title: Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect.
abstract: OBJECTIVE
  Limited dorsal myeloschisis (LDM) is a distinctive form of spinal dysraphism characterized by two constant features: a focal "closed" midline skin defect and a fibroneural stalk that links the skin lesion to the underlying cord. The embryogenesis is hypothesized to be incomplete disjunction between cutaneous and neural ectoderms, thus preventing complete midline skin closure and allowing persistence of a physical link (fibroneural stalk) between the disjunction site and the dorsal neural tube.
  
  
  OBJECTIVE
  We utilize the experience gained from the management of 63 patients with LDM to illustrate these features.
  
  
  METHODS
  All patients were studied with MRI or CT myelogram, operated on, and followed for a mean of 9.4 years.
  
  
  RESULTS
  There were 11 cervical, 16 thoracic, 8 thoracolumbar, and 28 lumbar lesions. Two main types of skin lesion were: saccular (26 patients; consisting of a skin base cerebrospinal fluid sac topped with squamous epithelial dome or a thin membranous sac) and nonsaccular (37 patients; with a flat or sunken squamous epithelial crater or pit). The internal structure of a saccular LDM could be a basal neural nodule, a stalk that inserts on the dome, or a segmental myelocystocoele. In nonsaccular LDMs, the fibroneural stalk has variable thickness and complexity. All fibroneural stalks contain glioneuronal tissues accompanied by variable quantities of nerves and mesodermal derivatives. In all LDMs, the fibroneural stalk was tethering the cord. Twenty-nine patients had neurological deficits. There was a positive correlation between neurological grade and age suggesting progression with chronicity. Treatment consisted of detaching the stalk from the cord. Most patients improved or remained stable. LDMs were associated with three other dysraphic malformations in more than coincidental frequencies: six LDMs were contiguous with dorsal lipomas, four LDMs shared the same tract or traveled in parallel with a dermal sinus tract, and seven LDMs were related to a split cord malformation. The embryogenetic implications of these associations are discussed.
  
  
  CONCLUSIONS
  LDM is a distinctive clinicopathological entity and a tethering lesion with characteristic external and internal features. We propose a new classification incorporating both saccular and flat lesions.
authors.affiliation: Paediatric Neurosurgery, University of California, Davis, USA. PangTV@aol.com
authors.forename: Dachling
authors.initials: D
authors.lastname: Pang
authors.forename: John
authors.initials: J
authors.lastname: Zovickian
authors.forename: Sui-To
authors.initials: ST
authors.lastname: Wong
authors.forename: Yong Jin
authors.initials: YJ
authors.lastname: Hou
authors.forename: Greg S
authors.initials: GS
authors.lastname: Moes
mesh_terms: D000328:Adult; D002648:Child; D002675:Child, Preschool; D006801:Humans; D054259:Neural Tube / Q000196:embryology*; D054261:Neurulation / Q000502:physiology*; D016135:Spinal Dysraphism / Q000150:complications / Q000473:pathology*