Fibromuscular Dysplasia

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Practice Essentials

Fibromuscular dysplasia (FMD) is an angiopathy that affects medium-sized arteries predominantly in young women of childbearing age. Among patients with identified FMD, renal involvement occurs in 60-75%, cerebrovascular involvement in 25-30%, visceral involvement in 9%, and arteries of the limbs in about 5%.[1, 2] FMD occurs in most other medium-to-large arteries as well, including the coronary arteries,[3] the pulmonary arteries,[4] and the aorta.[5]

Signs and symptoms

Most patients with craniocervical FMD are asymptomatic. No particular symptoms are pathognomonic for FMD. Any history compatible with a stroke in younger individuals may indicate underlying FMD. The family history should include information about relatives who have had vascular events at a young age.

In symptomatic patients, manifestations of FMD may include the following:

Physical examination should include the following:

See Clinical Presentation for more detail.

Diagnosis

Routine laboratory investigations are usually nonproductive but may show renal impairment.

Imaging considerations include the following:

Pathologically, FMD is classified into 3 main types, as follows[10, 11, 12] :

Because these frequency figures are largely based on findings from renal studies, they may not reflect the distribution of FMD types in carotid disease.

See Workup for more detail.

Management

Partly because of the unknown etiology of FMD, no curative therapy exists. Fortunately, FMD is often benign when asymptomatic, and medical treatment is not indicated. In symptomatic cases, management depends on the presentation, as follows:

Considerations for surgical treatment include the following:

See Treatment and Medication for more detail.

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Angiogram of the descending aorta demonstrates the stenoses of FMD in the renal arteries bilaterally.

Background

Fibromuscular dysplasia (FMD) was first observed in 1938 by Leadbetter and Burkland in a 5-year-old boy, and described as a disease of the renal arteries. Involvement of the craniocervical arteries was recognized in 1946 by Palubinskas and Ripley.

FMD is an angiopathy that affects medium-sized arteries predominantly in young women of childbearing age. FMD most commonly affects the renal arteries and can cause refractory renovascular hypertension. Of patients with identified FMD, renal involvement occurs in 60-75%, cerebrovascular involvement occurs in 25-30%, visceral involvement occurs in 9%, and arteries of the limbs are affected in about 5%.[1, 2] Case reports have shown FMD in most other medium-to-large arteries as well, including the coronary arteries[3] , the pulmonary arteries[4] , and the aorta[5] . In 26% of patients, disease is found in more than one arterial region[6] .

In patients with identified cephalic FMD, 95% have internal carotid artery involvement and 12-43% have vertebral artery involvement. Although FMD can affect arteries of any size[7] , involvement of smaller ones, including intracranial vessels, is rare. Although an early autopsy series of 819 consecutive patients found the prevalence of FMD in the internal carotid arteries to be 1%[8] , a larger, more recent autopsy series of 20,244 patients recently identified the overall prevalence of FMD of the internal carotid arteries to be only 0.02%[9] . From a neurologic perspective, FMD is an important cause of stroke in young adults.

Pathophysiology

The etiology of FMD is not known, although the histopathologic findings have been described in detail (see Histologic Findings).

Although the etiology of FMD is unknown, several other associated vascular pathologies have been identified. In 1982, Mettinger and Ericson[14] scrutinized 4000 consecutively performed cerebral angiographies and found 37 that were consistent with FMD. Of these, 19 patients had aneurysms. In 1988, Cloft et al performed a meta-analysis including 498 FMD patients as well as examined 117 of their own patients and found a combined prevalence of aneurysms to be 7.3%.[15]

In 1975, Stanley et al found that 8 of their 17 cerebrovascular FMD cases had intracranial aneurysms, and they proposed a classification system that includes a "medial fibroplasias with aneurysms" subtype.[11] The beadlike dilatations observed within FMD lesions share gross and histologic characteristics of aneurysms. The casual link between FMD and aneurysms is less clear but is possibly related to an underlying connective tissue problem that results in loss of arterial wall strength. This wall weakness may allow for vessel dilation (aneurysm formation and beading in FMD) as well as injury, which then causes compensatory fibroplasia. Besides aneurysms, many case series and reports have identified FMD in patients presenting with arterial dissection.[16, 17]

FMD is a predisposing factor in 15% of spontaneous cervical carotid dissections. Dissections in FMD are more commonly multiple than in patients without an identified underlying arteriopathy.

