Name: role of diffusion mri tractography in endoscopic endonasal skull base surgery
Uploaded: 2021-07-05T13:00:00
Description: Watch this Scientific Journal Video about Role of Diffusion MRI Tractography in Endoscopic Endonasal Skull Base Surgery at JoVE.com

We would like to thank the radiology technicians and nurses&#8217;staff of the Neuroradiology Area, IRCCS Istituto delle Scienze Neurologiche di Bologna, and their Coordinator Dr. Maria Grazia Crepaldi, for their collaboration.

The protocol is following the Local Research Committee&#39;s ethical standards and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
1. Selection of the patients
<ol>
	<li>Adopt the following inclusion criteria: patients older than 18 years old, fully collaborating, presenting a tumor of the skull base, or pituitary-diencephalic region.</li>
	<li>Exclude patients with contraindication to MRI (i.e., a pacemaker or ferromagnetic material) or presentin...

The application of the presented protocol resulted in a safe and effective treatment of one of the most challenging intracranial tumors such as a craniopharyngioma invading the 3rd ventricle, possibly opening up a new horizon for a lesion that was defined by H. Cushing about a century ago as the most baffling intracranial neoplasm1. The combination of accurate preoperative planning, integrating advanced MRI techniques, and multidisciplinary clinical assessments have permitted us to tail...

The possibility to approach the skull base midline and paramedian regions through an anterior route, adopting the nasal fossae as natural cavities, has a long history, dating back more than one century1. However, in the last 20 years, the visualization and operative technologies have improved enough to expand their possibility of including the treatment of the most complex tumors such as meningiomas, chordomas, chondrosarcomas, and craniopharyngiomas1 due to the (1) introduction of the endoscope, which gives a panoramic and detailed 2D/3D view of these regions to the surgeon, (2) the development of intraoperative neuronavigation systems, and (3) the implementation of dedicated surgical instruments. As painstakingly demonstrated by Kassam et al. and confirmed by multiple reviews and meta-analyses, the advantages of this surgical approach are mainly represented by its chances to resect challenging skull base tumors, avoiding any direct brain retraction or nerve manipulation, thus reducing the risk of surgical complications and long-term neurological and visual sequelae2,3,4,5,6,7,8,9,10,11,12.
For multiple skull base and pituitary-diencephalic tumors, the ideal surgical goal has changed in the last years from the most extensive tumor removal possible to the safest removal with preservation of the neurological functions to preserve the patient&#39;s quality of life3. This limitation could be compensated by innovative and effective adjuvant treatments, such as radiation therapy (adopting massive particles such as proton or carbon ions when appropriate) and, for selected neoplasms, by chemotherapy as inhibitors of the BRAF/MEK pathway for the craniopharyngiomas13,14,15.
However, to pursue these goals, a careful preoperative assessment is crucial, to tailor the surgical strategy to each case&#39;s specific feature2. In most centers, the MRI preoperative protocol is usually performed only with standard structural sequences, which provide the morphological characterization of the lesion. However, with these techniques it is not always possible to assess the anatomical relationship of the tumor with adjacent structures reliably3. Moreover, each patient may present different pathology-induced functional reorganization profiles detectable only with diffusion MRI tractography and functional MRI (fMRI), which can be used to provide guidance both in the surgery planning and in the intraoperative steps16,17.
Currently, fMRI is the most commonly used neuroimaging modality for mapping brain functional activity and connectivity, as guidance for surgical planning18,19 and to improve the patients&#39; outcome20. Task-based fMRI is the modality of choice to identify &#34;eloquent&#34; brain regions that are functionally involved in specific task performance (e.g., finger tapping, phonemic fluency), but is not applicable for the study of skull base tumors.
Diffusion MRI tractography permits in vivo and noninvasive reconstruction of white matter brain connections as well as cranial nerves, investigating the brain hodological structure21. Different tractography algorithms have been developed to reconstruct axonal pathways by linking water molecule diffusivity profiles, evaluated within each brain voxel. Deterministic tractography follows the dominant diffusivity direction, whereas probabilistic tractography evaluates possible pathways&#39; connectivity distribution. Additionally, different models can be applied to evaluate diffusivity within each voxel, and it is possible to define two main categories: single fiber models, such as the diffusion tensor model, where a single fiber orientation is evaluated, and multiple-fiber models, such as spherical deconvolution, where several crossing-fiber orientations are reconstructed22,23. Despite the methodological debate about diffusion MRI tractography, its utility in the neurosurgical workflow is currently established. It is possible to evaluate white matter tract dislocation and distance to the tumor, preserving specific white matter connections. Moreover, diffusion tensor imaging (DTI) maps, especially fractional anisotropy (FA) and mean diffusivity (MD), can be applied to assess microstructural white matter alterations related to possible tumor infiltration and for longitudinal tract monitoring. All these features make diffusion MRI tractography a powerful tool both for pre-surgical planning and intra-operative decision making through neuronavigation systems24.
However, the application of tractography techniques to skull base surgery has been limited by the need for specialized technical knowledge and the time-consuming work-up to optimize diffusion MRI sequence acquisition, analysis protocol, and incorporating tractography results in neuronavigation systems25.Finally, further limitations are due to the technical difficulties extending these analyses from intraparenchymal to extra-parenchymal white matter structures, as cranial nerves. Indeed, only recent studies presented preliminary results attempting to integrate advanced MRI and skull base surgery26,27,28.
The present paper presents a protocol for the multidisciplinary management of pituitary-diencephalic and skull base tumors using diffusion MRI tractography. The implementation of this protocol in the institution resulted from the collaboration between neurosurgeons, neuro-endocrinologists and the neuroimaging team (including clinical and bioinformatics expertise) to offer an effective integrated multi-axial approach to these patients.
In the center, we have integrated multidisciplinary protocols for managing patients with skull base tumors, to provide the most informative description possible, and to tailor and personalize the surgical plan. We show that this protocol can be adopted both in the clinical and the research setting for any patient with a skull base tumor to guide the treatment strategy and to improve the knowledge on the brain modifications induced by these lesions.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>BRAF V600E-specific clone VE1</td>
			<td>Ventana</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dural Substitute</td>
			<td>Biodesign, Cook Medical</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Endoscope</td>
			<td>Karl Storz, 4mm in diameter, 18 cm in length, Hopkins II &#8211; Karl Storz Endoscopy</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Immunohistochemical staining instrument&#160;</td>
			<td>Ventana Benchmark, Ventana Medical Systems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MRI</td>
			<td>3T Magnetom Skyra, Siemens Health Care</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Neuronavigator</td>
			<td>Stealth Station S8 Surgical Navigation System, MEDTRONIC</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

