MRA finds value in hydrocephalus interventions

Imaging research from the University Medical Center Utrecht, the Netherlands, suggests that measuring with MRI the intracranial pressure of infants with progressive hydrocephalus helps physicians to determine the right time for surgical intervention.

According to a study published in the Journal of Neurosurgery: Pediatrics (2008;2[3]:163-170), the clinical signs of raised intracranial pressure associated with hydrocephalus can be unreliable and even misleading, mak-ing it difficult to tell if a shunt system is needed to divert excess cerebro-spinal fluid. Adding to the uncertainty, after sutures close in infants, actual intracranial pressure does not always correlate with ventricular size or clinical signs or symptoms.

Dr. Paul H. Leliefeld and colleagues prospectively assessed 15 children, from newborn to seven months old, with MR angiography before and after CSF diversion procedures. After CSF diversion (a shunt in 12 patients, and a third ventriculostomy in three), cerebral blood flow and intracranial pressure improved to values in the normal range. The researchers found the quantitative flow measurement, obtained with phase-contrast MRA though the internal carotid arteries and the basilar artery, accurately reflected cerebral blood flow.

The study may have been the first ever to associate a significant decrease in cerebral blood flow with progressive hydrocephalus, Leliefeld said. The decline may be explained by disturbed cerebral auto-regulation, a distortion of the periven-tricular vessels caused by ventricular dilation, or possibly an increase in blood flow resistance from the compression of arterioles and veins.

Hydrocephalus is a common pediatric disorder affecting one in 1000 live births characterized by abnormal dilation of the ventricles of the brain. Clinical signs of the disorder in infants include a larger-than-normal head circumference, bulging of the fontanel, engorgement of scalp veins, the downward gaze known as "sunset eyes," and decreased consciousness. Pressure from an oversupply of CSF can cause irreversible brain damage, making timely intervention critical.

Leliefeld prefers MRA to ultra-sound because it measures blood supply to the entire brain while ultra-sound measurement using transcranial Doppler is limited to the middle cerebral artery. MRA also detects early ischemia or restricted flow to the brain.

"When MRA is used for the diagnosis of hydrocephalus in infants, it's not harmful to make it last 10 minutes longer to perform the quantitative flow measurements," he said.

Not everyone is convinced. MRA and its accompanying high costs can be avoided with a better clinical analysis of suspected hydrocephalus, said Dr. Erin Simon Schwartz, a pediatric neuroradiologist at Children’s Hospital of Philadelphia. But she still considers MR to be cost-effective.

-By Marjorie Preston