FMD lesions likely predispose the artery to dissection through weakening of the arterial wall. Although the multiple manifestations of a structural arteriopathy in FMD hint of a genetic cause, such as collagen or elastin mutation, epidemiologic data suggesting familial transmission are generally weak.

The increased incidence of FMD in women as compared with men suggests a possible hormonal or genetic influence. Some authors have proposed the sex difference to be related to immune system functioning, but overt inflammation, as is observed in most classic autoimmune diseases, is histologically lacking.

Many reports exist of familial occurrences of FMD, mostly in siblings. Some studies have even suggested that familial occurrence is relatively common. For example, Rushton in 1980 suggested familial occurrences in relatives of 12 out of 20 identified probands.[18] However, histologic proof was established in only the index cases, and vascular events such as early strokes and hypertension were used to identify the other affected family members. Most large series have reported that the great preponderance of FMD cases are sporadic. Bilateral renal FMD has been noted in a pair of identical twins.[19]

In case reports, FMD has been associated with mutations in collagen[20] , with cutis laxa[21] , and with alpha1-antitrypsin deficiency[22] . Associative links to neurofibromatosis, Alport syndrome, and pheochromocytoma have also been suggested.[2]

Epidemiology

Frequency

United States

Although early autopsy and radiologic series suggested that FMD involving the craniocervical arteries occurs at a frequency of approximately 1%, a more recent large series looking at FMD in the carotid arteries only suggests a lower frequency, on the order of 0.02%.[9]

International

The frequency is unknown.

Mortality/Morbidity

FMD generally follows a benign course and is frequently an incidental finding. However, cranial involvement bears worse prognosis because of the occurrence of dissection and strokes and the coexistence of saccular aneurysms. Specific mortality and morbidity data are lacking.

Regarding the risk of recurrent carotid artery dissection, de Bray et al prospectively reviewed 103 consecutive patients with carotid artery dissection with follow-up for an average of 4 years. Of those, 5 had recurrent dissections and 4 of the 5 patients with recurrent dissections were diagnosed with FMD. If considering the presentation of recurrent dissection of the carotid artery, FMD was associated in 80% of their series.[23]

Race

Whites are considered to be more commonly affected than blacks, although specific statistics on racial predilection are not available.

Sex

FMD occurs more frequently in women, at a ratio of approximately 3:1 to 4:1.

Age

FMD most commonly presents in young to middle-aged adults. One angiographic series found a mean age of 48 years with a range of 24-70 years.[14] Cases have even been described in the pediatric population, including infantile-onset cases.[24]

History

Most patients with craniocervical FMD are asymptomatic. Others report nonspecific problems such as headache, lightheadedness, vertigo, and tinnitus. Neck pain or carotidynia may be an initial presenting symptom due to arterial dissection. The symptoms of stroke can be varied but most often involve the anterior circulation because of the predilection of FMD to affect the extracranial carotid arteries.

Patients may provide a history of transient or permanent neurologic deficits of the face or extremities such as weakness or numbness, or they may experience visual changes or speech difficulties. No particular symptoms are pathognomonic for FMD, and any history compatible with a stroke in younger individuals may indicate underlying FMD. The family history should include information about relatives who have had vascular events at a young age.

One report notes an extremely unfortunate case of locked-in syndrome due to autopsy-proven basilar artery FMD.[16] FMD may be complicated by stroke because of direct effects of craniocervical stenosis, dissection, or intracranial aneurysm, or the indirect effects of concomitant renovascular hypertension.

