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Hemorrhagic stroke
Review
A review and comparison of three neuronavigation systems for minimally invasive intracerebral hemorrhage evacuation
  1. Alexander G Chartrain1,
  2. Christopher P Kellner1,
  3. Kyle M Fargen2,
  4. Alejandro M Spiotta3,
  5. David A Chesler4,
  6. David Fiorella4,
  7. J Mocco1
  1. 1 Department of Neurosurgery, Icahn School of Medicine at Mount Sinai, New York City, New York, USA
  2. 2 Department of Neurological Surgery, Wake Forest University, Winston-Salem, North Carolina, USA
  3. 3 Department of Neurosurgery, Medical University of South Carolina, Charleston, South Carolina, USA
  4. 4 Department of Neurosurgery, Stony Brook University Medical Center, Stony Brook, New York, USA
  1. Correspondence to Dr Christopher P Kellner, Department of Neurosurgery, The Mount Sinai Hospital Klingenstein Clinical Center, New York 10029, USA; christopher.kellner{at}mountsinai.org

Abstract

Advances in stereotactic navigation technology have helped to improve the ease, reliability, and workflow of neurosurgical intraoperative navigation. These advances have also allowed novel, minimally invasive neurosurgical techniques to emerge. Minimally invasive techniques for intracerebral hemorrhage (ICH) evacuation, including endoscopic evacuation and passive catheter drainage, are notable examples, and as these gain support in the literature and their use expands, stereotactic navigation will take on an increasingly important and central role. Each neurosurgical navigation system has unique characteristics. Operators may find that certain aspects are more important than others, depending on the environment in which the evacuation is performed and operator preferences. This review will describe the characteristics of three popular stereotactic neuronavigation systems and compare their advantages and disadvantages as they relate to minimally invasive ICH evacuation.

  • intracerebral hemorrhage
  • neuroendoscopy
  • neuronavigation
  • stereotaxy

https://doi.org/10.1136/neurintsurg-2017-013091

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    Introduction

    Over the past three decades, neuronavigation has become a crucial aide in the neurosurgical operating theater. Ever since the first stereotactic neurosurgery technique in humans was introduced near the end of the 19th century, neuronavigation has evolved into a practically indispensable neurosurgical tool. Advances in neuronavigation technology have allowed neurosurgeons to set aside the skull-mounted frame and even avoid rigid head fixation that was traditionally needed to perform stereotactic procedures. Intracranial hemorrhage evacuation procedures have benefited enormously from these technological advances, and have allowed minimally invasive techniques to emerge. These evacuations were once performed via a large craniotomy, but advances in stereotactic guidance systems over the years have permitted the precise targeting of hematomas through progressively smaller craniotomies and, now, can be performed through a small burr hole. The use of these minimally invasive approaches for intracerebral hemorrhage (ICH) evacuation requires surgical neuronavigation assistance during the procedure. Despite their importance, there are, to our knowledge, no practical comparisons of the neuronavigation systems available to neurosurgery departments. A review of these systems would be of use to institutions planning to develop a minimally invasive ICH evacuation programme. Here we compare the three most popular neuronavigation systems and outline the advantages and disadvantages of each as they apply to minimally invasive ICH evacuation.

    Neuronavigation systems

    Medtronic AxiEM stereotactic navigation system

    Technology background

    The Medtronic AxiEM stereotactic navigation system uses three orthogonal electromagnetic coils to create a low-energy magnetic field that extends around and encompasses the head in a spherical field measuring approximately 50 cm in diameter.1 2 The strength and direction of the magnetic field created by the electromagnetic coils is defined and known by the system for each point within this space.3 The sensor contained within the AxiEM stylet can measure the strength and direction of the magnetic field and can be compared with the known electromagnetic map to determine its exact position and orientation within the field.2 3 Similarly, the patient tracker, attached to the scalp by an adhesive sticker, also contains a sensor that can measure its position and orientation within the magnetic field (figure 1). Registration of the patient’s cranial anatomy to the skin-based patient tracker provides the Medtronic system with the digital information needed to locate the patient’s head in space at all times, even if the head position is adjusted afterwards.4

    Figure 1
    Figure 1

    The Medtronic AxiEM patient tracker is attached to the patient’s head in proximity to the electromagnetic emitter/receiver.

