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Aneurysms of the Carotid Artery
Aneurysms of the Carotid Artery G. Matthew Longo, MD and Melina R. Kibbe, MD Carotid artery aneurysms are an uncommon but important problem. The available data suggests that, untreated, these aneurysms lead to neurologic symptoms from embolization. Pseudoaneurysms of the carotid artery result from injury or may be the long-term sequelae of a spontaneous carotid dissection. While open surgery has been the primary mode of treatment, these aneurysms are being treated more commonly with endovascular approaches. This trend is partly the result of the increasing experience with the endovascular treatment of carotid artery stenosis. The endovascular approach offers advantages in other situations where open access to the distal extent of the aneurysm is difficult or neck radiation leads to concerns about wound healing. This article outlines the etiology, new diagnostic modalities, and treatment of aneurysms of the carotid artery. Semin Vasc Surg 18:178-183 © 2005 Elsevier Inc. All rights reserved.
I
N 1808, SIR ASTLEY COOPER documented the first successful procedure for an aneurysm of the extracranial carotid artery.1 This consisted of a proximal ligation of a painful, bulbous aneurysm of the internal carotid artery. During the next century and a half, ligation remained the mainstay of treatment for this disease. However, this was associated with a high incidence of neurological sequelae. By the 1970s, reconstruction of the carotid arterial system became the standard. Currently, carotid aneurysms still invoke a substantial amount of interest due to the multiple etiologies, therapeutic challenges, and uncommon occurrence. Aneurysms of the extracranial carotid artery fall within two broad categories; true aneurysms or false (pseudoaneurysm) aneurysms. This is an important factor in determining the best treatment.
Etiology True Aneurysms Atherosclerosis is often cited as the most common cause of extracranial carotid artery aneurysms, accounting for anywhere between 34% and 70% in published series.2,3 Often, these aneurysms occur at or near the carotid bifurcation and are typically fusiform, although saccular aneurysms can also occur in this location.4 These aneurysms are found along the common or internal carotid artery but rarely at the carotid bulb (Fig 1). The patients often have severe hypertension.5 The male-to-female ratio is 1.9:1, in contrast to aortic aneu-
Division of Vascular Surgery, Northwestern University, Chicago, IL. Address reprint requests to: Melina R. Kibbe, Division of Vascular Surgery, Northwestern University, 201 E Huron Street, Galter 10-105, Chicago, IL 60611. E-mail: [email protected]
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0895-7967/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.semvascsurg.2005.09.002
rysms, where the ratio is more heavily weighted towards males.3,6 In cases where atherosclerosis is not the underlying cause, patients are often younger and may suffer from tuberculosis, human immunodeficiency virus, or arteritis (Takayasu’s).7 Mycotic aneurysms are usually caused by Salmonella or syphilis.8,9 Other rare causes of carotid aneurysms that have been described in case reports of fibromuscular dysplasia, collagen-vascular disease, and irradiation (Table 1).2,10,32
False Aneurysms False aneurysms of the carotid artery occur when there is disruption of the continuity of the arterial wall. There are multiple causes of pseudoaneurysm of the carotid artery (Table 1). Rupture or dilation of a patch angioplasty following endarterectomy, particularly when an earlier generation of Dacron was used for the patch.2 El-Sabrout and Cooley2 from the Texas Heart Institute have reported one of the largest single institution series of extracranial carotid artery aneurysms. In this series of 67 cases, 38 (57%) of the aneurysms were pseudoaneurysms following Dacron patch after endarterectomy.2 Among the 38 patients, 7 were found to have suture line disruption secondary to degeneration or infection of the silk suture, 13 were secondary to patch infection, and 18 were secondary to atherosclerotic degeneration of the artery at the site of the endarterectomy.2 However, it should be noted that this institutional experience appears to represent an atypically high percentage of pseudoaneurysms relative to true aneurysms. A review of the literature revealed that only about 14% of all extracranial aneurysms are pseudoaneurysm.2 Both blunt and penetrating trauma have also been reported as a cause of pseudoaneurysms.11,12 Blunt injury can
Aneurysms of the carotid artery
179 out direct contact. Finally, a carotid artery dissection can evolve into a carotid artery pseudoaneurysm in up to 30% of individuals with this condition.13 Therefore, careful monitoring of the carotid artery following detection of a dissection is important for both short- and long-term follow-up.
Incidence Occurrence of a carotid artery aneurysm is rare, accounting for 0.1% to 3.7% of all carotid procedures performed at major centers.2,14 There are very few large series within the literature, thus the natural history is difficult to discern. Most large series report a 2-3:1 male-to-female ratio, however, there are reports documenting a higher frequency in women.2,3,15 Overall, the incidence of these aneurysms is from 0.4% to 4% of all peripheral artery aneurysms.2,15,16 Bilateral carotid artery aneurysms are exceedingly rare.
