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Marcos Veiga, Mariana Cardoso Diogo, Carla Conceição

1- Department of Neuroradiology, Hospital Dona Estefania, CHLC

Oporto Neuroradiology 50th Anniversary International Symposium, 30 setembro – 1 outubro 2016, Porto, Portugal

Brief history: A 17 years old woman, with a history of ventriculomegaly with a permanent ventriculo-peritoneal shunt, presents for a control CT.
Questions: 1-What are the findings? 2-What is the Differential diagnosis? 3-Is this finding frequent?
Answers to the questions: 1-Globus contoured and dysmorphic ventricles, with a shunt positioned on the left lateral ventricle. Widened cortical sulcus, which are particularly noticed on the lateral sulcus and fronto-parietal region. On the bone window, a general calvaria thickening is visualized, as well as marked calcification of the falx cerebri.2- Chronic shunting; advanced cerebral atrophy; Sturge-Weber disease; healed rickets; severe longstanding anaemia; thalassemia; raniometaphyseal dysplasia; Paget's disease; fibrous dysplasia; hyperostosis frontalis interna. 3- This is a rare finding. Although, probably under-reported, if “hyperostosis cranii ex vacuo” is searched on PubMed, only 4 results are obtainable (1966, 1994, 2001, 2003). On a wide internet search engine, more reports are found.
Discussion: By definition, hyperostosis cranii ex vacuo only involves the calvaria bones, remaining facial bones unaffected. The sparing of facial and body bones differentiates it from metabolic causes of calvaria thickening. It is believed that cranial development is modulated by the pressure applied to it. When there is hydrocephalus, the augmented pressure tends to lead the calvaria into thinning. However, in the case of diminished pressure, the process goes the opposite way and it can result in skull thickening. This can happen as a result of chronic shunting, advanced cerebral atrophy and is even seen unilaterally in hemiatrophy, as in patients with Sturge-Weber disease (encephalotrigeminal angiomatosis). The pattern of calvarial thickening, globus contoured and dysmorphic ventricles, widening of cortical sulcus in a 17 years old woman and visualization of a ventriculoperitoneal shunt positioned on the left ventricle, suggests the diagnosis of hyperostosis cranii ex vacuo. In a retrospective study, that analyzed 230 patient operated for Hydrocephalus, a 3% incidence rate of “hyperostosis cranii ex vacuo” was concluded. This incidence rate proves that, although being a rare finding, has been clearly under-reported.