Obex position is associated with syringomyelia and use of posterior fossa decompression among patients with Chiari I malformation

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Chiari I malformation (CM-I) has traditionally been defined by measuring the position of the cerebellar tonsils relative to the foramen magnum. The relationships of tonsillar position to clinical presentation, syringomyelia, scoliosis, and the use of posterior fossa decompression (PFD) surgery have been studied extensively and yielded inconsistent results. Obex position has been proposed as a useful adjunctive descriptor for CM-I and may be associated with clinical disease severity.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>A retrospective chart review was performed of 442 CM-I patients with MRI who presented for clinical evaluation between 2003 and 2018. Clinical and radiological variables were measured for all patients, including presence/location of headaches, Chiari Severity Index (CSI) grade, tonsil position, obex position, clival canal angle, pB-C2 distance, occipitalization of the atlas, basilar invagination, syringomyelia, syrinx diameter, scoliosis, and use of PFD. Radiological measurements were then used to predict clinical characteristics using regression and survival analyses, with performing PFD, the presence of a syrinx, and scoliosis as outcome variables.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Among the radiological measurements, tonsil position, obex position, and syringomyelia were each independently associated with use of PFD. Together, obex position, tonsil position, and syringomyelia (area under the curve [AUC] 89%) or obex position and tonsil position (AUC 85.4%) were more strongly associated with use of PFD than tonsil position alone (AUC 76%) (P<jats:sub>diff</jats:sub> = 3.4 × 10<jats:sup>−6</jats:sup> and 6 × 10<jats:sup>−4</jats:sup>, respectively) but were only slightly more associated than obex position alone (AUC 82%) (P<jats:sub>diff</jats:sub> = 0.01 and 0.18, respectively). Additionally, obex position was significantly associated with occipital headaches, CSI grade, syringomyelia, and scoliosis, independent of tonsil position. Tonsil position was associated with each of these traits when analyzed alone but did not remain significantly associated with use of PFD when included in multivariate analyses with obex position.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>Compared with tonsil position alone, obex position is more strongly associated with symptomatic CM-I, as measured by presence of a syrinx, scoliosis, or use of PFD surgery. These results support the role of obex position as a useful radiological measurement to inform the evaluation and potentially the management of CM-I.</jats:p></jats:sec>

Cerebellar tonsil reduction for surgical treatment of Chiari malformation type I in children

“…9,24,[30][31][32] A recent study by Haller et al found that a low obex position was a stronger predictor than tonsillar ectopia for predicting whether the patient underwent surgery. 33 Also, recently Alford et al showed that greater tonsil length was associated with increased risk for surgery. 34 To our knowledge, however, the present study is the first study to demonstrate that tonsil length is an independent predictor of a more invasive surgical technique.…”

A Novel Craniocervical Junction Compression Severity Index-Based Grading System for Multidirectional Quantification of the Biomechanics at Foramen Magnum of Chiari Malformation Type I

“…Considering that the CVJ is a crucial anatomical location for the onset and decompression of CMIs 31,[34][35][36][37] and based on our previous study about ventral compression, 10 we developed a comprehensive index, the CVJCSI, that can fully reflect the CVJ compression of CMIs to guide treatment. To ensure that the CVJCSI would fully reflect the CVJ compression and data from previous studies, the TH, [23][24][25][38][39][40][41] brainstem hernia (obex option), 6,8,[42][43][44] and CVJ ventral compression 10 were considered as CVJCSI factors.…”

Phenotypes and Prognostic Factors of Syringomyelia in Single-Center Patients With Chiari I Malformation: Moniliform Type as a Special Configuration

“…13 There have been numerous case series of pediatric and adult patients describing clinical presentation and prognosis following surgical procedure, with widely varying surgical outcomes. [14][15][16][17][18] Neither the extent of tonsillar herniation nor the size of the posterior cranial fossa would necessarily predict the presence or resolution of syringomyelia and surgical outcome. 17,[19][20][21] Therefore, there may be other factors playing a role in the pathogenesis and prognosis of syringomyelia.…”

“…[14][15][16][17][18] Neither the extent of tonsillar herniation nor the size of the posterior cranial fossa would necessarily predict the presence or resolution of syringomyelia and surgical outcome. 17,[19][20][21] Therefore, there may be other factors playing a role in the pathogenesis and prognosis of syringomyelia. The morphometric characteristics of the syrinx in CM-I patients may contain different parameters, such as the size, length, configuration, and deviation of the syrinx, while the specific association between morphometric characteristics of syrinx with the prognosis seems to have not been elaborated.…”