Hyperostosis Cranii Ex Vacuo with Layered Imaging Appearance of Skull in a Patient of Dandy-Walker Malformation with Early CSF Shunting

A 26-year-old male presented with seizures characterised by clonic posturing of the bilateral upper limbs, deviation of the angle of the mouth, vertigo and an unstable gait for one month. He had a known history of Dandy-Walker syndrome with hydrocephalus, for which ventriculoperitoneal shunt placement and shunting of the posterior fossa cyst were performed at six months and nine years of age, respectively. The patient had mild cognitive impairment and an ataxic gait; however, no focal neurological deficits were evident. Laboratory parameters, including complete blood count and haemoglobin, serum calcium, phosphate, alkaline phosphatase, and parathyroid hormone levels, were within normal limits. Magnetic Resonance Imaging (MRI) of the brain revealed a posterior fossa cyst communicating with the fourth ventricle, with a hypoplastic vermis and right cerebellar hemisphere, consistent with Dandy–Walker malformation [Table/Fig-1]. Diffuse calvarial thickening with widening of the diploic space was noted, with layered hyperostosis along the inner table of the calvarium [Table/Fig-1]. No associated brain sagging, engorgement of dural venous sinuses, or pachymeningeal enhancement was present. Computed Tomography (CT) images demonstrated diffuse calvarial thickening with diploic space widening, fused cranial sutures and distinct layered hyperostosis along the inner table of the skull [Table/Fig-2]. The density of the skull bones, including the skull base, was normal. Lumbar puncture revealed normal CSF pressure, effectively excluding an active low Cerebrospinal Fluid (CSF) pressure state. Hyperostosis cranii ex vacuo was diagnosed based on distinct imaging features in the context of longstanding early CSF shunting.