Symptoms compatible with a sentinel bleed, namely a sudden explosive headache followed later by neck stiffness, may signify the existence of an aneurysm, which in turn, may be associated with FMD.

A review of symptoms may provide clues of noncraniocervical FMD. Long-standing involvement of the renal arteries may lead to a history of hypertension. Rarely, abdominal pains, and even a history of ischemic bowel, may indicate mesenteric or visceral artery involvement. Vascular compromise of the limbs by FMD lesions may cause ischemic symptoms such as intermittent leg claudication. A case of FMD associated with spinal subdural hematoma has been reported.[25]

Physical

Because of the broad possibilities of neurologic dysfunction due to stroke caused by FMD, a thorough neurologic examination should be performed. Findings may include anything from cranial nerve deficits to weakness, numbness, and coordination difficulties.

Sensitive signs of motor dysfunction such as pronator drift and plantar responses may yield deficits when formal power assessment does not. The neurovascular examination would not be complete without auscultation for carotid and vertebral artery bruits. If a headache history is provided, assessment for meningismus (eg, nuchal rigidity, Kernig sign, Brudzinski sign) may prove positive.

Because of the systemic nature of FMD, the general physical examination should include a search for signs of renal, visceral, and limb arterial involvement. These signs may include hypertension, decreased peripheral pulses, and even asymmetric limb pressures. Bruits may be found on auscultation of the renal, abdominal, iliac, or subclavian arteries.

Causes

The cause of FMD is unknown, despite some speculations related to its associations with some rare genetic conditions and predilection for young white females. Strokes can be caused by the FMD stenoses themselves, generally by thromboembolic events. Even without trauma, FMD lesions predispose the afflicted individual to arterial dissection, which in turn can cause embolic events or, rarely, local thrombosis and massive hemispheric stroke. Hypertension due to renovascular FMD may be a risk factor for lacunar and large vessel infarcts and even intracerebral hemorrhage.

Laboratory Studies

Although usually nonproductive, routine laboratory investigations may show renal impairment (eg, with high creatinine or BUN levels).

Imaging Studies

Other Tests

No other tests are specifically indicated in the workup of FMD.

Procedures

In general, procedures are not indicated in the diagnosis of FMD.

Histologic Findings

Pathologically, FMD is a nonatherosclerotic noninflammatory narrowing of medium-sized arteries characterized by fibrodysplastic changes. In 1979, Bragin and Cherkasov described the ultrastructural changes that occur in FMD as smooth muscle assuming fibroblastic characteristics.[30] FMD has been classified according to the arterial wall layer that is predominantly affected.[10]

The pathologic classification of FMD is as follows:[10, 11, 12]

The percentage occurrence of each type of FMD is largely based on findings from large renal studies and may not reflect the distribution of FMD types in carotid disease. In fact, the medial dysplasia type may be even more predominant when carotid FMD is considered alone.

Staging

No formal staging system exists for FMD, although 4-vessel angiography of the cerebrovasculature is used to identify the extent of the craniocervical disease and the presence of comorbid dissections and aneurysms.

Medical Care

Partly because of the unknown etiology of FMD, no curative therapy exists. Fortunately, FMD is often benign when asymptomatic, and medical treatment is not indicated. Patients presenting with hypertension should be evaluated by a nephrologist and possibly considered for vascular intervention.

When FMD manifests as a transient ischemic attack or as an ischemic stroke, then initial management depends on many factors. If the patient presents in the emergency department with symptoms of stroke within 3 hours of onset, then they may be considered for intravenous (IV) tissue plasminogen activator (tPA) treatment (see Acute Stroke Management). Intra-arterial mechanical embolectomy and intra-arterial pharmacologic fibrinolysis may be considered to extend the acute treatment window to 6 hours. If TPA treatment is employed, then anticoagulants and antiplatelet agents are avoided for at least the ensuing 24 hours.

The diagnosis of FMD should be considered in any young individual presenting with a stroke or subarachnoid hemorrhage. Fortunately, cerebral angiography is the investigation of choice to detect not only FMD but also arterial dissection, vasculitis, and aneurysms, which are other major etiologies of stroke in this population. Thus, cerebral angiography should be performed if another cause for the stroke is not clear. The treatment options are influenced by the findings on angiography.

