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Fibromuscular dysplasia (FMD) is an arterial disease of unkn
Fibromuscular Dysplasia (Carotid Artery)
AUTHOR INFORMATION Section 1 of 11
Authored by Jeffrey P Kochan, MD, Director of Interventional Neuroradiology, Associate Professor of Radiology and Neurosurgery, Department of Diagnostic Imaging, Temple University Hospital
Edited by Gary P Siskin, MD, Division Chief, Associate Professor, Department of Radiology, Division of Vascular and Interventional Radiology, Albany Medical Center; Bernard D Coombs, MBChB, PhD, Assistant Professor, Department of Radiology, University of Colorado Health Sciences Center; Kyung J Cho, MD, Program Director, Professor, Department of Radiology, Division of Vascular and Interventional Radiology, University of Michigan Health System; Robert M Krasny, MD, Visiting Assistant Professor of Radiology, University of California at Los Angeles Medical Center; Consulting Staff, Tower Imaging, Los Angeles, California; and Ziv J Haskal, MD, Professor, Departments of Radiology and Surgery, Columbia University College of Physicians and Surgeons; Director, Division of Vascular and Interventional Radiology, Department of Radiology, New York Presbyterian Hospital/Columbia
Author's Email: Jeffrey P Kochan, MD
Editor's Email: Gary P Siskin, MD
eMedicine Journal, March 22 2002, Volume 3, Number 3
INTRODUCTION Section 2 of 11
Background: Fibromuscular dysplasia (FMD) is an arterial disease of unknown etiology typically affecting the medium and large arteries of young to middle-aged women. This chapter focuses on FMD of the carotid arteries.
Pathophysiology: First described by Leadbetter and Burkland in 1938, FMD is an arterial disease typically affecting the renal arteries in 85% of patients and often presenting as renovascular hypertension. The internal carotid artery is the second most common location and is affected bilaterally in 65% of patients and may present as cerebral ischemia (20%), transient ischemic attack (29%), or thromboembolic stroke (6%). FMD has been associated with intracranial aneurysms in as many as 30% of patients and spontaneous carotid artery dissection in 10-20%. One third of patients with carotid FMD also have renal artery FMD and 10% have vertebral artery involvement. Other arteries potentially affected by FMD include lumbar, mesenteric, celiac, hepatic, and iliac arteries.
While FMD is a disease of unknown etiology, studies have described an association with alpha-1 antitrypsin deficiency. Other etiologic factors suspected of involvement in the pathogenesis of FMD include hormonal effects on smooth muscle, mechanical stress on the wall of affected arteries, and mural ischemia in the dysplastic vessels.
Histologically, FMD has been classified into 3 distinct types: intimal fibroplasia, medial fibroplasia, and subadventitial (perimedial) fibroplasia of the arterial wall. The different types of FMD are not easily differentiated by their findings on angiography. The medial type of FMD is by far the most common and is classically diagnosed on angiography by noting the "string of beads" appearance. This appearance is explained by the presence of luminal stenosis alternating with aneurysmal outpouchings. Classically, the intimal form of FMD is associated with smooth focal stenoses on angiography.
Frequency:
In the US: The reported incidence of FMD in adults is 0.6% via angiography and 1.1% via autopsy.
Sex: Male-to-female ratio is 1:3.
Age: FMD most typically presents in persons aged 25-50 years.
Clinical Details: FMD may present as a transient ischemic attack or thromboembolic stroke as a result of thrombogenic tandem stenoses or carotid artery dissection. FMD has been associated with intracranial aneurysms and should be considered in patients who present with intracranial hemorrhage. Patients with carotid FMD also may have renal artery FMD and, less commonly, FMD of the lumbar, mesenteric, celiac, hepatic, and iliac arteries. If FMD is encountered anywhere in the circulation, the carotid arteries should be evaluated.
Preferred Examination: Angiography is the criterion standard for diagnosing FMD. The string of beads appearance is considered pathognomonic for medial fibroplasia on diagnostic angiography.
CT angiography (CTA) and MR angiography (MRA) also may identify the pathognomonic string of beads appearance of the internal carotid artery.
Ultrasound (US) is useful in imaging the common carotid artery and the carotid artery but since most lesions occur at the level of the first and second cervical vertebrae, this modality may fail to identify the more cephalad lesions.
Limitations of Techniques: Current resolution (voxel sizes) of MRA and CT may limit diagnostic ability for subtle cases. As these techniques both improve, they may develop sufficient negative predictive value to be used as exclusive diagnostic tools.
