Association of Chiari malformation type I and tethered cord syndrome: preliminary results of sectioning filum terminale

Abstract

Objective The pathogenesis of CM-I is incompletely understood. We describe an association of CM-I and TCS that occurs in a subset of patients with normal size of the PCF. Methods The prevalence of TCS was determined in a consecutively accrued cohort of 2987 patients with CM-I and 289 patients with low-lying cerebellar tonsils (LLCT). Findings in 74 children and 244 adults undergoing SFT were reviewed retrospectively. Posterior cranial fossa size and volume were measured using reconstructed 2D computed tomographic scans and MR images. Results were compared to those in 155 age- and sex-matched healthy control individuals and 280 patients with generic CM-I. The relationships of neural and osseus structures at the CCJ and TLJ were investigated morphometrically on MR images. Intraoperative CDU was used to measure anatomical structures and CSF flow in the lumbar theca. Results Tethered cord syndrome was present in 408 patients with CM-I (14%) and 182 patients with LLCT (63%). In 318 patients undergoing SFT, there were no significant differences in the size or volume of the PCF as compared to healthy control individuals. Morphometric measurements demonstrated elongation of the brain stem (mean, 8.3 mm; P < .001), downward displacement of the medulla (mean, 4.6 mm; P < .001), and normal position of the CMD except in very young patients. Compared to patients with generic CM-I, the FM was significantly enlarged (P < .001). The FT was typically thin and taut (mean transverse diameter, 0.8 mm). After SFT, the cut ends of the FT distracted widely (mean, 41.7 mm) and CSF flow in the lumbar theca increased from a mean of 0.7 cm/s to a mean of 3.7 cm/s (P < .001). Symptoms were improved or resolved in 69 children (93%) and 203 adults (83%) and unchanged in 5 children (7%) and 39 adults (16%) and, worse, in 2 adults (1%) over a follow-up period of 6 to 27 months (mean, 16.1 months ± 4.6 SD). Magnetic resonance imaging 1 to 18 months after surgery (mean, 5.7 months ± 3.8 SD) revealed upward migration of the CMD (mean, 5.1 mm, P < .001), ascent of the cerebellar tonsils (mean, 3.8 mm, P < .001), reduction of brain stem length (mean, 3.9 mm, P < .001), and improvement of scoliosis or syringomyelia in some cases. Conclusions Chiari malformation type I/TCS appears to be a unique clinical entity that occurs as a continuum with LLCT/TCS and is distinguished from generic CM-I by enlargement of the FM and the absence of a small PCF. Distinctive features include elongation and downward displacement of the hindbrain, normal position of the CMD, tight FT, and reduced CSF flow in the lumbar theca. There is preliminary evidence that SFT can reverse moderate degrees of tonsillar ectopia and is appropriate treatment for cerebellar ptosis after Chiari surgery in this cohort.

The Relationship of the Posterior Cranial Fossa, the Cerebrum, and Cerebellum Morphometry with Tonsiller Herniation

“…This length was found to be smaller in CMI patients in the literature, with researchers reporting that the difference was statistically significant (4,8,20,26,29,30). In this study, we found that the length of the supraocciput was 37.22 ± 4.17 mm in the CMI patients and 40.29 ± 4.79 mm in the controls.…”

“…On the other hand, despite a larger diameter of the foramen magnum ın the CMI group, Karagoz et al (20), Sekula et al (3), and Milhorat et al (29,30) reported that the difference was not statistically significant.…”

“…Milhorat et al (30) defined herniation as tonsilla cerebelli lying more than 5 -7 mm below the level of the foramen magnum; those authors described a prolapse of 0 -4 mm as cerebellar tonsils.…”

Are herniated cerebellar tonsils the main culprit of chiari malformation type i symptoms? brainstem compression hypothesis seems to be re-elucidated and revised

“…The association of CM I and TCS, in which pathophysiological mechanisms are not clearly understood, has been reported only a few times previously (2,7,10,16). In this article, the authors reported 7 patients with association of CM I and TCS, who were managed by cutting the filum terminale only with good outcomes.…”

“…However, the additional complaints of these cases that are related to tethered cord directed us to discuss whether these symptoms may be related to tethered spinal cord instead of CM I. Spinal somatosensory evoked potential (SSEP) study performed on these cases and conduction delay or blockade was considered a positive clue for tethered spinal cord, and we have performed surgical untethering procedure on these cases before an approach for herniated cerebellar tonsils as suggested by Milhorat et al (7).…”