If only FMD is identified on angiography, medical treatment usually incorporates antiplatelet agents, similar to the treatment of atherosclerotic disease. Often, daily aspirin is considered first-line therapy, and another antiplatelet agent is substituted or added if another ischemic event occurs (such as clopidogrel or combination acetylsalicylic acid and extended-release dipyridamole).

If arterial dissection with FMD is identified with cerebral angiography, then initial treatment primarily addresses the dissection (see Dissection Syndromes). Although evidence from randomized trials is lacking, anticoagulation is often used after cerebral hemorrhage has been ruled out. Anticoagulation is with heparin initially, then Coumadin is administered on an outpatient basis for 3-6 months. Some neurologists advocate reassessment of the arteries for dissection before discontinuation of anticoagulation and initiation of an antiplatelet agent for life. Often, if the dissection could be observed with MRA or CTA, these modalities are used in follow-up because of its less invasive nature.

If the presentation is that of subarachnoid hemorrhage, then acute treatment is primarily focused on preventing rebleeding, and preventing arterial vasospasm and further ischemic cerebral injury. Aneurysms may be closed by endovascular coiling or surgical clipping. Nimodipine, a calcium channel blocker, is generally used to reduce vasospasm-mediated brain injury. See Cerebral Aneurysms for a more in-depth discussion of aneurysm management.

After the aneurysms have been dealt with, either surgically or through an endovascular approach, then unless further history is consistent with thromboembolic phenomena, management may be conservative. Antiplatelets are unnecessary if the FMD lesions themselves are asymptomatic and not causing emboli.

Some authors have suggested that FMD could be caused by arterial wall injury fragility followed by hemodynamic stress. Hence, treating FMD by reducing hemodynamic stress (ie, aggressive blood pressure control) may be reasonable.[31]

Surgical Care

Surgical vascular reconstruction of renal FMD has met with good success.[13] However, because the end organ of cervicocranial FMD is the brain, more serious risks are involved. Thus, the role of surgery in carotid and vertebrobasilar FMD is not well understood.

Although medical management of stroke prophylaxis in FMD is quite similar to the management of atherosclerotic disease, the lesions in FMD are not amenable to endarterectomy. Thus, surgical management is used as a last resort in cases where stenosis is critical and global cerebral hypoperfusion is an issue or for ischemic events refractory to medical management. No trials exist comparing medical and surgical management of cerebrovascular FMD. However, many authors have published series of operative graduated dilatation of FMD stenosis and report good results.[32, 33, 34] (See images below.)


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Illustration of the operative approach of graduated dilatation of the internal carotid artery (ICA). The common carotid and external carotid arteries ....


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Illustration depicts the intraluminal appearance of graduated dilatation of the stenoses of FMD. The dilator is passed into the vessel and opens the b....

A few cases with vascular graft placements and surgical bypass of FMD lesions have been reported.

Aneurysms that may coexist with FMD should be managed in a similar manner to non-FMD–associated ones.

Because of the emergence of endoluminal angioplasty and stenting for cerebrovascular disease, interventional radiologic management of FMD lesions may be suitable for some patients, especially those who are not good surgical candidates. Again, no studies have assessed this management option as compared to more established medical or surgical treatment, but it may be deemed an appropriate option in some instances. One case report describes a good outcome after 9 months of follow-up in a patient with bilateral carotid stents placed for bilateral medically-refractory symptomatic lesions.[35]

Consultations

A stroke presentation, whether acute or not, is usually managed by a neurologist. If associated aneurysms or subarachnoid hemorrhages are detected, then a neurosurgeon and interventional radiologist should be consulted. If a history of chest pain is noted, this may signify FMD in the coronary arteries, and a cardiologist should be consulted. If blood pressure is elevated, then the renovasculature should be assessed and a nephrologist consulted if necessary. Symptoms of an ischemic gut should be managed by a general surgeon, and limb claudication should be assessed by a vascular surgeon.