Differential Diagnosis Figure 1 Diagram demonstrating the multiple anatomic positions and sizes of extracranial carotid artery aneurysms. From Alexander E, Wigser SM, Davis CH: Bilateral extracranial aneurysms of the internal carotid artery. J Neurosurg 25:437-442, 1966. Reprinted with permission.
cause shearing of the vessel secondary to compression and stretching of the artery against the cervical vertebrae or skull base from either a direct blow or hyperextension and rotation of the head. Pseudoaneurysm formation can occur following direct carotid puncture for arteriography, or secondary to accidental carotid artery puncture when using the jugular vein approach for gaining central venous access. Low-velocity, low-energy missiles or penetrating trauma caused by hand-driven weapons can disrupt the normal architecture of the arterial wall, causing development of a pseudoaneurysm. A low-velocity gunshot wound requires penetration of the wall for injury. High-velocity missiles are associated with a blast injury that can result in necrosis of the artery wall withTable 1 Etiology of Carotid Artery Aneurysms True aneurysms Atherosclerosis Arteritis Infection Fibromuscular dysplasia Tuberculosis Human immunodeficiency virus Collagen-vascular disease Irradiation Behçet’s disease Cystic medial necrosis False aneurysms (pseudoaneurysm) Patch infection Suture degeneration or infection Blunt trauma Penetrating trauma Dissection
The most common entity masquerading as a carotid aneurysm is a kinked or coiled carotid artery (Table 2). This can produce a large, pulsatile mass within the neck that can be mistaken for an aneurysm. It has been suggested that tortuosity can be distinguished on physical examination by evaluating the pulsation. The pulsation of a kinked carotid artery is said to run parallel to the long axis of the vessel as opposed to radiating laterally, as occurs in an aneurysm.17 Carotid body tumors can also present as a painless mass that, because of its proximity to the carotid artery, is pulsatile. In this case, the mass is vertically fixed but laterally mobile. Enlarged lymph nodes, cystic hygromas, neoplastic lesions of the neck, peritonsillar abscesses, and branchial cleft cysts should also be included in the differential diagnosis of a carotid artery aneurysm. Ultrasound is useful in the initial evaluation of any pulsatile mass that can be palpated in the neck. Diagnosis of a carotid artery aneurysm or pseudoaneurysm should be confirmed with radiographic imaging. Computed tomography (CT) or magnetic resonance imaging (MRI) can accurately assess the extent of aneurysmal dilation, thrombus formation, and the relationship to surrounding structures. MRI and spiral CT have been shown to be especially helpful when carotid dissection is suspected because these imaging modalities are able to identify old blood in the dissection plane. While many practitioners still consider arteriography the gold standard, CT angiography and magnetic resonance angiography (MRA) have replaced conventional angiography in many centers. These studies offer advantages over arteriograTable 2 Differential Diagnosis of a Pulsatile Neck Mass Carotid artery aneurysm or pseudoaneurysm Kinked or coiled carotid artery Carotid body tumor Enlarged lymph node Cystic hygroma Neoplasm Peritonsillar abscess Branchial cleft cyst
G.M. Longo and M.R. Kibbe
180 phy, including cost savings, eliminating the stroke risk associated with angiography, and providing information about surrounding soft tissues. The ability to reconstruct and rotate the images of the intracranial circulation obtained on MRA often allows for better assessment of collateral circulation than can be obtained with conventional arteriography. The quality of CT and MRI varies among institutions and depends on both the imaging equipment and computer software available for reconstruction of the images.
Clinical Features Aneurysms of the carotid artery often do not come to attention until symptoms develop. The most common presentation is central neurologic dysfunction (either a transient ischemic attack or a stroke). In reported series, a neurologic event was the presenting symptom anywhere from 37.5% to 100% of cases.2,5,18-20 These events are typically due to embolization of thrombus from the aneurysm. Rarely, a large aneurysm can cause symptoms by compressing the internal carotid artery. On examination, a pulsatile neck mass is noted in up to 90% of patients.5,18-20 Classically, this mass is described just inferior to the angle of the mandible. Occasionally, the aneurysm will protrude inward toward the throat.21 This can cause dysphagia due to compression of the pharyngeal constrictor muscle and mucous membrane or compression of the glossalpharyngeal nerve with subsequent pharyngeal dysfunction. Glossopharyngeal compression can also cause auricular pain as well as radiation into the occipital area. In a Mayo Clinic report, pain was associated with 40% of aneurysms, whereas only 4% of patients in the Texas Heart Institute experience had pain.2,22 The pain experienced can also be retro-orbital in location or result in the form of throbbing headaches. Aside from glossopharyngeal dysfunction, several other nerves may be affected by a carotid aneurysm. If the cervical sympathetic chain is affected, a Horner’s syndrome may result. Vagal compression often causes hoarseness. Palsy of cranial nerves I, IV, V, VI, and VII through XII have all been reported in association with carotid aneurysms.2,3,23,24 When the aneurysm is at the base of the skull, a Raeder’s paratrigeminal