Disclosure
Background: Carotid-cavernous fistulas (CCFs) are abnormal communications between the carotid arterial system and the venous cavernous sinus. Most often, CCFs are broadly classified as either direct or indirect, as depicted on angiograms. Further classification is based on their etiologic and hemodynamic qualities. Clinical manifestations of CCFs frequently involve ophthalmologic abnormalities. Pathophysiology: CCFs can develop either because of trauma or spontaneous causes. Traumatic CCFs may occur after head injuries in which the intracavernous carotid artery is torn. These head injuries range from minor falls to severe penetrating wounds. In addition, iatrogenic causes resulting from endovascular therapy may contribute to traumatic CCFs. Spontaneous CCFs usually result from a ruptured carotid aneurysm; however, some have hypothesized that these fistulas may be congenital arteriovenous connections that open spontaneously in the setting of collagen vascular disease, atherosclerotic disease, hypertension, or childbirth. Fundamentally, CCFs are classified as direct or indirect (dural), traumatic or spontaneous, and high flow or low flow. The classification scheme established by Barrow et al is used frequently. It divides CCFs into 4 angiographic types: Type A fistulas are direct communications between the internal carotid artery and the cavernous sinus. Types B, C, and D are indirect (dural) shunts because fistulas to the cavernous sinus arise from dural arteries and not directly from the internal carotid artery. Signs and symptoms of CCFs can be correlated with the specific anatomy of the cavernous sinus. Because the sinus directly communicates with the ophthalmic veins, an abnormal shunt between the sinus and carotid artery can transmit arterial pressure to these veins. Concurrently, arterial perfusion to the globe is decreased. Both events lead to orbital manifestations. Palsies involving cranial nerve III, VI, and/or VII may also be evident from mass effect in the cavernous sinus.
Mortality/Morbidity:
Race: No particular racial background has been shown to be correlated with a predisposition to the development of CCFs. Sex:
Age: CCFs are most frequently found in young men and in women who are postmenopausal. Anatomy: The anatomy of the cavernous sinus (see Image 1) is truly unique because it is the only anatomic location in the body in which an artery travels completely through a venous structure. The cavernous sinus receives venous blood from both the superior and inferior ophthalmic veins. Many interlacing fibrous filaments throughout the cavernous sinus provide for an irregular flow of venous blood through the sinus. After entering the sinus, the venous blood is drained via the sphenoparietal sinus, the superior petrosal sinus, the basilar plexus (which drains to the inferior petrosal sinus), and the pterygoid plexus. The right and left cavernous sinuses are connected both anteriorly and posteriorly by way of the circular sinus. The internal carotid artery normally enters the cavernous sinus near the posterior aspect of the base of the sinus. Shortly after entering the cavernous sinus, the internal carotid artery turns anteriorly, where it travels forward before turning superiorly and exiting near the anterior aspect of the superior wall of the cavernous sinus through the anterior clinoid bone. The intracavernous carotid artery can be considered to be composed of 3 continuous segments: (1) The intracavernous carotid artery enters the sinus as the posterior ascending segment. (2) The artery then turns anteriorly, where it becomes the horizontal segment, which is also the longest segment of the intracavernous carotid artery. (3) Finally, the artery turns superiorly, where it becomes the anterior ascending segment. Several branches of the carotid artery originate in the cavernous sinus, as well. Direct CCFs (type A) result from a direct connection between the cavernous segment of the intracavernous carotid artery and the cavernous sinus itself. Indirect CCFs arise from abnormal shunts to the cavernous sinus from the meningeal branches of the intracavernous carotid artery (type B), from the meningeal branches of the external carotid artery (type C), and from the meningeal branches of both the intracavernous carotid artery and the external carotid artery (type D). Clinical Details: All patients with CCFs invariably present with some degree of pulsating exophthalmos due to dilated ophthalmic veins and swelling within the orbits. Other presentations are related to the type of CCF. Direct fistulas (type A) have an acute onset, and