Translational Research in Anatomy (Mar 2023)
Hyperostosis cranialis interna and an ectopic ossification on the endosteal dura deep to the trigeminal ganglion: Case analysis and clinical implications
Abstract
Introduction: Hyperostosis cranialis interna (HCI) is a hereditary sclerosing bone dysplasia characterized by excessive endosteal bone growth in the cranium. Its marked basicranial hyperostosis has been known to cause stenosis of neuroforamina and impinge the cranial nerves that traverse them. While descriptions of HCI and its progression are well documented, a coincidental ectopic ossification (EO) in the cranial dura has not been described in the literature. The objective of this study was to investigate and discuss the clinical implications of an EO discovered on the endosteal dura deep to the trigeminal ganglion (TG) in a female cadaver donor of advanced age (>90 years) who appeared to have diffuse HCI. Methods: An EO adhered to the endosteal dura was discovered deep to the right TG on a human cadaver donor during routine dissection. The EO was photographed in situ, removed, photographed again with a scale, weighed, and measured. The internal surface of the calvaria, a cross-section of the frontal calvaria, and the anterior, middle, and posterior cranial fossae were photographed to document the magnitude of HCI disease progression. Using an 8mm trephine, a mid-frontal core sample was collected where HCI was progressive. Control core samples lacking HCI were collected from mid-parietal (same donor) and mid-frontal (different donor) calvaria. The EO and all core samples were subjected to high-resolution micro-CT and three-dimensionally reconstructed. Subsequently, core samples were morphometrically analyzed. Results: The dimensions of the EO were approximately 4.34 mm × 4.12 mm x 2.60 mm, and it weighed 0.046 g. The face of the EO was relatively circular except for one noteworthy 1.10 mm process. The EO grossly indented the TG, and the motor root of the mandibular nerve formed a groove in the EO. Diffuse HCI bony growths were observed throughout the anterior and middle cranial fossae, including near the area of the TG. The cross-sectioned frontal calvaria revealed gross deformities along the inner table and diploe. Micro-CT analysis confirmed decreased bone volume and trabecular number and increased trabecular separation within the HCI core sample, while the EO revealed distinctive surface topography with many small foramina and notable medullary porosity with little trabecular framework. Conclusions: Since the EO formed from the endosteal layer of dura, the EO and HCI may have logically shared a common pathophysiology. However, a review of HCI literature and the micro-CT analyses in this study suggest the EO was more likely an unrelated, coincidental finding. Regardless, the current study presents a unique case of concurrent EO and HCI where the trigeminal nerve could be impinged by an EO without impact from HCI progression, resulting in possible pain and/or paresthesia of the face, scalp, oral mucosa, teeth, and dura mater. Albeit rare, this report justifies consideration of a concurrent ossification of the endosteal dura deep to the TG in the differential diagnosis for trigeminal neuralgia and trigeminal neuropathy in patients with HCI when the neuroforamina of the trigeminal nerve branches are not yet stenosed by HCI progression and thus may help inform treatment options.