syndrome (oculosympathetic paresis and intermittent facial pain) can result.25 Spontaneous rupture and hemorrhage from a carotid aneurysm is rare. Mycotic aneurysms secondary to peritonsillar infection or middle ear infections were much more common prior to the widespread use of antibiotics. These aneurysms were susceptible to rupture and bleeding.1,26 Although rare, rupture and hemorrhage can be fatal in certain circumstances. Attempted incision and drainage of a carotid artery pseudoaneurysm thought to be a peritonsillar abscess has proven to be fatal.21 If spontaneous rupture occurs into the oropharynx, massive hemorrhage, suffocation, and death can result. Tracheal compression and death can also result from a large, expanding neck hematoma. Current series have reported rupture following suture line disruption in cases where silk was used to suture Dacron patches into place.2
Also, rupture has occurred in cases where wound infection caused suture line disruption.2,15
Treatment The treatment for these lesions depends on the etiology as well as the location of the aneurysm. Surgical treatment is the preferred manner of dealing with this entity, regardless of whether the aneurysm is defined as a dilatation of 150% of the diameter of the common carotid artery (CCA), 200% of the internal carotid artery (ICA), or 120% of the diameter of the normal ipsilateral ICA.24,26 This recommendation is based on early reports of a 60% to 70% mortality rate, and current reports documenting a ⬎50% stroke rate for untreated carotid aneurysms.1,3,27 Historically, direct proximal and distal ligation and extirpation of the CCA was the procedure of choice. Currently, restoration of arterial continuity is preferred. However, other factors taken into account in planning the surgical procedure include the proximal and distal extent of the aneurysm, size, etiology, and status of collateral flow from the contralateral carotid and posterior circulation. Direct ligation of the vessel is reserved for some cases of mycotic aneurysms or cases where distal control for bypass cannot be obtained for anatomical reasons. Ligation may also be the best option in situations of uncontrollable hemorrhage. Reconstruction of the carotid circulation can be performed in a multitude of ways.3-5,10,12,18,28 The most common method is with a venous conduit, usually using the proximal greater saphenous vein. If the aneurysm is within the CCA or the proximal one-third of the ICA, polytetrafluoroethylene can be used when suitable vein is not available. Alternatively, the external carotid artery can be utilized as a proximal transposition site if the CCA is free from aneurysmal degeneration. On occasion, an elongated or redundant carotid artery is present with a small aneurysm, allowing for resection and primary end-to-end anastomosis. Other approaches have been described. These are particularly helpful if dealing with a large aneurysm, where resection would result in a high risk of injury to the cranial nerves, or if the aneurysm extends to the skull base and distal control is difficult to obtain. El-Sabrout and Cooley advocated partial aneurysmectomy and patch angioplasty, thus reducing the risk of injury to the vagus, recurrent laryngeal, and glossopharyngeal nerves, while preserving external carotid artery flow.2 Miksic et al discussed endarterectomy coupled with internal placation of the aneurysm although this approach has the theoretical disadvantage of leaving an irregular luminal surface that might represent a source of thrombus.5 Others have coupled aneurysmorrhaphy with partial resection and patch angioplasty. Furthermore, extracranial-to-intracranial (EC-IC) bypass has been discussed as a treatment option.28 However, this is a difficult procedure with poorly studied patency rates. In addition, the EC-IC bypass requires time to enlarge and mature; therefore, it would not be an option in a patient requiring therapy for ongoing neurologic symptoms. If an EC-IC bypass were utilized, it should be
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181
Figure 2 (A) Cerebral angiogram revealing a large carotid pseudoaneurysm containing thrombus. (B) Cerebral angiogram demonstrating successful exclusion of a pseudoaneurysm with two Wallgraft stents. From McCready RA et al.32 Reprinted with permission.
coupled with carotid artery ligation to avoid future embolization and potential aneurysm expansion. Recently, several case reports have appeared advocating an endovascular approach to carotid artery aneurysms (Fig
2).20,29-33 The combination of newer nitinol stents, covered stent grafts, and cerebral protection devices have theoretically reduced the risk of intraoperative atheroembolism. This is added to the experience that many practitioners have
Figure 3 (A) Computed tomography scan demonstrating a true carotid artery aneurysm at the carotid bulb (arrow) with extension into the internal carotid artery. (B) Angiogram of the right carotid artery following placement of a covered stent graft. Note the complete exclusion of the carotid artery aneurysm and the external carotid artery.
G.M. Longo and M.R. Kibbe
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Figure 4 (A) Anteroposterior (AP) view of the left internal carotid artery showing a pseudoaneurysm with a 20-mm⫺wide neck and a 5-cm segment of irregular luminal narrowing of the vessel. (B) AP view taken after deployment of two overlapping Wallstents demonstrating successful occlusion of the pseudoaneurysm with normalization of the carotid lumen. From Benndorf et al.33 Reprinted with permission.
