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

Abstract

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.

Keywords: bone flap; craniectomy; craniotomy; diploic bone; dural-based tumor; hyperostosis; hyperostosis frontalis interna; inner table; meningioma; superior sagittal sinus.

Figure 1. Post-contrast (gadolinium-based) axial MR imaging of the brain showing a right frontal parasagittal meningioma (green arrowheads) along with hyperostosis of the right frontal bone (yellow arrowheads) shown in two different MR sections (A and B).

MR: magnetic resonance

Figure 2. CT scan of the head demonstrated hyperostosis of the right frontal bone (red arrowheads) in the bone window, as shown here in two different sections (A and B).

CT: computed tomography

Figure 3. Parasagittal bone flap removed as a first step.

SSS: superior sagittal sinus Original figure by Ken Probst, University of California, San Francisco

Figure 4. Intraoperative image demonstrating the thickening and irregularity of the inner table of the frontal bone, indicating “hyperostosis frontalis interna.”

Figure 5. Irregularity of the inner table of the frontal bone adjacent to the superior sagittal sinus

SSS: superior sagittal sinus Original figure by Ken Probst, University of California, San Francisco

Figure 6. Intraoperative image showing drilling of diploic space to facilitate dissection

Figure 7. Drilling of the diploic channel to create a thin rim that can be carefully removed with an upbiting Kerrison rongeur.

SSS: superior sagittal sinus Original figure by Ken Probst, University of California, San Francisco

Figure 8. Drilling of the diploic channel to create a thin rim of the inner table that can be safely removed with an upbiting Kerrison rongeur.

SSS: superior sagittal sinus Original figure by Ken Probst, University of California, San Francisco

Figure 9. Safe dissection across the midline using a periosteal dissector. A Penfield 1 may also be utilized.

SSS: superior sagittal sinus Original figure by Ken Probst, University of California, San Francisco

Figure 10. Safe removal of the secondary bone piece across the midline providing full exposure to the midline.

Original figure by Ken Probst, University of California, San Francisco

Figure 11. Final result of the two-part parasagittal craniotomy technique with diploic bone drilling to avoid injury to the superior sagittal sinus.

Original figure by Ken Probst, University of California, San Francisco