Diet

No specific dietary modifications are indicated in FMD. If a stroke has occurred, then a swallowing assessment may be required and the diet modified accordingly.

Activity

Activity restrictions should be individualized depending on the clinical details and possible neurologic deficits. Neck trauma, including chiropractic manipulation, should be avoided if craniocervical FMD is established because of the possibility of dissection. If cerebral aneurysms exist, strenuous activity that would increase blood pressure should be avoided.

Medication Summary

As discussed above, acute treatment of any ischemic stroke may involve tPA, regardless of the presence or absence of FMD.

Secondary prevention of stroke generally involves the use of antiplatelet agents, and failure of a first agent results in either the switch to another agent or the addition of a second antiplatelet agent. Selection of a particular antiplatelet agent is variable, depending on physician preference. The complication of arterial dissection is generally treated with anticoagulation, first intravenously then orally. Finally, subarachnoid hemorrhage due to aneurysm rupture precludes anticoagulation and indicates a need for antivasospastic medications.

Alteplase (Activase)

Clinical Context:  Used in management of acute ischemic stroke, acute MI, and PE. Safety and efficacy with concomitant heparin or aspirin during first 24 h after symptom onset not investigated.

Class Summary

tPA exerts an effect on fibrinolytic system to convert plasminogen to plasmin. They are used for dissolving blood clots and have a role in the acute management of ischemic strokes.

Aspirin (Anacin, Ascriptin, Bayer Aspirin, Bayer Buffered Aspirin)

Clinical Context:  Treats mild to moderate pain and headache. Inhibits prostaglandin synthesis, which prevents formation of platelet-aggregating thromboxane A2. Generally considered first-line therapy in the secondary prophylaxis of cerebrovascular disease.

Clopidogrel (Plavix)

Clinical Context:  Selectively inhibits ADP binding to platelet receptor and subsequent ADP-mediated activation of glycoprotein GPIIb/IIIa complex, inhibiting platelet aggregation.

May have positive influence on several hemorrhagic parameters and may exert protection against atherosclerosis (inhibition of platelet function and changes in hemorrhagic profile).

Ticlopidine (Ticlid)

Clinical Context:  Second-line antiplatelet therapy for patients who cannot tolerate acetylsalicylic acid therapy or for whom such therapy is unsuccessful. Rarely used because of serious adverse effects and replacement by newer agents.

Aspirin 25 mg/Dipyridamole 200 mg (Aggrenox)

Clinical Context:  Drug combination with antithrombotic action. Aspirin inhibits prostaglandin synthesis, preventing formation of platelet-aggregating thromboxane A2. May be used in low dose to inhibit platelet aggregation and improve complications of venous stasis and thrombosis. Dipyridamole is a platelet adhesion inhibitor that possibly inhibits RBC uptake of adenosine, itself an inhibitor of platelet reactivity. May also inhibit phosphodiesterase activity, leading to increased cyclic-3', 5'-adenosine monophosphate levels in platelets and formation of the potent platelet activator thromboxane A2.

Class Summary

These agents are used for secondary stroke prophylaxis after previous stroke or transient ischemic attack.

Heparin

Clinical Context:  Augments activity of antithrombin III and prevents conversion of fibrinogen to fibrin. Does not actively lyse but is able to inhibit further thrombogenesis. Prevents reaccumulation of clot after spontaneous fibrinolysis.

Most centers have protocols to titrate heparin rate to achieve specific anticoagulation levels on blood work.

Warfarin (Coumadin)

Clinical Context:  Interferes with hepatic synthesis of vitamin K–dependent coagulation factors. Used for prophylaxis and treatment of venous thrombosis, pulmonary embolism, and thromboembolic disorders.

Class Summary

The use of anticoagulation in the acute management of stroke has been under hot debate for many years. However, many neurologists advocate the use of heparin acutely in stroke in the setting of an arterial dissection. Heparin is used acutely in this case, followed by several months of warfarin.