gained with carotid artery stenting, and thus made an endovascular approach more attractive. The potential advantages of using a covered stent for carotid aneurysms include the avoidance of cranial nerve damage, the ability to access lesions that may be difficult to control during open operation and the avoidance of general anesthesia. Additional circumstances in which an endovascular approach may be preferred include aneurysms that extend to the skull base and aneurysm formation secondary to irradiation. Both of these circumstances are associated with a higher risk of nerve injury during open surgical repair. In the rare situation where a pseudoaneurysm is discovered shortly after an endarterectomy due to patch disruption, the intense inflammatory changes surrounding the carotid artery makes an endovascular approach attractive.32 We recently treated a carotid artery aneurysm that developed at the carotid bifurcation secondary to irradiation with a self-expanding covered stent graft (Fig 3).34 Although no long-term follow-up is available, the patient tolerated the procedure well with no intraoperative or postoperative complications. Aspects of this form of endovascular treatment that differs from conventional carotid artery angioplasty and stenting include the need for a larger sheath due to the larger profile of the covered stent grafts. Due to the presence of mural thrombus lining the aneurysm, care must be taken when delivering the cerebral protection device to avoid inadvertent emboliza-
tion. Additionally, strict attention to the size of the proximal and distal landing sites is important. For aneurysms that span the bifurcation, two overlapping, self-expanding covered stent grafts of different diameters may be more beneficial compared to one given the large difference in diameter between the internal and common carotid artery. Other forms of stenting beside covered stent grafts have included bare metal stents and vein-covered stents.20,31-36 In the case of bare metal stents, it is believed that the stent promotes thrombosis of the aneurysm/pseudoaneurysm, while maintaining luminal patency (Fig 4). Bare metal stents can also be coupled with coil embolization of the aneurysm/ pseudoaneurysm by utilizing microcatheters to inject the coils between the interstices of the stents (Fig 5).36 The obvious concern regarding endovascular treatment is the lack of long-term data. The case reports in the literature contain only short- and mid-term follow-up. As endoluminal devices are used with greater frequency, more data will be collected with respect to the outcome of these patients and the behavior of these devices over time. In addition, as the profile of the covered stents continues to decrease, they will become even more attractive for the treatment of peripheral aneurysms. These factors will likely cause current treatment paradigms to continue to shift in favor of endovascular treatment.
Conclusions Carotid artery aneurysms remain a rare entity. Due to paucity of data and lack of large series, a number of unanswered
Figure 5 A pseudoaneurysm of the distal internal carotid artery in a 30-year-old man diagnosed 10 years after a motor vehicle accident. It was treated with a bare metal stent followed by coil embolization of the pseudoaneurysm. The coils were delivered by microcatheters through the interstices of the stent. (A) Completion angiography demonstrates a patent internal carotid artery with aneurysm exclusion. (B) Arteriography 5 months postprocedure demonstrates flow through the internal carotid artery with exclusion of the pseudoaneurysm. From Bush et al.36 Reprinted with permission.
Aneurysms of the carotid artery questions regarding the natural history and management of these lesions remain. However, a consistent theme throughout the reports of carotid artery aneurysms is the need for a careful preoperative evaluation. In some cases, the operative approach to the aneurysm may be the most daunting task, requiring a multispecialty approach due to the anatomic location. The endovascular approach is gaining acceptance as experience increases with interventions in the carotid artery and the technology continues to evolve.
References 1. Hertzer NR: Extracranial carotid aneurysms: A new look at an old problem. J Vasc Surg 31:823-825, 2000 2. El-Sabrout R, Cooley DA: Extracranial carotid artery aneurysms: Texas Heart Institute experience. J Vasc Surg 31:701-712, 2000 3. Zwolak RM, Whitehouse WM, Knake JE, et al: Atherosclerotic extracranial carotid artery aneurysms. J Vasc Surg 1:415-422, 1984 4. Painter TA, Hertzer NR, Beven EG, et al: Extracranial carotid aneurysms: report of six cases and review of the literature. J Vasc Surg 2:312-318, 1985 5. Miksic K, Flis V, Kosir G, et al: Surgical aspects of fusiform and saccular extracranial carotid artery aneurysms. Cardiovasc Surg 5:190-195, 1997 6. McCann RL. Basic data related to peripheral artery aneurysms. Ann Vasc Surg 4:411-414, 1990 7. Nair R, Robbs JV, Naidoo NG: Spontaneous carotid artery aneurysms. Br J Surg 87:186-190, 2000 