Calvarial Biopsy Using Augmented Reality Technology: A Case Report and Technical Note

Abstract

Calvarial lesions are uncommonly encountered and are often a slow and progressive process. Biopsies of calvarial lesions can be uniquely challenging due to its proximity to critical structures. Augmented reality (AR) offers a potential alternative to computed tomography guidance that reduces radiation exposure and provides hands-free intraoperative guidance through complex and challenging surgical approaches. The patient is an 86-year-old female with significant past medical history of coronary heart disease. The patient underwent imaging which demonstrated a left parietal lytic skull lesion with extracranial extension. Using Surgical AR (Medivis, New York, New York, United States), a trajectory was planned centered on the lesion. Surgical AR was registered using point-to-point registration reliant on four anatomic fiducials. We used a ground truth, which is a bi-faced adhesive tag that measures 2 cm × 1 cm, with a QR code on each side that the Surgical AR system recognizes. This ground truth was placed on the patient's forehead, which linked to the registered holographic overlay. A small incision was made and after removal of a small portion of the overlying skull, multiple pieces of the lytic skull lesion were sampled. A specimen was obtained for frozen sectioning. Intra-operative pathology was consistent with metastatic carcinoma. Total surgical time was 35 minutes from incision to closure. The frameless AR navigation system successfully allowed accurate location, visualization, and biopsy of a calvarial lesion that had minimal surface landmarks. More so, this was completed without obscuring the surgical field or requiring time-consuming setup or registration.

 

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Keywords

augmented reality (AR) - calvarial biopsy - hands-free - neuronavigation - guidance

Introduction

Calvarial lesions are uncommonly encountered, compromising approximately 0.8% of bone neoplasms.[1] These intraosseous lesions of the calvarium are often slow, progressive processes that are either asymptomatic and found incidentally or have localized symptoms such as pain or a palpable mass. In addition, a variety of diseases can present as calvarial lesions, such as arachnoid, dermoid, or epidermoid cysts, fibromas, intraosseous hemangiomas, low-grade meningiomas, osteoid osteomas, and metastases, among others.[2] Most often, these lesions have a wide differential with variable imaging features,[3] and therefore, tissue sampling may be the best option for diagnosis,[3] understanding pathology, and to guide treatment.[2]

However, biopsies of calvarial lesions can be uniquely challenging due to its proximity to critical structures including the cortex and neurovascular structures near the skull base.[3] Current methods of biopsy include magnetic resonance (MR)-guided, computed tomography (CT)-guided biopsy, and CT-fluoroscopy, of which the last two have an increased level of radiation exposure.[3] [4] Augmented reality (AR) offers a potential alternative to CT guidance that reduces radiation exposure and provides hands-free intraoperative guidance through complex and challenging surgical approaches.[5] [6] [7] [8] The purpose of this study was to introduce and evaluate the feasibility, safety, and diagnostic yield of a novel method of preoperative AR guidance to perform a calvarial biopsy.[5] [6] [7] [8]

 

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Clinical Presentation

Presentation

The patient is an 86-year-old female with significant past medical history of coronary heart disease. She presented to the hospital after two transient episodes of right upper extremity incoordination and paresthesia. Upon arrival, the patient underwent head CT without contrast ([Fig. 1A]) and MR imaging (MRI) with and without contrast ([Fig. 1B, C]). These demonstrated a left parietal lytic skull lesion with extracranial extension. A chest CT also demonstrated a left upper lobe spiculated mass ([Fig. 1D]). At that time, the patient reported no known history of malignancy and no prior seizures.

Fig. 1 Preoperative imaging. (A) Preoperative CT, (B) preoperative T1 MRI, (C) preoperative T2 MRI. White arrows point to lesion. (D) Preoperative CT of the thorax. Blue arrow demonstrates the left upper lobe spiculated mass. CT, computed tomography; MRI, magnetic resonance imaging.

 

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Preoperative Imaging

The left parietal intraosseous calvarial lesion measured 4.5 cm (anterior posterior) × 2.2 cm (cranial caudal) × 2.9 cm (right to left), with extension into the overlying scalp and underlying pachymeninges. There was also mass effect and vasogenic edema within the underlying left parietal and posterior frontal lobe. There were no enhancing intraparenchymal lesions. Differential from imaging studies included metastasis, primary osseous lesion, or meningioma. The chest CT found a 3.2 × 2.2 × 2.8 cm left upper lobe spiculated pulmonary mass concerning for neoplasm and thus raised suspicion that the calvarial lesion was indeed a metastasis.

