Stereological and Morphometric Analysis of MRI Chiari Malformation Type-1

Abstract

Objective: In this study, we aimed to investigate the underlying ethiological factors in chiari malformation (CM) type-I (CMI) via performing volumetric and morphometric length-angle measurements.

Methods: A total of 66 individuals [33 patients (20-65 years) with CMI and 33 control subjects] were included in this study. In sagittal MR images, tonsillar herniation length and concurrent anomalies were evaluated. Supratentorial, infratentorial, and total intracranial volumes were measured using Cavalieri method. Various cranial distances and angles were used to evaluate the platybasia and posterior cranial fossa (PCF) development.

Results: Tonsillar herniation length was measured 9.09±3.39 mm below foramen magnum in CM group. Tonsillar herniation/concurrent syringomyelia, concavity/defect of clivus, herniation of bulbus and fourth ventricle, basilar invagination and craniovertebral junction abnormality rates were 30.3, 27, 18, 2, 3, and 3 percent, respectively. Absence of cisterna magna was encountered in 87.9% of the patients. Total, IT and ST volumes and distance between Chamberlain line and tip of dens axis, Klaus index, clivus length, distance between internal occipital protuberance and opisthion were significantly decreased in patient group. Also in patient group, it was found that Welcher basal angle/Boogard angle increased and tentorial slope angle decreased.

Conclusion: Mean cranial volume and length-angle measurement values significantly decreased and there was a congenital abnormality association in nearly 81.5 percent of the CM cases. As a result, it was concluded that CM ethiology can be attributed to multifactorial causes. Moreover, congenital defects can also give rise to this condition.

Keywords: Cavalieri method; Chiari malformation; MRI; Morphometry.

Fig. 1. A MR imaging of Chiari malformation type-I. ^*Tonsillar herniation.

Fig. 2. A MR imaging of McRae line (a), Chamberlain line (b), Klaus index (c), clivus length (d), Twining line (e), and length of supraocciput line (f).

Fig. 3. A MR imaging of Welcher basal angle (a), Wackenheim klivus angle (b) and Slope of Tentorium Cerebelli (c).

Fig. 4. A MR imaging of Basal angle (a), Boogard angle (b), Nasion-basion-opisthion (N-B-O) angle (c), and Tentorium Cerebelli-Twining Line angle (d).

Fig. 5. The midsagittal MRI for the cranial fossa and cerebellum with a grid overlaid for the calculation of volumes using the Cavalieri method.

Fig. 6. The distribution of abnormalities associated with cerebellar tonsil herniation in cases with CMI.