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Adult basilar invagination
Introduction
Basilar invagination (BI) is among the common pathological conditions afflicting the cranio-cervical junction. Primary development is associated with syndromic conditions such as trisomy 21, Ehlers-Danlos syndrome, and Marfan syndrome; secondary development is associated with inflammatory conditions such as rheumatoid arthritis and bony abnormalities such as cervical-vertebral body fusions. Other associated conditions include Chiari malformation, platybasia, and atlanto-axial (AA) instability. BI is a dynamic condition characterized by progressive caudal displacement of the cervico-medullary junction that can be related to untreated odontoid displacement into the skull base. The majority of patients present with occipital pain and gait ataxia as a result of bulbomedullary compression and instability. No management guidelines have been established for patients with BI thus far. The surgical management of BI is complex and must be tailored based on the inciting pathology, patient condition, and stability of the craniocervical junction and AA joints. Patients may require prolonged traction before surgical fixation. A posterior-only approach may be employed, as the majority of cases involving a pannus from AA instability resolve after fusion. Other cases with a significantly retroflexed odontoid process may require a combined anterior/posterior approach with anterior odontoid resection. In this chapter, we present the case of a patient with progressive quadriparesis and associated rheumatoid arthritis.
Example case
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Chief complaint: progressive upper and lower extremity weakness
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History of present illness: This is a 65-year-old female with a history of rheumatoid arthritis, hypothyroidism, and cervical stenosis status post C4–7 anterior cervical decompression and fusion (ACDF) in 2009 with progressive upper and lower extremity weakness. Approximately 6 months prior, she developed bilateral upper extremity weakness that has progressed to her legs, and she is now wheelchair bound. She also presented with dysphagia and urinary incontinence since a month ago. She underwent computed tomography and magnetic resonance imaging demonstrating compression of the cervico-medullary junction ( Fig. 63.1 ).
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Medications: levothyroxine
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Allergies: no known drug allergies
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Past medical and surgical history: rheumatoid arthritis, hypothyroidism, cervical stenosis, anterior cervical decompression and fusion 10 years prior
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Family history: none
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Social history: healthcare worker, no smoking, occasional alcohol
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Physical examination: awake, alert, and oriented to person, place, and time; cranial nerves II–XII intact; bilateral deltoids/triceps/biceps 5/5; interossei 5/5; iliopsoas/knee flexion/knee extension/dorsi, and plantar flexion 5/5
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Reflexes: 3+ in bilateral biceps/triceps/brachioradialis with positive Hoffman; 3+ in bilateral patella/ankle; two beats of clonus; positive Babinski
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| Preoperative | ||||
| Additional tests requested |
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Parasagittal CT to evaluate articulation of the occipital condyles to C1 |
| Surgical approach selected | Endoscopic endonasal odontoidectomy with C1 arch preservation | C1-3 laminectomy, occipital-C5 fusion | Posterior occiput to C6 fusion, C1 laminectomy, distraction C1-2 with possible staged odontoidectomy |
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| Goal of surgery | Decompress cervico-medullary junction | Decompress cervico-medullary junction, stabilize spine | Decompress cervico-medullary junction, stabilize spine | Decompress cervico-medullary junction, stabilize spine |
| Perioperative | ||||
| Positioning | Supine with pins | Prone, with halo-ring | Prone, with Gardner-Wells tongs |
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| Surgical equipment |
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| Medications | None | MAP >80 | None | MAP >80 |
