Planning and positioning
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The initial assessment of a patient with a suspected intradural nerve sheath tumor begins with a detailed history and physical examination.
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Magnetic resonance imaging (MRI) with gadolinium contrast agent for lesion localization is essential for planning the surgical approach. Schwannomas are characteristically isointense or hypointense to the spinal cord on T1-weighted images, with cystic areas represented by high T2 signal. Areas of hemorrhage or collagen are seen as low attenuation on T2 sequences. Schwannomas and neurofibromas enhance intensely in a homogeneous or heterogeneous pattern. Patients with neurofibromatosis may have multiple lesions along the entire spinal cord.
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X-rays may show enlargement of neural foramina, a classic finding associated with these lesions, and associated skeletal deformities.
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Intraoperative neurophysiologic monitoring with motor evoked potentials (MEPs) is essential when operating on intradural nerve sheath tumors. The anesthetic regimen should be coordinated with the anesthesiologist before the start of the case because many anesthetic agents cause depression of MEPs. Commonly used agents that do not cause a decline in motor potentials include propofol, fentanyl, and etomidate.
Figure 97-1:
Preoperative T2 sagittal and axial MRI showing a lumbar intradural nerve sheath lesion, with central T2 hyperintensity representing cystic areas.
Figure 97-2:
The patient is turned prone after intubation, and electrodes are placed for neurophysiologic monitoring. For cervical lesions, the patient is pinned in a three-point Mayfield head fixator and positioned prone on two chest rolls. The neck is slightly flexed to aid in surgical exposure. For patients with thoracic or lumbar lesions, prone positioning can be accomplished on a Wilson frame or chest rolls without head fixation. All dependent surfaces (e.g., knees, elbows) are padded to avoid peripheral nerve injury or pressure-related tissue damage.
Procedure
