When reviewing a brain MRI, the term “flow void” might appear in the report. While this phrase can sound concerning, implying an empty space, it often represents a normal and expected finding. Many flow voids actually indicate healthy, robust blood flow within the brain’s vessels.
Understanding Flow Voids
A “flow void” on an MRI scan appears as a dark or absent signal within a blood vessel. This phenomenon occurs because rapidly flowing blood does not remain in the imaging slice long enough to fully interact with the magnetic fields and radiofrequency pulses of the MRI machine, resulting in a signal “void” or darkness. This is a common characteristic of actively flowing fluids, not just blood, and is often a sign of normal vascular patency.
Common Reasons for Flow Voids
Flow voids can be categorized into physiological (normal) and pathological (abnormal) causes. Physiological flow voids are frequently observed in major arteries and veins within the brain, such as the internal carotid and basilar arteries. Their presence indicates that blood is flowing briskly and unimpeded through these vessels, which is a healthy sign.
However, flow voids can also be associated with certain medical conditions that cause abnormal blood flow patterns. These pathological flow voids might suggest an underlying issue, such as an aneurysm, an arteriovenous malformation (AVM), or a dissection.
When Flow Voids Are a Concern
When flow voids are indicative of a problem, they typically point to conditions involving abnormal vascular structures or high-speed, turbulent blood flow. An aneurysm, which is a balloon-like bulge in a blood vessel wall, might show a flow void within its sac if blood is circulating rapidly inside it. This indicates a weakened vessel wall that carries a risk of rupture.
Arteriovenous malformations (AVMs) are abnormal tangles of blood vessels where arteries connect directly to veins. The rapid, turbulent blood flow within an AVM’s nidus (the central tangle) often appears as numerous flow voids on an MRI. Such AVMs can lead to complications like hemorrhage or neurological issues. Dissections, which are tears in the inner lining of a blood vessel, can also alter blood flow dynamics and sometimes present with abnormal flow voids, particularly if there’s an associated occlusion or stenosis.
What to Do Next
If your MRI report mentions a flow void, it is important to discuss these findings with your healthcare provider. A qualified medical professional, such as a neurologist or radiologist, can accurately interpret its significance in the context of your overall health and medical history. They will consider the specific location, size, appearance, and any other findings from the scan. Your doctor may recommend further specialized tests, such as a magnetic resonance angiography (MRA) or conventional angiography, to gain a more detailed understanding.