Published by ICSEB at 20 July, 2009
Surgical Neurology 72 (2009) 20-35. English.
Harvey Institute for Medical Genetics, Greater Baltimore Medical Center, Baltimore, MD 21204, USA cNational Institute on Aging, National Institutes of Health, Bethesda, MD 21224, USA Received 4 September 2008; accepted 5 March 2009.
Department of Neurosurgery, The Chiari Institute, Harvey Cushing Institutes of Neuroscience, North Shore-Long Island Jewish Health System, Manhasset, NY 11030, USA
Thomas H. Milhorat, MDa,⁎, Paolo A. Bolognese, MDa, Misao Nishikawa, MD, PhDa,
Clair A. Francomano, MDb, Nazli B. McDonnell, MD, PhDc,
Chan Roonprapunt, MD, PhDa, Roger W. Kula, MDa
An association of CM-I and TCS is described that mimics generic CM-I but is distinguished from it by the presence of a normally sized PCF. Typically, the FT is thin and taut and the CMD is positioned above the lower endplate of L2. TCS was found to be accompanied by varying degrees of tonsillar herniation and was particularly common in patients with LLCT. Associated abnormalities included cerebellar ptosis in patients with failed Chiari surgery, terminal thoracic syringomyelia, and idiopathic scoliosis. The most reliable diagnosis of occult spinal cord tethering was made by morphometric evidence of brain stem elongation, downward displacement of the hindbrain, and enlargement of the FM. The absence of a hypoplastic PCF and the presence of an enlarged FM are consistent with cord-traction as the proximate cause of tonsillar ectopia. The apparently contra- dictory phenomenon of a normally positioned CMD may be explained by variations in the elasticity and plasticity of the tight FT which allow the conus to ascend with somatic growth while maintaining some degree of pathological tension. Simple SFT may be effective in relieving sympto- matology, restoring normal brain stem length, normalizing the position of the cerebellar tonsils, and, in many cases, avoiding the need for posterior fossa surgery.
Abbreviations: 4VH, height of the fourth ventricle; ADHD, attention deficit hyperactivity disorder; BSL, axial length of the brain stem; CCJ, craniocervical junction; CDU, color Doppler ultrasonography; CM-I, Chiari malformation type I; CMD, conus medullaris; CSF, cerebrospinal fluid; CT, computed tomography; EMG, electromyography; FM, foramen magnum; FT, filum terminale; KPS, Karnofsky Performance Scale; LLCT, low-lying cerebellar tonsils; MH, height of the medulla; MR, magnetic resonance; MTH, minimal tonsillar herniation; PCF, posterior cranial fossa; PCFV, posterior cranial fossa volume; PFBV, posterior cranial fossa brain volume; SFT, section of the FT; SSEP, somatosensory evoked potential; TCS, tethered cord syndrome; TLJ, thoracolumbar junction; TH, tonsil herniation.
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