PMC10198216_01
Case 1 imaging - Atlantoaxial instability. (a-c) Preoperative cervical rotational CT turned to the right with C1 axial view. (a) C2 axial view (b) and sagittal view. (c) Demonstrating 45  rotation of C1 on C2. (d) 19-months postoperative sagittal cervical CT demonstrating expected postopertive changes of a C1-2 posterior cervical fusion. CT: Computed tomography
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F1
Magnetic resonance imaging (MRI) and computed tomography (CT) imaging studies suggested AAI, with rotational CT scans illustrating increased rotation of C1 on C2 [Figure 1a-c]. The improvement of her symptoms has been consistent since her procedure and remained true at her most recent follow-up, 14 months after her initial procedure, with subsequent 19-month postoperative CT scans showing stable fusion with expected postoperative changes [Figure 1d].
PMC10198216_02
Case 2 imaging - Chiari malformation and craniocervical instability. (a and b). Preoperative T2-weighted sagittal cervical MRI demonstrating cerebellar tonsillar herniation below the ring of C1 and acute clivoaxial angle < 130 . (c) One-day postoperative sagittal cervical CT demonstrating expected postoperative changes of a SOC and O-C2 fusion. (d) Postoperative sagittal T1-weighted flair MRI brain 67 months after initial operation and 15 months after C6-7 fusion demonstrating expected postoperative changes of a SOC and O-C2 fusion. MRI: Magnetic resonance imaging, CT: Computed tomography, SOC: Suboccipital craniectomy
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F2
Dynamic imaging demonstrated acute CXA <130  with some retroflexion of the dens [Figure 2a and b]. Following her procedure, she reported near-resolution of her symptoms for approximately the first few months [Figure 2c]. Subsequent postoperative imaging illustrates stable fusion with expected postoperative changes [Figure 2d].
PMC10198216_03
Case 3 imaging - Pseudoarthrosis (a) Preoperative sagittal rotational cervical CT turned to the left which demonstrates rotational subluxation in conjunction with axial views not shown. (b and c) Postoperative sagittal cervical CT 24 months after initial operation demonstrating pseudoarthrosis with bone graft incorporated into the C2 lamina but without bridging bone between C1 and the bone graft. (d) Postoperative sagittal cervical CT 47 months after the initial operation and 18 months after revision surgery demonstrating bony fusion and expected postoperative changes from a C1-2 posterior fusion. CT: Computed tomography
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F3
Dynamic CT imaging demonstrated C1-2 rotational subluxation worse when turned to the left that was suggestive of AAI [Figure 3a]. Further, over time her postoperative CT scans began to demonstrate pseudoarthrosis at C1-2 by demonstrating that while the bone graft incorporated into the C2 lamina, bridging bone did not fully form between the C1 lamina and the bony graft [Figure 3b and c]. Her symptoms and radiographic studies have remained stable at 48 months after her index procedure and 19 months after her revision, with imaging at that time demonstrating adequate fusion and expected postsurgical changes [Figure 3d].
PMC10198216_04
Case 4 imaging - Odontoidectomy (a) Preoperative T2-weighted sagittal cervical MRI demonstrating restricted CSF flow posterior to the cerebellum, pannus formation posterior to the dens, a slightly retroflexed odontoid process, and slight kinking of the anterior brainstem. (b) Postoperative sagittal cervical CT 1-day after OC2 fusion demonstrating expected postsurgical changes. (c) Postoperative T2-weighted sagittal cervical MRI 10 months after O-C2 fusion and 1-day after odontoidectomy showing expected postsurgical changes. MRI: Magnetic resonance imaging, CSF: Cerebrospinal fluid, CT: Computed tomography
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F4
MRI imaging demonstrated restricted CSF flow posterior to the cerebellum, pannus formation posterior to the dens, a slightly retroverted odontoid process, and slight kinking of the anterior brainstem [Figure 4a]. Given her symptoms and these findings, she elected to undergo an O-C2 posterior spinal instrumentation and fusion, which was done without complication and with follow-up imaging demonstrating expected postoperative changes [Figure 4b]. Following the odontoidectomy, the patient reported an immediate improvement in her symptoms with imaging demonstrating excepted postsurgical changes [Figure 4c].
PMC10198216_05
Case 5 imaging - Tethered cord release. (a) Preoperative T1-weighted sagittal MRI brain demonstrating 5 mm of tonsillar herniation below the foramen magnum and anterior kinking of the brainstem from the mild basilar impression and C2 pannus. (b and c) Postoperative T2-weighted sagittal cervical MRI 64 months after the initial operation and 36 months after tethered cord release demonstrating expected postoperative changes. MRI: Magnetic resonance imaging
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F5
MRI imaging demonstrated a Chiari malformation with 5 mm of tonsillar herniation below the foramen magnum and anterior kinking of the brainstem from mild basilar impression and C2 pannus formation, along with suspected CCI based on flexion/extension imaging [Figure 5a]. While these symptoms did not abate completely, she continued to report improvement from preoperative state at follow-up, with imaging demonstrating expected postoperative changes [Figure 5b and c].