Fibromuscular dysplasia (FMD) is a condition that affects the arteries throughout the body, causing them to narrow, bulge, or appear beaded. This article focuses on how ultrasound is used to diagnose FMD, covering preparation, the procedure, and what findings an ultrasound can reveal. Understanding this non-invasive imaging technique can help patients know what to expect.
What is Fibromuscular Dysplasia?
Fibromuscular dysplasia is a disease involving abnormal cell growth within the walls of arteries. This growth is neither caused by plaque buildup (atherosclerosis) nor by inflammation. The arterial walls can become thickened, enlarged, or irregular in shape, leading to narrowed sections or weakened, bulging areas.
FMD most commonly affects the renal arteries, which supply blood to the kidneys, and the carotid arteries in the neck, which deliver blood to the brain. Narrowing of these arteries can restrict blood flow, potentially leading to high blood pressure or stroke. While rare, FMD can affect individuals of any age or gender, though it is more frequently diagnosed in middle-aged women.
Why Ultrasound for FMD Diagnosis?
Ultrasound is a common imaging method for diagnosing fibromuscular dysplasia due to its advantages. It is non-invasive, meaning it does not involve needles or incisions, and it does not expose the patient to radiation. This makes it suitable for initial screening and ongoing monitoring of FMD.
The real-time imaging capability of ultrasound allows healthcare providers to visualize blood flow dynamically. This helps in assessing how blood moves through arteries and identifying turbulence or changes in flow patterns that might suggest FMD. While other imaging techniques like CT angiography and MR angiography can also detect FMD, ultrasound offers a safe, accessible, and often first-line approach for evaluation.
Preparing for and Undergoing the Ultrasound
Preparing for an ultrasound for fibromuscular dysplasia involves specific instructions for clear images. For renal artery scans, patients typically fast for about 8 hours to reduce bowel gas. Patients may also be advised to drink water prior to the procedure to aid in imaging. For carotid artery ultrasounds, fasting is generally not required.
During the procedure, you will lie on an examination table. A sonographer will apply a warm, water-based gel to the skin over the area being examined. This gel helps the ultrasound transducer, a small handheld device, glide smoothly and allows sound waves to travel effectively into the body. The sonographer moves the transducer across the skin, applying gentle pressure, to capture images of the arteries and assess blood flow.
The specific arterial systems scanned depend on the suspected location of FMD. If renal artery involvement is suspected, the sonographer focuses on the arteries supplying the kidneys and the abdominal aorta. For suspected carotid artery FMD, the neck arteries leading to the brain are examined.
A specialized type of ultrasound, Duplex ultrasound, is commonly employed because it combines traditional imaging with Doppler technology to measure blood flow. During the scan, you might be asked to hold your breath or change positions to improve image clarity. The entire procedure usually takes between 15 to 90 minutes, depending on the complexity and number of arteries examined.
What the Ultrasound Reveals
When an ultrasound is performed for fibromuscular dysplasia, sonographers and physicians look for specific characteristics in artery walls and blood flow patterns. A hallmark sign of FMD, particularly the multifocal type, is the “string of beads” appearance. This represents alternating areas of narrowing (stenosis) and bulging (aneurysms or dilatations) along the artery.
Beyond the visual appearance of artery walls, ultrasound also provides dynamic information about blood flow. Sonographers can detect turbulent blood flow, which appears as chaotic or irregular movement within the vessel. This turbulence often occurs in narrowed areas. Another indicator is an increase in blood flow velocity in narrowed segments. As blood passes through a restricted area, its speed accelerates, a phenomenon Doppler ultrasound can measure. Elevated velocities in artery segments are suggestive of FMD. These combined visual and flow-related findings help healthcare professionals diagnose FMD and understand its extent.