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. 2022 Aug 4;11(15):4556. doi: 10.3390/jcm11154556

Figure 1.

Figure 1

Figure 1

Illustrative cases: CM-I subtypes. (A): CM-I type A, (B): CM-I type B, (C): CM-I type C, and (D): CM-borderline. Left panel: 2D CT axial image at the level of the foramen magnum; right panel: magnetic resonance (MR) sagittal midline image. (E,F): MR midsagittal images demonstrating the character of CM-I type with HDCT. VPCF, VAFM, and occipital bone size are normal in size. (E): MR midsagittal image in supine position showing normal interval BDI (7.7 mm), normal BAI (3.5 mm), normal CXA) (141°), large retro-odontoid pannus (asterisk), and low-lying cerebellar tonsils. (F): Upon observation of the upright position, there is evidence of cranial settling (2.5 mm decrease in BDI), posterior gliding of occipital condyle, 4.3 mm increase in BAI, anterior flexion of the occipito–atlantal joint (decrease of 8° in CXA), and increased cerebellar ptosis with downward displacement cerebellar tonsils to C1 (white arrow). Note the significantly increased impaction of the foramen magnum anteriorly and posteriorly. Bilateral black dotted arrow = CXA, white arrow = tonsillar herniation. (G): MR midsagittal image demonstrating the character of CM-I type A with TCS. VPCF, VAFM, and occipital bone size are normal in size. MR image showing elongation and downward displacement of the brainstem and cerebellum, as well as large supracerebellar cistern (double asterisk). Abbreviations: CM-I = Chiari malformation type I, BDI = the interval between basion and dens, BAI = the interval between basion and atlas, CXA = the clivo-axial angle, HDCT = hereditary disorders of connective tissue, TCS = tethered cord syndrome.