PMC8571294_01
Preoperative radiograph demonstrating the Chamberlain line suggestive of basilar invagination.
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F1
Chiari I malformation (i.e., with 4-mm of tonsillar descent), with BI/platybasia (i.e., defined based >3-mm extension cranial to Chamberlain's line, extension cranial to McRae's line, and with a nasion/clival angle >143 degrees) [Figures 1-3]. Cervical X-rays also confirmed odontoid instability with anterolisthesis of C2 over C3 and C3 over C4 on flexion which reduces on extension [Figure 4].
Preoperative lateral cervical spine radiograph demonstrating the McRae line connecting the basion and opisthion.
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F2
Chiari I malformation (i.e., with 4-mm of tonsillar descent), with BI/platybasia (i.e., defined based >3-mm extension cranial to Chamberlain's line, extension cranial to McRae's line, and with a nasion/clival angle >143 degrees) [Figures 1-3]. Cervical X-rays also confirmed odontoid instability with anterolisthesis of C2 over C3 and C3 over C4 on flexion which reduces on extension [Figure 4].
Preoperative lateral cervical spine radiograph demonstrating the angle of the nasion to the pituitary to the anterior margin of the foramen magnum. The angle of >143-degees is suggestive of platybasia.
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F3
Chiari I malformation (i.e., with 4-mm of tonsillar descent), with BI/platybasia (i.e., defined based >3-mm extension cranial to Chamberlain's line, extension cranial to McRae's line, and with a nasion/clival angle >143 degrees) [Figures 1-3]. Cervical X-rays also confirmed odontoid instability with anterolisthesis of C2 over C3 and C3 over C4 on flexion which reduces on extension [Figure 4].
Preoperative lateral cervical spine X-rays in neutral, extension, and flexion.
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F4
Chiari I malformation (i.e., with 4-mm of tonsillar descent), with BI/platybasia (i.e., defined based >3-mm extension cranial to Chamberlain's line, extension cranial to McRae's line, and with a nasion/clival angle >143 degrees) [Figures 1-3]. Cervical X-rays also confirmed odontoid instability with anterolisthesis of C2 over C3 and C3 over C4 on flexion which reduces on extension [Figure 4].
Preoperative lateral CT scan of the cervical spine with 12 lbs of traction demonstrating ~2-mm of reduction when compared to Chamberlain line.
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F5
Illustrations of key steps of endoscopic endonasal odontoidectomy. (a) Localization of the proper area of the posterior oropharynx. (b) Midline incision. (c) Localization and identification of the anterior tubercle of C1.
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F6
A small incision was made in the soft palate, and the posterior portion of the hard palate was removed using the zero-degree endoscope allowing access to remove the inferior odontoid [Figures 6a and b]. In addition, soft tissue from the anterior arch of C1 and the small intervening portion of the clivus between C1 and C2 were removed [Figures 6c and  7].
Intraoperative imaging showing the initial approach to the odontoid. Imaging was obtained with an O-Arm.
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F7
In addition, soft tissue from the anterior arch of C1 and the small intervening portion of the clivus between C1 and C2 were removed [Figures 6c and  7].
Illustrations of key steps of endoscopic endonasal odontoidectomy (a) Removal of the odontoid. (b) Identification of the thecal sac.
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F8
As stereotactic navigation appeared to be inaccurate, 3D fluoroscopy was additionally employed to complete the endoscopic/endonasal odontoidectomy [Figures 8a and b].
Intraoperative imaging demonstrating a small remnant of odontoid before final resection. Imaging was obtained with an O-Arm. The navigated drill model is in blue.
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F9
A second O-arm spin demonstrated a small residual portion of the left lateral base of odontoid, which was then removed [Figure 9].
Postoperative lateral CT scan of the cervical spine demonstrating removal of the odontoid and reduction of compression on the cervical spinal cord.
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F10
Further, the final post-operative CT of confirmed good decompression [Figure 10].