A rare case of hyperostosis frontalis interna in an 86-year-old Japanese female cadaver
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CASE REPORT
A rare case of hyperostosis frontalis interna in an 86‑year‑old Japanese female cadaver Kazuma Morita1 · Akiko Nagai1 · Munetaka Naitoh2 · Ayako Tagami1 · Yayoi Ikeda1 Received: 15 April 2020 / Accepted: 19 September 2020 © Japanese Association of Anatomists 2020
Abstract Hyperostosis frontalis interna (HFI) is a condition characterized by abnormal bone outgrowth on the inner surface of the frontal bone. Most HFI cases occur in post-menopausal elderly women. The pathology of HFI development is uncertain. The estimated incidence of HFI ranges from 5 to 12% in Western countries, but few cases have been reported in the Japanese population. Here, we report a case of HFI in an 86-year-old Japanese female cadaver. Macroscopically, the internal surface of the frontal bone exhibited bilateral nodular protrusion with sparing of the midline, while the external surface was normal. According to the morphological classification of HFI proposed by Hershkovitz et al. this case belongs to type D, the most severe type. Using computed tomography (CT), we defined five layers, designated as I–V from the inner to the outer layer, in the nodular region of HFI; however, the normal frontal bone is composed of three layers. Histological results demonstrated that layers I, III, and V consisted of the cortical bone, and layers II and IV consisted of the trabecular bone. We also observed increases in the numbers of lamellar bone and blood vessels on the dural side of layer I, indicating increased vascularization and active osteogenesis. These results indicate that layer II represents a new diploe within the inner table, which split into layers I and III, suggesting that diploization within the inner table by activated remodeling may be involved in the development of hyperostosis in this case. Keywords Hyperostosis frontalis interna · Calvaria · Bone outgrowth · Inner table
Introduction Hyperostosis frontalis interna (HFI) is a condition presenting with bilateral nodular protrusion, specifically on the internal surface of the frontal bone, sparing the midline. It is distinguished from conditions with diffuse calvarial bone thickening (e.g., hyperostosis calvaria interna and hyperostosis cranialis diffusa) and diseases affecting the calvarium (e.g., Paget’s disease, acromegaly, and osteoma). HFI showed variable morphology and a degree of bone outgrowth in previous cases and has been classified into four types (A–D) according to the extent and severity of bone thickening (Hershkovitz et al. 1999). * Yayoi Ikeda [email protected] 1
Departments of Anatomy, Aichi-Gakuin University School of Dentistry, 1‑100 Kusumoto‑cho, Chikusa‑ku, Nagoya 464‑8650, Japan
Oral and Maxillofacial Radiology, Aichi-Gakuin University School of Dentistry, Nagoya 464‑8650, Japan
2
HFI was initially considered an aspect of other syndromes, including Morgagni-Stewart-Morel syndrome, which is associated with virilism and obesity (Moore 1955), but other cases occurred independently of these diseases. Most HFI cases are found incidentally during im
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