    Registration

    High-resolution preoperative imaging is required for accurate registration. The manufacturer recommends slice thickness no greater than 3 mm, with thickness of 1 mm preferred for optimal accuracy. However, in our experience, the system can accommodate poor quality preoperative scans, including scans in which the nose is not visible, using acquisition of known points and bony landmarks.

    Registration can be performed in any of three different ways, depending on surgeon preference. Tracer registration is carried out by tracing the patient’s face and scalp with the tracer instrument, which automatically gathers information from 300 surface points and matches them to the three-dimensional surface geometry of the patient’s preoperative scan (figure 2). Alternatively, PointMerge registration requires the surgeon to mark points on the preoperative imaging scan and use the tracer instrument to touch these same points on the patient in a predefined order. Prone registration is possible with PointMerge point acquisition on identifiable bony landmarks. The AxiEM offers a third method for patient registration, using the Touch-n-Go instrument, but is only compatible with skull-mounted fiducials, which require a skin incision and securing to the skull with screws, thus making this a less desirable option when submillimeter accuracy is not required.

    Figure 2
    Figure 2

    The registration process with the Medtronic AxiEM system is carried out by tracing the patient’s head.

    Surgical planning

    Preoperative planning is performed on the StealthStation machine, directly. The surgical planning window efficiently displays the patient scan in axial, coronal, and sagittal planes, simultaneously (figure 3). A three-dimensional reconstruction CT scan of the surface anatomy can also be displayed to plan the entry point.

    Figure 3
    Figure 3

    Medtronic AxiEM stereotactic navigation targeting screen. The planned trajectory can be viewed in three planes simultaneously, and the ‘probe’s-eye-view’ (bottom left corner) can be used to monitor the position of the stylet with respect to the planned trajectory.

    Operative setup

    The Stealth AxiEM station divides into three separate components: a computer workstation, a touchscreen monitor, and the AxiEM portable box that can be hung close to the operative field (figure 4). The computer workstation does not need to be adjacent to the patient, but its distance is restricted by cord length. The AxiEM portable box should be hung close to the patient, preferably from the operating room or angiosuite table because the wire length of the stylet is short. The touchscreen monitor is larger than the monitor attached to the workstation and can be used with a sterile pointer. The monitor is compatible and can be used with video inputs from other systems. The most unique component of the AxiEM operating room setup is the electromagnetic emitter, which must be fixed to the table near the patient’s head with a support bracket. In our experience, accuracy diminishes slightly with increased distance from the emitter even if the signal continues to appear strong.

    Figure 4
    Figure 4

    The room layout of the Medtronic AxiEM stereotactic navigation system in the neurointerventional angiography suite.

    Intraoperative use

    The patient tracker is affixed to the patient’s forehead close to the emitter and the adhesive is reinforced with additional tape or Tegaderm. A non-sterile, disposable pointer is used for registration before draping the patient. During the procedure, a sterile, long, thin, flexible stylet is used to verify burr hole placement, corticectomy incision location, and endoscope sheath insertion trajectory. The AxiEM stylet is placed within the introducer sheath during its initial placement. The ‘probe’s-eye’ viewing option allows the surgeon to monitor the progress of the stylet in relation to the planned trajectory. If the stylet is advanced off-track, the guidance screen indicator turns red, alerting the surgeon to adjust the trajectory. Unlike the probes associated with optical systems, the AxiEM stylet reports the actual location of the probe tip rather than an extrapolated position from the handle. Because the stylet is thin and flexible, it can be used even through the endoscope port itself.

    Advantages

    The electromagnetic mechanism by which the Medtronic AxiEM system operates provides several advantages over infrared optical navigation systems. The primary advantage is that there is no requirement for direct line-of-sight between the emitter, receiver, or probe. This makes the electromagnetic systems ideal for several reasons: (1) the electromagnetic system can be fully draped and is therefore more likely to maintain sterility, (2) surgical instruments and staff can move freely throughout the operating room without having to worry about interrupting the navigation signal, and (3) the sensor can be inserted into an endoscope and can provide stereotactic information from the tip of the stylet.

