Atypical cerebellar slump syndrome and external hydrocephalus following craniocervical decompression for Chiari I malformation: case report

Abstract

Symptomatic cerebellar slump (CS) and external hydrocephalus (EH) are amongst the rarer complications of foramen magnum decompression (FMD) for Chiari I malformation (CM). CS typically presents with delayed onset headache related to dural traction or with neurological deficit offsetting the benefit of FMD. EH, consisting of ventriculomegaly along with subdural fluid collection(s) (SFCs), has been related to cerebrospinal fluid egress from a tiny breach in an otherwise intact arachnoid. We describe the case of a 21-year-old man with CM and syringomyelia who presented with impaired gag, spastic quadriparesis, and raised intracranial pressure 1 week following an uneventful FMD during which the arachnoid had been widely fenestrated. Magnetic resonance imaging (MRI) showed an infratentorial SFC, dilated aqueduct and triventriculomegaly, features of CS, and a residual but resolving syrinx. His symptoms resolved following a high pressure ventriculo-peritoneal shunt. At a 6-month follow-up visit, he was asymptomatic and demonstrated partial resolution of the syrinx, with no recurrence of the SFC. The unusual features in the clinical course of this patient were an atypical CS syndrome presenting with concomitantly resolving syringomyelia, and the development of EH after a wide arachnoidal fenestration. This is the first case in indexed literature describing such a combination of unusual postoperative complications of a FMD. A hypothesis is presented to explain the clinico-radiological findings of the case.

Fig. 1.

Preoperative cervical spine magnetic resonance imaging (MRI), sagittal sections: A: T₁ weighted image (WI) and B: T₂ WI, showing tonsillar herniation up to the C1 posterior arch level, a syrinx in the upper cervical cord and edema in the cord extending down up to C6 level.

Fig. 2.

A: Postoperative cervical spine MRI done one day after the FMD-T₂WI, sagittal section, showing a persisting syrinx and significant reduction in the cord edema. B: MRI cervical spine-T₂WI, sagittal section, done a week after the FMD, showing complete resolution of the cord edema and reduction in the size of the syrinx. There is cerebellar slump as evidenced by decreased cranio-caudal sagittal dimension of the cerebellum as compared to that in Figs. 1B and 2A and impaction of the caudal cerebellum at the cervicomedullary junction. The aqueduct is dilated. C: MRI brain-T₂ WI, coronal section, demonstrating an infratentorial subdural hygroma on the left side. D: Plain CT brain, axial section, showing triventriculomegaly with periventricular lucency and the left sided infratentorial subdural hygroma. WI: weighted image, MRI: magnetic resonance imaging, FMD: foramen magnum decompression, CT: computed tomography.

Fig. 3.

Follow-up magnetic resonance imaging cervical spine, T₂ WI, sagittal section, showing further resolution of the syrinx as compared to that in Figs. 1 and 2. There is resolution of the cerebellar slump and of the infratentorial subdural hygroma. WI: weighted image.