MRA aids in refiningtiming of hydrocephalussurgical intervention

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, making it difficult to tell if a shunt system is needed to divert excess cerebrospinal 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 autoregulation, a distortion of the periventricular 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 characterized by abnormal dilation of the ventricles of the brain. Pressure from an oversupply of CSF can cause irreversible brain damage, making timely intervention critical.

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

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.

"If this can help a surgeon move forward more confidently with surgery, or prevent one child from an unnecessary neurological procedure, that would pay for lots of MRAs," she said.

-By Marjorie Preston