    The flexible stylet, which accompanies the AxiEM system, is the only available probe that can maintain positioning accuracy when it is flexed and offers a unique benefit to neuronavigation.4 An electromagnetic sensor, because of its sleek dimensions, is built into the stylet shaft and provides direct localization of the tip itself. By contrast, optical systems, which require maintenance of line-of-sight with the infrared camera, can only provide probe-tip location information by extrapolating from the handle reference reflectors.1

    Because individual electromagnetic sensors are typically tube-shaped, they can sense pitch and yaw in addition to position in three-dimensional space. Because of this, a single sensor is all that is required for accurate tracking.3 This obviates the need for triangulation of multiple reference markers separated by several centimeters, which is needed for optical tracking systems, and allows for the electromagnetic tracking system to have a smaller, low-profile design.1

    Registration with the non-invasive patient tracker and the tracer instrument avoids the need to trim the hair, create skin incisions, and screw fiducials into the skull. The tracer may have an advantage over the laser because it can be used with ease behind the hairline. Registration is consistent and easy with this system compared with laser-guided optical systems. Additionally, because metal pins are not needed for accurate registration and localization of the cranial anatomy, distortion artifacts are effectively avoided when obtaining intraoperative CT scans. Finally, the head does not need to be pinned and fixed to the table, which allows for patient head rotation to improve surgical ergonomics or should adjustments in approach trajectory be needed.

    Disadvantages

    The electromagnetic property by which the Medtronic AxiEM system operates is vulnerable to interference by other electromagnetic fields and instruments. Many surgical instruments and computers produce and distort electromagnetic fields, including retractors, a drill, ultrasound probe, and anesthesia equipment, and may disrupt the navigation accuracy of the AxiEM system. Without interference, the AxiEM system has a measurement accuracy of approximately 0.1 mm, but in the presence of electromagnetic distortion, the accuracy is reduced to within 0.21–0.56 mm of the true location of the stylet.5 The Medtronic AxiEM system detects irregular distortion and will drop the signal of the probe if that preset threshold is exceeded. The potential for interference from metal instruments is usually easily overcome with simple fixes, such as using sutures placed into the wound edges or lone stars for retraction instead of using self-retaining metal retractors.

    The patient tracker must be placed on the skin surface, and in certain patients with loose or diaphoretic skin, it may shift from its original position after registration. If this occurs, the location of the cranial anatomy is rendered inaccurate unless registration is repeated. In our experience, shift of the skin tracker and loss of registration is rarely a concern. Additionally, the cord length of stylet and patient tracker limit the distance that the AxiEM components can be positioned from the operative field. The AxiEM stylet is a single-use, disposable piece of equipment and, if used frequently, can increase departmental expenditures.

    Stryker iNtellect stereotactic navigation system

    Technology background

    The Stryker iNtellect stereotactic navigation system operates via active optical tracking of light-emitting diodes (LEDs) placed directly on the skin. A facemask with 31 infrared LEDs is attached to the patient’s face and forehead before surgery (figure 5). The facemask is strategically designed to cover areas of the face that represent the unique geometrics of the cranial and facial anatomy.6 Infrared LEDs are also located on surgical instruments. As long as the LEDs stay within the line-of-sight of the camera system, the instruments and cranial anatomy can be correctly localized in space. The Stryker facemask can accommodate full draping, but only with a specialized transparent drape that allows for maintenance of direct line-of-sight with the overhead camera.

    Figure 5
    Figure 5

    The Stryker iNtellect facemask, with 31 light-emitting diodes, is placed on the patient’s face and forehead.

    Registration

    Registration is performed with an LED-equipped tracking device. During registration, the facemask and tracking device must remain in view of the overhead camera for accurate registration. Registration of the facemask LED reference markers allows for head movement without loss of registration accuracy. Accurate registration requires that the overhead camera visualize at least 27 LEDs. Owing to the rounded shape of the patient’s face, this requires the camera to be positioned near the patient’s midline, with the ideal position being directly over the patient’s chest directed forward and downwards to the face. As only 27 LEDs need to be visualized, the facemask may be trimmed with scissors to remove LED sensors that might interfere with a frontal surgical incision. After registration, only five LEDs are required to track the patient.

    Surgical planning

    The burr hole placement and endoscope trajectory are planned before the procedure, directly on the workstation in the operating room (figure 6).

    Figure 6
    Figure 6

    Stryker iNtellect stereotactic navigation targeting screen with trajectory views in multiple planes.

