The odontoid process invagination in normal subjects, Chiari malformation and Basilar invagination patients: Pathophysiologic correlations with angular craniometry

Abstract

Background: Craniometric studies have shown that both Chiari malformation (CM) and basilar invagination (BI) belong to a spectrum of malformations. A more precise method to differentiate between these types of CVJM is desirable. The Chamberlain's line violation (CLV) is the most common method to identify BI. The authors sought to clarify the real importance of CLV in the spectrum of craniovertebral junction malformations (CVJM) and to identify possible pathophysiological relationships.

Methods: We evaluated the CLV in a sample of CVJM, BI, CM patients and a control group of normal subjects and correlated their data with craniocervical angular craniometry.

Results: A total of 97 subjects were studied: 32 normal subjects, 41 CM patients, 9 basilar invagination type 1 (BI1) patients, and 15 basilar invagination type 2 (BI2) patients. The mean CLV violation in the groups were: The control group, 0.16 ± 0.45 cm; the CM group, 0.32 ± 0.48 cm; the BI1 group, 1.35 ± 0.5 cm; and the BI2 group, 1.98 ± 0.18 cm. There was strong correlation between CLV and Boogard's angle (R = 0.82, P = 0.000) and the clivus canal angle (R = 0.7, P = 0.000).

Conclusions: CM's CLV is discrete and similar to the normal subjects. BI1 and BI2 presented with at least of 0.95 cm CLV and these violations were strongly correlated with a primary cranial angulation (clivus horizontalization) and an acute clivus canal angle (a secondary craniocervical angle).

Keywords: Arnold–Chiari malformation; basilar impression; cephalometry; platybasia.

Figure 1

Chiari malformation patient. Solid line is the Chamberlain's line. Dotted arrow above CL represent Chamberlain's line violation

Figure 2

Basilar Invagination type 1. Note that in all cases the odontoid process is inside foramen magnum. The white arrows point to the anterior atlas assimilation and black arrow point to the posterior atlas assimilation. D: Dorsum sellae; B: Basium; O: Opistium

Figure 3

Type 2 Basilar Invagination. At left, CT scan. Lower black line represents Chamberlain's Line (CL). Upper line represents foramen magnum line. Black arrow is inserted in the C2 axis. The Odontoid above CL is the amount of odontoid CL violation

Figure 4

Control group image. Note the odontoid tip at the Chamberlain's line and the vertical clivus

Figure 5

Type 2 Basilar invagination. The red line is the Chamberlain's Line (CL). The dotted red arrow represents CLV. Dotted white lines above represents Welcher's angle. The angle formed by the inferior dotted white line and solid black line is the Boogard's angle. The vertical lines along with C2 and C7 axis forms the cervical spine lordosis angle

Figure 6

At left are represented the primary angles: Basal angle (Welcher) and Boogard's angle. The Chamberlain's line is represented from the hard palate to the opistion. At right are represented secondary craniocervical angles: Clivus canal angle and cervical lordosis

Figure 7

The Chamberlain's line violation by odontoid process in Control group, Chiari malformation, Basilar type1 (BI1) and Type 2 groups (BI2). Upper and lower values are the 95% confidence limit values and the median value is the media of sample values

Figure 8

Illustration of descriptive statistcs for Chamberlain's line violation, Boogard's angle, Clivus canal angle, cervical lordosis angles (Lordosis) and Welcher's angle (Welcher). In the x-axis, 1, 2, 3, and 4 is referred to control group, Chiari malformation, Basilar Invagination type 1 and Basilar invagination type 2 groups, respectively. Note that as the as the CLV increases, Boogard's values increase and Clivus canal and Cervical lordosis angle decrease

Figure 9

Scatter dot plot. Upper part: At left, data from CLV are plotted against Boogard's angle. The “R” numbers are referred to the amount of correlation between data. At right, data from CLV and Clivus canal angle are plotted. Lower left: Relation between cervical lordosis angle and CLV. At right, relation between Welcher angle and CLV

Figure 10

Upper part: T1 (left) and T2 acquisitions showing BI1. Note the ventral cord and brainstem compression by odontoid process. Lower part: CT scan sagittal reconstruction. At left, the odontoid process in inside foramen magnum (Dotted line passing below anterior assimilated C1 arc)

Figure 11

The importance of head in reducing BI1. Note the reduction of ventral brainstem compression and CLV with extension of head and caniocervical junction kyphosis normalization