by a lesion of oculomotor nerves in a wall of the cavernous sinus and edema of orbital tissues. The 6th cranial and oculomotor nerves are subject to such lesions most often; the trochlear and the first branch of the trigeminal nerve are affected less frequently. Sometimes external or total ophthalmoplegia is watched. Thus, aneurysmal noise, pulsating exophthalmos, reduced vision and lesions of oculomotor nerves are the most typical manifestations of CCF. Correct diagnosis can be made on the basis of these symptoms in the majority of cases.
A clinical course of CCF may be divided into three periods:
Serbinenko F. A. (1986) distinguishes three types of anastomoses, depending on the disease course: 1) compensated fistula; 2) decompensated fistula; 3) decompensated fistula at the stage of stabilization. Periods of compensation and sub- and decompensation can follow each other, but usually CCF is characterized by gradual progression, augmentation of hemodynamic and trophic changes, watched first of all in the orbit and brain. Thinning of walls of the cavernous sinus results in their rupture and fatal intracerebral or nasal bleeding in some cases.
Prognosis of a spontaneous course of CCF is unfavorable. Recovery from spontaneous thrombosis of fistula is watched only in 50-10% of cases; 10-15% of patients die from intracranial and nasal bleeding and 50-60% of them are disabled due to blindness and psychic disorders.
Usually diagnosis of CCF based on clinical data presents no difficulty. Such sympyoms as pulsating exophthalmos, noise in a head, congestion in the orbit, limited mobility of an eyeball are quite enough for correct diagnosis. Certain difficulties arise in an acute period of craniocerebral trauma when a patient is unconscious and cannot complain of noise in the head. Auscultation is of crucial importance in such cases. Transcranial Doppler can be used for diagnosis of CCF at the prehospital echelon as it helps to detect arteriovenous shunting in the internal carotid artery, impaired venous outflow in the system of superior ophthalmic and basal veins.
Despite the fact that CCF can be diagnosed on the basis of clinical findings in the majority of cases, angiographic examination is of extreme importance for estimation of its type and differentiation between it and such diseases as carotid-jugular fistula, AVM of the orbit, fistula between branches of the external carotid artery and sigmoid, petrosal and transverse sinuses. Angiographic findings are of decisive importance in choosing an operation method.
According to angiographic findings all anastomoses of the cavernous sinus are divided into two types:
An “A” type – anastomoses with high velocity (CCF proper and fistula with massive flow). These are typical CCF formed usually as a result of traumatic rupture of the carotid artery in the cavernous sinus area or spontaneous rupture of aneurysm of the same localization.
A “B” type – anastomoses with low velocity (DAVM in the area of the cavernous sinus). The carotid system is connected with the cavernous sinus both by branches of ICA (the cavernous part) and branches of the external carotid artery (ECA). This type has several subtypes:
B1 – only branches of the cavernous segment of ICA are involved. It is an extremely rare phenomenon.
B2 - only branches of ECA are involved. It is watched in 9-12%.
B3 – both branches of ICA and ECA are involved. It is the most spread type watched in 90% of cases with DAVM in the cavernous sinus area.
Angiographic examination is aimed at estimation of:
Development of CCF surgery was a rather complicated process. It is proved by existence of more than 40 combinations of interventions. They are divided into extra-and intracranial. The first group includes embolization of fistula by muscular emboli according to Brooks or by polystyrene emboli, occlusion with a balloon-catheter according to F.A. Serbinenko (with preservation of patency of the internal carotid artery or its occlusion).
The second group comprises exclusion of ICA above or below fistula (clipping in the skull cavity and ligation on the neck), clipping of ICA with subsequent embolization, direct operations (sinus tamponade or clipping of the fistula).
Today the method of choice is endovascular occlusion of fistula with a balloon-catheter or microcoils from the side of the cavernous sinus, using arterial or venous approach and preserving patency of ICA.