    Operative setup

    The Stryker navigation system comprises an overhead camera and its associated workstation, and a large touchscreen monitor. The overhead camera is located at the end of a long arm that is unfolded over the operative table (figure 7). The workstation is connected to the overhead camera, but can be placed farther away from the operative field (figure 8). The workstation provides mirrored video output to the touchscreen monitor, which can be used both preoperatively and intraoperatively with a sterile probe.

    Figure 7
    Figure 7

    Intraoperative photo during minimally invasive intracerebral hemorrhage evacuation of a hematoma performed in the neurointerventional angiography suite. The transparent drapes allow for overhead camera visualization of the Stryker iNtellect facemask light-emitting diodes.

    Figure 8
    Figure 8

    The room layout of the Stryker iNtellect stereotactic navigation system in the neurointerventional angiography suite.

    Intraoperative use

    The tracker probe can be placed within the endoscope sheath during its placement along the trajectory. The tip of the probe instrument is extrapolated from the LED sensors present on its handle and is represented virtually on the monitor as the probe is advanced. Throughout the initial placement of the introducer sheath, the facemask (at least five of its LEDs) and probe handle must be in view of the overhead camera or the navigation signal will be lost. If the facemask becomes dislodged, the navigation system can detect the change in the LED conformation. In minor cases, the software is able to adjust the initial registration to accommodate the slight shift in facemask position, but in major cases will automatically halt the navigation until registration is repeated.

    Advantages

    The stereotactic probe is wireless and therefore can be freely moved within the view of the infrared camera. Pin-less stereotaxy with the facemask provides little imaging artifact, allowing for high-quality intraoperative DYNA CT scans.

    Disadvantages

    The facemask optical system is challenging to use with minimally invasive ICH evacuation when surgeries are performed with the entry point on the forehead. This limitation may be overcome by trimming the facemask if a portion of it will interfere with the incision or surgical procedure, as long as 27 LEDs remain visible to the camera for registration and five LEDs after registration. The facemask requires transparent drapes which may result in loss of registration if blood, gauze, or instruments obscure the camera’s view of the mask.

    As the facemask may be very close to the incision for frontal approaches, maintaining sterility may be challenging. In lateral or posterior approaches, positioning of the overhead camera will require alteration to the standard room arrangement to allow for accurate registration and navigation.

    BrainLab VectorVision stereotactic navigation system

    Technology background

    The BrainLab VectorVision stereotactic navigation system operates through passive optical tracking using defined geometry reference arrays with spherical reflectors affixed either directly to the patient via a skull-mounted array or by an articulating arm connected to the skull clamp. An infrared camera, acting as both an emitter and receiver, is able to localize both the patient anatomy and the surgical instruments in space by reflection of infrared light off spherical fiducials attached to the reference array and the various surgical instruments. Adapter clamps allow for the integration of essentially any instrument into the BrainLab space facilitating intraoperative navigation. With the use of the skull-mounted array, the head position can be adjusted intraoperatively so long as direct line-of-sight between the array and camera is preserved (figure 9).

    Figure 9
    Figure 9

    Registration with the BrainLab VectorVision passive optical system. In this case, the BrainLab skull- mounted reference array was used.

    Registration

    As with the other navigation systems discussed, registration requires high-resolution preoperative imaging. Patient registration is accomplished by correlating skin surface anatomy, bony landmarks, or fiducials (skin or bone) on the preoperative imaging with the patient’s anatomy. Acquisition of landmarks can be accomplished through several methods dependent on positioning considerations and surgeon preference. Surface registration is accomplished with ‘Z-touch’ surface scanning or using the SoftTouch wand. Registration using preoperatively placed fiducials can be accomplished using the standard BrainLab wand or the SoftTouch wand (figure 10). Both point-to-point marking and skin surface matching methods require the spherical reflectors to be in view of the camera during registration.7 After registration, the head must remain in the exact same orientation relative to the fiducial array attached either to the skull clamp or directly to the patient via the skull-mounted array for accuracy to be maintained.

    Figure 10
    Figure 10

    Operative planning with the BrainLab VectorVision passive optical system. In this case, the BrainLab reference array mounted to an articulated arm attached to the skull clamp was used.

    Surgical planning

    Surgical planning is performed preoperatively using the iPlan workstation or directly on the BrainLab navigation system in the operating theatre (figure 11). The burr hole placement and endoscope trajectory are planned before the procedure directly on the workstation in the operating room.

    Figure 11
    Figure 11

    BrainLab VectorVision stereotactic navigation targeting screen with multiple views of the planned trajectory.