8. Rice HE, Arbabi S, Kremer R, et al: Ruptured Salmonella mycotic aneurysm of the extracranial carotid artery. Ann Vasc Surg 11:416-419, 1997 9. Grossi RJ, Onofrey D, Tvetenstrand C, Blumenthal J: Mycotic carotid aneurysm. J Vasc Surg 6:81-83, 1989 10. Rosset E, Albertini JN, Magnan PE, et al: Surgical treatment of extracranial internal carotid artery aneurysms. J Vasc Surg 31:713-723, 2000 11. Berguer R: Aneurysms of the extracranial carotid and vertebral arteries, in Yao JST, Pearce WH (eds): Aneurysms: New Findings and Treatment. Norwalk, CT, Appleton & Lange, 1994, pp 475-491 12. Coffin O, Maiza D, Galateau-Salle F, et al: Results of surgical management of internal carotid artery aneurysm by the cervical approach. Ann Vasc Surg 11:482-490, 1997 13. Schievink WI: Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med 344: 898-906, 2001 14. Welling RE, Talisa A, Tarun G: Extracranial carotid artery aneurysms. Surgery 93:319-323, 1983 15. McCollum CH, Wheeler WG, Noon GP, et al: Aneurysms of the extracranial carotid artery Twenty-one years’ experience. Am J Surg 137: 196-200, 1979 16. Welling RE, Taha A, Goel T, et al: Extracranial carotid artery aneurysms. Surgery 93:319-323, 1983 17. Bergan JJ, Hoehn JG: Evanescent cervical pseudoaneurysms. Ann Surg 162:213-217, 1965
183 18. Zhang Q, Duan ZQ, Xin SJ, et al: Management of extracranial carotid artery aneurysms: 17 years’ experience. Eur J Vasc Endovasc Surg 18: 162-165, 1999 19. Faggioli G, Freyrie A, Stella A, et al. Extracranial internal carotid artery aneurysms: Results of a surgical series with long-term follow-up. J Vasc Surg 23:587-595, 1996 20. Szopinski P, Ciostek P, Kielar M, et al. A series of 15 patients with extracranial carotid artery aneurysms: Surgical and endovascular treatment. Eur J Vasc Endovasc Surg 29:256-261, 2005 21. Lane RJ, Weisman RA: Carotid artery aneurysms: An otolaryngologic perspective. Laryngoscope 90:897-911, 1980 22. Mokri B, Piepgras DG, Sundt TM, et al: Extracranial internal carotid artery aneurysms. Mayo Clin Proc 310-321, 1982 23. Moreau P, Albat B, Thevenet A: Surgical treatment of extracranial internal carotid artery aneurysm. Ann Vasc Surg 8:409-416, 1994 24. de Jong KP, Zondervan PE, van Urk H: Extracranial carotid artery aneurysms. Eur J Vasc Surg 3:557-562, 1989 25. Dehn TC, Taylor GW: Extracranial carotid artery aneurysms. Ann R Coll Surg Engl 66:247-250, 1984 26. Siablis D, Karnabatidis D, Katsanos K, et al: Extracranial internal carotid artery aneurysms: Report of a ruptured case and review of the literature. Cardiovasc Intervent Radiol 27:397-401, 2004 27. Winslow N: Extracranial aneurysms of the internal carotid artery. Arch Surg 13:689-729, 1926 28. Sundt TM, Pearson BW, Piepgras DG, et al: Surgical management of aneurysms of the distal extracranial internal carotid artery. J Neurosurg 64:169-182, 1986 29. May J, White GH, Waugh R, et al: Endoluminal repair of internal carotid artery aneurysm: A feasible but hazardous procedure. J Vasc Surg 26:1055-1060, 1997 30. van Sambeek MR, Segeren CM, van Dijk LC, et al: Endovascular repair of an extracranial internal carotid artery aneurysm complicated by heparin-induced thrombocytopenia and thrombosis. J Endovasc Ther 7:353-358, 2000 31. Cil BE, Ucar I, Ozsoy F, et al: Successful endovascular treatment of a left common carotid artery aneurysm following failed surgery of a right common carotid artery aneurysm. Cardiovasc Intervent Radiol 28:367371, 2005 32. McCready RA, Divelbiss JL, Bryant A, et al: Endoluminal repair of carotid artery pseudoaneurysms: A word of caution. J Vasc Surg 40: 1020-1023, 2004 33. Benndorf G, Campi A, Schneider GH, et al: Overlapping stents for treatment of a dissecting carotid artery aneurysm. J Endovasc Ther 8:566-570, 2001 34. Vijungco JD, Kibbe MR: Stent graft treatment of a right carotid artery aneurysm. Images and cases. Available at: VascularWeb: www.vascularweb.org 35. Martin JB, Bednarkiewicz M, Christenson JT, et al: Endovascular repair using vein covered stents in the carotid bifurcation. Cardiovasc Surg 8:499-502, 2000 36. Bush RL, Lin PH, Dodson TF, et al: Endoluminal stent placement and coil embolization for the management of carotid artery pseudoaneurysms. J Endovsac Ther 32:824-828, 2001
I
N 1808, SIR ASTLEY COOPER documented the first successful procedure for an aneurysm of the extracranial carotid artery.1 This consisted of a proximal ligation of a painful, bulbous aneurysm of the internal carotid artery. During the next century and a half, ligation remained the mainstay of treatment for this disease. However, this was associated with a high incidence of neurological sequelae. By the 1970s, reconstruction of the carotid arterial system became the standard. Currently, carotid aneurysms still invoke a substantial amount of interest due to the multiple etiologies, therapeutic challenges, and uncommon occurrence. Aneurysms of the extracranial carotid artery fall within two broad categories; true aneurysms or false (pseudoaneurysm) aneurysms. This is an important factor in determining the best treatment.
