In this article, the relevant anatomy of the cavernous and paraclinoid internal carotid artery is examined. Then the classic presentation of aneurysms in these locations and methods of diagnosis are reviewed. Finally, considerations for deciding to treat these aneurysms and the various endovascular techniques available are discussed.
Key points
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Cavernous and paraclinoid aneurysms are among the most challenging microsurgical lesions due to location and complex anatomy.
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Endovascular methods have evolved over the last 2 decades with coiling, liquid embolic agents, stent-assisted coiling, and flow diverters being developed and used over time.
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The concept of flow diversion is based on placing a stent across the neck of an intracranial aneurysm, which then results in flow away from the aneurysm, inducing thrombosis and occlusion of the aneurysm over time.
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The stent itself experiences neointimal coverage, thus resulting in a remodeling of the parent vessel. As the use and application of flow diverters become more widespread, some important questions remain relating to the effective treatment of dual antiplatelet therapy, the occurrence of delayed aneurysm ruptures and intraparenchymal hemorrhages, and long-term patency rates.
Introduction
In this article the endovascular treatment of aneurysms arising from the internal carotid artery between its exit from the foramen lacerum and the takeoff of the posterior communicating artery is considered. These aneurysms often present a challenge for microsurgery because of the complex anatomy of the internal carotid artery in the region of the cavernous sinus and anterior clinoid process. Microsurgery of paraclinoid aneurysms frequently requires extensive bone removal for exposure of the neck and to achieve proximal control. Delicate dissection and manipulation of the optic nerve may be required for obtaining a surgical corridor. Aneurysms located more proximally in the cavernous sinus are often inoperable and require internal carotid artery sacrifice with or without bypass. These challenges have encouraged clinicians to develop alternative solutions to reduce morbidity and have ushered in an age of minimally invasive techniques.
In the modern era, endovascular treatment began with the use of balloons, when in 1974, Serbinenko reported 82 patients treated by occlusion of the carotid siphon with latex detachable balloons. In 1991, Guglielmi detachable coils became available and revolutionized the way neurosurgeons thought about cerebral aneurysms and their treatment. Since this time, endovascular techniques have evolved into stent- and balloon-assisted coiling and most recently the concept of flow diversion. In this article these techniques as well as the pertinent anatomy, clinical findings, and complications that arise when treating aneurysms of the cavernous and paraclinoid internal carotid artery are reviewed.
Introduction
In this article the endovascular treatment of aneurysms arising from the internal carotid artery between its exit from the foramen lacerum and the takeoff of the posterior communicating artery is considered. These aneurysms often present a challenge for microsurgery because of the complex anatomy of the internal carotid artery in the region of the cavernous sinus and anterior clinoid process. Microsurgery of paraclinoid aneurysms frequently requires extensive bone removal for exposure of the neck and to achieve proximal control. Delicate dissection and manipulation of the optic nerve may be required for obtaining a surgical corridor. Aneurysms located more proximally in the cavernous sinus are often inoperable and require internal carotid artery sacrifice with or without bypass. These challenges have encouraged clinicians to develop alternative solutions to reduce morbidity and have ushered in an age of minimally invasive techniques.
In the modern era, endovascular treatment began with the use of balloons, when in 1974, Serbinenko reported 82 patients treated by occlusion of the carotid siphon with latex detachable balloons. In 1991, Guglielmi detachable coils became available and revolutionized the way neurosurgeons thought about cerebral aneurysms and their treatment. Since this time, endovascular techniques have evolved into stent- and balloon-assisted coiling and most recently the concept of flow diversion. In this article these techniques as well as the pertinent anatomy, clinical findings, and complications that arise when treating aneurysms of the cavernous and paraclinoid internal carotid artery are reviewed.
Relevant anatomy and pathophysiology
For the purposes of this article, it is concerned with aneurysms arising from the internal carotid artery from the entrance into the cavernous sinus until just before the takeoff of the posterior communicating artery, which contains segments C4 through C6 in the classification of Bouthillier and colleagues.
