Post CSF shunting Chiari I malformation—sequel or complication? Hypertension or hypotension?

Abstract

Dear Editor: We read with great interest the article by Caldarelli et al. [1]. It is an excellent thought-provoking and truly intriguing “late complication” of CSF shunt surgery. However, we would like to take issue on few pertinent points. The authors have tried to explain this “developmental” anomaly as the result of modifications of skull growth induced by shunt, and consider this finding as a “variant” of slit ventricle syndrome. Here, we illustrate a preterm infant shunted at fourth month of infancy for posthaemorrhagic hydrocephalus, with MRI at 11 months of age showing an acquired postshunt Chiari I malformation (Fig. 1). Is “posterior fossa disproportion” enough to explain tonsillar herniation of such an early onset? The authors have not explored the possibility of intracranial hypotension secondary to shunting, primarily causing Chiari I malformation. Chiari I malformation and syringomyelia [3–5] have been described in association with cerebral hypotension, probably secondary to the sagging induced by the lack of buoyant action of intracranial CSF (one patient in the authors’ series had syringomyelia). Relief of hydrocephalus alleviating tonsillar herniation [2, 6] and contrary of shunt failure causing disappearance of tonsillar herniation [personal communication, Swift. D, March 27, 2009] have been well documented. In addition to tonsillar herniation, the authors describe thickening of the skull vault and base, increase in paranasal sinuses volume, and reduced ventricular volume, as effects of “satisfactorily working CSF shunt”. It is therefore not surprising that in this series, there is a lack of correlation of the radiological findings to the symptomatology (some patients had severe Chiari I but were asymptomatic) and the patient’s response to surgery. Out of six patients who underwent surgical treatment, only one patient underwent suboccipital craniectomy and still developed syringomyelia. Additionally, five patients underwent cranial vault enlargement, implying the posterior fossa disproportion has never been addressed or implicated directly in the authors’ series. Fig. 1 Sagittal MR of a shunted premature infant with posthaemorrhagic hydrocephalus with evidence of acquired Chiari I malformation