Click on any image below to see an enlargement of that image.

Case 1:
(A) Cardiac systole causes caudad flow of CSF (CSF Systole)—depicted in white (arrow).	(B) Cardiac diastole causes a reversal of flow with cephalad movement of CSF (CSF Diastole) – depicted in black (arrow).
Case 2:
(A) Patient presents with hydrocephalus with enlargement of all ventricles. Communicating, non-obstructive hydrocephalus was the initial consideration.	(B) & (C): CSF flow study demonstrates lack of outflow of CSF from the fourth ventricle (arrow) into the foramen of Magendie indicating an obstructive hydro-cephalus that may benefit from third ventriculostomy.
Case 3:
(A) Patient presents with headaches. Midline sagittal T1-weighted MR demonstrates tonsillar ectopia (arrow).	(B) & (C): CSF flow study demonstrates altered flow at the foramen magnum with no flow in the cisterna magna (arrow).
Case 4:
(A) Third ventriculostomy. Midline sagittal T1-weighted image shows enlargement of the ventricles indicating hydrocephalus.	(B) & (C): CSF flow study following third ventriculostomy shows patency of the orifice (arrows) at the anteroinferior wall of the third ventricle and lack of outflow/inflow at the inferior fourth ventricle (arrowheads) indicating the site of obstruction.

Above images are all original MR scans performed at Parkside MR Center.

Discussion

The parts of the central nervous system are often considered static structures. In fact, there is motion of the brain and spinal cord as well as considerable motion of the cerebrospinal fluid (CSF). There are early MR studies on brain and spinal cord motion and its relation to disease processes, however in recent years considerable research and clinical work have been performed with regard to CSF flow. CSF flow takes place in a relatively orderly fashion within the skull and spinal canal with oscillatory motion resulting from cardiac pulsations. Cardiac systole results in a pressure wave transmitted to intracranial arteries and capillaries that causes caudad flow of CSF (CSF systole) through the ventricular system, basilar cisterns and foramen magnum into the cervical subarachnoid space (Fig 1a). Following cardiac diastole, there is reversal of flow with cephalad movement of CSF (CSF diastole) (Fig 1b).

The normal flow of CSF can be disrupted with disease processes such as hydrocephalus (obstructive and communicating/normal pressure) (Fig 2), Chiari I malformation (Fig 3) and intracranial/intraspinal cysts. The normal flow of CSF can also be altered therapeutically for the treatment of hydrocephalus with third ventriculostomy (Fig 4). These processes can be evaluated using ECG gated two-dimensional cine phase-contrast MR. This imaging technique is sensitive to velocity changes in a specific direction, while canceling signal from stationary protons and from motion in other directions. These velocity changes are depicted on a gray scale with white indicating caudad flow and black indicating cephalad flow. The images are displayed as a repetitive loop to simulate cine motion.

The site of CSF obstruction in non-communicating hydrocephalus can be difficult to determine with conventional MR imaging. A cine phase contrast CSF flow study provides functional information that may depict the site of obstruction that may guide the appropriate therapy (Fig 2).

Chiari I malformations (cerebellar tonsillar ectopia through the foramen magnum) are increasingly recognized with MR imaging. Patients are often asymptomatic, with headaches the most common symptom. Patients need clinical evaluation, although a CSF flow study may provide useful information regarding the flow dynamics at the foramen magnum. With Chiari I malformation, the herniated cerebellar tonsils fill the foramen magnum with a reduction of CSF flow at the craniocervical junction (Fig 3). This altered CSF flow has been postulated as the mechanism for syringohydromyelia. CSF flow study can also monitor the restoration of normal CSF flow following cranial decompression surgery.

Third ventriculostomy is an endoscopic procedure for the treatment of hydrocephalus that establishes flow of CSF from the anterior third ventricle into the prepontine cistern. In selected cases, the procedure is an alternative to a standard ventriculoperitoneal shunt. The procedure can subsequently fail due to orifice closure with recurrence of symptoms. CSF flow study can determine patency of the ventriculostomy and the need for repeat surgery (Fig 4).

Phase-contrast CSF flow study can also give quantitative information regarding CSF flow that may be beneficial in the diagnosis and treatment of normal pressure hydrocephalus. Elderly patients with dementia are often evaluated with MRI to determine a possible cause of the dementia. These patients often have ventriculomegaly that may be due to cerebral atrophy or communicating hydrocephalus. Although there are MRI signs that are used to distinguish atrophy from hydrocephalus (sulcal size, anterior third recess and temporal horn size, mamillopontine distance, etc.), differentiating these two entities can be difficult. Patients with communicating hydrocephalus have impairment of CSF resorption at the arachnoid villi with subsequent expansion of the ventricular system. Following cardiac systole, the brain is already fully expanded against the inner table of the skull and therefore fully contracts downward resulting in a greater CSF stroke volume in the cerebral aqueduct. Phase-contrast CSF flow study can measure the stroke volume in the cerebral aqueduct. Initial reports indicated a greater response to VP shunting in patients with elevated aqueductal CSF stroke volumes, although a recent report indicated no similar association.

Barry M. Rabin, M.D.
Director of Neuro MR
Parkside MR Center

References:

Enzmann DR, Pelc NJ. Normal flow patterns of intracranial and spinal cerebrospinal fluid defined with phase-contrast cine MR imaging. Radiology 1991;178:467-474.

Oldfield EH, Muraszko K, Shawker TH, Patronas NJ. Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. J Neurosurg 1994;80:3-15.

Toru Fukuhara, Sarel J. Vorster, Paul Ruggieri, and Mark G. Luciano. Third Ventriculostomy Patency: Comparison of Findings at Cine Phase-Contrast MR Imaging and at Direct Exploration AJNR Am J Neuroradiol 1999;20:1560-1566.

Bradley WG, Scalzo D, Queralt J, Nitz WN, Atkinson DJ, Wong P. Normal-pressure hydrocephalus: evaluation with cerebrospinal fluid flow measurements at MR imaging. Radiology 1996;198:523-529.

Dixon GR, Friedman JA, Luetmer PH, Quast LM, McClelland RL, Petersen RC, Maher CO, Ebersold MJ. Use of cerebrospinal fluid flow rates measured by phase-contrast MR to predict outcome of ventriculoperitoneal shunting for idiopathic normal-pressure hydrocephalus. Mayo Clin Proc. 2002 Jun;77(6):507-8.

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