He concluded that the latter group requires treatment, while moderate and small fistulas may not. This classification has rather limited value for clinical practice, because many patients with moderate or small AV shunts may still need treatment because they suffer from “non-cerebral” symptoms. In addition, DCSFs are not considered.

Much later Lin et al. (1994) applied duplex carotid sonography criteria such as flow volume and resistance index (RI) for a classification of CSFs (see also Sect. 7.1.2.). The authors were able to separate three groups of fistulas: (1) small RI and increased flow volume in the ICA: direct (Type A) CCF; (2) normal RI and flow volume in the ICA and ECA: dural branch of ICA-cavernous sinus fistulas (Type B); (3) small RI with or without increased flow volume in the ECA: dural branch of ECA-cav- ernous sinus fistulas (Type C) or dural branches of ICAand ECA-cavernous sinus fistulas (Type D). This approach has not found a wider acceptance.

Some dural CSFs may recruit a large number of feeding pedicles causing a large AV shunting volume and may have an angiographic appearance that resembles an AVM. They are therefore erroneously called high-flow fistulas. Because quantitative data on flow are lacking so far, only direct AVF should be named as such.

Based on the various aspects discussed above, a truly consequent classification of DCSFs with or without etiological aspects would require incorporating the arterial and venous patterns as well as hemodynamic parameters. Such an approach, however, would necessarily result in a confusingly large number of different types of fistulas without significant impact on prognosis or therapy. Although a proper classification for DCSFs is of prime importance, it seems for the time being an aim difficult to accomplish. Because these fistulas represent a relatively infrequent disease, it may be practical to simplify or not a cortical drainage is present, whether the AV-shunt is located unior bilateral, and which transvenous route is accessible.

Today the majority of DCSFs are treated by transvenous occlusion techniques and transarterial embolization is mainly reserved for Type A fistulas, regardless of their etiology spontaneous or traumatic. From an endovascular therapy point of view, the differentiation of B–D fistulas appears no longer very useful and is more of academic interest. While it has little prognostic value, for the purpose of endovascular strategy, the old classification in direct and indirect fistulas still seems suitable.

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C O N T E N T S

Introduction 65

5.1Etiology and Pathogenesis of

Type A Fistulas 66

5.2Etiology and Pathogenesis of

Type B–D Fistulas 67

5.2.1Pregnancy 68

5.2.2Hormonal Factors 68

5.2.3Thrombosis 69

5.2.4Venous Hypertension 72

5.2.5Trauma 72

5.2.6Embolization 73

5.2.7Congenital 73

5.3Prevalence 76

5.3.1Natural History 78

References 79

Introduction

Although the clinical phenomenon of the “pulsating exophthalmos” has been known since Benjamin Travers (1811) observation, the discussion about its underlying pathophysiological substrate remained controversial for a long time. He assumed early on that the pathological anatomy of the pulsating exophthalmos would be a carotid-cavernous fistula, while other reports in the nineteenth century on “intraorbital aneurysms”, causing similar signs and symptoms, interpreted those as the main cause. It was mostly the English school that assumed an intraorbital pathology as underlying mechanism, whereas in France the cavernous sinus was considered the true source of the pulsating exophthalmos. This was to a large extent due to the popular work of Nelaton (1876), physician of Napoleon and Garibaldi, who was able to demonstrate post mortem a direct arteriovenous communication between

carotid artery and cavernous sinus in two patients with a pulsating exophthalmos after trauma (see also Chap. 2). Inspired by this, Bartholow (1872) published more clinical observations on pulsating exophthalmos. But it was not until Rivington (1875) and Sattler (1880) presented their extensive monographs that the anatomical concept of (direct) carotid cavernous fistula found broader acceptance. The term “pulsating exophthalmos” was nonetheless used throughout the following 70 years (Locke 1924; Sattler 1920; Sugar and Meyer 1940;

Wolff and Schmid 1939; Dandy 1937; Hamby and Gardner 1933; Noland and Taylor) until it was eventually replaced by “carotid cavernous fistula” (Potter 1954; Echols and Jackson 1959; Hayes 1958; Walker and Allegre 1956; Parkinson 1967;

Hamby 1966).

Although indirect fistulas frequently may cause symptoms similar to direct fistulas, they represent in terms of etiology and pathogenesis entirely different lesions. Reports on pulsating or non-pulsating exophthalmos in the pre-angiography era did not differentiate between indirect and direct fistulas. Even after introduction of cerebral angiography by Moniz (1927) at the beginning of the last century, it took decades until diagnostic arteriograms in a quality allowing for detailed analysis of angiomorphology became available. Only when the fine, minute network of dural arteries could be angiographically visualized, did separating Type A from Types B–D fistulas become possible (Castaigne et al. 1966b; Lie 1968; Newton and Hoyt 1970). Thus, it can be assumed that because of the lacking suitable imaging tools such as selective external and internal carotid arteriography, in many of the historic series some “spontaneous” or “idiopathic” fistulas were in fact dural cavernous sinus arteriovenous fistulas. Newton and Hoyt (1970) described and characterized clinical, etiological and angiographic features of dural arteriovenous shunts in the CS region.