 

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Operative Technique

The patient was placed supine on the operating table and underwent general anesthesia. The head was placed in a Mayfield horseshoe head holder. Pinning was not required. Using Surgical AR-based (Medivis, New York, New York, United States) navigation, a trajectory was planned centered on the lesion. Surgical AR was registered using point-to-point registration reliant on four anatomic fiducials (lateral canthi, tip of the nose, tragus, and nasion). A ground truth, a bi-faced adhesive tag that measures 2 cm × 1 cm with a QR code on each side that the AR system tracks, was placed on the patient's forehead, which linked to the registered holographic overlay. Visualization was achieved with a head-mounted display (HMD), the HoloLens2 (Microsoft, Redmond, Washington, United States). The center of the lesion was marked according to the designated preplanned trajectory ([Fig. 2]). A small incision was made over this mark. A combination of Leksell and Kerrison rongeurs was used to remove a small portion of the overlying skull. Multiple pieces of the lytic skull lesion were biopsied. Diagnostic yield was appropriate on initial sampling. Intra-operative pathology was consistent with metastatic carcinoma. Total surgical time was 35 minutes from incision to closure, including intraoperative pathology analysis.

Fig. 2 Intraoperative AR workflow. (A) Planning the registration points on the holographic AR rendering. (B) Planning the trajectory for the calvarial biopsy. (C) Intraoperative overlaid hologram with the biopsy trajectory planned, which is outlined in orange. AR, augmented reality.

 

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Postoperative Course

Postoperative CT and MRI imaging showed interval postoperative changes related to the biopsy in the center of the lesion as planned ([Fig. 3A, B]). It is important to note that the planned incision and postoperative analysis matched perfectly. Given the pathology, the patient underwent subsequent resection and cranioplasty a few days later. A small subjacent mixed collection and pneumocephalus were seen next to the surgical bed, with persistent left frontal and parietal vasogenic edema, similar in distribution to the preoperative scan. While the immunohistochemical profile of this metastatic adenocarcinoma is not entirely specific to a single organ, it was most consistent with lung as the primary site of origin, supported by the presence of a lung lesion on chest CT. As there was concern for residual disease, the patient opted for gamma knife radiosurgery treatment 10 days after resection. The resection cavity bed was targeted, including both dural and bony edges. Unfortunately, follow-up MRI imaging on 4/2/2023 found recurrent disease leading to the patient requiring whole brain radiation therapy. The patient passed from disease progression 5 months after initial diagnosis.

Fig. 3 Postoperative imaging. (A) Postoperative CT scan and (B) postoperative T2 MRI demonstrate interval postoperative changes related to the biopsy in the center of the lesion as planned. White arrows point to the site of entry. CT, computed tomography; MRI, magnetic resonance imaging.

 

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Discussion

Surgical navigation systems have continuously improved since their introduction in the 1990s.[7] [8] [9] These systems have traditionally allowed surgeons to track instrumentation relative to a patient's anatomy based on co-registration, with a dynamic reference frame and preoperative imaging.[10] However, computer-based surgical planning and stereotactic navigation are notably limited by the time needed for registration and the requirement for a separate viewing screen outside of the surgical field.[11] In addition, the need for framed fixation, which computer-based surgical planning and stereotactic navigation require, has their own complication and risk profile, which is well documented in the literature.[12] Guidance systems that force the operator to shift their attention from the surgical field may interfere with attention and efficient workflow.[13] In addition, any contact with the reference array will lead to inaccurate navigation. Reregistration intra-operatively is often difficult and in most cases, not possible unless the patient is re-draped, which increases risk of infection.

