Pediatric CCJ Companion Nadja Kadom, Gilbert Vezina, Raymond Sze

C-spine measurements Trauma Basilar Invagination Platybasia

Assess the C-Spine/skull base Trauma: Alignment Soft tissue swelling Occiput-C1 dissociation C1-C2 instability Basilar Invagination Chamberlain McGregor Platybasia Standard Modified

Trauma

Prevertebral/Retropharyngeal Soft Tissues False thickening: flexion, end of expiration FlexedExtended

Prevertebral/Retropharyngeal Soft Tissues Normal thickness: < 7 mm anterior to C2 and < 5 mm anterior to C3/C4 or less than half the diameter of the vertebral bodies

Prevertebral/Retropharyngeal Soft Tissues Loss of physiological mucosal step off ~C4/5 is ABNORMAL! Step-off ~ C4-6 Lost step-off

Alignment

Soft Tissue Swelling In children: Retropharyngeal tissues should NOT exceed 1/2 to 2/3 vertebral body AP diameter

Evaluate Occiput-C1 dissociation: Suggestion: Get C0-C2 CT scan Landmarks not seen on x-ray, get limited CT

CT Basion-Dens-Interval (BDI): 8.37 (pediatric normal < 12.5 mm) Basion-Axial Line-Interval (BAI): 5.56 (adult normal < 12 mm)

Other methods Power ratio Lee X

Power Ratio A = the anterior tubercle of the atlas. B.= the basion. C = the spinolaminar line of the atlas. O = the opisthion The value BC/AO should be less than 1. BC/AO = 30.21/39.59 < 1 normal

C1-C2 instability Atlanto-dens interval (ADI) and posterior atlanto-dens interval (PADI) ADI = 3.24 mm (normal < 5 mm) PADI = (abnormal < 13 mm)

Occiput-C1 Pathology Axial dislocation (dislocation in the axial plane, anterior or posterior “listhesis” of occiput versus C1, best seen on sagittal images) Sagittal dislocation (dislocation in the sagittal plane, increased height of space between occipital condyles and C1 articulation, seen on coronal and sagittal images)

Occipital Condyle-C1 Interval (CCI) 1. CCI physiologically narrow normal pediatric mean is 1.28 mm, normal range mm 2. The left and right OC1 joints are normally highly symmetrical RightLeft

Example of CCI enlargement

Example of asymmetry

Wackenheim line Assess antlanto-occipital dissociation Line along the posterior border of the clivus should inferiorly touch the odontoid tangentially

Examples NormalPosterior dislocation

Rotatory subluxation C1-C2 4 types Assess the facet joints, look for: => displaced facets on sagittal views => visualization of both articular surfaces in one axial image

Type I: simple rotatory displacement; < 3 mm with an intact transverse ligament. Type II: anterior displacement of C1 on C2 of 3-5 mm (one lateral mass serving as a pivot point) + deficiency of the transverse ligament. Type III: injuries involve > 5 mm of anterior displacement. Type IV: injuries involve the posterior displacement of C1 on C2. Both Type III and IV are highly unstable injuries.

Basilar Invagination

Definition The tip of the dens projects more than 5 mm above Chamberlain's line Or the tip of the dens is >7 mm above McGregor's line

Chamberlain’s line line joining the hard palate to the posterior lip of the foramen magnum

McGregor’s line the back of the hard palate to the lowest point of the occipital squama

Platybasia Standard technique: measuring the angle formed by two lines: 1 st line: nasion to center of the pituitary fossa 2 nd line: anterior border of foramen magnum with center of the pituitary fossa (= tip of clivus to center of pituitary) Normal: Adult: 129° +/- 6° Pediatric: 127° +/- 5° Koenigsberg RA, Vakil N, Hong TA, Htaik T, Faerber E, Maiorano T, Dua M, Faro S, Gonzales C. Evaluation of platybasia with MR imaging. AJNR Am J Neuroradiol Jan;26(1):89-92.

Standard: Pediatric: 127° +/- 5°

Platybasia Modified technique: Uses different landmarks measuring the angle formed by two lines: 1 st line: extending across the anterior cranial fossa to the tip to the dorsum sellae 2 nd line: connecting with a line drawn along the posterior margin of the clivus Normal: Adult: 117° +/- 6° Pediatric: 114.4° +/- 5°

Modified: Pediatric: 114.4° +/- 5°