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Surgical Imaging


Figure 9: Example Case of a 46-year-old Right-handed Woman with a Left Fronto-temporo-insular Low-grade Glioma


A B


Figure 10: Motor Map of the Precentral Gyrus Generated with Transcranial Magnetic Stimulation


C


D


A: Magnetoencephalography analysis showing increased cortical connectivity values posterior to the tumor in the posterior frontal operculum (indicated by the orange and yellow regions marked by the green cross). B: Intra-operative neuronavigation image indicating the area where speech arrest was elicited during direct cortical mapping, marked by the blue cross. Comparison of images A and B revealed good correlation between the area of speech arrest and an area of increased cortical connectivity. C: Intra-operative photograph taken before tumor resection; #9 and #10 mark the area of speech arrest. D: Intra-operative picture after tumor resection. The temporal and insular components of the tumor have been removed; the functional language points identified (marked with the numbers 9 and 10) have been preserved.


is required. Second, intra-operative MRI allows the surgeon to evaluate the extent of resection using a gadolinium contrast agent if desired, and to continue to remove any residual tumor if found. In traditional glioma surgery, this interim assessment is impossible; the surgeon must finish the case and the post-operative scan is completed the next day. Third, if brain shift occurs during surgery, an interim intra-operative scan can provide updated imaging data that accurately reflect the current anatomy.


Intra-operative MRI has been shown to improve surgical outcomes.14–16 In comparison with traditional methods, it improves the extent of resection17–19


in both low-grade2,20 and high-grade16,21 gliomas, and has


been shown to reduce the size of residual tumor in the case of subtotal resection.22


In a randomized controlled trial, patients undergoing surgery for contrast-enhancing gliomas with intra-operative MRI had a significantly higher rate of gross total resection than those in the control group.23


Despite the mounting evidence that glioma surgery with intra-operative MRI leads to better surgical outcomes, there are as yet no clear data that it leads to increased progression-free or overall survival. Although further studies will likely demonstrate these advantages, the cost of this technology is still an obstacle to its widespread adoption beyond tertiary referral centers.


166


Variably colored pins indicate the amplitude of motor-evoked potentials in the abductor pollicis brevis during the mapping procedure.


Intra-operative Ultrasound


IUS is a modality that has been employed by neurosurgeons for decades. First discussed in the 1970s, IUS has been used intracranially for tumor localization, tumor biopsy, cyst drainage, and navigational guidance of ventriculo-peritoneal shunts.24


The advantages are


many: IUS, like MRI, uses no ionizing radiation; unlike MRI, ultrasound units are relatively inexpensive, portable, and quick to use; finally, IUS can be used by the surgeon directly without the need for additional personnel (see Figure 4).


In the last decade, IUS techniques have become more suited to neurosurgical procedures.25


able to localize lesions within the brain parenchyma.26,27


In particular, 3D ultrasound is increasingly Because IUS


has the ability to resolve small anatomic structures, such as the small vessels on the cortical surface, it can be used to achieve highly accurate co-registration in a frameless stereotactical neuronavigation system.26 Similarly, IUS can be used for intra-operative re-registration of an existing MRI to account for brain shift.27


Despite these advantages, there


are limitations to this technique. IUS is not optimal for deep lesions because of their distance from the probe. Additionally, it does not allow for as much tissue differentiation as other modalities, such as intra-operative MRI. Finally, IUS requires experience on the part of the user to be able to take and interpret IUS images successfully.


5-Aminolevulinic Acid


5-ALA is a small-molecule precursor that causes certain types of cancerous cells to synthesize or accumulate fluorescent porphyrins.28–31 One such porphyrin, protoporphyrin IX (PPIX), specifically accumulates in glioma cells. PPIX, when illuminated with a violet-blue (375–440 nm)


US NEUROLOGY


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