80 Neuronavigation and Intraoperative Imaging

Case 80 Neuronavigation and Intraoperative Imaging

Lahbib B. Soualmi and Abdulrahman J. Sabbagh

Fig. 80.1 (A) Magnetic resonance imaging (MRI) preoperative, three-dimensional (3D) reconstruction (top left) with ventricular system in purple and tumor in yellow. T1-weighted MRIs preoperative with contrast showing tumor in axial (top right), sagittal (bottom left), and coronal (bottom right) images. (B) MRI intraoperative, 3D reconstruction (top left) with ventricular system in purple and tumor in yellow. T1-weighted MRIs intraoperative with contrast showing tumor in axial (top right), sagittal (bottom left), and coronal (bottom right) images.

Fig. 80.2 Intraoperative axial T1-weighted magnetic resonance images with contrast showing progression of tumor resection.

Clinical Presentation

A 7-year-old right-handed girl presents with slowly progressive headaches and blurred vision.

Examination is normal with the exception of early papilledema.

Magnetic resonance imaging (MRI) of the brain shows a large right parietooccipital cystic lesion that is rim-enhancing (Fig. 80.1).
You decide to take the patient to surgery, for diagnostic and therapeutic reasons.

Questions

How will you plan the surgery?
What are the characteristics of images needed for navigation in general?
What are the types of information that can be utilized for navigation?
How does neuronavigation work?
What are the types of registration available?
What are the existing types of localizers?
How do you classify intraoperative imaging?
Give examples where intraoperative imaging may be useful.
Compare the advantages and disadvantages of intraoperative computed tomography (iCT) and intraoperative MRI (iMRI).

Answers

How will you plan the surgery?

This patient has a cystic lesion. As the cyst leaks during surgery, the brain will shift and navigation will be very inaccurate. For this reason the surgical team may decide to use intraoperative imaging and do the following (Fig. 80.1B):

Placing the head in a rigid MRI- or CT-compatible head holder in preparation for surgery

Obtaining a preoperative MRI and calculating the cyst volume (Fig. 80.1A)

Performing craniotomy and frameless stereotactic aspiration of the cyst

Performing iMRI after cyst aspiration to compensate for the brain shift caused by cyst aspiration and craniotomy (Fig. 80.1B)^1,2

Taking an interhemispheric approach to the lesion and complete resection (Fig. 80.2)
What are the characteristics of images needed for navigation in general?
- Three-dimensional (3D) global acquisition: Contiguous slices covering the whole region of interest such as the head or spine.
  - Anatomic isotropic scan with high resolution: Fine cuts are required to be able to create an accurate volumetric data.
  - After computerized fusion, the functional data can then be superimposed on the anatomic data.
What are the types of information that can be utilized for navigation?
- Anatomic information^3,4
  - MRI
    - T1-weighted, ± contrast, T2-weighted, inverse recovery, fluid-attenuated inversion-recovery sequences, etc.
    - Diffusion tensor imaging, tractography
    - MR angiography, MR venography
  - CT
    - CT ± contrast,
    - CT angiography (CTA)
  - Ultrasound 3D acquisition
    - B-mode information
    - Doppler information
  - Conventional biplanar angiography
- Functional information^5–8
  - Positron emission tomography (PET)
  - Single photon emission computerized tomography
  - Functional MRI (fMRI)
  - Magnetoencephalography (MEG)
  - Cortical electroencephalography
  - Depth electrode recordings
  - Transcranial magnetic stimulation
- Biochemical information
  - MR spectroscopy
  - Other chemical imaging modalities
How does neuronavigation work?
- The following are steps required for the workings of neuronavigation.9–12
  - Image acquisition (Fig. 80.3)
  - Image data analysis: anatomical ± functional data analysis—segmentation and 3D reconstruction and volume rendering of objects of interest
  - Fusion and superimposition of different anatomical ± functional images (Fig. 80.4): The example given is PET data superimposed on MRI data.
  - Registration: correlating and alignment of the 3D volumetric data with the actual patient (brain or spine)
  - Tracking: The neuronavigation platform should track the patient and surgical tools through the available localizer. This is done through different available tools (Fig. 80.5).
What are the types of registration available?
- Anatomic: Using anatomic landmarks (bridge of the nose, inner and outer canthi, tragus valleys, spinous processes, transverse process, etc.)¹³
- Fiducials: Using radiopaque markers fixed before scanning the patient. These markers must be detected by the imaging modality used.¹⁴
- Surface fitting: Pinpointing a mesh of points on the surface of the region of surgical interest using a probe or a laser scanning device, to be correlated with the 3D object surface (i.e., face or spine of the patient).^13,15
- Automatic: Automatic recognition of geometric position of dedicated markers, which are fixed to a head-holder (in cases of iMRI) or scanner gantry (in cases of iCT) and are scanned with the patient. They are used by the navigation platform to achieve the registration.
What are the existing types of localizers?
- Optical localizers (using an infrared camera)14
  - Passive tracking: Using reflective spheres that are placed on the reference frame (patient), probes, and/or any surgical instrument (Fig. 80.5).
  - Active tracking: The reference frame (patient) and probes are equipped with light emitting diodes.
- Magnetic localizers: Magnetic signals that are emitted by the probe and picked up by a receiver indicating its location in space. This modality avoids the disadvantage of a clear line of sight required for optical localizers.¹⁶
- Mechanical localizers: Articulated arms equipped with transducers giving the angular position.
- Ultrasound localizers: Navigation probes transmit ultrasonic signals that are picked up by a receiver indicating its location in space.
How do you classify intraoperative imaging?
- Real time^3,17
  - Intraoperative ultrasound (iUS)
  - Intraoperative angiography
  - Fluoroscopy
- Preacquired¹¹
  - iMRI
  - iCT
Give examples where intraoperative imaging may be useful.
- Here are some examples of the use of intraoperative imaging.
  - iMRI, iCT, or iUS for detection or residual tumor¹⁸
  - iMRI, iCT, or iUS to compensate for brain shift
  - Reregister using intraoperative landmarks if the patient moves during surgery
  - iMRA, iCTA, or intraoperative angiography after clipping aneurysms or resecting arteriovenous malformations from the brain or spinal cord^17,19
  - iUS to localize ventricles, cysts, and lesions in the brain and spinal cord
  - iUS for recalibration of navigation
  - iCT or iMRI for immediate localization of depth electrodes, strips, and grids (in epilepsy surgery), or deep brain stimulators (in functional and behavioral neurosurgery) to readjust them if needed²⁰
Compare the advantages and disadvantages of iCT with iMRI.
- See Table 80.1^20–24