Nimodipine (Nimotop)

Clinical Context:  To improve neurologic impairments resulting from vasospasm after subarachnoid hemorrhage caused by a ruptured congenital intracranial aneurysm in patients who are in good neurologic condition postictus.

Studies show benefit on the severity of neurologic deficits caused by cerebral vasospasm after subarachnoid hemorrhage, but no evidence indicates that the drug either prevents or relieves spasm of the cerebral arteries. Actual mechanism of action unknown, and a neuroprotective effect is suggested.

Therapy should start within 96 h of the subarachnoid hemorrhage. If capsule cannot be swallowed because patient is undergoing surgery or unconscious, a hole can be made at both ends of the capsule with an 18-gauge needle and the contents extracted into a syringe and emptied into the patient's in situ nasogastric tube and flush with 30-mL isotonic saline.

Class Summary

These agents are used in cases of subarachnoid hemorrhage.

Further Inpatient Care

Physical and occupational therapy and speech therapy may be important aspects of patient care should neurologic deficits exist.

Further Outpatient Care

Neurorehabilitation generally helps to recover function if any residual neurologic deficits are present.

Inpatient & Outpatient Medications

Deterrence/Prevention

Complications

Prognosis

Author

James A Wilson, MD, MSc, FRCPC, Neurologist and Clinical Neurophysiologist, Oconee Neurology Services

Disclosure: Nothing to disclose.

Coauthor(s)

Richard L Hughes, MD, Professor of Neurology, University of Colorado at Denver School of Medicine; Chief, Division of Neurology, Denver Health Medical Center

Disclosure: Nothing to disclose.

Specialty Editors

Jeffrey L Saver, MD, FAHA, FAAN, Professor of Neurology, Director, UCLA Stroke Center, University of California, Los Angeles, David Geffen School of Medicine

Disclosure: University of California The University of California Regents receive funds for consulting services on clinical trial design provided to Covidien, Stryker, and Lundbeck. Consulting

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Howard S Kirshner, MD, Professor of Neurology, Psychiatry and Hearing and Speech Sciences, Vice Chairman, Department of Neurology, Vanderbilt University School of Medicine; Director, Vanderbilt Stroke Center; Program Director, Stroke Service, Vanderbilt Stallworth Rehabilitation Hospital; Consulting Staff, Department of Neurology, Nashville Veterans Affairs Medical Center

Disclosure: Nothing to disclose.

Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, Tampa General Hospital, University of South Florida College of Medicine

Disclosure: UCB Pharma Honoraria Speaking, consulting; Lundbeck Honoraria Speaking, consulting; Cyberonics Honoraria Speaking, consulting; Glaxo Smith Kline Honoraria Speaking, consulting; Sleepmed/DigiTrace Honoraria Consulting; Sunovion Consulting fee None; Supernus Speaking, consulting; Upsher-Smith Grant/research funds None

Chief Editor

Helmi L Lutsep, MD, Professor and Vice Chair, Department of Neurology, Oregon Health and Science University School of Medicine; Associate Director, Oregon Stroke Center

Disclosure: Stryker Neurovascular Consulting fee Review panel membership

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Angiogram of the descending aorta demonstrates the stenoses of FMD in the renal arteries bilaterally.

Digital subtraction angiogram of the right internal carotid artery demonstrates an irregular extracranial portion that is consistent with FMD.

Conventional angiogram of the left carotid artery demonstrates a 1.5-cm, long, smooth, severe stenosis of the extracranial internal carotid artery. Note that the artery is not completely occluded and a thin continuous string of contrast is present along the length of the stenosis. This smooth tubular stenosis is suggestive of the intimal fibroplasia form of FMD but can be observed with any of the subtypes.

Cerebral angiogram of the left carotid artery territory demonstrates a long, irregular stenosis with a string-of-beads appearance along the entire extracranial length of the internal carotid artery (ICA). This is consistent with the most common medial dysplasia form of fibromuscular dysplasia. Also note similar involvement of the first 3 cm of the external carotid artery (ECA). Such extensive ICA involvement, as well as ECA involvement, is atypical. Note sparing of the carotid bulb.

