Name:
10.3171/2024.10.FOCVID24110
Description:
10.3171/2024.10.FOCVID24110
Thumbnail URL:
https://cadmoremediastorage.blob.core.windows.net/054754fd-63da-4734-8d32-ab5d0fa5aa6f/videoscrubberimages/Scrubber_249.jpg
Duration:
T00H10M10S
Embed URL:
https://stream.cadmore.media/player/054754fd-63da-4734-8d32-ab5d0fa5aa6f
Content URL:
https://cadmoreoriginalmedia.blob.core.windows.net/054754fd-63da-4734-8d32-ab5d0fa5aa6f/2. 24-110.mp4?sv=2019-02-02&sr=c&sig=QJ2tIgrbNdLFT5UTlYXIXFRKaK0WWY%2BxrrsJR%2FRG%2Bhg%3D&st=2026-03-13T05%3A55%3A43Z&se=2026-03-13T08%3A00%3A43Z&sp=r
Upload Date:
2024-11-21T00:00:00.0000000
Transcript:
Language: EN.
Segment:0 .
[MUSIC PLAYING]
SPEAKER: We present a case of motor mapping–guided resection of a brainstem recurrent pilocytic astrocytoma. A 25-year-old man who was initially diagnosed with a left ventral midbrain glioma at age 3, treated with biopsy through a retrosigmoid approach and several rounds of chemotherapy, presented with new-onset double vision, corresponding to progressive growth of a multinodular tumor extending from the midbrain to the pons.
SPEAKER: His original imaging revealed a faintly enhancing expansile tumor abutting the midline of the ventral midbrain. This then developed to a small enhancing nodule of T2-hyperintense and contrast-enhancing lesion medially around 5 years of follow-up, which grew gradually over time. A second enhancing and T2-hyperintense nodule emerged at the lateral inferior aspect of the tumor around 15 years of follow-up, which also steadily grew.
SPEAKER: At 20 years of follow-up, the tempo of growth accelerated with acquisition of additional enhancing nodules within the tumor. The tumor originated medial to their cerebral peduncle and subsequently grew laterally and caudally. Therefore, the corticospinal tract was deflected from the posterior lateral to the entire medial aspect of the tumor over time, as supported by the tractography.
SPEAKER: Of note, on the raw DTI imaging, there is a thin sliver of potential fibers seen in yellow that may course between the dominant posterior lateral nodule and a more medial enhancing nodule. His neurologic exam prior to the operation was notable for a mild abducens palsy and excellent strength throughout, except for trace right-sided weakness from his childhood. Surgery was offered given the escalating tempo of tumor growth to alleviate symptomatic mass effect for cytoreduction and to obtain tumor tissue from molecular genotyping given the potential for targeted therapies in certain pediatric-type gliomas.
SPEAKER: Risks of the operation discussed with the patient included worsening weakness, worsening double vision, facial numbness and weakness, stroke, cerebral spinal fluid leak, and hydrocephalus. The patient was positioned supine with trunk elevated, the ipsilateral shoulder bumped up, and the head turned away, with the vertex tilted towards the contralateral shoulder. Intraoperative neuromonitoring was key for this operation and included transcranial motor-evoked potentials for monitoring of high-density coverage of the right upper and lower extremity muscles and cortically stimulated motor-evoked potentials for bilateral face, left oculomotor, left abducens, and left masseter muscles.
SPEAKER: Subcortical motor mapping was set up to allow real-time tracking of the corticospinal tract for the contralateral extremity muscles and the course of ipsilateral motor cranial nerves from the nuclei to the cisternal segment. Sensory function of the head and body were monitored with the somatosensory-evoked potentials, left trigeminal somatosensory-evoked potentials, and bilateral brainstem auditory-evoked potentials.
SPEAKER: The recording electrode positions for the left ocular motor, left abducens, left masseter, bilateral face muscles, and nerves are shown here. The left trigeminal SSEP electrodes are shown in pale blue. I began with extending the prior retrosigmoid craniotomy to allow full exposure of the sigmoid and transverse sinuses from mobilization of the sinus. The dura was opened in a C-shape fashion, beginning with a foramen magnum to release CSF.
