Introduction

Fibromuscular dysplasia (FMD) is an idiopathic (spontaneous), non-atherosclerotic (not caused by the accumulation of substances like fats in the artery), non-inflammatory vascular disease that mostly affects medium-sized arteries.¹ It involves abnormal growth within the arterial walls, leading to stenosis (narrowing), aneurysms (a bulging in the artery due to weakness), and dissections (partial tears) in the affected vessels.¹

FMD most commonly impacts the renal and carotid arteries, so FMD often presents with renovascular hypertension (high blood pressure caused by the narrowing of arteries supplying the kidneys) but it’s currently believed that FMD can affect any arteries in the body, with the symptoms depending precisely on which blood vessels are affected.² Ultimately, early diagnosis and treatment are important for the long-term prognosis of the condition.

Cerebrovascular fibromuscular dysplasia is a specific type of FMD which affects the arteries supplying the brain, most commonly the extracranial carotid and vertebral arteries. Since the clinical presentation of FMD depends on which blood vessels are affected, cerebrovascular FMD has unique neurological manifestations. Structural abnormalities in blood vessels supplying the brain can cause a host of issues, including an increased risk of stroke, aneurysms and diagnostic challenges due to the symptoms of cerebrovascular FMD overlapping with other disorders.³

Epidemiology

Fibromuscular dysplasia (FMD) in general affects up to approximately 7% of the population.³ The prevalence of cerebrovascular involvement in FMD is less clearly defined due to issues of underdiagnosis, although it is estimated to be a significant subset of FMD cases. The risk that cerebrovascular FMD is underdiagnosed stems from its potential to be asymptomatic, meaning that a proportion of people living with cerebrovascular FMD may not seek guidance or diagnostic testing from a healthcare provider due to not identifying or experiencing any significant issues.⁴

Cerebrovascular FMD affects those assigned female at birth (AFAB) to a greater degree than those assigned male at birth (AMAB) - over 90% of FMD patients are AFAB, according to the Cleveland Clinic. Cerebrovascular FMD is mainly diagnosed in adults, with most cases being identified in individuals who are between the ages of 30 and 60. However, it can occur at any age, including in children and the elderly.⁵

There is evidence suggesting a genetic predisposition to FMD. A family history of FMD or other vascular diseases increases the likelihood of developing the condition. Additionally, there appear to be higher rates of FMD among smokers.¹ FMD has been reported worldwide and does not appear to have a strong geographic marker.

Pathophysiology

Even though FMD affecting the renal arteries has been well-researched, data on the epidemiology and pathophysiology of cerebrovascular FMD are still emerging. Cerebrovascular FMD tends to affect the extracranial internal carotid or vertebral arteries with radiographic and histologic features that resemble those of the renal arteries.

In people unaffected by any form of FMD, the healthy arteries respond to the rhythmic flow of blood by expanding and contracting as blood flows through it. However, when an artery is affected by FMD, it can be too stiff or not stiff enough. These both cause problems - if the artery is overly stiff, the artery can’t expand as blood rushes through it with the same efficacy, leading to hypertension (high blood pressure). If the arteries are not stiff enough, the artery can balloon or dilate - this is called an aneurysm. Aneurysms can cause internal bleeding, impede the supply of oxygenated blood to tissues and cause abnormal pressure. Most commonly, the tunica media (middle structure in the walls of the artery) alternates between these two states of excess and insufficient stiffness, causing the affected area to adopt an appearance resembling a string of beads. This appearance plays an important role in the diagnosis of the condition. 

In cerebrovascular FMD, the walls of the arteries which supply the brain become either too weak or too stiff (as described). One cause of this is fibroplasia the abnormal growth of fibrous tissue within the arterial wall. This causes the layers of the artery to get thicker and stiffer. Furthermore, certain sections of the arterial wall may weaken and balloon out - these dilated segments are less stiff than the nearby narrowed regions. The overall changes in the composition of arterial walls can cause neurological problems of varying severity due to the altered blood flow to the brain.