Cavernous Aneurysms
Cavernous aneurysms arise from segments C4 and C5. Segment C4, or the cavernous segment, extends from the petrolingual ligament to the proximal dural ring. Within this segment, the carotid is intimately associated with the cavernous sinus, which transmits cranial nerves III, IV, VI, V1, and V2. Therefore, aneurysms of this segment can present with any of the above cranial neuropathies. The postganglionic sympathetic fibers running with the internal carotid artery enter the cavernous sinus here, raising the possibility of Horner syndrome as well.
The carotid then proceeds to segment C5, or the clinoidal segment. This segment is defined by the proximal and distal dural ring. The distal dural ring completely surrounds the carotid, making hemorrhage proximal to this point unlikely to result in subarachnoid hemorrhage.
Paraclinoid Aneurysms
Paraclinoid aneurysms are defined as those aneurysms occurring in segment C6, or the ophthalmic segment. This segment begins at the distal dural ring and continues until just before the takeoff of the posterior communicating artery. The ophthalmic segment contains 2 main arterial branches, the ophthalmic artery originating dorsomedially, followed by the superior hypophyseal artery arising from the ventromedial surface. Aneurysms of the ophthalmic artery generally project in a superomedial direction, whereas those of the superior hypophyseal artery generally project medially. Various classification schemes exist for these aneurysms, but they can be broadly grouped into 3 categories:
Carotid ophthalmic—these aneurysms arise at the base of the ophthalmic artery or just distal to this on the dorsal side of the internal carotid artery
Ventral paraclinoid—aneurysms arising from the ventral C6 segment and not associated with any particular branch of the internal carotid artery
Superior hypophyseal—those aneurysms arising from the medial aspect of the C6 segment and associated with the superior hypophyseal artery.
Approximately 33% to 59% of paraclinoid aneurysms are associated with the ophthlamic artery; 27% to 47% are associated with the superior hypophyseal artery, and 14% to 20% are not associated with any arterial branch.
Clinical presentation and diagnosis
Presentation
Cavernous aneurysms
True cavernous aneurysms are located proximal to the proximal dural ring and account for about 4% of all intracranial aneurysms. There is a strong female preponderance and average age at presentation is 60. They almost never present with subarachnoid hemorrhage because of their extradural location. Most commonly, they are found incidentally during evaluation for an unrelated problem, or in investigating cranial neuropathy of those nerves traveling within the cavernous sinus (III, IV, VI, V1, and V2). In cases of rupture, the patient typically presents with signs and symptoms of carotid-cavernous fistula rather than subarachnoid hemorrhage. Carotid cavernous fistula was the presenting symptoms in 9% of cases in a series of 87 cavernous aneurysm patients by Higashida and colleagues.
Diplopia is the presenting symptom in approximately 65% of cases, whereas retro-orbital pain or headache is the presenting symptom in approximately 59% of cases. A relatively high percentage (18%–20%) present asymptomatically. Decreased visual acuity affects approximately 16% of patients presenting with cavernous segment aneurysm. With regards to visual symptoms, a variety of constellations may present ( Table 1 ). Epistaxis has also been reported rarely.
| Clinical Finding | Treated Patients (n = 74) | Untreated Patients (n = 132) |
|---|---|---|
| Third, fourth, sixth pareses (8 with trigemninal involvement) | 26 | 12 |
| Third and sixth pareses (2 with V1) | 12 | 9 |
| Third and fourth nerve pareses (4 with V1) | 3 | 4 |
| Isolated third nerve paresis | 11 | 14 |
| Fourth nerve paresis alone | 0 | 0 |
| Sixth nerve paresis alone | 16 | 18 |
| Reduced or absent corneal reflex | 15 | 1 |
| V dysesthesia | 11 | 5 |
| Horner pupil | 3 | 0 |
| Compressive optic neuropathy | 8 | 7 |
Subarachnoid hemorrhage has been reported as a presenting symptom of cavernous aneurysms in 0% to 5% of cases. The varying rates are likely due to variations in classification scheme and whether the aneurysm was truly of the cavernous segment and therefore completely intradural. The annual risk of rupture is estimated to be between 0% and 1.6%.
