Hyperostosis of the skull is a rare bone dysplasia described in disorders such as hyperostosis cranialis interna (HCI) and hyperostosis frontalis interna (HFI). Other syndromes presenting with hyperostosis include Morgagni-Stewart-Morel (MSM) and Troell-Junet. HCI is an abnormal hyperostosis of most endosteal skull and calvarium surface regions. A more specific hyperostosis, HFI, is an unusual bone growth based on its volume and porosity; it is primarily located bilaterally on the frontal portions of the calvarium. However, the hyperossification does not cross the superior sagittal sinus. Upon cadaveric dissection, we found hyperossification beyond the frontal area, extending to the parietal and occipital bones with the significant characteristic of no midline interference. Hyperossification results in gross indentations on the corresponding frontal, parietal, and occipital hemispheric brain tissues. This report discusses possible differentials for this rare cadaveric finding of frontal, parietal, and occipital bone hyperostosis. This case report includes some major characteristic features indicative of HCI and HFI with some interesting variations and features suggestive of MSM and Troell-Junet syndromes. Due to the lack of patient history and medical records, no further conclusions about clinical differentials, symptoms, or causative syndromes could be drawn; further research needs to be conducted on HCI, HFI, and related syndromes to understand their presentations better.

OBJECTIVE: Hyperostosis cranialis interna (HCI) is an autosomal dominant sclerosing bone dysplasia affecting the skull base and the calvaria, characterized by cranial nerve deficits due to stenosis of neuroforamina. The aim of this study is to describe the value of several neurophysiological, audiometric and vestibular tests related to the clinical course of the disorder.
METHODS: Ten affected subjects and 13 unaffected family members were recruited and tested with visual evoked potentials, masseter reflex, blink reflex, pure tone and speech audiometry, stapedial reflexes, otoacoustic emissions, brainstem evoked response audiometry and electronystagmography.
RESULTS: Due to the symmetrical bilateral nature of this disease, the sensitivity of visual evoked potentials (VEPs), masseter reflex and blink reflex is decreased (25-37.5%), therefore reducing the value of single registration. Increased hearing thresholds and increased BERA latency times were found in 60-70%. The inter-peak latency I-V parameter in BERA has the ability to determine nerve encroachment reliably. 50% of the patients had vestibular abnormalities. No patient had disease-related absence of otoacoustic emissions, because the cochlea is not affected.
CONCLUSIONS: In patients with HCI and similar craniofacial sclerosing bone dysplasias we advise monitoring of vestibulocochlear nerve function with tone and speech audiometry, BERA and vestibular tests. VEPs are important to monitor optic nerve function in combination with radiological and ophthalmologic examination. We do not advise the routine use of blink and masseter reflex.