Neural groove- dorsum of embryoDeepens- FurrowCloses- Neural canalCENTRAL NERVOUS SYSTEM4thweek of IUL
Lumen persists as – Central neural canal. Closure◦ Starts in cervical region◦ Proceeds caudally & cranially◦ Cranium closing last – 26 days Neural tube◦ Proliferating cells of neuroepithelium differentiate –NEUROBLASTS or NEURONS. Motor axons – out growing processes. Sensory neurons – from neural crests (Ectoderm & Postsurface of neural tube).
Meninges – arise from loose mesenchymaltissue surrounding the N. tube.◦ Pia mater – 40 days◦ Dura – later. Neural canal separates from ectodermalcovering – ingrowth of mesoderm. Notochord –◦ solid rod of cells◦ Anterior to N. canal Vertebral bodies develop around this all.
From each of the Vertebral bodies◦ Extend backwards 2 projections◦ Grow around N. canal◦ Form – Vertebral arch◦ Fuse behind thoracic region – extend up & down.
FUSION FAILS – Gap in vertebral N arch SPINA BIFIDA◦ m.c. in Lumbosacral region
Latin word for “split spine”. Literally means “cleft spine,” Most common group of birth defects called neuraltube defects (NTD). Incidence◦ World wide about 1 per 1000 live births.
Antenatal screening of AFP - 15–18 mths.◦ Identify at risk women.◦ If high AFP – Amniocentesis and USG. Previous neural tube defect fetus –◦ 10 fold increased risk◦ 50 fold for third pregnancy. Genetic predisposition. Some environmental factors
The exact cause of spina bifida remains amystery. Genetic, nutritional, and environmentalfactors may play a role. Combination of genetic and environmental riskfactors, such as a family history of neural tubedefects, folic acid deficiency and medicalconditions such as diabetes and obesity.
Race: more common among Hispanics andwhites of European descent. Family history of neural tube defects.However, most babies with spina bifida are bornto parents with no known family history of thecondition.
Folic acid deficiency (vitamin B-9)increases the risk of spina bifida and otherneural tube defects.◦ MRC recommend F. acid supplimentation for high riskmothers. Some medications. Anti-seizure medications,such as valproic acid, seem to cause neuraltube defects when taken during pregnancy,perhaps because they interfere with the bodysability to use folic acid.
Diabetes: Especially when the mothers bloodsugar is elevated early in her pregnancy. Muchof this risk is preventable by careful blood sugarcontrol and management. Obesity. Theres a link between pre-pregnancyobesity and neural tube birth defects, includingspina bifida. Obese women may have morebabies with spina bifida possibly because ofnutritional deficits from poor eating habits orbecause they may have diabetes.
Increased body temperature. Some evidencesuggests that increased body temperature(hyperthermia) in the early months of pregnancymay increase the risk of spina bifida. Contaminated potatoes – blamed in humans. Experimental defects – Vit A def., Azodyes, X rays& disturbed Zn metabolism.
Von Recklinghausen 1886◦ Due to failure of the posterior mass of neural tube.
Saccular trusion ofonly meninges Pia & Arachnoid Dura stops at bonymargins Spinal cord is not involved No paralysis Sac contains only CSF
5 % of Spina bifida cystica. Surgical closure required – to prevent rupture andmeningitis. Associated lesions◦ Lipomata◦ Cyst formation◦ Dilation of spinal canal – hydromyelin.
Majority of SBC Gap in spinal columnthrough which protrudes1. Flat plaque of N. tissue.2. Meninges surrounding it. Spinal cord – open on theback surface for 3-4segments.
Plaque and meninges – enlarge to sac –increasing CSF within few hours of birth. Sac – burst – during or just after birth. CSF leak – infection. 3 Zones on surface:1. Central neural plaque (Vasculosa)2. The meninges (Serosa)3. Surrounding hairy & thickened skin (Dermatica)
Spinal cord is spread out to form lining of the sac& is thinned into a cyst by distension of centralcanal of the cord.
Myelocele:◦ Gross spinal cord deformity◦ Elongated fissure surrounded by telangiectases or hair –in direct contact with central canal.◦ m.c. in lumbosacral region. Anterior Spina Bifida◦ Very rare – anterior defect.
Often unnoticed Incidentally on radiograph. Spinal cord and meninges normal One or more bony arches are incompletely closedposteriorly. Dura may be attached to skin – fibrous band –MEMBRANA REUNIENS
Lipomata or Angiomata – in or outside thevertebral canal. Hairy patch – overlying skin. Membrana reuniens doesn’t elongate with growth– traction lesion of cord – praralytic deformity of Llimbs or bladder.
Called by Till - Occult spinal dysraphism:1. Diplomyelia2. Diastematomyelia3. Others – Intraspinal lipomata or hydromyelia of centralcanal. Urinary incontinence, neurological abnormalities(esp in L limbs) or meningitis by infected dermalsinus. Need Radiography, myelography or MRI beforesurgery.
The American Academy of OrthopaedicSurgeons Committee for the Care of theHandicapped Child (1974)1. Open defects:1. Myelomeningocele (Hydromyelia, dysraphismrachischisis)2. Meningocele3. Dermal sinus.
Closed defects:1. Spina bifida occulta:1. Diastematomyelia2. Intraspinal tumor (Lipoma, chondroangioma,dermoid).2. Myelodysplasia:1. Aplasia or hypoplasia of nerve roots or cord.2. Absent anterior horn cells (Arthrogryposis)3. Diplomyelia (Double cord)
3. Errors in skeletal segmentation:1. Absence of sacrum2. Absent lumbar vertebrae3. Hemivertebrae4. Congenital segmental fusion5. Failure of fusion or absent odontoid process6. Others.
Stark & Baker (1967) – two main types:◦ TYPE-I (~33%) – Complete loss of all spinal cord funtionbelow the lesion level – flaccid paralysis, sensorydeficiency & absent reflexes.◦ TYPE-II (~66%) – Preservation of reflex activities fromintact distal segment but interruption corticospinal tractswith paralysis. Three subgroups depending on severity.
Early operation at 48 hrs. without selection – Initialoptimism – by Sharrard◦ Survival rate improved◦ Quality of life – pitiful.
Lorber 1971 defined factors associated with badprognosis – used as basis for selection:◦ Gross paralysis in TLS region.◦ Esp with scoliosis or kyphosis◦ Enlarging hydrocephalus◦ Intracerebral injury◦ Heart abnormality◦ Meningitis or gross mental disturbance.
Principles of combined management – bySharrard et. al in Sheffield – directed to 5 majorproblems:1. Myelomeningocele2. Hydrocephalus3. Urinary tract paralysis4. Locomotor system5. Education
To achieve INDEPENDENCE asfar as possible. Role of Orthopaedic surgeon –provide – by surgical or nonsurgical means, the ability to sitand stand as well as effective butnot excessive demandingwalking.
Surgical closure of myelomeningocele – wheneverindicated – within 48hrs. Baseline neurological examination, headcircumference & assessment of any hipdislocation. Hydrocephalus drained from dilated lateralventricle.