In case of the typical “A” type fistulas transfemoral (sometimes carotid) catheterization by a catheter with a diameter of 8-9 F (1 F=0.33 mm) is performed. A pair of balloon-catheters is introduced into a vascular bed through it. One or both of them are split balloon-catheters. A balloon volume depends on a size of defect in walls of ICA and the cavernous sinus. One or several balloons are introduced in succession into the cavernous sinus cavity through a rupture in the arterial wall. After its inflation with a hardening silicon compound it is dropped into the sinus cavity, occluding fistula on the outside and preserving a lumen of ICA. If a reconstructive operation is impossible balloon-occlusion of ICA at the fistula level is performed or fistula is done away with in some other way. Removal of CCF, using an arterial approach, can be achieved in 94% of cases; patency of ICA is preserved in 60-95% (Debrun G., 1993). When a reconstructive operation is impossible a venous approach is used (6-10% of cases); retrograde catheterization of the cavernous sinus through the superior ophthalmic vein or the inferior petrosal sinus is made and sinus is embolized with microcoils; balloons are introduced occasionally. Embolization of fistula with mircrocoils or microemboli through a catheter with a diameter of 1.8-2.5 F can be carried out in some cases with decompensated collateral blood supply or recurrent fistulas. The rate of complications does not exceed 3%; all of them are connected with defects of surgical interventions. It predetermines the necessity of improvement of both surgical technique and instruments. Results of angiographic examination and reconstructive balloonization of posttraumatic CCF of the “A” type are given in fig.2.
|Fig. 2. Straight and lateral carotid angiograms before an operation (a) and after reconstructive balloon-occlusion of CCF with a balloon-catheter (b): patency of ICA is preserved, fistula does not function. Arrows show balloon’s position in the cavernous sinus cavity.|
Surgical treatment of the “B” type fistulas is less radical due to polyafferent structure of a fistula. There are five interventions used in combination with each other:
The results of some kinds of treatment (%) are shown in the table (Halbach V., 1993):
An angiographic picture of nontraumatic fistula of the “B3” type and results of embolization of branches of ECA and the cavernous segment of ICA are presented in fig. 3.
|Fig. 3. Selective angiography of internal (a) and external (b) carotid arteries in nontraumatic malformation of the “B3” type in the area of the cavernous sinus. It does not function after embolization of branches of ECA (c) by PVA particles. Superselective ICA angiography in distal ballon-occlusion (d) and control angiography – malformation does not function, ICA is patent (e).|
Regress of CCF symptoms after occlusion and its dynamics depend on a degree to which they were marked before the operation, completeness of exclusion of fistulas from blood flow, the extent of development of collateral cerebral circulation. Noise in the head stops on an operating table immediately after CCF exclusion; besides there is reduction of exophthalmos and congestive phenomena. There appear weak movements of eyeballs in 1/3 of patients with ophthalmoplegia. Complete regress of exophthalmos takes place in 1-2 weeks. The mobility of eyeballs grows and visual disorders become less marked.
Sometimes fistulas of the cavernous sinus are associated with the so-called false traumatic aneurysms of the cavernous segment of ICA. They are formed in severe craniocerebral trauma accompanied by a fracture of the skull base and, in particular, a lateral wall of the sphenoid sinus. Typical carotid-cavernous fistulas are watched in this pathology rather frequently. According to Khilko V.A. et al. (1980), profuse arterial nasal bleeding caused by injuries of carotid arteries is observed in 6.5% of parabasal fractures of the skull base. In some cases such aneurysms are iatrogenic and result from intraoperative damage of the carotid artery in interventions on the sphenoid sinus. There are several factors, increasing a risk of damage of the cavernous segment of ICA: the artery wall in this area is less dense because of immaturity of a muscular layer and an elastic framework, the siphon curvatures create conditions for an uneven effect of a hydraulic impact on the artery walls, the cavernous segment of ICA is characterized by transition from the part fixed to cranial bones to the part which is relatively mobile in subarachnoid space. Proximity to bone structures of the skull conditions a high risk of the artery damage by splinters. Blood penetrates into the sphenoid sinus cavity through a slit-like rupture of the ICA wall in the anterior segment of the siphon localized extradurally in the carotid sulcus of the sphenoid bone. It is detached from the nasopharynx cavity by duplication of a mucous membrane of the sinus whose rupture often leads to fatal recurrent nasal hemorrhages. According to Moore D. et al. (1979), such hemorrhages result in fatal outcomes in 50% of cases without timely surgical care. This situation is urgent and demands carrying out emergency angiographic diagnosis. If false aneurysm is diagnosed, intravascular balloon-occlusion of the damaged carotid artery is performed at the level of rupture. In case of a small cavity, reconstructive operations can be a success in 6-10% of cases. They consist in balloon-occlusion of false aneurysm with preservation of the artery lumen (Lazarev V.A., 1983). Intravascular operations ensure reliable control of bleeding. Serbinenko F.A. et al. (1981) described their experience of surgical treatment of 16 patients and reported that hemostasis had been achieved in all of them Working ability was preserved in 75% of cases; nonfatal complications were present in 31.1% of patients; there were no fatal outcomes.
