Dear Editor,With regards to our recent paper on the phenomenon ofchronic uncal herniation [1], we came across an 11-year-oldchild with open spina bifida, associated with a temporallobe herniation, albeit with a difference.TheboywedescribewasbornwithanopenspinabifidaofL4level.Hehadahistoryoflumbarmyelomeningocelerepairat day1 of life. He had a ventriculoperitoneal shunt forprogressive hydrocephalus at 2 weeks of age. Subsequently,he had foramen magnum decompression when he was2 months old for persistent symptoms of brainstem compres-sionincludingrecurrentapneas.Presentlythechildhasseverepsychomotor retardation and is spastic quadriparetic.A recent follow-up MRI of the brain showed herniationof the temporal lobe and downwardly displaced occipitallobes associated with a thinned out vermis, an almostnonexistent cerebellum, thinning of the brainstem, and adeficient tentorium cerebelli (Fig. 1). His older imagingfrom his infancy demonstrated the same phenomenon oftemporal lobe herniation in association with the otheranomalies usually associated with Chiari II malformation[2, 3]. The finding of cerebral herniation in Chiari IImalformation to the best of our knowledge has previouslynot been described.In our previous paper on the similar phenomenon, wehad proposed that chronic uncal herniation was a conse-quence of the presence of a cystoperitoneal shunt and thenegative pressure gradient it created across the tentorium,and it was a treatment sequel of posterior fossa cysticcollection shunting [1]. We propose that the cerebral uncalherniation in this described child with Chiari II malforma-tion may be a sequel of the open spinal defect-associatedpressure gradient between the supratentorial compartmentand infratentorial compartment, existing prior to the closureof the CSF leak at the spinal level, analogous to thetonsillar herniation (as explained by the unified hypothesisby McLone and Knepper [4]) occurring in open spinaldefects and hence is a developmental intrauterine anomaly.The cerebral herniation probably represented an extremityof the spectrum. Note the severely hypoplastic cerebellum(“ vanishing” cerebellum [4]) in the figure (Fig. 1). It ispossible a relatively “spacious” posterior fossa instead ofthe usual tight posterior fossa, due to lack of cerebellum incombination with a widened tentorial hiatus and partlydeficient tentorium contributed to the picture in this specificchild and situation (Fig. 1). Also, the perinatal hydroceph-alus may have been contributory to the picture.Chiari II malformation is characterized by mesodermaldysplasia and premature condensation of the basilar skullanlagen, small and dysplastic lower cranial nerve ganglia,deficient tentorium cerebelli, hypoplastic and dysmorphiccerebellum, and thickened basal meninges. These anomaliesall are attributable to defective or deficient mesenchyme,which presumably deprived the skull base, hindbrain, andrhombencephalon of normal inductive effects [5].Our patient had no significant progression of neurolog-ical status; hence, probably the finding of temporal lobe
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Aug 30, 2011
C Alvarez Sedó + 5
Open Access
