The Comparative Morphometric Study of the Posterior Cranial Fossa : What Is Effective Approaches to the Treatment of Chiari Malformation Type 1?

Abstract

ObjectiveThe objective of this study was to investigate changes in the posterior cranial fossa in patients with symptomatic Chiari malformation type I (CMI) compared to a control group.MethodsWe retrospectively reviewed clinical and radiological data from 12 symptomatic patients with CMI and 24 healthy control subjects. The structures of the brain and skull base were investigated using magnetic resonance imaging.ResultsThe length of the clivus had significantly decreased in the CMI group than in the control group (p=0.000). The angle between the clivus and the McRae line (p<0.024), as the angle between the supraocciput and the McRae line (p<0.021), and the angle between the tentorium and a line connecting the internal occipital protuberance to the opisthion (p<0.009) were significantly larger in the CMI group than in the control group. The mean vertical length of the cerebellar hemisphere (p<0.003) and the mean length of the coronal and sagittal superoinferior aspects of the cerebellum (p<0.05) were longer in the CMI group than in the control group, while the mean length of the axial anteroposterior aspect of the cerebellum (p<0.001) was significantly shorter in the CMI group relative to control subjects.ConclusionWe elucidate the transformation of the posterior cranial fossa into the narrow funnel shape. The sufficient cephalocaudal extension of the craniectomy of the posterior cranial fossa has more decompression effect than other type extension of the craniectomy in CMI patients.

Prevalence of Chiari type I malformation on cervical magnetic resonance imaging: a retrospective study

“…[4,11,17] The patients with cerebellar tonsils below that line were divided into three groups: patients with a herniation of 3-5 mm, 5-10 mm and over 10 mm (Figure 1). …”

“…[2,3,6,11,15,19] There may be a variety of symptoms and signs in Chiari malformation type I. Patients may be asymptomatic, may have nonspecific symptoms, or they may have progressive and severe neurological deficits.…”

“…More frequent in females, it usually causes symptoms in third and fourth decades, and it is also called as the "adult form". [1,3,6,[8][9][10][11][12] Although there are a number of hypotheses proposed, its etiology is still not clear. These hypotheses include bony malformation at the craniocervical junction, small posterior fossa cranial defects caused by hypoplasia of the basilar part of the occipital bone or platybasia, vertebral defects, traction, and primary mesodermal insufficiency.…”

“…Chiari type I is the caudal herniation of cerebellar tonsils through foramen magnum by no more than 3 or 5 mm. [1,3,4,6,7,[9][10][11] In Chiari type II, there is a caudal herniation of the brainstem and the fourth ventricle into upper cervical canal through foramen magnum, frequently associated with myelomeningocele, and rarely associated with spina bifida occulta. Chiari type III is the most severe form in which posterior fossa structures herniate into an occipitocervical meningocele sac.…”

“…These hypotheses include bony malformation at the craniocervical junction, small posterior fossa cranial defects caused by hypoplasia of the basilar part of the occipital bone or platybasia, vertebral defects, traction, and primary mesodermal insufficiency. [3,6,7,11,13] It was postulated that a small posterior fossa caused Chiari malformation type I due to a congenital abnormality of cephalic mesoderm causing occipital hypoplasia or to early stenosis of sphenooccipital synchondrosis. [14] Neurological signs and symptoms of different severities that increase in time occur in Chiari type I.…”