SPEAKER: Extensive adhesions were released until the cyst capsule was exposed medial to the trigeminal nerve. Sharp dissection of the cyst capsule from the undersurface of the trigeminal nerve and the surface of the brain stem was performed to allow for initial decompression of the cyst.
SPEAKER: This then allowed for handling of the cyst wall to begin dissection against the brain stem. I continued with internal debulking of the tumor using a monopolar stimulating section throughout the resection to allow for dynamic motor mapping until low responses were elicited. Here, 1.5 mA of stimulus elicited robust responses from the right hand and smaller responses from the proximal right upper extremity and down to 0.5 mA of stimulus to see the right-hand responses corresponding to 1 mm or less of distance to the corticospinal tract.
SPEAKER: Perforator vessels are carefully preserved. The final rim of tumor was shaved away until ipsilateral left facial brainstem responses are also elicited on dynamic motor mapping down to 0.8 mA of stimulus, corresponding to less than 1 mm of distance from the facial tract or nucleus. Hemostasis is achieved with Gelfoam saturated with Tisseel fibrin glue.
SPEAKER: A hypertensive challenge was performed to verify the hemostasis. The dynamic subcortical motor mapping responses throughout the operation is summarized here from top to bottom as time progresses. We began with eliciting right upper extremity muscle responses at between 7 to 8 mA of stimulus, corresponding to 7 to 8 mm of distance to the corticospinal tract.
SPEAKER: This then gradually worked down to 1 and 0.5 mA of stimulus, corresponding to 1 or less than 1 mm of distance to the corticospinal tract in the right-hand responses. Of note, the responses go up and down to reflect the 3D contour of reflection with the surrounding corticospinal tract. The same subcortical mapping also reveals ipsilateral facial responses in the oris and mentalis muscles at various points of the resection, down to 0.8 mA of stimulus, corresponding to less than 1 mm from the left facial nucleus or tract.
SPEAKER: This differs from the robust responses seen when the monopolar stimulating section touches the facial nerve as seen in the responses up above. At the end of the operation, stable transcranial motor evoked potentials are seen along with stable corticobulbar motor evoked potentials for the bilateral face and the left masseter muscles. Cortically induced motor evoked potentials for the left oculomotor nerve, as seen by the superior rectus, the left abducens nerve as seen with the lateral rectus, and the third branch of the trigeminal nerve, as revealed by the masseter muscle, are also stable at the end of resection.
SPEAKER: Trigeminal SSEPs remained stable for all three branches of the left trigeminal nerve. The pathology revealed the classic features of a pilocytic astrocytoma with a BRAF KIAA1549 fusion on genotyping, prompting initiation of tovorafenib therapy. The patient experienced resolution of his preoperative double vision and maintained his strength and sensation after the operation.
SPEAKER: He was begun on tovorafenib at 2 months following the operation. His postoperative MRI shows near-total resection of the dominant posterior lateral nodule immediately following surgery, with stable to improved disease at 8 months following the operation. Key points of this case demonstrate the benefit of exposing and mobilizing the transverse and sigmoid sinuses fully to allow exploration of the supracerebellar infratentorial and lateral cerebellar surfaces without fixed cerebellar retraction.
SPEAKER: Internal debulking creates space before dissection of the tumor capsule from eloquent tracts. Dynamic motor mapping is able to elicit robust responses from the corticospinal tract at the level of the midbrain and pons. The monopolar stimulating suction allows simultaneous detection of the corticospinal tract for contralateral limb responses and the course of the motor cranial nerves from the ipsilateral side.
SPEAKER: Hemostasis is ensured using Gelfoam with Tisseel fibrin glue without electric cauterization to minimize risk of ischemia.
Form Title Download
Form Title Bookmark
Form Title Share
Form Title Cite
