“Major intracranial flow voids are present” is a specific observation made during a Magnetic Resonance Imaging (MRI) scan of the brain. It describes an imaging finding related to blood flow within the head’s vessels. This finding is not a final diagnosis but a sign requiring further investigation. The radiologist is alerting the physician to large or unusually prominent areas where the blood flow signal is absent.
Understanding Intracranial Flow Voids
“Intracranial” means the finding is located inside the skull. A “flow void” relates to the physics of how MRI scans image moving fluids like blood. Standard MRI sequences are designed to pick up signals from stationary tissues.
When blood flows quickly through a vessel, the hydrogen protons move rapidly in and out of the imaging slice. These moving protons miss the full radiofrequency pulse sequence and do not emit a signal back to the scanner. This absence of signal appears as a dark or black area, known as a void. Normal arteries and veins show flow voids, indicating brisk blood flow. The descriptor “major” indicates these voids are either larger than normal (suggesting a dilated vessel) or more pronounced (suggesting unusually high flow velocity).
Clinical Significance of Major Flow Voids
The presence of major flow voids often points to an underlying vascular abnormality, typically suggesting a high-flow lesion. The velocity of the blood is increased because it is taking an abnormal, low-resistance pathway.
One significant condition indicated by major flow voids is an Arteriovenous Malformation (AVM). An AVM is a congenital defect where arteries connect directly to veins, bypassing the capillary network. This direct connection creates a high-pressure shunt, and the collection of abnormal vessels (the nidus) appears as numerous, serpiginous flow voids on the MRI.
Another related condition is a Dural Arteriovenous Fistula (DAVF), an abnormal connection between arteries and veins located in the dura mater, the brain’s tough outer covering. Major flow voids can also be caused by a large or complex aneurysm, which is a ballooning of a blood vessel wall that creates turbulent flow and an unusually large signal void.
Subsequent Diagnostic Steps and Evaluation
The finding of major intracranial flow voids necessitates specialized imaging to map the vascular anomaly. The first step after a routine MRI is typically a Magnetic Resonance Angiography (MRA) or a Computed Tomography Angiography (CTA). These non-invasive tests visualize blood vessels, often using contrast dye to highlight the flow and structure of arteries and veins.
They provide a clearer picture of the size, location, and connections of abnormal vessels, helping confirm conditions like an AVM or DAVF. The definitive diagnostic procedure is often Digital Subtraction Angiography (DSA), or conventional angiography. DSA is an invasive procedure where a catheter is threaded through a vessel (usually in the groin) up to the brain. Contrast dye is injected directly into the cerebral vessels while real-time X-ray images are taken. This provides the most detailed, high-resolution images of blood flow dynamics, which is crucial for treatment planning.