Modification to the “Key-Hole” Burr Hole, Technique and Nuances

Introduction: Historically, the word “keyhole” was coined during the era of the Gigli saw because the guide for the saw had to be introduced both superiorly and inferiorly from this hole for a fronto-temporal craniotomy. Over time, the influence of pioneers such as Perneczky, McCarty and Yasargil, have led to refined microsurgical-instruments, improvement in microsurgical techniques and modifications to this “keyhole” burr hole. These advancements have placed a greater emphasis on minimally invasive cranial approaches with variable incision lengths, size of the craniotomy and several other modifications that focus on less trauma, better cosmesis, and shorter hospital stay. The aim of this study is to describe our modification to the “keyhole” burr hole and directly compare this modification to traditional techniques, while performing a pterional craniotomy.

Methods: Using 8, formalin fixed, latex injected cadaveric heads, 3D CT reconstruction was performed on all specimens prior to dissection. Bilateral pterional craniotomies were performed on all specimens (Left: standard pterional with fronto-temporal “keyhole” burr hole, Right: modified “keyhole” burr hole.”) Several measurements were recorded during dissection. Bone flap(s) were reconstructed with standard cranial plating system (Synthes MatrixNeuro). All specimens underwent post-dissection CT scan with 3D reconstruction. Volumetric analysis was performed on post-dissection specimens using 3D Slicer software.

Results: The measurements were recorded during each dissection; all specimens were dissected by a single person. The mean modified “key hole” burr hole size was 2.5 × 2.5 cm, the mean craniotomy size was 6 × 5 cm. The size of the burr hole plate to cover the modified key hole was 3.5 × 2.5 cm. The number of cranial plates needed to secure modified flap were 3. The number of burr hole(s) for the traditional fronto-temporal craniotomy was 3, mean craniotomy size was 7.5 × 6.5 cm, the mean sphenoid bone remaining (after bone flap): Length: 2.5 cm, Depth: 3 cm. Number of plates needed to secure flap: 4. The 3D volumetric analysis demonstrated a mean voxel number of 15,440 in the modified burr hole and 19,179 with the traditional. Mean volume of bone removed was 3.42 cm³ with the modified burr hole and 4.32 cm³ with the traditional.

Discussion: The modified “key-hole” technique is an excellent alternative to the classic technique and has several advantages. The utilization of the modified burr-hole obviates the need for multiple burr-holes, requires less overall boney removal and provides an excellent cosmetic reconstruction. We believe this technique is an excellent augmentation to any minimally invasive cranial approach when attempting to access the anterior-lateral cranial fossa ([Figs. 1] and [2]).

Fig. 1 Modified “key hole” burr hole Steps: 1: After identification of the pterion, frontal and temporal troughs are made. 2: sphenoid bone is removed; meningo-orbital band is identified. 3: Using a B1/foot-plate a craniotomy flap is fashioned. 4: dura is opened in a C-shaped fashion.

Fig. 2 Volumetric analysis using Slicer 3D software.

No conflict of interest has been declared by the author(s).

Publication History

Article published online:
15 February 2022