The Perforator Bone Chip as a Convenient and Effective Autologous Bone Graft for Middle Fossa Encephalocele Repair: A Technical Report

Spontaneous middle fossa encephaloceles can precipitate classic symptoms of spontaneous cerebrospinal fluid rhinorrhea or otorrhea, as well as recurrent bouts of meningitis. Additionally, patients may experience years of frustratingly persistent middle ear effusions and infections, conductive hearing loss, and drug-resistant epilepsy prior to recognition of the underlying cause. We describe one such patient who underwent surgical repair, which can be performed using a variety of techniques and materials, some costly and/or time-consuming. During the procedure we utilized an as-yet undescribed technique of bony repair utilizing the bone chip created from the perforator drill as an autologous graft. The perforator drill bit is widely utilized and creates up to a 14-mm bone chip which we felt would be convenient, effective, and economical for use as a bone graft, rather than allograft, split thickness calvarial graft, or other synthetic and biological adjuncts.

The patient discussed is a 55-year-old female with a right sided middle fossa defect discovered in the setting of chronic Beta-2 transferrin positive otorrhea and tegmen erosion demonstrated on computed tomography with an accompanying encephalocele on magnetic resonance imaging. Neurosurgery and Otolaryngology performed a transmastoid/right middle fossa craniotomy for resection of the encephalocele and repair of the skull base defects. A perforator drill was utilized to create burr holes around the circumference of the middle fossa craniotomy in standard fashion. The nature of the automatic clutch mechanism of this widely available drill bit results in an eggshell wafer of bone, the “bone chip,” to remain once the drill disengages. Intraoperatively, the decision was made to save the bone chips created by the drill, and use them as autologous bone grafts to repair the skull base defects. At the time of skull base repair, the bone chips were harvested and placed intracranially such that they fully covered the bony defects. These were then reinforced with fascia harvested from the temporalis muscle. The opposing sides of the defects were reinforced from the transmastoid aspect using bone pate and additional temporalis fascia.

The patient had an uncomplicated postoperative course and has since enjoyed sustained resolution of symptoms, further demonstrating the efficacy of perforator bone chip grafting. We posit that the use of perforator bone chips as autologous graft is reasonable as a practical, expedient, far less expensive alternative to commercial products for bony defect repair in encephalocele where the defect is of smaller diameter than the perforator graft.

Fig. 1 Middle fossa craniotomy revealing defect (arrow) in the skull base after encephalocele is resected.

Fig. 2 The perforator bone chip (arrow) is brought into the field in preparation for placement across the skull base defect.

Fig. 3 The perforator bone chip (arrow) provides convenient, adequate bony coverage over the skull base defect.

Fig. 4 Right-sided middle fossa skull base dehiscence (arrow) visualized on coronal CT of the right temporal bone.