Augmented Reality for Retrosigmoid Craniotomy Planning

Abstract

While medical imaging data have traditionally been viewed on two-dimensional (2D) displays, augmented reality (AR) allows physicians to project the medical imaging data on patient's bodies to locate important anatomy. We present a surgical AR application to plan the retrosigmoid craniotomy, a standard approach to access the posterior fossa and the internal auditory canal. As a simple and accurate alternative to surface landmarks and conventional surgical navigation systems, our AR application augments the surgeon's vision to guide the optimal location of cortical bone removal. In this work, two surgeons performed a retrosigmoid approach 14 times on eight cadaver heads. In each case, the surgeon manually aligned a computed tomography (CT)-derived virtual rendering of the sigmoid sinus on the real cadaveric heads using a see-through AR display, allowing the surgeon to plan and perform the craniotomy accordingly. Postprocedure CT scans were acquired to assess the accuracy of the retrosigmoid craniotomies with respect to their intended location relative to the dural sinuses. The two surgeons had a mean margin of d _avg = 0.6 ± 4.7 mm and d _avg = 3.7 ± 2.3 mm between the osteotomy border and the dural sinuses over all their cases, respectively, and only positive margins for 12 of the 14 cases. The intended surgical approach to the internal auditory canal was successfully achieved in all cases using the proposed method, and the relatively small and consistent margins suggest that our system has the potential to be a valuable tool to facilitate planning a variety of similar skull-base procedures.

Keywords: acoustic neuroma; augmented reality; craniotomy; magicleap; retrosigmoid approach; schwannoma.

Fig. 1

A schematic of the craniotomy window placement behind the sigmoid sinus (blue structure) during the retrosigmoid approach. Picture taken from Jackler. The copyright holders (Jackler and Gralapp) grant permission for the publisher to use the illustrations for this paper, in both its printed and digital version, but reserve copyright.

Fig. 2

(Left) The segmentation of the skin and pinna with the sigmoid and transverse sinuses in blue. (Right) The segmentation of the skull, including the dural sinuses, mastoid process and associated air cells, the internal auditory canal (IAC), and the planned craniotomy.

Fig. 3

A timeline of the complete AR-guided skull base procedure. ( A ) A cadaver head is placed inside a recipient with the ear pointing up. A view through the MagicLeap see-through display shows that the virtual rendering of the skin (white area in the top of the picture) is not yet aligned. ( B ) Using the MagicLeap controller, the surgeon aligns the virtual rendering of the anatomy with the real world head using the pinna and underlying bone such as the mastoid tip as landmarks. The view through the MagicLeap shows a rendering of the bone and the sigmoid sinus. ( C ) Once the virtual rendering and the real head are aligned, the surgeon marks the location of the planned craniotomy window. ( D ) After cutting the skin flap, the surgeon adjusts the alignment of the virtual rendering by visualizing the bone. ( E ) The drilling to create the craniotomy is performed with a microscope without the AR display. ( F ) Following bone flap removal, a view through the MagicLeap shows the rendering of the dural sinuses adjacent to the craniotomy. A video of the complete procedure for a single case can be found in the supplemental material ( Video 1 ). AR, augmented reality.

Fig. 4

The visualization techniques used to display the anatomy. ( A ) The skin with the opaque shader. ( B ) The transparent skin shader with the underlying skull bone. ( C ) The wireframe shader, ( D ) the Fresnel shader, and ( E ) the outline shader with the underlying sigmoid sinus. ( F ) The skull bone with the Fresnel shader with the underlying sigmoid sinus and the planned craniotomy window (red).

Fig. 5

A rendering of the inside of the skull showing the craniotomy, the transverse and sigmoid sinus and the internal auditory canal (IAC). We measured the margins d1 to d6 as a measure of how closely the surgeons were able to place the craniotomy to the transverse and sigmoid sinus without overlapping.

Fig. 6

Box plots depicting the measured margins between the craniotomy and the transverse and sigmoid sinus. ( A, B ) The margins measured for the seven cases performed by both surgeons. The symbols o represent the six individual margin measurements, the x is the mean margin and the center line of the box plot the median margin. ( C ) An overview of the mean margins for all cases performed by surgeon A (cases 1–7) and surgeon B (cases 8–14; error bars indicate ± one standard deviation). ( D ) The mean margins over all cases at each anatomical location d1 to d6 for both surgeons (error bars indicate ± one standard deviation).