5.1

Etiology and Pathogenesis of Type A Fistulas

Direct communications between ICA and CS can be considered Type A fistulas, regardless of their etiology. The clinical picture of a spontaneous fistula (true Type A fistulas according to Barrows classification) is usually indistinguishable from a traumatic CCF. Since very early on, it was believed that an inherent weakness of the intracavernous portion of the ICA is a predisposing factor to the formation of a CSF. Delen (1870) found that if the carotid artery is cannulated and liquid is injected with force, the vessel will rupture within the CS: “Aussi, en injectant le système carotidien, avon-nous constater que la carotide interne se rompt facilement dans le sinus si l’on pousse un peu fortment l’injection. Sur un sujet auquel nous avions lié les deux vertebrales et la carotide primitive droite en poussant par la carotide primitive gaunche une injection solidifiable, nous avons obtenu la rupture de la carotide interne dans le sinus cavereux. La matière à injection pénétrant dans le sinus passa dans la veine opthalmique et les veines de la face, realisant ainsi, sur le cadaver, les conditions anatomiques de l’anévrysme artérioveineux.”

In some early series, fistulas of traumatic origin represent 69%–77% of all CSFs (Locke 1924; Sattler 1920) and usually develop following severe head trauma with sharp or blunt head injuries. In the past, they were seen most frequently in men, being more often involved in wars, and industrial or traffic accidents. The modern environment with a high prevalence of automobile accidents may have erased this gender difference (Hamby 1966; Debrun et al. 1988b; Vinuela et al. 1984). On the other hand, improved head protection for motorcycle riders seem to have decreased the number of traumatic CCFs. Only large populations riding bicycles and still being exposed to frequent severe head trauma in some areas of the world, like South-East Asia, may explain the relatively high rate of traumatic CCFs there.

A characteristic morphologic feature of traumatic CCFs is a tear of the carotid wall allowing a high-flow arteriovenous shunt to develop directly and rapidly. Patients often present with dramatic ophthalmic symptoms developing within a few days and usually require emergency treatment. In some cases, however, a delay of several months may occur before symptoms, such as a bruit or an exophthal-

mos, become evident. The size of the tear can vary from 1 to 5 mm and it may occur as single or multiple laceration or in some cases as complete transsection. Bilateral Type A fistulas, although rare, may occur and have been observed even among the earliest reported cases (Sattler 1930). They have a less favorable prognosis and may present with delayed clinical deterioration (Ambler et al. 1978). Angiographically, Type A fistulas show a rapid AV shunting with venous drainage into efferent and afferent veins, often significant cortical or leptomeningeal drainage, and sometimes associated with complete arterial steal. In some cases, the traumatic rupture of an intracavernous branch of the ICA or a dural branch of the ICA can cause a Type A fistula that may present with only little arteriovenous shunting (Obrador et al. 1974; Parkinson 1973). Under rare circumstances traumatic CSFs occur due to a rupture of a trigeminal artery (Berger and Hosobuchi 1984; Kerber and Manke 1983; Debrun et al. 1988a; Flandroy et al. 1987; Guglielmi et al. 1990; Tokunaga et al. 2004). Whether unrecalled microtrauma may be an etiologic factor for spontaneous CCFs is uncertain (Tomsick 1997a).

The etiology of spontaneous CSFs is more difficult to ascertain (Hamby 1966). Spontaneous rupture of an intracavernous aneurysm can cause Barrow’s Type A fistula that may result in a high-flow arteriovenous shunt, clinically and angiographically indistinguishable from a traumatic direct fistula (Barrow et al. 1985). Dandy (1937) reported on an 18-year-old male who complained about progressive exophthalmos over 6 years with no history of an injury and he considered a congenital intracavernous aneurysm being the only possible cause. Locke (1924) observed in his autopsy series 7 traumatic and 33 spontaneous cases. Fromm et al. (1967) demonstrated angiographically the existence of a saccular aneurysm of the cavernous carotid artery (C4-C5-segment) in a patient who spontaneously developed a direct CCF. Taptas (1950) found in his series a true communication between ICA and CS in only 50% of cases. Debrun et al. (1988b) reported 5 spontaneous Type A fistulas in 132 patients, among whom 3 had a ruptured cavernous aneurysm, 1 developed after pregnancy and another was seen in a 5-year-old child. Taki et al. (1994) saw 2 out of 44 patients with spontaneous direct shunts without any clinical angiographic evidence of congenital disorder, and thus considered them caused by rupture of an infraclinoid aneurysm.