they have more overt signs and symptoms than indirect fistulas (types B, C, and D). Direct CCFs often occur days or weeks after a closed-head injury. Patients present with the classic triad of chemosis, pulsatile exophthalmos, and ocular bruit. Proptosis, diplopia, and visual loss also may result with these fistulas. Unlike direct fistulas, indirect fistulas have a gradual onset, with generally milder presentations. Dural fistulas often do not demonstrate the classic triad of symptoms. Patients with these fistulas usually have chronically red eyes as a result of tortuous arterialization of the conjunctiva. Often, no ocular bruit is associated with these fistulas. Direct fistulas occasionally occur in patients with connective tissue disorders. Preferred Examination: CT scanning and MRI are the preferred radiologic modalities. Compared with angiography, both CT and MRI have a much lower incidence of complications. Furthermore, CT scans and MRIs depict peripheral pathologies associated with CCFs (eg, enlargement of cavernous sinus and the ophthalmic vein). The findings of these imaging modalities are confirmed with the angiographic results prior to treatment. Limitations of Techniques: CT findings may be sufficient for diagnosis in most patients; however, MRI and angiography are superior in evaluating venous distension, the aneurysm lumen, and the increased flow to cavernous sinus. Indirect signs associated with CCFs are not readily seen on angiographic images. MRIs and CT scans are limited because precise filling of the cavernous sinus and other signs of abnormal blood flow are not readily seen.
Brain, Aneurysm
Findings: Plain radiographic findings are most useful after intervention for evaluating balloon positioning or possible leakage. |
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Findings: CT findings in CCFs include the following:
Degree of Confidence: If the superior ophthalmic vein appears to be either asymmetric or larger than 4 mm in diameter, a CCF is suggested. CT scans do not depict a CCF if it is too small or recently formed. False Positives/Negatives: Regarding false-positive findings, the superior ophthalmic vein may be enlarged in patients with other orbital pathologies, eg, cavernous angioma of the orbit, or in patients with other vascular malformations with orbital venous drainage. In particular, other dural malformations of the head and neck can be associated with unusual orbital venous drainage. Regarding false-negative findings, venous drainage of CCFs can vary, and they do not always drain into the superior ophthalmic vein. Therefore, the absence of this sign does not exclude the possibility of an underlying CCF.
Findings: MRI findings in CCFs include the following:
Degree of Confidence: The role of MRI is limited by the ability to visualize dural CCFs; however, when it is used in conjunction with contrast-enhanced CT scanning, better diagnostic capability is achieved. False Positives/Negatives: Regarding false-positive findings, MRI results are similar to CT findings in that the superior ophthalmic vein may be enlarged in patients with other orbital pathologies, eg, cavernous angioma of the orbit, or in patients with other vascular malformations with orbital venous drainage. In particular, other dural malformations of the head and neck can be associated with unusual orbital venous drainage resulting in enlargement of the orbital veins. Regarding false-negative findings, MRI results are similar to CT findings in that the venous drainage of CCFs varies, and they do not always drain into the superior ophthalmic vein. Therefore, the absence of enlargement or lack of a prominent flow void does not exclude the possibility of an underlying CCF.
Findings: Orbital sonograms demonstrate signs similar to those on CT scans and MRIs. In addition, orbital sonogram may demonstrate a reversal of flow direction in the superior ophthalmic vein. Dilated tortuous veins may be prominent on B-scan echograms. With the A-scan method, dilated ophthalmic veins may be evident. The scans may also demonstrate evidence of arterialized blood coursing through the ophthalmic veins, which are seen as several low-amplitude spikes that are in constant motion. A-scan ultrasonography also can show thickening of the optic nerve.
Findings: Radionuclide cerebral angiography performed with technetium-99m pertechnetate shows increased uptake of the tracer in the area of the carotid siphons, with rapid clearance. Degree of Confidence: This study is useful in the early postoperative period in a patient with a large CCF repair when angiography may be dangerous.