The implementation of AR in surgical navigation has allowed image overlay of computer-generated patient information directly onto the surgical field[14] or in a HMD device.[7] [8] [15] This, in turn, has allowed for better visualization of anatomical structures and surgical targets in the operating room (OR), as well as the attention of the operating surgeon is not shifted away from the field. Additionally, AR with the use of anatomic fiducial markers requires less setup time compared with conventional neuronavigation methods, which may reduce the financial burden to patients and the hospital system from overall decreased OR utilization.[11] This efficiency, more recently, has been further improved by the optical “snap-to” registration, which uses artificial intelligence, to map and match the face to the preoperative imaging.[11] The main limitations of AR navigation, such as latency and a lack of real-time feedback, are not limited to the use of AR and are intrinsic to intraoperative navigation systems that rely on preoperative imaging. The use of dynamic AR systems that adjust preoperative imaging based on real-time data either from ultrasound or computer vision analysis of cortical architecture with point cloud renderings constructed from the HMD sensor inputs can adapt to parenchymal deformation. These are future areas for advancement to address these shortcomings.[16]

The use of frameless AR-guidance in a patient with calvarial metastatic adenocarcinoma of the lung is described here. The novelty of the Surgical AR system in conjunction with an HMD for biopsy is that it obviates the need for pinning the patient. In fact, with the use of a ground truth as an environmental anchor, the hologram moves with the patient's head and stays accurately registered, as demonstrated here ([Video 1]). The accuracy of a similar hands-free AR-based navigation system (VisAR, Novarad, American Fork, Utah, United States) has previously been reported and studied in gelatin-based models.[6] This report adds to the current evidence of literature that the use of AR for cranial biopsies is accurate and safe, while also minimizing cognitive load and improving efficiency in the OR through workflow simplification. Since pinning with a Leksell G-frame or Mayfield C-clamp is unnecessary, the biopsy can then be done under light sedation with local anesthetic. This has immense impact, especially in the older or sicker population, where general anesthesia may not be tolerated with the patient's risk profile.

Video 1 The surgeon quickly registers the patient by mapping out key points on the anatomic image to the hologram. The hologram produced by the AR system can be seen with anatomic landmarks as well as the designated planned trajectory. As the patient's head is manipulated for a more preferred or comfortable positioning, the hologram is appropriately changed to be in line with the patient's head based on the ground-truth fiducial. This is demonstrated in a real-time manner.

For more complicated intra-operative applications, AR navigation for cranial surgery has been investigated previously in the setting of tumor resection.[17] This has afforded better visualization of deep-seated lesions surrounded by complex anatomical structures. Roethe et al performed a prospective randomized control trial comparing the use of a HMD-based AR navigation system to conventional neuronavigation for intracranial tumor resection.[18] [19] The study demonstrated that the integrated continuous display allows for decreased work-flow interruption and reduced intraoperative cognitive load to the surgeon. Skyrman et al developed an AR navigation system that can achieve biopsy at submillimeter accuracies in a skull phantom.[10] [20] This was performed within a hybrid OR comprised of a robotic C-arm with intraoperative cone-beam CT and integrated video tracking. To the best of our knowledge, AR navigation has not been implemented for biopsies of the calvarium, and as such, this is the first reported case of successful calvarial biopsy utilizing AR navigation.

Despite the successful localization and collection of biopsy samples, there are several limitations in the current study. First, this was completed on a single patient. While the purpose of the article was to understand the utility of AR in a biopsy case, a larger cohort of patients needs to be evaluated to fully understand the safety, efficacy, and functionality of the use of AR in biopsies. Finally, this case was particularly straight-forward as the biopsy in question was more superficial. In future cases, it would be helpful to have a broader range of depth of biopsies to see how AR helps in those cases.

 

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Conclusion

The frameless AR navigation system in this study successfully allowed accurate location, visualization, and biopsy of a calvarial lesion. More so, this was completed without obscuring the surgical field or requiring time-consuming setup or registration. This report adds to the current body of literature that AR can be used successfully in calvarial biopsies.

 

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Conflict of Interest

None declared.

Acknowledgment

This study was approved by the Institutional Review Board (IRB) at the home institution (protocol number STUDY20050495).

Authors' Contributions

N.S., E.G.A., A.N.M., J.B., and C.H. were involved in the design and conception of this manuscript. N.S., S.B., M.K., R.S., A.T., S.A., M.R., N.M.K., L.C., and F.S. performed the literature review and compiled the primary manuscript. N.S., A.T., S.A., N.M.K., L.C., J.R.H., M.R., F.S., and S.P.C. collected and analyzed data. N.S., A.T., S.A., and E.G.A. compiled the figures and video. All authors critically revised the manuscript. All authors approved the manuscript as it is written.

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Publication History

Article published online:
21 May 2025