Clinical presentation

Patients with cerebrovascular FMD are usually asymptomatic at disease identification. Furthermore, the presenting signs and symptoms are nonspecific, including headache, dizziness and tinnitus which may be confused for other conditions or not considered serious enough to seek medical advice. A smaller subset of patients will present with more consequential cerebrovascular disease including stroke, transient ischemic attacks, subarachnoid haemorrhage, or arterial dissection.³

Headache is a common first complaint, being reported by 50%–78% of patients.⁶ Because of this, FMD should be considered as a diagnosis in patients with a new onset of headache later in adulthood. The headache often has migrainous features, such as nausea and photophobia, and may require chronic medication to manage this.⁶ Another common symptom of cerebrovascular FMD is pulsatile tinnitus (a ‘whooshing’ sound in the ears synchronous with the patient’s heartbeat), observed in approximately 25% of those with FMD. Pulsatile tinnitus can be diagnosable for healthcare providers during the differential diagnosis process. An equal number of patients report nonpulsatile tinnitus (where the whooshing sound is asynchronous with the individual’s heartbeat). Neck pain is reported in 18%–22% of cases and is usually unilateral (only affecting one side of the body).⁶ In one review, 50% of patients with FMD complained of depression and anxiety.⁷ This may suggest that psychiatric and counselling support may be a beneficial aspect in the treatment of cerebrovascular FMD.

Diagnosis 

Vascular imaging is the most significant method by which FMD is diagnosed. 

The Mayo Clinic outlines several diagnostic tests that may be used by healthcare providers to ascertain the patient’s condition. These include:

• Blood tests: blood tests may be done to check for signs of other conditions that can narrow arteries. The patient may have their blood sugar and cholesterol levels checked. This is important in eliminating other possible conditions which may cause the patient’s symptoms
• Angiogram: X-rays are used to create pictures of the arteries. A dye is injected to help the arteries show up more clearly on the X-ray images. The most common radiographic observation is alternating areas of arterial constriction and dilation forming a beaded appearance
• Duplex ultrasound: this test can show whether an artery is narrowed. It utilises sound waves to create pictures of blood flow and the shape of blood vessels

Treatment and management

There is no cure for FMD, and treatment options depend on:

1. The area of the narrowed artery
2. The symptoms experienced by the patient
3. Any comorbidities

Some people only need regular health checkups to monitor the condition and assess its severity and progression. Other treatments may include medicines and procedures to widen or repair an artery.

Cerebrovascular FMD requires a focus on preventing and managing neurological complications, as these are the primary complaints - particularly control of chronic headache and pulsatile tinnitus as these are significant influencers of the quality of life in patients with FMD.

Patients with both fibromuscular dysplasia and high blood pressure are usually given medicines to control their blood pressure. Some medications which treat high blood pressure can affect the functioning of the kidneys. As a result, the patient may need regular blood and urine tests to make sure the kidneys are working as they should.

The Cleveland Clinic outlines the following options:

• Antiplatelet drugs or anticoagulant drugs: these thin the blood to help prevent clots and stroke
• ACE inhibitors and angiotensin receptor blockers: these are medications prescribed to treat high blood pressure
• Aspirin: to treat headaches/pain
• Angioplasty: uses a tiny balloon inserted through a catheter to widen the artery, improving blood flow and alleviating hypertension 
• Surgery: to repair aneurysms and prevent rupture

Summary

• Cerebrovascular fibromuscular dysplasia is a specific type of FMD which affects the arteries supplying the brain
• Structural abnormalities in blood vessels supplying the brain can increase the risk of stroke, aneurysms and diagnostic challenges
• Cerebrovascular FMD can remain clinically asymptomatic and is sometimes only diagnosed when imaging studies are performed for other purposes
• Neurological symptoms of cerebrovascular FMD can include headache, dizziness, tinnitus, neck pain, strokes or temporary vision loss
• Vascular imaging is typically used in the diagnostic process
• Treatment methods include medications and/or surgery, varying on a case-by-case basis