Radiological evaluation of Hyperostosis frontalis interna: is it of clinical importance?

Hyperostosis frontalis interna (HFI) presents irregular thickening of the frontal bone. Even though HFI is frequently seen during routine radiological imaging, it usually remains unrecorded owing to a common belief that it just represents an incidental finding or anatomical variant. Recent studies implied that HFI may be clinically relevant. Etiology of HFI is still debated, while presumptions are mainly based on altered sex steroids impact on skull bone growth. Some authors implied that frontal bone might be particularly affected by this condition due to specificity of its underlying dura. In this paper we present a 27-years old female patient with a treatment resistant headache. Head CT showed massive, irregular bony mass, with lobulated contours arising from the right frontal bone, but did not cross the fronto-parietal suture, spearing the superior sagittal sinus and skull midline. After surgery, histopathological analysis of the frontal bone sample in our patient showed thickening pattern similar to those described in micro-CT studies of HFI. Furthermore, in an attempt to test speculation of the possible role of estrogen in pathogenesis of HFI, we investigated the expression of α-estrogen receptors on dura of the frontal region. These analyses confirmed nuclear expression of estrogen on frontal region dural tissue, supporting previous speculation of the development mechanisms of HFI and contributing to a better understanding of this common condition of the frontal bone. Additionally, the presence of HFI may result in severe symptomatology, which could be misinterpreted and related to other disorders if HFI is not radiologicaly recognized and reported.