    Operative setup

    The BrainLab navigation system has an overhead camera, a workstation, and a large touchscreen monitor. The overhead camera is positioned at the end of a long arm that is extended over the operating table (figure 12). The workstation is connected to the overhead camera, but can be kept farther away from the operative field. The workstation provides mirrored video output to the touchscreen monitor, which can be used both preoperatively and intraoperatively.

    Figure 12
    Figure 12

    The room layout of the BrainLab VectorVision stereotactic navigation system in the neurointerventional angiography suite.

    Intraoperative use

    A fiducial array can be attached to operative instruments and registered with the BrainLab system for continuous intraoperative monitoring. During minimally invasive endoscopic ICH evacuation, the array is often attached to the endoscope to provide the operator with continuous intraoperative guidance about the location of the tip of the endoscope relative to the hematoma and cavity. The tip of the probe is extrapolated from the spherical reflectors present on its handle and is represented virtually on the monitor as the probe is advanced. For a signal to be well maintained, the probe and head-holder reference array must be in view of the overhead camera throughout the initial placement of the introducer sheath.

    Advantages

    Although pinning has its disadvantages, there are several advantages, including head stabilization and increased accuracy. Accuracy in minimally invasive ICH evacuation, however, is only required such that the endoscope sheath enters the clot cavity, and small deviations can be accommodated. When pinning is not an option as is the case in the angiography suite, or alternatively is not desired, as the ability to change the head position is preferred, the localizing array can be directly affixed to the patient using the skull-mounted array. Like the Stryker system, the BrainLab pointer is wireless, permitting its use on the sterile field, and can be used at any distance from the BrainLab computer. Unlike the Medtronic AxiEM system, the BrainLab system allows continuous navigation and can be used in the vicinity of metallic instruments.

    Disadvantages

    Laser optical registration is difficult to use behind the hairline and on patients with diaphoretic or shiny skin. Registration behind the hairline or over various surface textures is possible, but requires transition to registration by multiple-point acquisition on the patient’s scalp using the pointer. Tracer registration is an option, but difficult to perform in lateral or prone positions without preoperatively placed and scanned fiducials.

    The Mayfield pinning system is incompatible with intraoperative DYNA CT, although a less rigid radiolucent headframe is available.

    Medtronic StealthStation optical navigation system

    The Medtronic StealthStation navigation system, which supports the electromagnetic AxiEM navigation technology (discussed above), is also equipped with a passive optical navigation system that is similar to the BrainLab VectorVision, both in technology and practical considerations.

    Discussion

    Stereotactic neurosurgery was first described in humans by Zernov in 18898 and dramatically expanded in scope after the advent of CT.9 In 1986, frameless stereotaxy was introduced to replace the cumbersome head frame required for conventional stereotaxy, allowing for improved maneuverability in the operative field.10 Certain procedures traditionally performed with pin-based rigid head fixation, including ventriculostomy placement and brain biopsy, were then replaced with pinless stereotaxy systems and scalp-mounted adhesive fiducials.4 11 These advanced neuronavigation systems were initially made possible by ultrasound localization using microphone recording,10 but were later improved with the development of optical and electromagnetic-based tracking technologies.

    ICH evacuation procedures were initially performed through a large craniotomy without the use of stereotactic guidance.12 13 However, owing to high mortality rates and lack of benefit in randomized trials with this approach, less invasive stereotactic techniques, including endoscopic evacuation and stereotactic aspiration with thrombolysis, were introduced to improve evacuation outcomes.13 14 Stereotactic aspiration was initially performed with the use of a frame, but frameless techniques are now common.15 16 By contrast, minimally invasive endoscopic evacuation, first described in 1989, was always performed without the use of a frame.14 Although rigid head fixation is still used for both procedures, depending on surgeon preference,17 many have adopted neuronavigation systems that can be used without rigid pin fixation.18

    Although there have been no comprehensive comparisons of the most popular neuronavigational systems to our knowledge, several investigators have tested the difference in stereotactic accuracy of various types of equipment. Several studies have found similarly excellent accuracy for both electromagnetic and optical stereotaxy, and navigational accuracy is considered equivalent.2 19–21 Furthermore, since minimally invasive ICH evacuations do not require perfect stereotactic accuracy, the small differences between electromagnetic and optical systems are not clinically important. Among the optical systems, one study compared navigational accuracy of the Stryker and BrainLab systems for stereotactic brain biopsies and found small differences in favor of the BrainLab.22 Although significant, the differences were on the submillimetric scale and the authors concluded that they would be of limited clinical importance. Overall, in the context of ICH evacuations, navigational system accuracy is equivalent among all three systems.

