MRI CSF Flow Study
Basics: What is a CSF Flow Study?
A “CSF Flow Study” is an MRI of the brain or spine that evaluates the flow of cerebrospinal fluid around the brain, brainstem and/or spinal cord.
An MRI Cerebral Spinal Fluid (CSF) Flow Study is an increasingly important tool that allows us to measure the velocity of cerebral spinal fluid as it flows from the cerebral ventricles (fluid reservoirs) inside the brain, down to the skull base via the cerebral aqueduct, and to the spinal canal via the fourth ventricle and foramen magnum”. Cerebral spinal fluid is continually produced within the center of the brain, (about 500 cc/day) and is continually reabsorbed at a number of locations along the surface of the brain. There are a number of events, and disease states that can significantly alter the velocity and behavior of CSF over time, these shifts are visible via the CSF waveform obtained through the MRI study. CSF is not a static fluid; it is continuously flowing back and forth between the head and the spine. The direction of flow is determined by the cardiac cycle. When the heart maximally contracts to pump blood out of its chambers and to the head and body (the systolic phase) the brain becomes engorged with blood, and as it temporarily swells up, ventricles filled with CSF are squeezed. This action pumps CSF downward towards the skull base and spine. Conversely, when the heart relaxes (the diastolic phase) blood fills the atria and the cerebral ventricles relax, which causes CSF flow to reverse its direction and the fluid flows upward from the upper spine and skull base, into the center of the brain again. Because of this cycling spinal fluid is pulsatile; its movement is determined by pulsation of the heart.
What situations can result in alterations in CSF flow?
Head trauma, intracranial hemorrhage, including subdural hematomas, parenchymal bleeding, and subarachnoid hemorrhage can all impact CSF flow. Additionally, physical obstructions can alter CSF flow, including aqueductal stenosis or narrowing (congenital or acquired), Chiari I malformations, tumors that obstruct CSF flow somewhere along the ventricular system, and infectious or inflammatory processes of the brain or meninges.
Once abnormal CSF velocities and waveforms are demonstrated, how does this affect the patient?
If the patient demonstrates CSF flow abnormalities, with elevated or abnormal velocities, they can then potentially be evaluated for possible placement of a VP (Ventriculo-peritoneal) shunt. A VP shunt can help normalize CSF drainage, which can lower CSF velocities and also reduce a number of symptoms, including those encountered with NPH (Normal Pressure Hydrocephalus). Patients with prior insult to the head who experience less classical symptoms, including headaches may aslo benefit from the placement of a shunt.
Answers to commonly asked questions by referring physicians:
Q: I don’t ever refer my patients for a MRI CSF FLOW STUDY. When should I be thinking about ordering one?
A: Patients with unexplained headaches, tinnitus, dementia, urinary incontinence, balance issues, and cognitive deficits may benefit from a CSF flow evaluation; CSF flow studies are quickly becoming an extremely important tool in sorting out a number of disease processes. This procedure's initial and best-known indication is for detecting Normal Pressure Hydrocephalus with patients complaining of incontinence, cognitive deficits, and balance issues. However, CSF flow patterns can change significantly after trauma, brain hemorrhage, previous meningitis, as well as a number of other insults, leading to vague symptoms including headaches. In addition, MRI CSF flow analysis is becoming an important tool to evaluate not only Chiari I patients (cerebellar tonsils extending down into the foramen magnum), but also individuals who don’t have a Chiari I abnormality, but who functionally have the same problem that results in suboccipital headaches ( “Chiari Zero” patients).
Discussion of images above:
This patient is a 38-year-old female with long standing suboccipital headaches. Standard MRI demonstrates a Chiari I malformation, which means the cerebellar tonsils descend into the foramen magnum at least 5 mm. Both the cine images, as well as the velocity data graphed below, demonstrate a functional obstruction at the foramen magnum, with elevated velocities, as well as markedly varied velocities at the same point in time at different locations around the cerebellar tonsils. Findings suggest that the cerebellar tonsils are causing the symptoms, and that the patient may benefit from a Suboccipital craniectomy, to decompress the tonsils at the cervicomedullary junction.