Table 1.
Morphometric analysis of the posterior cranial fossa in patients with cerebellar tonsil herniation stratified according to etiology
| Variable | Normal controls | CM-I | CM-I/OAAJI | CM-I/TCS |
|---|---|---|---|---|
| Total no. cases | 80 | 388 (52%) | 225 (30%) | 55 (7%) |
| Male/female | 25/55 | 111/277 | 44/181 | 15/40 |
| Mean age (years) | 31.7 ± 11.8 | 33.6 ± 10.1 | 31.4 ± 10.7 | 30.1 ± 11.4 |
| Occipital bone size | ||||
| Clivus | ||||
| Axial length (mm) | 47.0 ± 2.17 | 38.4 ± 3.27 (<0.001) | 45.7 ± 3.11 | 46.1 ± 3.24 |
| Distance between carotid canals (mm) | 20.4 ± 1.86 | 18.0 ± 3.02 (<0.001) | 20.2 ± 2.28 | 20.5 ± 2.40 |
| Supraocciput | ||||
| Axial length (mm) | 47.7 ± 2.52 | 39.6 ± 3.87 (<0.001) | 46.8 ± 3.23 | 47.0 ± 2.77 |
| Distance between asterions (mm) | 101.8 ± 3.73 | 96.8 ± 3.18 (<0.001) | 100.5 ± 6.34 | 102.3 ± 8.47 |
| Condyle | ||||
| Axial height right (mm) | 24.1 ± 1.75 | 18.7 ± 3.51 (<0.001) | 23.7 ± 2.87 | 23.6 ± 2.65 |
| Axial height left (mm) | 24.3 ± 1.54 | 19.1 ± 3.87 (<0.001) | 23.8 ± 3.01 | 24.0 ± 2.78 |
| Width of condyles (mm) | 50.5 ± 2.48 | 46.8 ± 3.69 (0.007) | 50.5 ± 4.33 | 55.2 ± 2.74 (<0.001) |
| Foramen magnum | ||||
| Anterior–posterior diameter (mm) | 32.5 ± 3.17 | 32.1 ± 3.72 | 33.2 ± 2.63 | 37.4 ± 2.41 (< 0.001) |
| Transverse diameter (mm) | 30.8 ± 3.74 | 26.7 ± 3.12 (<.001) | 30.8 ± 2.78 | 35.1 ± 2.71 (<0.001) |
| Inferior outlet area (mm²) | 787.7 ± 118.4 | 651.7 ± 121.8 (<0.001) | 802.7 ± 131.6 | 1,000.4 ± 123.8 (<0.001) |
| Superior outlet area (mm²) | 1,774.2 ± 128.2 | 1,523.5 ± 125.7 (<0.001) | 1,756.5 ± 124.5 | 2,001.3 ± 127.4 (<0.001) |
| Volumetric analysis | ||||
| PCFV (ml) | 190.1 ± 7.84 | 165.8 ± 8.17 (<0.001) | 188.2 ± 7.78 | 188.0 ± 8.72 |
| PCFV-ATL (ml) | 44.5 ± 5.22 | 48.1 ± 4.84 (<0.001) | 44.7 ± 4.96 | 45.2 ± 5.35 |
| PCFV-BTL (ml) | 145.7 ± 4.88 | 117.6 ± 8.65 (<0.001) | 143.5 ± 7.40 | 142.8 ± 7.20 |
| PFBV (ml) | 151.8 ± 3.14 | 148.7 ± 4.77 | 149.7 ± 4.77 | 150.5 ± 4.48 |
Numbers in parentheses denote P values. Results are expressed as mean values ± 1 SD. Abbreviations: CM-I Chiari malformation type I, OAAJI occipitoatlantoaxial joint instability, TCS tethered cord syndrome, PCFV posterior cranial fossa volume, ATL above Twining’s line, BTL below Twining’s line, PFBV posterior fossa brain volume