Optic nerve sheath diameter as a criterion for endoscopic third ventriculostomy failure in children.

Abstract

Dear Editor: One of the biggest issues paediatric neurosurgeons carry is the lack of solid criteria for defining endoscopic third ventriculostomy (ETV) failure. Current data is not suitable for infants, and most articles describe failure as a Bneed to shunt^. Imaging is sometimes disorienting, given that some degree of ventriculomegaly can persist, and although several radiological markers of success like third ventricular narrowing or flow void have been described, none of them are infallible or close to perfect. Dr. Padayachy and colleagues recently brought back interest in optic nerve sheath diameter (ONSD) measurement as a parameter of success after treating hydrocephalus endoscopically [4]. ONSD sonographic evaluation has been widely used in intensive care units, and it perfectly correlates with variations in intracranial pressure (ICP), even before papilledema or ventricular dilation ensue [1, 3]. Magnetic resonance imaging measurement has also been described successfully in adults with simultaneous ICP monitoring [1]. Several aspects of Dr. Padayachy’s article are worth to discuss: Their patients experienced a 7.5 % decrease in ONSD after a successful ETV. Singhal et al. previously observed an 8 % mean reduction in ONSD measurement within the first week post operatively [5]. While Dr. Padayachi studied only patients after an ETV, Dr. Singhal analysed both ONSD changes after tumor resection and ETV. Interestingly, Dr. Singhal’s patients with hydrocephalus experienced a 6.5 % ONSD reduction after ETV while tumor resection patients experienced a greater reduction of 10.2 %, possibly related to the almost always asymptomatic, self-limited adaptation period of the cerebrospinal fluid (CSF) absorptive systems after an endoscopic third ventriculostomy. This is important, because shunting appears to have a more pronounced decrement in intracranial hypertension, with ONSD reduction of at least 30 %; thus, we cannot expect a similar reduction in ONSD measurement with an ETV as with placement of a ventriculoperitoneal shunt [3]. Remarkably, 60 % of patients experiencing Bfailed procedures^ in Dr. Padayachy’s article also had ONSD decrease, which probably represents what happens to many of us: sometimes we cannot know by clinical and radiological means if an ETV is functional [4]. Dr. Newman defined the upper limits of normal ONSD as 4.0 mm for those children under 1 year of age and 4.5 mm for older children, which was further corroborated by Dr. Malayery and colleagues [2, 3]. Both Padayachi and Singhal’s patients achieved supra-normal values after a clinical and radiological successful endoscopic procedure [4, 5]. Eventually, ONSD will be a useful criterion for determining ETV failure in children but cutoff values should be higher than that expected after placing a shunt. I congratulate Dr. Padayachy and colleagues for bringing this subject into discussion, and motivating further research. * Rolando Jimenez-Guerra rolandojg@gmail.com