In addition, signal/noise artifacts or reconstruction artifacts in CTA or MRA occasionally can mimic the contour irregularity of FMD. DIFFERENTIALS Section 3 of 11
Arteritis, Takayasu
Carotid Artery, Dissection
Carotid Artery, Stenosis
Other Problems to be Considered:
Arteritis
Vasospasm
Pseudoaneurysm
CAT SCAN Section 4 of 11
Findings: While conventional CT has no role in the diagnosis of FMD, it is essential for assessing the intracranial consequences of the disease. CTA may be used as a noninvasive means of diagnosing the vascular changes of FMD. Confirmation of the findings using carotid angiography is recommended. MRI Section 5 of 11
Findings: Similar to conventional CT, MRI has no role in the diagnosis of FMD but is essential for assessing the intracranial consequences of the disease. Like CTA, MRA may be used as a noninvasive means of diagnosing the vascular changes of FMD. Although MRA does not require the use of contrast, intravenous (IV) administration of a gadolinium contrast agent often yields superior imaging results. Confirmation of the findings using carotid angiography is recommended before endovascular or surgical interventions are considered.
False Positives/Negatives: MRI is sensitive to motion and metallic artifacts. The image may appear artifactually beaded as a result of the patient's swallowing during the examination. The presence of a ferrous metal also may result in a distorted contour of the vessels. ULTRASOUND Section 6 of 11
Findings: Power Doppler sonography may be useful in imaging lesions accessible within the acoustical window. Since the cervical segment C1-C2 most often is affected, most lesions of FMD may be missed as this segment is poorly visualized sonographically. NUCLEAR MEDICINE Section 7 of 11
Findings: Currently, no role exists for nuclear medicine in the diagnosis or management of FMD. ANGIOGRAPHY Section 8 of 11
Findings: Angiographically, FMD may present the classic string of beads contour to the vessel, a long-segment tubular stenosis, or ovoid-shaped outpouchings. When the carotid arteries are involved, the cervical segment C1-C2 most often is affected. Intracranial disease is rare but on those rare occasions, the beaded appearance may extend to the supraclinoid segment of the internal carotid artery or to the middle cerebral artery. A diagnosis of intracranial FMD should not be considered in the absence of cervical carotid disease.
The 3 angiographic classifications of carotid FMD are as follows:
Type 1: This is the most common form. In 80-85% of patients with FMD, angiography reveals a typical string of beads appearance with alternating segments of stricture and dilation. This type usually is a result of medial fibroplasia of the arterial wall. The differential diagnosis for this finding includes atherosclerotic disease, arteritis, and vasospasm.
Type 2: In 6-12% of patients with arterial fibroplasia, a long tubular stenosis can be seen. This can be associated with any of the histologic types but is most commonly seen with the intimal form. The differential diagnosis for a long tubular narrowing of the internal carotid artery includes dissection, arteritis, congenital hypoplasia, extrinsic compression by an adjacent structure or mass, vasospasm, and narrowing secondary to decreased inflow or outflow from the carotid artery secondary to proximal or distal stenotic lesions.
Type 3: This form is unusual (4-6%) and is characterized by involvement of only one side of an artery. This leads to diverticularizations of the arterial wall. These lesions can be difficult to distinguish from atherosclerotic ulceration and pseudoaneurysm.
As previously mentioned, patients with carotid FMD also may have renal artery FMD and, less commonly, FMD of the lumbar, mesenteric, celiac, hepatic, and iliac arteries. Therefore, consider peripheral angiography in those patients manifesting symptoms of arterial stenosis or thromboembolic disease. Conversely, if fibromuscular dysplasia is encountered anywhere in the peripheral circulation, evaluate the carotid arteries.
Degree of Confidence: Confidence in making the diagnosis is high when the above findings are identified. INTERVENTION Section 9 of 11
Intervention: The principle risk of FMD, as with any occlusive disorder affecting the cervicocerebral arterial circulation, is thromboembolism. Many patients with documented FMD may have no symptoms. Surgical treatment or percutaneous transluminal balloon angioplasty is indicated only in those patients with symptomatic carotid arterial disease. FMD, when it produces minimally stenotic lesions, even those affecting a long segment of vessel, can be managed conservatively using antiplatelet and/or anticoagulant therapy.
Historically, the management of FMD with severely stenotic symptomatic lesions and angiographically static flow in a dilated segment has been surgical. Options have included arterial resection with a saphenous interposition graft or intraoperative intra-arterial dilation with graduated rigid dilators. Surgical excision of carotid FMD is more complex technically, usually requiring mandibular disarticulation to access the upper cervical segment of the internal carotid artery most commonly affected.
