Computed tomographic study of posterior cranial fossa, foramen magnum, and its surgical implications in Chiari malformations

Abstract

Objective: The aim of this study is to measure the height and volume of the bony part of the posterior cranial fossa (PCF) and the surface area of the foramen magnum (FM) using computed tomography (CT) scans and to correlate our clinical findings with the available current literature.

Materials and methods: This cross-sectional study was conducted in a tertiary care referral hospital in the Southern part of India during the period from January 2015 to August 2015. A total of 100 CT scans of the suspected head injury patients were collected retrospectively form the basis for this study. The height, volume of PCF and the anteroposterior (AP), transverse diameter, and surface area of the FM were measured. The values of all parameters were subjected to statistical analysis using SPSS version 16.

Results: The age of the patients were ranged between 18 and 70 years with the mean age of 41.22 ± 13.93 years. The dimensions of the posterior fossa and FM were larger in males compared to females. The mean height of the posterior fossa was 38.08 (±4.718) mm (P = 0.0001), and the mean volume of the posterior fossa was 157.23 (±6.700) mm³ (P = 0.0001). The mean AP, transverse diameter, and the surface area of the FM were 33.13 (± 3.286) mm, 29.01 (± 3.081) mm, and 763.803 (±138.276) mm², respectively.

Conclusion: The normal dimensions of the posterior fossa and FM were less in females than males and were useful to radiologists and neurosurgeons to better their diagnostic inferences, as well as to determine the proper treatment options in Chiari malformation type I (CMI) and other posterior fossa anomalies. The posterior fossa tissue volume can be reliably measured in patients with CMI using our method. More studies were required because there were variations in dimensions among individuals of different races in different regions of the world.

Keywords: Chiari malformation type I; computed tomography scans; foramen magnum; posterior cranial fossa.

Figure 1

(a) Brain computed tomography midsagittal film demonstrating the boundaries of posterior fossa. (b) Brain computed tomography midsagittal film (bone window) demonstrating the measurement of height of the posterior fossa. DS – Dorsum sellae; IOC – Internal occipital crest; TL – Twining's line; BS – Basion; OS – Opisthion; ML – McRae's line; H – Height of posterior fossa. (c) Brain computed tomography axial film demonstrating anteroposterior and transverse diameters of posterior cranial fossa. DS – Dorsum sellae; IOC – Internal occipital crest; PT – Base of Petrous temporal; APD – Anteroposterior diameter; TD – Transverse diameter. (d) Brain computed tomography axial film (bone window) demonstrating the measurement of anteroposterior and transverse diameters of posterior cranial fossa. (e) Brain computed tomography axial film demonstrating anteroposterior and transverse diameters of foramen magnum. (f) Brain computed tomography axial film (bone window) demonstrating the measurement of anteroposterior and transverse diameters of foramen magnum. BS – Basion; OS – Opisthion; APD – Anteroposterior diameter; TD – Transverse diameter

Figure 2

(a) Posterior fossa height (mm) in relation to genders. (b) Posterior fossa volume (mm3) in relation to genders. (c) Anteroposterior diameter (mm) of foramen magnum in relation to genders. (d) Transverse diameter (mm) of foramen magnum in relation to genders. (e) Surface area (mm²) of foramen magnum in relation to genders