47 - Ectopic Ossification on the Endosteal Dura Deep to the Trigeminal Ganglion: Case Analysis and Clinical Implications

Poster Board Number: 47
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Abstract Body : Introduction: Hyperostosis cranialis interna (HCI) is a hereditary sclerosing bone dysplasia characterized by excessive endosteal bone growth in the frontal, parietal, temporal, and occipital regions of the skull. The marked osteosclerosis from HCI in the basicranium has been known to cause stenosis of neuroforamina, causing impingement of the cranial nerves that traverse them. While imaging studies and descriptions of the HCI disease and its progression are well documented, to our knowledge, a coincidental ectopic ossification (EO) in the cranial dura has not been described. The objective of this study was to investigate HCI and a coincidental EO discovered on the endosteal dura deep to the trigeminal ganglion in a female cadaveric donor of advanced age (> 90 years) and discuss its clinical implications.

Materials and Methods: An EO adhered to the endosteal dura was discovered deep to the right trigeminal ganglion on a human cadaveric donor from an ethically approved anatomical donor program. The EO was photographed in situ on the reflected trigeminal ganglion, removed, photographed again in faced view with scale (Dino-Lite Edge Digital Microscope, F4515ZT), weighed (Ohaus Micro Balance, Model AR3130), and measured (ImageJ, 1.52q). The anterior, middle, and posterior cranial fossae, as well as a magnified cross section of the frontal calvaria, were photographed (iPad Pro, Apple Inc.; Dino-Lite Edge Digital Microscope, F4515ZT) to grossly document the magnitude of the HCI disease progression.

Results: The dimensions of the EO were approximately 4.34 mm x 4.12 mm x 2.60 mm, and it weighed 0.046 g. The depth of the EO was consistent, and face view of the EO was relatively circular except for one pointed 1.10 mm process. Indentation of the trigeminal ganglion where the EO was positioned was grossly visible. Diffuse HCI bony growths were observed throughout the anterior and middle cranial fossae, including near the area of the trigeminal ganglion; however, the posterior cranial fossa appeared relatively unaffected. The cross-sectioned frontal calvaria revealed gross deformities along the inner table. Larger spacing within the cancellous bone of the diploe along the side bordering the inner table of cortical bone was also visible and presented with a noticeable purple-gray hue compared to the outer diploe. No evidence of neuroforamina stenosis was found.

Conclusion: HCI is known to cause endosteal hyperostosis, and since the EO formed from the endosteal layer of dura, the EO and HCI may have shared a common pathophysiology. However, the EO could also have been an incidental finding unrelated to the HCI since ossification of intracranial dura can be caused by trauma and is seen in higher incidence with advanced age. 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, and teeth. Albeit rare, this report justifies consideration of a concurrent ossification of the endosteal dura deep to the trigeminal ganglion as differential diagnosis for trigeminal neuralgia 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.