Etiology True Aneurysms Atherosclerosis is often cited as the most common cause of extracranial carotid artery aneurysms, accounting for anywhere between 34% and 70% in published series.2,3 Often, these aneurysms occur at or near the carotid bifurcation and are typically fusiform, although saccular aneurysms can also occur in this location.4 These aneurysms are found along the common or internal carotid artery but rarely at the carotid bulb (Fig 1). The patients often have severe hypertension.5 The male-to-female ratio is 1.9:1, in contrast to aortic aneu-
Division of Vascular Surgery, Northwestern University, Chicago, IL. Address reprint requests to: Melina R. Kibbe, Division of Vascular Surgery, Northwestern University, 201 E Huron Street, Galter 10-105, Chicago, IL 60611. E-mail: [email protected]
178
0895-7967/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.semvascsurg.2005.09.002
rysms, where the ratio is more heavily weighted towards males.3,6 In cases where atherosclerosis is not the underlying cause, patients are often younger and may suffer from tuberculosis, human immunodeficiency virus, or arteritis (Takayasu’s).7 Mycotic aneurysms are usually caused by Salmonella or syphilis.8,9 Other rare causes of carotid aneurysms that have been described in case reports of fibromuscular dysplasia, collagen-vascular disease, and irradiation (Table 1).2,10,32
False Aneurysms False aneurysms of the carotid artery occur when there is disruption of the continuity of the arterial wall. There are multiple causes of pseudoaneurysm of the carotid artery (Table 1). Rupture or dilation of a patch angioplasty following endarterectomy, particularly when an earlier generation of Dacron was used for the patch.2 El-Sabrout and Cooley2 from the Texas Heart Institute have reported one of the largest single institution series of extracranial carotid artery aneurysms. In this series of 67 cases, 38 (57%) of the aneurysms were pseudoaneurysms following Dacron patch after endarterectomy.2 Among the 38 patients, 7 were found to have suture line disruption secondary to degeneration or infection of the silk suture, 13 were secondary to patch infection, and 18 were secondary to atherosclerotic degeneration of the artery at the site of the endarterectomy.2 However, it should be noted that this institutional experience appears to represent an atypically high percentage of pseudoaneurysms relative to true aneurysms. A review of the literature revealed that only about 14% of all extracranial aneurysms are pseudoaneurysm.2 Both blunt and penetrating trauma have also been reported as a cause of pseudoaneurysms.11,12 Blunt injury can
Aneurysms of the carotid artery
179 out direct contact. Finally, a carotid artery dissection can evolve into a carotid artery pseudoaneurysm in up to 30% of individuals with this condition.13 Therefore, careful monitoring of the carotid artery following detection of a dissection is important for both short- and long-term follow-up.
Incidence Occurrence of a carotid artery aneurysm is rare, accounting for 0.1% to 3.7% of all carotid procedures performed at major centers.2,14 There are very few large series within the literature, thus the natural history is difficult to discern. Most large series report a 2-3:1 male-to-female ratio, however, there are reports documenting a higher frequency in women.2,3,15 Overall, the incidence of these aneurysms is from 0.4% to 4% of all peripheral artery aneurysms.2,15,16 Bilateral carotid artery aneurysms are exceedingly rare.
Differential Diagnosis Figure 1 Diagram demonstrating the multiple anatomic positions and sizes of extracranial carotid artery aneurysms. From Alexander E, Wigser SM, Davis CH: Bilateral extracranial aneurysms of the internal carotid artery. J Neurosurg 25:437-442, 1966. Reprinted with permission.
cause shearing of the vessel secondary to compression and stretching of the artery against the cervical vertebrae or skull base from either a direct blow or hyperextension and rotation of the head. Pseudoaneurysm formation can occur following direct carotid puncture for arteriography, or secondary to accidental carotid artery puncture when using the jugular vein approach for gaining central venous access. Low-velocity, low-energy missiles or penetrating trauma caused by hand-driven weapons can disrupt the normal architecture of the arterial wall, causing development of a pseudoaneurysm. A low-velocity gunshot wound requires penetration of the wall for injury. High-velocity missiles are associated with a blast injury that can result in necrosis of the artery wall withTable 1 Etiology of Carotid Artery Aneurysms True aneurysms Atherosclerosis Arteritis Infection Fibromuscular dysplasia Tuberculosis Human immunodeficiency virus Collagen-vascular disease Irradiation Behçet’s disease Cystic medial necrosis False aneurysms (pseudoaneurysm) Patch infection Suture degeneration or infection Blunt trauma Penetrating trauma Dissection
The most common entity masquerading as a carotid aneurysm is a kinked or coiled carotid artery (Table 2). This can produce a large, pulsatile mass within the neck that can be mistaken for an aneurysm. It has been suggested that tortuosity can be distinguished on physical examination by evaluating the pulsation. The pulsation of a kinked carotid artery is said to run parallel to the long axis of the vessel as opposed to radiating laterally, as occurs in an aneurysm.17 Carotid body tumors can also present as a painless mass that, because of its proximity to the carotid artery, is pulsatile. In this case, the mass is vertically fixed but laterally mobile. Enlarged lymph nodes, cystic hygromas, neoplastic lesions of the neck, peritonsillar abscesses, and branchial cleft cysts should also be included in the differential diagnosis of a carotid artery aneurysm. Ultrasound is useful in the initial evaluation of any pulsatile mass that can be palpated in the neck. Diagnosis of a carotid artery aneurysm or pseudoaneurysm should be confirmed with radiographic imaging. Computed tomography (CT) or magnetic resonance imaging (MRI) can accurately assess the extent of aneurysmal dilation, thrombus formation, and the relationship to surrounding structures. MRI and spiral CT have been shown to be especially helpful when carotid dissection is suspected because these imaging modalities are able to identify old blood in the dissection plane. While many practitioners still consider arteriography the gold standard, CT angiography and magnetic resonance angiography (MRA) have replaced conventional angiography in many centers. These studies offer advantages over arteriograTable 2 Differential Diagnosis of a Pulsatile Neck Mass Carotid artery aneurysm or pseudoaneurysm Kinked or coiled carotid artery Carotid body tumor Enlarged lymph node Cystic hygroma Neoplasm Peritonsillar abscess Branchial cleft cyst
G.M. Longo and M.R. Kibbe
180 phy, including cost savings, eliminating the stroke risk associated with angiography, and providing information about surrounding soft tissues. The ability to reconstruct and rotate the images of the intracranial circulation obtained on MRA often allows for better assessment of collateral circulation than can be obtained with conventional arteriography. The quality of CT and MRI varies among institutions and depends on both the imaging equipment and computer software available for reconstruction of the images.