    Although they have similar navigation accuracy, optical and electromagnetic stereotactic neuronavigation systems possess advantages and disadvantages that pertain to their applicability in ICH evacuations (table 1).

    View this table:
    Table 1

    Characteristics, advantages, and disadvantages of the three stereotactic neuronavigation systems

    Cost is a major concern for most neurosurgical departments working with a budget. The Medtronic AxiEM stylet is not reusable and needs to be discarded after each procedure. By contrast, optical system probes can be sterilized and reused, making Stryker and BrainLab more affordable options if used frequently.

    Facility characteristics also need to be considered when choosing a navigational system. ICH procedures are routinely carried out in both the operating room and the angiography suite, two settings with contrasting space availabilities. In crowded settings, an optical system, with its requirement for good line-of-sight, may be less ideal than an electromagnetic system. This may be particularly important when non-frontal approaches are used, as the overhead camera for BrainLab and Stryker systems may need to be moved to an alternative site from the usual room arrangement to allow for accurate registration and instrument navigation.

    The various techniques and devices used for ICH evacuation may also be a determining factor in navigation system preference. For centers that perform stereotactic catheter placement and drainage similar to the MISTIE trial protocol, the Medtronic AxiEM system may be preferable, as the AxiEM stylet can be inserted within the catheter during placement to provide real-time feedback about its position with respect to the preoperative imaging. The BrainPath endoport system (NICO, Indianapolis, Indiana, USA), a transcortical speculum inserted through a 3 cm craniectomy, has been reportedly used with the pinned, passive optical Medtronic StealthStation system.23 24 The added stability of the pinned headholder may be optimal for the slightly larger craniectomy that is needed to insert the BrainPath endoport. The Apollo system (Penumbra, Alameda, California, USA), which includes an aspiration wand 2.6 mm in diameter, is performed through a smaller 1.5 cm craniectomy. It is compatible with all three neuronavigation systems and can be used without the need for pinning. Its use has been documented with passive optical navigation (BrainLab VectorVision), and, although details have not yet been published, the authors report its successful use with both active optical (Stryker iNtellect) and electromagnetic (Medtronic AxiEM) systems.25 26 As mentioned above, the Medtronic AxiEM electromagnetic neuronavigation is not compatible with the metal body of the endoscope and, therefore, is useful only during the initial cannulation phase of endoscopic approaches (including with both the Apollo and BrainPath devices). The active and passive optical navigation systems (ie, Stryker iNtellect, Medtronic StealthStation, BrainLab VectorVision), however, can be applied continuously during all phases of endoscopic ICH evacuation, as they are not affected by proximity to metallic instruments.

    Stereotactic navigational systems are designed to be versatile. The Medtronic AxiEM electromagnetic system is particularly ideal for ventriculostomy and ventricular shunt placements, as well as endoscopic procedures, owing to its direct detection of the sensor at the tip of the stylet. The Medtronic neuronavigation system, which can house both the passive optical and electromagnetic systems, may provide added flexibility when adjustment to the requirements of the procedure is needed (eg, switching from minimally invasive endoscopic to open craniotomy). In addition, pinless neuronavigation systems, which include Medtronic AxiEM and Stryker iNtellect, are ideal for pediatric cases and for other circumstances in which rigid head fixation is contraindicated.27

    Conclusion

    In this review, we have provided a practical comparison of three popular neuronavigation systems that are commonly used for ICH evacuation. Although navigational accuracy may be equivalent between the three systems, procedural preferences, cost, facility characteristics, and system versatility are important factors to consider when choosing a system for the procedure.

    Acknowledgments

    We would like to thank Sophie Greenberg for providing the illustrations.

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    Footnotes

    • Contributors All authors contributed to the manuscript through manuscript composition and critical review. All authors provided final approval for publication.

    • Funding This paper was supported in part by a grant from Arminio and Lucyna Fraga.

    • Competing interests None declared.

    • Patient consent Obtained.

    • Provenance and peer review Not commissioned; externally peer reviewed.