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.