PMC9479549_01
Imaging findings consistent with atlantoaxial subluxation and instability. (a) T2-weighted sagittal view of the cervical spine demonstrating sequelae of cord compression just below the level of the foramen magnum. The predental space is markedly increased measuring approximately 1.5 cm. Definite stenosis and cord compression at this level likely attributed to supine position during image acquisition. (b) The cord is flattened and of abnormal signal characteristic at C2 level, where there appears to be an anteriorly displaced os odontoideum. (c) Sagittal bone window of computerized tomography redemonstrating atlantoaxial subluxation and dystopic os odontoideum. Dynamic changes appreciated on plain radiographs in (d) flexion and (e) extension.
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F1
Evidence of encephalomalacia at the craniocervical junction was also noted secondary to acute angulation of the cord [Figure 1].
Transcranial motor-evoked potential recordings during closed cervical traction. Decreased amplitude in the right hand and leg noted during application of Gardner-Wells tongs and extension of neck (a) with subsequent return to baseline in the right lower extremity after initial weight placement and correction of cervical alignment (b). RAPB: Right abductor pollicis brevis, RTA: Right tibialis anterior.
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F2
Neuromonitoring detected decreased MEP signals even with the smallest changes in position [Figure 2a]. We then placed 3 pounds of weight and positioned his head in a more extended position with return to baseline neuromonitoring [Figure 2b].
Transcranial motor-evoked potential recordings during occipitocervical instrumented fusion. Following C1 lateral mass placement, a decrease in amplitude was detected in the right hand thought to be secondary to excessive atlas mobility (a). Baseline signal acquisition occurred after rapid C1 laminectomy (b). RAPB: Right abductor pollicis brevis, RTA: Right tibialis anterior, RAH: Right abductor hallucis.
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F3
TceMEP demonstrated a decrease in the right hand [Figure 3a], thought to be secondary to excessive atlas mobility during screw placement despite the use of countertraction. The decision was then made to proceed with laminectomy of C1, at which point significant improvement was noted in TceMEP signals [Figure 3b].
Intra and postoperative images demonstrating adequate reduction of atlantoaxial subluxation and occipitocervical fixation. Plain lateral radiograph of the cervical spine during traction with 3 pounds of weight; significant atlantoaxial reduction with some degree of distraction noted (a). Computerized tomography (b) and radiographic (c) studies performed 1 year after staged occipitocervical reduction and fixation with evidence of osseous fusion and no failure of instrumentation.
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F4
Interval imaging studies were also obtained demonstrating no instrumentation failure and adequate osseous fusion [Figure 4].