DAVM in the area of transverse and sigmoid sinuses are the most spread forms of dural malformations. They are watched in patients with postoperative sequelae of craniocerebral trauma, especially if they had fractures in projection of the sinuses, and in cases with systemic diseases of vessels. However, histories of the majority of them contain no information on such states. Appearance of malformation on a wall of a thrombosed sinus is explained by a hypothetical factor of angiogenesis and its potentiating effect on normal arteriovenous anastomoses of the dura mater.
Clinical manifestations of DAVM in the area of transverse and sigmoid sinuses are conditioned by drainage direction, a degree to which shunting is marked and fistula localization. A dominating sign is subjective or objective pulsating vascular noise which disappears or decreases in digital compression either of the carotid artery on the neck or the occipital artery. Drainage into the system of cortical veins can be a cause of headaches, congestion in the eye fundus, ophthalmologic symptoms typical of CCF, subarachnoid-parenchymal hemorrhages, venous infarctions of the brain.
Instrumental methods of diagnosis include craniography, CT of the brain with a contrast substance, MRI and MRA. As a rule, results of examinations are not highly informative as diagnosed changes (an increased vascular pattern of the skull fornix, secondary changes of the Turkish saddle, parenchymal or mixed hemorrhages, selective increase or widening of pial and parenchymal venous collectors, widening of arteries of soft tissues) are not pathognomonic. Thus, neither CT nor MRI can be used as screening methods.
Angiographic examination is of decisive importance in diagnosis of DAVM. Separate catheterization of the internal and external (or its branches) carotid arteries is carried out. DAVM of lateral sinuses are supplied with arterial blood from the system of the external carotid artery, in particular, occipital, middle meningeal, deep maxillary, posterior auricular, ascending pharyngeal arteries. The system of the internal carotid artery participates in blood supply of DAVM by branches of the cavernous segment (the meningo-hypophyseal trunk). Large fistulas can have pial blood supply by temporal or parietal branches of the middle and posterior cerebral arteries.
Depending on a character of drainage there distinguish three types of arteriovenous anastomoses in the area of lateral sinuses.
The first type - Drainage through an ipsilateral sinus. This type is attributed to low-risk malformations. Its manifestations are headache and vascular noise. Neurologic deficit and hemorrhages are rare.
The second type - Drainage through a contralateral sinus because of stenosis or occlusion of a damaged sinus below fistula. It is characterized by more marked clinical manifestations up to intracranial hemorrhages.
The third type - Drainage into cortical veins. It is characterized by a severe course with development of areflexia, venous infarctions and hemorrhages (up to 42% of cases). A risk of intracranial hemorrhages in DAVM of the third type becomes greater in presence of stenosis and varicosity of draining veins.
As a rule, DAVM has a progressive course. Dymanics of progression from the first type to the third one can be both gradual and acute. In the latter case the disease has manifestations of acute disorder of cerebral circulation.
Indications for surgical treatment are estimated with taking into account a character of clinical manifestations, the disease course, a type of DAVM and a patient’s desire. A marked pulsating vascular noise can be the only indication for an operation. Today it is not clear, if partial exclusion of DAVM is a factor of prevention of intracranial hemorrhages. Thus, patients with the first type of DAVM should be treated conservatively with dynamic angiographic control in case of any changes in a character of symptoms. It is necessary to avoid prescription of desaggregants and anti-inflammatory drugs.
The most spread methods of treatment are compression therapy, transarterial and transvenous embolization.
Compression therapy can be recommended to patients with contraindications for embolization and the first type of DAVM, when there are no absolute indications for an operation. Periodic compression of the occipital artery in the retroauricular area for 30 min is used. Recovery is achieved in 27% of patients with small DAVM, supplied by the occipital artery. These procedures have a preventive or autosuggestive character in all the rest cases and especially in inoperable situations.