Findings: To accurately identify a CCF, selective catheterization of the right and left external and internal carotid arteries and the vertebral arteries is necessary. Including the entire skull in lateral projection imaging is important.
Degree of Confidence: The degree of confidence is high. Angiography unequivocally demonstrates the presence or absence of a CCF.
Intervention: Radiologic techniques have proven to be helpful in aiding embolization in patients with CCFs. Angiography is invaluable for the guidance of catheter placement and delivery of the embolization materials. Angiography, CT, MRI, and magnetic resonance angiography (MRA) are also useful in assessing the effectiveness of treatment. Symptomatic direct CCFs (type A) spontaneously resolve only in rare cases. Therefore, they almost always require urgent treatment. The goal of treatment is to eliminate flow through the fistula but also to maintain internal carotid patency. Most direct CCFs can be effectively treated by occluding the fistula with transarterially deployed detachable balloons, with preservation of the internal carotid artery. Silicone detachable balloons are currently the balloons of choice for this procedure because, compared with others, they are less thrombogenic, less likely to deflate early, and more easily maneuvered. A detachable flow-guided balloon can be delivered percutaneously via the affected artery, through the fistula, and into the cavernous sinus. Once the balloon is placed in the sinus, it can be inflated in such a position that it occludes the fistula but still permits flow through the carotid artery. Once proper placement is ensured, the balloon can be detached. After the fistula is closed, imaging, including anteroposterior and lateral skull radiography, should be performed the following day. Special attention should be paid to the balloon placement; if the balloon appears to have moved, additional angiography should be considered. In the event that the balloon cannot be fed through the fistula via a transarterial approach, electrolytically detachable platinum coils are often deployed via a transarterial route. In addition, an interventional approach using both detachable silicone balloons and electrolytically detachable platinum coils may be considered if either method of treatment alone is not sufficient. In the event that a transarterial route is impossible or ineffective, a transvenous approach using platinum coils may be warranted. This can be achieved either via the femoral route or surgically via the superior ophthalmic vein. Dural CCFs (types B, C, and D) sometimes resolve spontaneously. For unknown reasons, the likelihood of spontaneous resolution appears to be increased after diagnostic angiography, although a recent analysis has not demonstrated this effect. Treatment is indicated in patients with dural CCFs who present with proptosis, visual loss, palsy of cranial nerve VI, neovascularization of the iris or retina, severely elevated intraocular pressure, intractable bruit, severe pain, or increased filling of the cortical veins (as demonstrated with angiography). In low-risk CCFs, manual carotid artery compression may be attempted because this therapy has a cure rate of almost 30%. In high-risk fistulas (patients presenting with retrograde filling of cortical veins, neurologic deficits, worsening ocular symptoms, significant atherosclerosis of the carotid bifurcation, or a history of previous hemorrhage), manual compression is not indicated. In these patients and in patients in whom carotid compression therapy is not successful in treating the fistula, transarterial endovascular embolization remains the treatment of choice. Embolization of the meningeal branches of the internal carotid artery should be avoided because of a high risk of stroke. Electrolytically detachable platinum coils may be used via a transvenous route for occlusion of the cavernous sinus. The use of fiber-coated coils also appears to show promising results. Phatouros et al recommend the deployment of electrolytically detachable coils via the superior ophthalmic vein to lead to better coil positioning. They also recommend a transfemoral transvenous approach, as opposed to embolization via a transarterial approach, because of a decreased incidence of severe complications with the former. When transvenous and transarterial approaches fail, surgery may be warranted. For this, pterional craniotomy with a Dolenc approach is an appropriate method to achieve access to the fistula. Once the fistula is successfully closed, the patient may experience pain, proptosis, and cranial nerve palsies. These are common transient occurrences that may last for several weeks. These temporary complications are believed to be the result of either cavernous sinus thrombosis or impingement of balloons or other embolic material on ocular motor nerves. Another possible complication after closure of the fistula is the development of a false aneurysm of the internal carotid artery. These false aneurysms commonly decrease in size with time. Medical/Legal Pitfalls:
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