It is important to determine whether an aneurysm is truly from the cavernous segment to stratify for risk of subarachnoid hemorrhage. On imaging, the optic strut can be used as a useful landmark to approximate the location of the distal dural ring. Computed tomographic angiography (CTA) can show this relationship well to define whether the aneurysm is intradural or extradural. In larger aneurysms, the bony anatomy may be distorted, which may make this more difficult. An alternative method is to identify a “waist” on cerebral angiography. Waist is an indentation on the dorsomedial aspect of the aneurysm where the aneurysm is compressed by the distal dural ring. The portion of aneurysm distal to this waist can be considered in the subarachnoid space.
Paraclinoid aneurysms
Paraclinoid aneurysms are defined above as those aneurysms arising from the distal dural ring to the origin of the posterior communicating artery. They present in bilateral fashion as much as 31% of the time. They present at a mean age of 53 to 55 with a female preponderance of 87% to 92%. Paraclinoid aneurysms can present with subarachnoid hemorrhage, headache, and visual symptoms, or incidentally. In unruptured aneurysms, approximately 80% present incidentally, whereas 10% present with headache, and 10% present with visual symptoms. The visual symptoms are due to mass effect from the aneurysm on the optic nerve and may result in visual field cut or reduced visual acuity. Risk of rupture is relatively rare. Ruptured paraclinoid aneurysms are thought to comprise between 1.4% and 9.1% of all ruptured aneurysms.
Diagnosis
The diagnosis of cerebral aneurysms is most often made by CTA or digital subtraction angiography (DSA). Although CTA has improved in resolution, DSA remains the gold standard for obtaining the greatest detail as well as dynamic data, such as flow stasis and inflow and outflow zones. In the case of ruptured cerebral aneurysms, CT scan defines the typical pattern of diffuse subarachnoid hemorrhage within the basal cisterns. In the event of a negative CT scan, subarachnoid hemorrhage can be confirmed or ruled out using lumbar puncture and testing for xanthocromia.
Endovascular considerations
Historically, the risk of open surgical treatment of cavernous and paraclinoid aneurysms is higher than other anterior circulation aneurysms given the complex anatomy of the cavernous sinus and skull base and the difficulty associated with establishing proximal control, which has led to an explosion of endovascular techniques. Indications and the techniques common to both locations of aneurysms are discussed, followed by technical nuances suited to each location.
Indications for Treatment
In determining the need for treatment, cavernous and paraclinoid aneurysms can be categorized as ruptured or unruptured. Ruptured aneurysms producing either subarachnoid hemorrhage or a carotid cavernous fistula should be treated to prevent rerupture in the former and to preserve cranial nerve function and decrease intraocular pressure and possible cortical venous drainage in the latter. The unruptured aneurysms can be further subdivided into symptomatic or asymptomatic.
The unruptured, asymptomatic aneurysm
For unruptured, asymptomatic lesions, the largest study regarding the natural history of these lesions comes from the International Study of Unruptured Intracranial Aneurysms (ISUIA). All told, this study involved 4060 patients from the United States, Europe, and Canada. With regard to the natural history, these patients were followed for a mean of 4.1 years. They were grouped into 2 categories, those patients without history of prior subarachnoid hemorrhage (group 1) and those with a prior history of subarachnoid hemorrhage (group 2). Aneurysms were then stratified for risk of rupture based on size. For all sizes, group 1 and group 2 had no statistically significant difference in rupture rates except for those aneurysms less than 7 mm. The data for ISUIA are summarized in Tables 2 and 3 .
| Classification | Description |
|---|---|
| Class 1 | Complete occlusion |
| Class 2 | Residual neck |
| Class 3 | Residual aneurysm |
Related posts:
General Technical Considerations for the Endovascular Management of Cerebral Aneurysms
Pitfalls and Complications Management in the Endovascular Treatment of Aneurysms
Cerebral Vasospasm
Vertebrobasilar Fusiform Aneurysms
Endovascular Management and Treatment of Acute Ischemic Stroke
Endovascular Management of Intracranial Atherosclerosis
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