Diploic Bone Channel Drilling Facilitates Dissection of the Midline Dura and Protects the Superior Sagittal Sinus in Hyperostosis Frontalis Interna

Patients with space-occupying lesions adjacent to the superior sagittal sinus (SSS) present several technical considerations. For craniotomies crossing the SSS, a two-part method allows for dissection of the epidural space and dura under direct vision after removing a more lateral parasagittal bone flap. However, when the inner table surface of the medial component of the two-part bone flap is irregular, this can be difficult. We describe a method for channel drilling of the diploic bone, which allows for the piecemeal removal of the inner table using an upbiting rongeur. This article presents the case of meningioma with documented growth and provides a technical note of this technique to facilitate safe dissection of the midline dura. A patient presented with headaches and an anterior one-third parasagittal meningioma with documented growth. She selected surgical removal for treatment. A right frontal two-part parasagittal craniotomy was recommended. The preoperative imaging showed that the frontal bone was thick, with irregularity of the inner table. Intraoperatively, a channel was drilled in the diploic space of the bone, leaving the outer table intact. This provided a thin lip of the inner table that could be dissected over a short distance and then removed with a 2-mm upbiting rongeur. This allowed for further dissection of the dura crossing the midline under direct vision and safe secondary bone piece removal. The dura was opened to the edge of the SSS, allowing full exposure of the parasagittal region and interhemispheric fissure, thus limiting retraction of the medial right frontal lobe. The bone flap was removed in two pieces without a dural tear over the midline in spite of inner table irregularities. A Simpson grade 1 removal was accomplished, including excision of the affected falx, and the postoperative course was uncomplicated. In conclusion, diploic bone channel drilling is a technique that can be used to create a thin lip of the inner table, which can be removed piecemeal for safe dissection of the midline dura crossing the midline.