Lateral view of a right carotid angiogram demonstrates multiple stenoses of FMD of the internal carotid artery. The string of beads appearance is suggestive of the medial dysplasia form of FMD.

Anteroposterior view of a right carotid angiogram demonstrates FMD of the extracranial portion of the right internal carotid artery.

Angiogram of the descending aorta demonstrates the stenoses of FMD in the renal arteries bilaterally.

Angiogram of the right vertebral artery demonstrating irregular stenoses of fibromuscular dysplasia at the level of C2-3.

Illustration of the operative approach of graduated dilatation of the internal carotid artery (ICA). The common carotid and external carotid arteries are cross-clamped, and the superior thyroid artery is clipped while the ICA is isolated, opened, and dilated with progressively larger dilators. This technique has been shown to be successful in the management of medically refractive FMD stenoses.

Illustration depicts the intraluminal appearance of graduated dilatation of the stenoses of FMD. The dilator is passed into the vessel and opens the bandlike narrowings.

Digital subtraction angiogram of the right internal carotid artery demonstrates an irregular extracranial portion that is consistent with FMD.

Conventional angiogram of the left carotid artery demonstrates a 1.5-cm, long, smooth, severe stenosis of the extracranial internal carotid artery. Note that the artery is not completely occluded and a thin continuous string of contrast is present along the length of the stenosis. This smooth tubular stenosis is suggestive of the intimal fibroplasia form of FMD but can be observed with any of the subtypes.

Cerebral angiogram of the left carotid artery territory demonstrates a long, irregular stenosis with a string-of-beads appearance along the entire extracranial length of the internal carotid artery (ICA). This is consistent with the most common medial dysplasia form of fibromuscular dysplasia. Also note similar involvement of the first 3 cm of the external carotid artery (ECA). Such extensive ICA involvement, as well as ECA involvement, is atypical. Note sparing of the carotid bulb.

Lateral view of a right carotid angiogram demonstrates multiple stenoses of FMD of the internal carotid artery. The string of beads appearance is suggestive of the medial dysplasia form of FMD.

Anteroposterior view of a right carotid angiogram demonstrates FMD of the extracranial portion of the right internal carotid artery.

Angiogram of the descending aorta demonstrates the stenoses of FMD in the renal arteries bilaterally.

Angiogram of the right vertebral artery demonstrating irregular stenoses of fibromuscular dysplasia at the level of C2-3.

Illustration of the operative approach of graduated dilatation of the internal carotid artery (ICA). The common carotid and external carotid arteries are cross-clamped, and the superior thyroid artery is clipped while the ICA is isolated, opened, and dilated with progressively larger dilators. This technique has been shown to be successful in the management of medically refractive FMD stenoses.

Illustration depicts the intraluminal appearance of graduated dilatation of the stenoses of FMD. The dilator is passed into the vessel and opens the bandlike narrowings.

Illustration depicts the locations of FMD lesions, which differentiate regions with typical and atypical angiographic appearances of this disease.

Digital subtraction angiography of the left internal carotid artery distribution demonstrates a large 1.5-cm-diameter aneurysm of the right anterior communicating artery. Aneurysms may be associated with systemic vasculopathies such as FMD.

Small infarct in woman with fibromuscular dysplasia from dissected vertebral artery. An incidental aneurysm, or ovoid diverticula, is noted in the supraclinoid left internal carotid artery.

Small infarct in woman with fibromuscular dysplasia from dissected vertebral artery. An incidental aneurysm, or ovoid diverticula, is noted in the supraclinoid left internal carotid artery. Dissected vertebral artery.

Small infarct in woman with fibromuscular dysplasia from dissected vertebral artery. An incidental aneurysm, or ovoid diverticula, is noted in the supraclinoid left internal carotid artery. Internal carotid angiogram.