Currently, with advances in balloon catheters and imaging systems technology, percutaneous transfemoral angioplasty (PTA), without or with stenting, has become an effective option for treatment in patients with hemodynamically significant stenoses, providing excellent results in a minimally invasive fashion. As the intima of the affected arteries is abnormal, angioplasty alone can result in dissection and occlusion. When performing PTA, the operator must be prepared to place stents as well should these complications occur. Note that in the renal arteries, angioplasty alone (without stents) typically provides good and durable results without thrombosis. For renal arteries, PTA alone is generally the treatment of choice for medial fibroplasia causing renovascular hypertension.
Medical/Legal Pitfalls:
The long-term outcome of endovascular stents in carotid FMD lesions is unknown. Currently, no stents are FDA labeled for carotid indications, whether they are atherosclerotic lesions, recurrent stenoses after surgery, or FMD.
Special Concerns:
Acknowledgments: My sincere thanks to Ms Nancy Washburne, Radiology Librarian, for her cheerful diligence in collecting the data for this article.
PICTURES Section 10 of 11
Caption: Picture 1. Diagram representing the 3 major characteristic angiographic patterns seen in fibromuscular dysplasia of the internal carotid artery. Courtesy of Neuroradiology Test and Syllabus, Part 2.
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Caption: Picture 2. Angiogram of type 1 fibromuscular dysplasia in a 43-year-old female patient with multiple transient ischemic attacks. Note the multiple saccular dilatations of the internal carotid artery between the first and second cervical vertebrae.
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Caption: Picture 3. Fibromuscular dysplasia. Subtracted digital angiogram demonstrating multiple saccular dilations and stenosing webs. Increased turbulence and foci of stasis predispose the patient to thrombus formation.
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Caption: Picture 4. Anterior communicating artery aneurysm. An increased association of aneurysm formation is seen in patients with fibromuscular dysplasia.
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Caption: Picture 5. Balloon angioplasty offers a minimally invasive means to improve the arterial flow dynamics in fibromuscular dysplasia.
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Caption: Picture 6. Fibromuscular dysplasia. Postangioplasty angiogram demonstrating improved luminal diameter of the internal carotid artery. Stenting may provide a more normal luminal contour, further decreasing thrombogenicity.
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BIBLIOGRAPHY Section 11 of 11
Batnitzky S, Bentson JR, Bryan RN, et al: Neuroradiology Test and Syllabus, Part 2. American College of Radiology; 1990: 763-89.
Connett MC, Lansche JM: Fibromuscular dysplasia of the internal carotid artery: report of a case. Ann Surg 1965; 162: 59-62.
Ehrenfeld WK, Wylie EJ: Fibromuscular dysplasia of the internal carotid artery. Arch Surg 1974 Nov; 109(5): 676-81[Medline].
Hasso AN, Bird CR, Zinke DE, Thompson JR: Fibromuscular dysplasia of the internal carotid artery: percutaneous transluminal angioplasty. AJR Am J Roentgenol 1981 May; 136(5): 955-60[Medline].
Moreau P, Albat B, Thevenet A: Fibromuscular dysplasia of the internal carotid artery: long-term surgical results. J Cardiovasc Surg (Torino) 1993; 34: 465-72[Medline].
Morris GC, Lechter A, DeBakey ME: Surgical treatment of fibromuscular disease of the carotid arteries. Arch Surg 1968 Apr; 96(4): 636-43[Medline].
Puri V, Riggs G: Case report of fibromuscular dysplasia presenting as stroke in a 16-year-old boy. J Child Neurol 1999 Apr; 14(4): 233-8[Medline].
Schievink WI, Meyer FB, Parisi JE, Wijdicks EF: Fibromuscular dysplasia of the internal carotid artery associated with alpha1-antitrypsin deficiency. Neurosurgery 1998 Aug; 43(2): 229-33; discussion 233-4[Medline].
Stewart MT, Moritz MW, Smith RB, et al: The natural history of carotid fibromuscular dysplasia. J Vasc Surg 1986 Feb; 3(2): 305-10[Medline].
Van Damme H, Sakalihasan N, Limet R: Fibromuscular dysplasia of the internal carotid artery. Personal experience with 13 cases and literature review. Acta Chir Belg 1999; 99: 163-8[Medline].
NOTE:
Medicine is a constantly changing science and not all therapies are clearly established. New research changes drug and treatment therapies daily. The authors, editors, and publisher of this journal have used their best efforts to provide information that is up-to-date and accurate and is generally accepted within medical standards at the time of publication. However, as medical science is constantly changing and human error is always possible, the authors, editors, and publisher or any other party involved with the publication of this article do not warrant the information in this article is accurate or complete, nor are they responsible for omissions or errors in the article or for the results of using this information. The reader should confirm the information in this article from other sources prior to use. In particular, all drug doses, indications, and contraindications should be confirmed in the package insert.FULL DISCLAIMER
eMedicine Journal, March 22 2002, Volume 3, Number 3
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