| Anatomical considerations | Nasal cavities, nasopharynx, clivus, atlas, dens, cranio-cervical junction ligaments, internal carotid artery, vertebral artery, dura | Inion, posterior arch of C1, bifid spinous process of C2, C1-2 joint | Vertebral arteries, spinal cord | Vertebral arteries, spinal cord hypoglossal nerve, carotid arteries, pharynx, recurrent laryngeal nerve, dura |
| Complications feared with approach chosen | CSF leak, vessel injury, dysphagia | Brainstem/spinal cord injury, vertebral artery injury, CSF leak | Hematoma, infection, instrumentation failure with pull-out, loss of fixation | Inability to reduce, dysphagia, meningitis, CSF leak, instability |
| Intraoperative | ||||
| Anesthesia | General | General | General | General |
| Exposure | C2 | Occiput-C5 | Occiput-C6 |
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| Levels decompressed | C2 | C1-3 | C1 |
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| Levels fused | None | Occiput-C5 | Occiput-C6 |
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| Surgical narrative | Position supine with head slightly tilted to left and flexed, navigation acquisition after intraoperative CT, find inferior margin of middle turbinate/nasopharynx and eustachian tubes and use as anatomical landmarks, displace inferior turbinates laterally, access nasopharyngeal cavity, remove posterior third of nasal septum, form a U-shaped nasopharyngeal mucosal and muscular layer flap with the laser from the inferior third of the clivus to the inferior edge of the C2 vertebral body, expose lateral masses of C1, subperiosteal skeletonization of anterior arch of C1 and odontoid process, resection of ALL and full exposure of atlanto-axial articulation, removal of lower clivus, removal of upper portion of anterior arch of C1, removal of tip and base of odontoid using ultrasonic curette, leave a residual shell to carefully dissect and section apical and alar ligaments, remove other adhesions, expose dura of the pontomedullary junction after excision of inflammatory tissue, use navigation to help with location, intraoperative CT to confirm adequacy of decompression, put U-shaped nasopharyngeal flap with fibrin glue, place foley catheter for 3 days to compress mucosal flap and allow its adhesion | CT immediately preoperative, awake transnasal endoscopic intubation, preoperative IOM baseline, positioned prone with maintaining traction, midline linear incision from inion to C5 spinous process, subperiosteal dissection, expose occipital bone/posterior arch of C1/spinous processes and lamina and lateral masses of C2-5, place C2 pedicle and C3-5 lateral mass screw holes, place occipital plates, C1-3 laminectomy, decorticate C1-2 articular surfaces, widen C1-2 joint space and place small cage filled with bone chips, place screws, bend titanium rods to fit into plate and screws connecting occipital plate down to lateral mass screws, decorticate bone lateral and caudal to occipital plate and lateral to screws, apply bone graft, layered closure with drain | Fiberoptic or awake intubation, placement in Garner-Wells tongs, position prone, obtain immediate fluoroscopy images to confirm no spinal malalignment, expose occiput to C6 using subperiosteal dissection, C1 laminectomy, instrument occiput and then C2 pedicles and then lateral mass C3-6, distract across C1-2 joint, add bone or cage into C1-2 joint to keep it distracted, fluoroscopy to evaluate amount of distraction, add structural allograft with BMP or take autograft, intraoperative CT, layered closure with subfascial drain; if neurologically not improved after 3-4 weeks, then anterior odontoidectomy | Stage 1: position prone, midline incision from C1-5, subperiosteal dissection of posterior arch of C1 and spinous processes/lamina of C2-5, dissection and mobilization of bilateral C2 nerve roots, ligate and section C2 nerve roots proximal to dorsal root ganglion if needed to access C1 lateral mass, expose and remove C1-2 joint, place pilot holes for C1 and C3-5 lateral mass instrumentation, C1-2 laminectomy, place lateral mass at C1 and C3-5 bilaterally, contour rods to span from C1-5 with extra length to allow distraction and reduction of deformity, attempt reduction by distracting C1-2 joints bilaterally with small laminar spreaders across joint, attempt reduction if prior did not work by fixing rods from C3-5 with locked locking nuts and loose locking nuts at C1, distract between C1 and C3 lateral mass screws