SPINAL DEFORMITIES IN NEUROFIBROMATOSIS

Introduction

• NF - hereditary hamartomatous disorder on neural crest derivation – appear from any organ system in body
• type 1 and 2
• classic – Type I – von Recklinghausen – auto dominant – Schwann cell tumors and pigmentation anomalies – spinal deformities
• central – Type II – auto dominant – less common – b/l acoustic neuromas – no bony/ orthopaedic involvement

Clinical criteria of NF I

• two of the following
  • minimum 6 cafe au lait spots larger than 1.5cm in post pubertal patient – larger than 5mm in prepubertal
  • 2 or more neurofibromas or 1 plexiform neurofibroma
  • freckling in inguinal/ axillary region
  • optic glioma
  • 2/more iris lisch nodules by slit lamp examination
  • distinct osseous lesion
  • first degree relative with definitive NF
• spinal deformity in NF two forms
  • non dystrophic
    • mimic idiopathic scoliosis
  • dystrophic
    • short segmented – sharply angulated curve with severe wedging of vertebral bodies – a/c angulation in sagittal plane – characteristic of NF kyphoscoliosis – striking deformity of vertebral body near apex
    • severe rotation of vertebrae – scalloping of vertebral bodies – spindling of transverse process – foraminal enlargement – rotation of the ribs 90⁰ in AP direction appears to be thin
    • functional scoliosis by leg length discrepancy
    • spinal deformity in dystrophic kyphoscoliosis – caused paraplegia ; not in dystrophic scoliosis alone
    • laminectomy when done alone worsens spinal cord compression in kyphoscoliosis

Treating non dystrophic NF

• same prognosis and evolution as idiopathic curves – except : higher risk of pseudo arthrosis after operative fusion
• spinal deformity before 7 yrs of age – closely observed for dystrophic changes : modulation – three penciled ribs – combination of 3 dystrophic features – clinical progression to dystrophic disease is certain
• treated same as idiopathic except watch for modulation
  • curves <20-25⁰ – observation
  • >30⁰ – brace
  • >40-45⁰ – posterior spinal fusion with segmental hook/ screw instrumentation
• CT myelography / MRI – before surgery to r/o any intraspinal canal NF

Treatment of dystrophic scoliosis

• brace not accepted in dystrophic curves
• surgical options decided by presence/ absence of kyphotic component and neurological deficits
• r/o intraspinal lesions : pseudomeningocele, dural ectasia, intraspinal neurofibromatosis ( dumbbell tumor) – impingement of this lesions on spinal cord after instrumentation
• Scoliosis w/o kyphosis
  • observed at 6 months interval if curve is <20⁰
  • curve progresses – posterior spinal fusion
  • >40⁰ – primary anterior and posterior spinal fusion – contraindicated in young age, osteoporosis, peculiar anatomical configurations
  • segmental hook/ screw instrumentation
  • spinal fusion mass inspected 1 yr after surgery – sooner if progression in curve occurs
• kyphoscoliosis
  • combined anterior and posterior spinal fusion
  • smaller scoliosis with kyphosis <40⁰ – posterior spinal fusion with arthrodesis – with periodic checking of fusion mass for progression
  • kyphosis >50⁰ – anterior disc excision – fibular strut bone grafting (vascularized rib graft augmentation) – posterior spinal fusion with instrumentation
  • anterior fusion should extend one or two levels past the both end vertebrae
  • fusion mass should be reexplores at least every 6 months
• kyphoscoliosis with spinal cord compression
  • cord compression by kyphosis should be differentiated from intra spinal lesion by investigations
  • severe scoliosis with paraplegia w/o significant kyphosis – assumed to have intra spinal lesions unless proved otherwise
  • laminectomy absolute CI – removal of valuable posterior bone available for fusion -aggravates the kyphosis
  • minor compression – halo pelvic traction
  • significant cord compression – anterior cord decompression – anterior strut graft fusion after this – posterior fusion as second stage
  • if intra spinal lesion is anterior causing cord compression – similar procedure
  • if lesion posterior – hemilaminectomy with tumor excision

Post op

• immobilized in cast/brace until fusion evident on AP, lateral, oblique X ray
• exploration of fusion mass periodically

Complications

• excessive bleeding
• pheochromocytoma
• patients without deficit developing paraplegia

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