Transarterial embolization is one of the most effective ways of DAVM correction. Superselective catheterization of arteries, branches of the external carotid artery, supplying fistula with blood, is carried out with the help of a microcatheter, with the tip diameter up to 1mm. The rate of radical interventions is 50-70%; subtotal occlusion with full regress of symptoms is achieved in 38% of cases. A guiding catheter with a diameter of 5-7 F is introduced into the opening of ECA or a branch, supplying DAVM with blood. Microcatheters are introduced into vessels, feeding DAVM, with the help of a guide and placed within malformation gates distally from places of separation of functionally important and cutaneous branches. Testing of arteries by injection of 100 mg of thiopental or lidocaine is carried out in dubious situations. Both solid (microparticles of polyvinylacetate) and liquid (N-butylcyanacrylate) embolizing substances are used for embolization of malformations. The latter give a more persistent effect, but are associated with a higher risk of ischemic complications. One should not perform occlusion of proximal segments of ECA with balloons or spirals, as it provokes appearance of collaterals, formed from the system of the contralateral ECA and internal carotid arteries and directed into fistula. Transarterial embolization can be used as a preoperative means of reduction of blood loss in direct operations whose main purpose is removal of pathologic vessels of DAVM; sometimes they are removed together with a part of a damaged sinus.
Transvenous embolization of DAVMs in the area of lateral sinuses is a method proposed by Mullan S. (1979) and Hosobuchi Y. (1975). It is done by placement of thrombogenic material into their lumen. Transvenous embolization is indicated in DAVM of the third type when drainage is directed into the system of cortical veins. As a rule, it is used after preliminary transarterial embolization. An embolizing substance (platinum microcoils) is brought to a fistula zone through a microcatheter, introduced into the sinus with the help of a transfemoral or intraoperative (in case of a direct operation) approach. Control angiographic examination is carried out only in three years.
The figure given below illustrates the results of angiographic examination in DAVM (the third type) of the transverse sinus before and after superselective embolization of the occipital and middle meningeal arteries.
|Fig. 4. a). The right-side carotid angiogram of DAVM in transverse sinus (a). Embolization led to considerable reduction of contrasting of fistula and deep draining veins (b).|
Localization of DAVM in the area of the superior sagittal, petrosal sinuses or anterior cranial fossa (ethmoidal DAVM) is less frequent. DAVM of the superior sinus are characterized by headaches, intracranial hemorrhages (40%) or a clinical picture of stroke (20%). As a rule, DAVMs have posttraumatic etiology. Diagnosis is based on clinical findings (objective vascular noise, neurologic symptoms of a lesion of parasagittal parts of the brain), results of craniography (an enhanced vascular pattern of the skull fornix, thinning of parietal bones in projection of the sagittal suture) and angiographic examination. Blood supply of DAVM is bilateral and symmetric. It is provided by middle or, sometimes, anterior meningeal arteries, perosseous perforating branches of superficial temporal and occipital arteries, posterior meningeal branches of vertebral arteries. CT and MRI are unacceptable in disgnosis of anstomoses of this localization.
Treatment of symptomatic DAVM in the area of the superior sagittal sinus is complex. The first stage is superselective embolization of meningeal arteries feeding fistula; usually cutaneous branches are embolized by an “open” method or during operations. Intravascular therapy is effective in a half of patients. As for the rest cases, cranial trepanation in the parasagittal area is performed and fistula on a wall of the superior sagittal sinus is closed. It allows to obtain obliteration of DAVM in all patients.
|Fig. 5. Bilateral superselective angiograms of meningeal arteries (a, b), feeding traumatic DAVM in the area of the superior cavernous sinus. Additional feeders from soft tissue branches of ECA (c, d). Result of embolization with subsequent direct closure of fistula on a superior-lateral wall of the sinus (e).|
Ethmoidal DAVM is a rare phenomenon. There are only a few reports on surgical treatment of this pathology. The disease dominates in men (87%). Usually it manifests itself as parenchymal hemorrhages (91%). Some patients complain of hemicrania-like headaches in the frontoorbital area. As a matter of fact, ethmoidal arteries (branches of the ophthalmic artery) are the single source of supplying fistula with blood. Sometimes terminal branches of ECA, anastomosing with the ophthalmic artery in the area of the upper internal angle of the orbit, take part in blood supply of DAVM. Drainage is provided by varicosities of the olfactory fossa or parasagittal veins. Varicosity of draining veins is revealed in all patients with hemorrhages. Diagnosis is based on findings of CT and MRI (hemorrhages, varicosity of veins of frontal lobes, manifesting itself as their mass lesion, dilated arteries and veins of the orbit and base of a frontal lobe). Ultrasound doppler is an additional means of diagnosis. It allows to detect arteriovenous shunting in the area of the ophthalmic artery. Results of angiographic examination are of extreme importance. Separate angiography of ICA and ECA helps to reveal feeding arteries, ways of drainage, a degree of varicosity. Usually ethmoidal DAVM are treated surgically. Embolization is dangerous as there is a risk of embolism of retinal arteries. Direct separation of fistula and removal of a draining vein are performed after trepanation of the skull in a frontal area. Sometimes an operation is limited to coagulation and dissection of the single draining vein. It gives rather good results.