and nuts locked down if reduction is achieved, continuous MEP and spinal cord visualization with ultrasound, reduce reduction if MEP changes, confirm reduction with O-arm and lateral x-rays, apply cross-link between C1 instrumentation, decorticate and apply autograft to joints, posterior arch can be used as a structural autograft if there is a large space from the distraction, layered closure with subfascial drain Stage 2 (same day): head fixed and secured in halo, attach array for surgical navigation, intraoperative O-arm and registered, incision made on prior side of previous ACDF ideally at C4-5 level staying above previous approach, standard ACDF approach, blunt dissection in loose areolar tissue to the level of anterior tubercle of C1, place beveled tubular retractor with lip sitting on anterior tubercle of C1 and opening of bevel over C2-C3 body, 30-degree endoscope inserted down fixed retractor, ventral surface of the mid portion of C3 and C2 body are removed with ultrasonic aspirator, continue to work toward tip of odontoid under C1 anterior arch, width of resection is width of odontoid estimated by resecting bone aided by navigation between medial aspect of bilateral C1-2 articulation, resect odontoid in top down fashion, caudal extent based on preoperative MRI and CT, remove transverse and apical ligaments with Kerrison, O-arm spin to confirm adequacy of decompression, layered closure |
| Complication avoidance | Use middle turbinate/nasopharynx/eustachian tubes as anatomical landmarks, laser to form nasopharyngeal and muscle flap, preserve lower portion of anterior arch of C1, leave a shell of bone to help with dissecting ligaments, surgical navigation to help check position, intraoperative CT to evaluate decompression, foley catheter to place against flap to promote adhesion | Preop traction, preflip IOM, open C1-2 joint to promote fusion, C1-3 laminectomy | Attempt at only prone approach, avoid odontoidectomy if possible, place bone in C1-2 joint to keep it distracted, BMP to promote fusion | Avoid incorporating occiput into fusion to minimize dysphagia, section C2 nerve roots if necessary for instrumentation, longer rods to allow for attempted distraction and reduction of deformity, continuous MEP and ultrasound of spinal cord during attempted reductions, ventral approach rostral to previous ACDF, beveled tubular retractor, preserve C1 anterior arch, resect odontoid in top down fashion, resection aided by navigation, O-arm to confirm adequacy of decompression |
| Postoperative | ||||
| Admission | ICU | ICU | Floor | ICU |
| Postoperative complications feared | CSF leak, dysphagia, C1-2 instability | Pseudoarthrosis, new neurological deficit | Hematoma, infection, instrumentation failure with pull-out, loss of fixation |
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| Anticipated length of stay | 4–5 days | 3–5 days | 3 days | 4–5 days |
| Follow-up testing | Dynamic CT 1 months after surgery |
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Cervical x-rays within 48 hours of surgery, 6 weeks, 6 months, 12 months after surgery | Cervical x-rays 2 weeks, 6 weeks, 3 months, 6 months, 1 year after surgery |
| Bracing | Philadelphia collar for 1 month | Rigid collar for 6–12 weeks | Hard collar for 6 weeks | None |
| Follow-up visits | 1 month, 3 months, 6 months, 12 months after surgery | 6 weeks, 3 months after surgery | 6 weeks, 6 months, 12 months after surgery | 2 weeks, 6 weeks, 3 months, 6 months, 1 year after surgery |
ACDF , Anterior cervical decompression and fusion; AP , anteroposterior; ALL , anterior longitudinal ligament; BMP , bone morphogenic protein; CSF , cerebrospinal fluid; CT , computed tomography; CTA , computed tomography angiography; DEXA , dual-energy x-ray absorptiometry; ENT , ear, nose and throat; ICU , intensive care unit; IOM , intraoperative monitoring; MAP , mean arterial pressure; MEP , motor evoked potential; SSEP , somatosensory evoked potential.
Differential diagnosis
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Basilar invagination
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Atlanto-axial instability
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Platybasia
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Chiari malformation
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Occipital condyle hypoplasia
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Cranio-cervical junction tumor
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