Clinical Features Aneurysms of the carotid artery often do not come to attention until symptoms develop. The most common presentation is central neurologic dysfunction (either a transient ischemic attack or a stroke). In reported series, a neurologic event was the presenting symptom anywhere from 37.5% to 100% of cases.2,5,18-20 These events are typically due to embolization of thrombus from the aneurysm. Rarely, a large aneurysm can cause symptoms by compressing the internal carotid artery. On examination, a pulsatile neck mass is noted in up to 90% of patients.5,18-20 Classically, this mass is described just inferior to the angle of the mandible. Occasionally, the aneurysm will protrude inward toward the throat.21 This can cause dysphagia due to compression of the pharyngeal constrictor muscle and mucous membrane or compression of the glossalpharyngeal nerve with subsequent pharyngeal dysfunction. Glossopharyngeal compression can also cause auricular pain as well as radiation into the occipital area. In a Mayo Clinic report, pain was associated with 40% of aneurysms, whereas only 4% of patients in the Texas Heart Institute experience had pain.2,22 The pain experienced can also be retro-orbital in location or result in the form of throbbing headaches. Aside from glossopharyngeal dysfunction, several other nerves may be affected by a carotid aneurysm. If the cervical sympathetic chain is affected, a Horner’s syndrome may result. Vagal compression often causes hoarseness. Palsy of cranial nerves I, IV, V, VI, and VII through XII have all been reported in association with carotid aneurysms.2,3,23,24 When the aneurysm is at the base of the skull, a Raeder’s paratrigeminal syndrome (oculosympathetic paresis and intermittent facial pain) can result.25 Spontaneous rupture and hemorrhage from a carotid aneurysm is rare. Mycotic aneurysms secondary to peritonsillar infection or middle ear infections were much more common prior to the widespread use of antibiotics. These aneurysms were susceptible to rupture and bleeding.1,26 Although rare, rupture and hemorrhage can be fatal in certain circumstances. Attempted incision and drainage of a carotid artery pseudoaneurysm thought to be a peritonsillar abscess has proven to be fatal.21 If spontaneous rupture occurs into the oropharynx, massive hemorrhage, suffocation, and death can result. Tracheal compression and death can also result from a large, expanding neck hematoma. Current series have reported rupture following suture line disruption in cases where silk was used to suture Dacron patches into place.2
Also, rupture has occurred in cases where wound infection caused suture line disruption.2,15
Treatment The treatment for these lesions depends on the etiology as well as the location of the aneurysm. Surgical treatment is the preferred manner of dealing with this entity, regardless of whether the aneurysm is defined as a dilatation of 150% of the diameter of the common carotid artery (CCA), 200% of the internal carotid artery (ICA), or 120% of the diameter of the normal ipsilateral ICA.24,26 This recommendation is based on early reports of a 60% to 70% mortality rate, and current reports documenting a ⬎50% stroke rate for untreated carotid aneurysms.1,3,27 Historically, direct proximal and distal ligation and extirpation of the CCA was the procedure of choice. Currently, restoration of arterial continuity is preferred. However, other factors taken into account in planning the surgical procedure include the proximal and distal extent of the aneurysm, size, etiology, and status of collateral flow from the contralateral carotid and posterior circulation. Direct ligation of the vessel is reserved for some cases of mycotic aneurysms or cases where distal control for bypass cannot be obtained for anatomical reasons. Ligation may also be the best option in situations of uncontrollable hemorrhage. Reconstruction of the carotid circulation can be performed in a multitude of ways.3-5,10,12,18,28 The most common method is with a venous conduit, usually using the proximal greater saphenous vein. If the aneurysm is within the CCA or the proximal one-third of the ICA, polytetrafluoroethylene can be used when suitable vein is not available. Alternatively, the external carotid artery can be utilized as a proximal transposition site if the CCA is free from aneurysmal degeneration. On occasion, an elongated or redundant carotid artery is present with a small aneurysm, allowing for resection and primary end-to-end anastomosis. Other approaches have been described. These are particularly helpful if dealing with a large aneurysm, where resection would result in a high risk of injury to the cranial nerves, or if the aneurysm extends to the skull base and distal control is difficult to obtain. El-Sabrout and Cooley advocated partial aneurysmectomy and patch angioplasty, thus reducing the risk of injury to the vagus, recurrent laryngeal, and glossopharyngeal nerves, while preserving external carotid artery flow.2 Miksic et al discussed endarterectomy coupled with internal placation of the aneurysm although this approach has the theoretical disadvantage of leaving an irregular luminal surface that might represent a source of thrombus.5 Others have coupled aneurysmorrhaphy with partial resection and patch angioplasty. Furthermore, extracranial-to-intracranial (EC-IC) bypass has been discussed as a treatment option.28 However, this is a difficult procedure with poorly studied patency rates. In addition, the EC-IC bypass requires time to enlarge and mature; therefore, it would not be an option in a patient requiring therapy for ongoing neurologic symptoms. If an EC-IC bypass were utilized, it should be
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Figure 2 (A) Cerebral angiogram revealing a large carotid pseudoaneurysm containing thrombus. (B) Cerebral angiogram demonstrating successful exclusion of a pseudoaneurysm with two Wallgraft stents. From McCready RA et al.32 Reprinted with permission.