The figure given below presents pre- and postoperative carotid angiograms of a patient with DAVM in the area of the anterior cranial fossa which was diagnosed initially as meningioma of the olfactory fossa.
|Fig. 6. CT-scan of draining vein varix, mimicking olphactory groove meningioma (a). Right-side carotid angiography before (b) and after stage-by-stage embolization of feeding vessels (ethmoidal arteries) and removal of DAVM of the olfactory fossa with varix of a cortical draining vein (c).|
Thus, dural arteriovenous malformations are a complex disease characterized by a variety of symptoms, versions of clinical manifestation and a different course. Abnormal venous drainage predisposes to intracranial hemorrhages and development of venous infarction. Decision making on surgical treatment of a specific patient is based on the analysis of the whole complex of symptoms, a character of a clinical course and manifestations, neurologic status, estimation of a risk and possible success attained by use of this or that method. Endovascular intervention is an optimum way for obliteration of the fistulas in the majority of cases.
Thrombosis of sinuses of the dura mater can be a result of trauma, compression of a sinus by a tumor, dural malformation or septic lesion. It can develop spontaneously in patients with leukemia, coagulopathy and systemic lesions of connective tissue.
Clinical manifestations of sinus thrombosis vary from an asymptomatic course up to severe neurologic dysfunction and death. Common clinical manifestations are conditioned by a syndrome of intracranial hypertension and include congestion in the eye fundus, headache, epileptic seizures, focal areflexia. Thrombosis of the cavernous sinus has a specific picture. There are marked non-pulsating exophthalmos, edema and conjunctival chemosis, venous hyperemia, marked congestion in the eye fundus.
Diagnosis of sinus thrombosis is very complicated. CT can be indicative of venous infarction of the brain, intracerebral hemorrhage. Thrombosis of the sagittal sinus is characterized by presence of the d -symptom (a triangular zone of reduced density in the sinus lumen surrounded by a contrast edging). MRI examination of the brain with MR phlebography is considered to be a method of choice. Final determination of localization and extent of thrombosis is carried out with the help of cerebral angiography and phlebography.
A natural course of thrombosis of dural sinuses is unknown. Mortality in acute thrombosis is equal to 10-50%, a rate of asymptomatic thrombosis not considered. A course and outcome of the disease may be dependent on such factors as age, thrombosis extent, presence of lesions of cortical veins. However, these data have not been analyzed thoroughly in any serial study. The disease outcome is conditioned by a speed of recanalization of an obliterated sinus or formation of venous collaterals. Considerable variability of these indices hampers carrying out profound analysis of results.
Medical therapy of thrombosis is limited from the point of view of its possibilities and aimed at sequelae in the form of venous infarctions with mass-effect phenomena. It also includes management of intracranial hypertension and a dislocation syndrome. Systemic heparinization prevents progression of thrombosis but does not promote lysis of a thrombus. As for recanalization of a thrombosed sinus, use of systemic fibrinolysis in combination with heparinization gives promising results. At the same time it is connected with a considerable risk of development of hemorrhagic complications. There are reports, describing direct surgical thromboectomy. However, this method is not widely practised. “Active” and widespread methods of correction comprise selective catheterization and local fibrinolysis with bolus administration of urokinase and subsequent systemic therapy. A microcatheter is left in a sinus for some days until restoration of its patency is achieved.
Management of septic sinus thrombosis consists in carrying out compulsory systemic and regional antibacterial therapy. Regional infusion of antibacterial drugs is ensured by introduction of a catheter at the level of bifurcation of the common carotid artery by means of catheterization of the superficial temporal or thyroid arteries.