role of diffusion mri tractography in endoscopic endonasal skull base surgery

Endoscopic endonasal surgery has gained a prominent role in the management of complex skull base tumors. It allows the resection of a large group of benign and malignant lesions through a natural anatomical extra-cranial pathway, represented by the nasal cavities, avoiding brain retraction and neurovascular manipulation. This is reflected by the patients' prompt clinical recovery and the low risk of permanent neurological sequelae, representing the main caveat of conventional skull base surgery. This surgery must be tailored to each specific case, considering its features and relationship with surrounding neural structures, mostly based on preoperative neuroimaging. Advanced MRI techniques, such as tractography, have been rarely adopted in skull base surgery due to technical issues: lengthy and complicated processes to generate reliable reconstructions for inclusion in the neuronavigation system. 
This paper aims to present the protocol implemented in the institution and highlights the synergistic collaboration and teamwork between neurosurgeons and the neuroimaging team (neurologists, neuroradiologists, neuropsychologists, physicists, and bioengineers) with the final goal of selecting the optimal treatment for each patient, improving the surgical results and pursuing the advancement of personalized medicine in this field.

A 55-year-old woman presented with progressive visual deficits. Her medical history was unremarkable. On ophthalmological evaluation, bilateral reduction of visual acuity (6/10 in the right eye and 8/10 in the left eye) was revealed, and the computerized visual field showed complete bitemporal hemianopia. No further deficits were evident on neurological examination, but the patient reported persistent asthenia and an increase in hunger and thirst sensation in the previous 2-3 months, with...

Watch this Scientific Journal Video about Role of Diffusion MRI Tractography in Endoscopic Endonasal Skull Base Surgery at JoVE.com

Role of Diffusion MRI Tractography in Endoscopic Endonasal Skull Base Surgery

We present a protocol to integrate diffusion MRI tractography in patient work-up to endoscopic endonasal surgery for a skull base tumor. The methods for adopting these neuroimaging studies in the pre- and intra-operative phases are described.

Endoscopic endonasal surgery has gained a prominent role in the management of complex skull base tumors. It allows the resection of a large group of ...

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