coupled with carotid artery ligation to avoid future embolization and potential aneurysm expansion. Recently, several case reports have appeared advocating an endovascular approach to carotid artery aneurysms (Fig
2).20,29-33 The combination of newer nitinol stents, covered stent grafts, and cerebral protection devices have theoretically reduced the risk of intraoperative atheroembolism. This is added to the experience that many practitioners have
Figure 3 (A) Computed tomography scan demonstrating a true carotid artery aneurysm at the carotid bulb (arrow) with extension into the internal carotid artery. (B) Angiogram of the right carotid artery following placement of a covered stent graft. Note the complete exclusion of the carotid artery aneurysm and the external carotid artery.
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Figure 4 (A) Anteroposterior (AP) view of the left internal carotid artery showing a pseudoaneurysm with a 20-mm⫺wide neck and a 5-cm segment of irregular luminal narrowing of the vessel. (B) AP view taken after deployment of two overlapping Wallstents demonstrating successful occlusion of the pseudoaneurysm with normalization of the carotid lumen. From Benndorf et al.33 Reprinted with permission.
gained with carotid artery stenting, and thus made an endovascular approach more attractive. The potential advantages of using a covered stent for carotid aneurysms include the avoidance of cranial nerve damage, the ability to access lesions that may be difficult to control during open operation and the avoidance of general anesthesia. Additional circumstances in which an endovascular approach may be preferred include aneurysms that extend to the skull base and aneurysm formation secondary to irradiation. Both of these circumstances are associated with a higher risk of nerve injury during open surgical repair. In the rare situation where a pseudoaneurysm is discovered shortly after an endarterectomy due to patch disruption, the intense inflammatory changes surrounding the carotid artery makes an endovascular approach attractive.32 We recently treated a carotid artery aneurysm that developed at the carotid bifurcation secondary to irradiation with a self-expanding covered stent graft (Fig 3).34 Although no long-term follow-up is available, the patient tolerated the procedure well with no intraoperative or postoperative complications. Aspects of this form of endovascular treatment that differs from conventional carotid artery angioplasty and stenting include the need for a larger sheath due to the larger profile of the covered stent grafts. Due to the presence of mural thrombus lining the aneurysm, care must be taken when delivering the cerebral protection device to avoid inadvertent emboliza-
tion. Additionally, strict attention to the size of the proximal and distal landing sites is important. For aneurysms that span the bifurcation, two overlapping, self-expanding covered stent grafts of different diameters may be more beneficial compared to one given the large difference in diameter between the internal and common carotid artery. Other forms of stenting beside covered stent grafts have included bare metal stents and vein-covered stents.20,31-36 In the case of bare metal stents, it is believed that the stent promotes thrombosis of the aneurysm/pseudoaneurysm, while maintaining luminal patency (Fig 4). Bare metal stents can also be coupled with coil embolization of the aneurysm/ pseudoaneurysm by utilizing microcatheters to inject the coils between the interstices of the stents (Fig 5).36 The obvious concern regarding endovascular treatment is the lack of long-term data. The case reports in the literature contain only short- and mid-term follow-up. As endoluminal devices are used with greater frequency, more data will be collected with respect to the outcome of these patients and the behavior of these devices over time. In addition, as the profile of the covered stents continues to decrease, they will become even more attractive for the treatment of peripheral aneurysms. These factors will likely cause current treatment paradigms to continue to shift in favor of endovascular treatment.
Conclusions Carotid artery aneurysms remain a rare entity. Due to paucity of data and lack of large series, a number of unanswered
Figure 5 A pseudoaneurysm of the distal internal carotid artery in a 30-year-old man diagnosed 10 years after a motor vehicle accident. It was treated with a bare metal stent followed by coil embolization of the pseudoaneurysm. The coils were delivered by microcatheters through the interstices of the stent. (A) Completion angiography demonstrates a patent internal carotid artery with aneurysm exclusion. (B) Arteriography 5 months postprocedure demonstrates flow through the internal carotid artery with exclusion of the pseudoaneurysm. From Bush et al.36 Reprinted with permission.
Aneurysms of the carotid artery questions regarding the natural history and management of these lesions remain. However, a consistent theme throughout the reports of carotid artery aneurysms is the need for a careful preoperative evaluation. In some cases, the operative approach to the aneurysm may be the most daunting task, requiring a multispecialty approach due to the anatomic location. The endovascular approach is gaining acceptance as experience increases with interventions in the carotid artery and the technology continues to evolve.
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