Special MRI Detects Abnormal Brain Membranes

A unique magnetic resonance imaging (MRI) sequence can now help distinguish abnormal membranes in the posterior fossa, a small space in the back of the skull near the brain stem and cerebellum, that are otherwise difficult to detect, according to a Cedars-Sinai case series recently published in the journal Pediatric Neurosurgery.

Using a technology called cine true fast imaging with steady-state precession (TrueFISP), a noninvasive imaging technique, the study investigators were able to directly observe the motion of cerebrospinal fluid through the brain as well as the presence of these pathological membranes. Cerebrospinal fluid, which fills the brain ventricles and surrounds the brain and spinal cord, pulsates in time with the heartbeat. Abnormal arachnoid veils and membranes that can be present in the space normally occupied by this fluid also pulsate with the heartbeat.

TrueFISP can confirm the success of corrective surgery, too, and could help establish predictive indicators for disorders of cerebrospinal fluid flow, according to the investigators.

The imaging sequence was originally developed to visualize a beating heart and its valves. "Our radiologists optimized the sequence parameters to capture and display brain and spinal fluid signals to help visualize very thin mobile membranes that can obstruct normal spinal fluid flow," said Moise Danielpour, MD, director of the Pediatric Neurosurgery Program at Cedars-Sinai and corresponding author of the study. "Alterations in normal spinal fluid flow in the brain can lead to hydrocephalus—an abnormal accumulation of in the brain—or even accumulation of spinal fluid that damages neural tissue," he added.

The study team, including colleagues in the Maxine Dunitz Neurosurgical Institute and the S. Mark Taper Foundation Imaging Center, based its findings on an exploratory case series of three children suspected of having an arachnoid veil or membrane obstructing the outflow of cerebral spinal fluid from the posterior fossa.

"Because these membranes are very thin and moving in the cerebrospinal fluid, they disappear on a standard MRI image, which is the average of signals acquired over several cardiac cycles," said Danielpour, associate professor of Neurosurgery and the Vera and Paul Guerin Family Chair in Pediatric Neurosurgery at Cedars-Sinai. "But when we acquire an MRI image that is synchronized with the cardiac cycle and string together multiple pictures over time, you get a cine MRI, which is like a movie. We optimized the signal so that we can see the movement of spinal fluid, brain pulsations, pulsation of the blood in a blood vessel and small mobile membranes."

Danielpour and colleagues reviewed the records of the three children with symptoms of cerebrospinal fluid obstruction who underwent both standard MRI and cine TrueFISP imaging. While routine imaging did not clearly show the sites of obstructive lesions, the TrueFISP imaging identified abnormal membranes in all three cases. After the lesions had been surgically removed, TrueFISP was used again to help verify that proper cerebrospinal fluid flow had been restored. Symptoms in all three children subsequently lessened.

"This technology can play a vital role in pre- and post-surgical decision-making, as it provides a more useful image of abnormal membranes in the posterior fossa and helps us better understand cerebrospinal fluid flow dynamics," said Danielpour. "Having these images available before surgery helps us improve surgical management and avoid surgical procedures that might hold unnecessary risk. For instance, if a child has obstructive hydrocephalus, by removing the obstruction, we can treat the hydrocephalus without placing a shunt."

Danielpour and colleagues believe that there is potential to use this technology in the future to identify patients at risk of developing other disorders related to increased cerebrospinal fluid flow pulsatility. It may also open doors to visualizing real-time blood flow in the cerebral vasculature in a noninvasive manner.

"Exploring new applications for noninvasive imaging is key to our ability to determine the exact nature of a patient's disorder and provide more effective treatment," said Keith Black, MD, professor and chair of the Department of Neurosurgery and the Ruth and Lawrence Harvey Chair in Neuroscience at Cedars-Sinai.

Funding: This research was supported in part by the Vera and Paul Guerin Family Chair in Pediatric Neurosurgery and The Smidt Foundation.