PMC4508731_01
A: Sagittal T2-weighted magnetic resonance (MR) imaging before operation showing compression of the medulla at the foramen magnum. B: Computed tomography (CT) before operation showing the horizontal orientation of the posterior rim of the foramen magnum, causing kinking of the cervicomedullary junction. C: Sagitt T2-weighted MR imaging after the operation showing decompression of the medulla at the foramen magnum.
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F1
Cervical CT and magnetic resonance (MR) imaging showed the horizontal orientation of the posterior rim of the FM, causing compression of the medulla (Fig. 1A, B). Postoperative MR imaging demonstrated decompression of the medulla (Fig. 1C).
A: Intraoperative computed tomography (CT) before surgery demonstrating the horizontal orientation of the posterior rim of the foramen magnum (arrow). B: Intraoperative CT demonstrating incomplete removal of the posterior rim of the foramen magnum, especially on the right side (arrow). C: Photograph just after intraoperative CT showing incomplete decompression of the foramen magnum on the right side (arrow). C-1 arch has been removed as well as the thick epidural band (arrowheads).
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F2
Just before the operation, iCT showed an overgrown opisthion, including the posterior rim of the FM (Fig. 2A). After drilling down the posterior rim of the FM using a diamond-tipped drill and removal of a thickened fibrous epidural band, iCT clearly showed incomplete decompression of the FM (Fig. 2B). We found incomplete osteotomy of the right side of FM as iCT had shown (Fig. 2C), and drilled down the residual bone to achieve sufficient decompression.
PMC4508731_02
A: Sagittal T2-weighted magnetic resonance (MR) imaging before the operation showing severe compression of the medulla. B: Computed tomography (CT) before operation showing the horizontal orientation of the posterior rim of the foramen magnum, causing severe stenosis of the cervicomedullary junction. C: CT demonstrated macrocrania showing incomplete removal of the posterior rim of the foramen magnum. D: Sagittal T2-weighted MR imaging after operation showing sufficient decompression of the medulla.
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F3
Cervical MR imaging showed the horizontal orientation of the posterior rim of the FM, causing compression of the medulla (Fig. 3A). Head CT demonstrated macrocrania without hydrocephalus and incomplete removal of the posterior rim of FM (Fig. 3B, C). Postoperative MR imaging demonstrated sufficient decompression of the medulla (Fig. 3D).
A: Photograph showing preoperative setting of intraoperative computed tomography (CT) with the navigation system (arrow) just before surgery. B: Intraoperative CT just before surgery demonstrating the horizontal orientation of the right posterior rim of the foramen magnum, causing kinking of the cervicomedullary junction. C: Intraoperative CT demonstrating the removal of the posterior rim of the foramen magnum.
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F4
In this case, FM decompression and C1 laminectomy were performed using iCT with a navigation system (Fig. 4A). Just before the operation, iCT showed an overgrown opisthion and incomplete decompression of FM at her first surgery (Fig. 4B). Therefore, we could not confirm the exact location using the pointer of the navigation system; however, iCT clearly showed sufficient removal of the occiput at FM (Fig. 4C).