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Proatlas Segmentation Anomalies
Natarajan Muthukumar
Prof. & Chairman
Dept. of Neurosurgery
Madurai Medical College
Madurai
India
Proatlas Segmentation Anomalies
• Developmental anomalies of the CVJ due to abnormal re-segmentation of the fourth occipital sclerotome are named as ProatlasSegmentation Anomalies.
• Increasingly being recognized after the routine use of three-dimensional CT for evaluation of CVJ anomalies
Patients & Methods
• Number : 5
• Gender : Males- 3, Females - 2
• Age : 14 yrs – 20 yrs
• Presentation : Myelopathy ± cerebellar signs
• Imaging : Plain radiographs, Thin
Section CT, MRI
• Surgery : Craniovertebral Realignment – 2;
Goel-Harms fusion – 2;
Distraction with Goel’s Fusion - 1
Case 119 yrs; male; cervical myelopathy
MRI: • Ventral brainstem compression• Horizontal clivus• Assimilated atlas• Tonsillar ectopia
AAD with basilar invagination
CT:• Horizontally oriented clivus• Anterior arch fused to Clivus• Invaginated odontoid• Accessory ossicle between clivus and odontoid (Red arrow)
Craniovertebral Realignment under Intra-operative Traction
O-C Fusion
Crossing C 2 translaminar screws
Procedure: under intra-op traction
• Occipito-cervical fusion• Crossing C 2 intralaminar screws• C4, C 5 lateral mass screws• Post-op: Descent of odontoid• Space between Occ. & C 2
Case 219 yrs female; Torticollis; Cervical Myelopathy
MRI – Basilar invagination; Klippel-Feil; cervical canal stenosis
Proatlas Segmentation Anomaly- Case 2
Basilar Invagination
ProatlasSegmentationanomaly
Klippel FeilAnomalyNotice the aplasia of
Atlas
C 2 articulates directly with OcciputOccipital condylar hypoplasia on RT.
Procedure: Intra-operative traction; O-C fusion; Cervical laminectomy at the level of
stenosis
Case 2Pre Operataive Post Operative
Odontoid insideForamen magnum
Yellow arrows point to the increase in the distance between the Foramen
magnum and C 2 between the preop & postop scans – evidence of distraction.
Case 314 yrs; ,male; Spastic Quadriparesis following
trivial trauma
Radiographs: AADMRI : High cervical cord compression
Os Avis or Dystopic OsOdontoideum
Anterior Arch placed directly over C 2 body
• Odontoid fused to basion
• “Os Avis”• “Dystopic Os
Odontoideum”
Case 3Os Avis/ Dystopic Os Odontoideum
Goel-Harms Fusion
Proatlas Segmentation AnomalyCase 4
• 16 years male; history of RTA
• Admission GCS 13
• CT Brain: diffuse cerebral edema
• GCS 15 – Complained of neck pain
• Plain radiographs – AAD with hypoplastic odontoid
• CT – Pre-basioccipital arch
• Surgery – Goel –Harms fusion
Proatlas – Case 5
20 yrs female; gait difficulty; cerebellar and pyramidal signs
Ventral brainstem compression; tonsillar ectopia upto C 2, cervical syrinx
Proatlas – Case 5
Horizontal clivus : Foreshortened basi-occiput
Case 5
• Patient under 5 kgs traction
• Exposure of AA JOINTS
• Denuding the joint
• Insertion of 4mms titanium spacers in the joints
• C 1 lateral mass & C 2 pars screws
• Foramen magnum Decompression
Pre-op Post- Op
Proatlas – Case 5
Preoperative Postoperative – 1 month
Compression of cervicomedullaryjunction with obliteration of subarachnoid spaces
Syrinx
Reduction of cervicomedullarycompression with opening of the subarachnoid spaces
Disappearance of syrinx
Proatlas – Case 5
Preoperative Postoperative – 1 month
Peg shaped tonsils extending upto the lower border of C 2
Tonsillar ascent
Principles of Surgical Management
1. Relieving neural compression, if present
2. Stabilizing the CVJ, if there is instability
Principles of Surgical Management
• Patients 1 and 2:
– Neurological deficits were due to ventral brainstem compression – treated by craniovertebral re-alignment by intra-operative traction and occipitocervical fusion
• Patients 3 and 4:
– Deficits due to instability – addressed by Atlantoaxial fusion using Goel-Harms technique
Principles of Surgical Management
• Patient 5:
– Deficits were due to congenital anterior basilar impression and “exuberant” apical segment of dens with retroflexed odontoid
– Small volume of posterior fossa by platybasialed to tonsillar ectopia
– Ventral compression of brainstem was addressed by craniovertebral re-alignment using AA spacers and AA fusion
– FMD was done to increase the PF volume and Tt. Tonsillar ectopia.
Conclusions
• Proatlas segmentation anomalies are rare
• Thin Section CT of CVJ absolutely mandatory to recognize this entity
• Neural compression requires decompression
• Instability, if present, requires stabilization.
Muthukumar N: Proatlas Segmentation anomalies: J Pediatric Neurosciences 11: 14-19,2016
References
• Menezes AH, Fenoy KA : Remnants of occipital vertebra: Proatlas Segmentation Anomalies. Neurosurgery 64: 945 -954;2009
• Pang D, Thompson DNP: Embryology and bony malformations of the CVJ. Childs Nerv Syst 27:523–564; 2011.