Spinal Dysraphic Lesion

Bernadette L. Koch, MD

DIFFERENTIAL DIAGNOSIS

Common

Incomplete Fusion, Posterior Element
Myelomeningocele
Lipomyelomeningocele (LMM)
Lipomyelocele (LM)

Less Common

Diastematomyelia
Dorsal Dermal Sinus

Rare but Important

Meningocele, Dorsal Spinal
Terminal Myelocystocele
Segmental Spinal Dysgenesis

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Spina bifida: Incomplete closure of posterior bony elements
Spina bifida aperta = spina bifida cystica: Protrusion of spinal canal elements through posterior bony defect
- Simple meningocele: Dura and arachnoid, no neural elements
- Myelocele: Midline plaque of neural tissue exposed, flush with skin surface
- Myelomeningocele: Myelocele protrudes above skin surface + expansion of subarachnoid space posterior to placode
Occult spinal dysraphisms develop beneath intact skin surface
- Meningocele, diastematomyelia, split notochord syndrome, dorsal dermal sinus, fibrolipoma of filum terminale, spinal lipoma, lumbosacral hypogenesis, segmental spinal dysgenesis, myelocystocele

Helpful Clues for Common Diagnoses

Incomplete Fusion, Posterior Element
- Key facts: Spina bifida occulta
- Imaging
  - Incomplete fusion of spinous process/lamina without underlying neural or dural abnormality
- Lumbosacral > cervical > thoracic
Myelomeningocele
- Key facts: Open neural tube defect, lacks skin coverage
  - Level of dysraphism determines neurological deficit
  - Rarely image spine preoperatively
  - Postoperative spinal imaging if neurological decline despite adequate treatment of hydrocephalus or if neurologic exam suggests additional underlying lesions
- Imaging
  - CSF sac and neural elements protrude through wide osseous dysraphism
  - Fetal elongation of low-lying cord, usually in dorsal aspect of canal deep to skin-covered postoperative repair
- Associated abnormalities
  - Chiari 2 malformation (≈ 100% )
  - Hydrocephalus, kyphoscoliosis, segmentation anomalies, diastematomyelia and dermal sinus, syrinx, intraspinal dermoid/epidermoid, orthopedic abnormalities
Lipomyelomeningocele (LMM)/Lipomyelocele (LM)
- Key facts: Cutaneous stigmata in up to 50%; hemangioma, dimple, dermal sinus, skin tag, or hairy patch
- Imaging
  - LMM = spinal subarachnoid space expanded ventrally → placode, tethered cord, subarachnoid space, and dura extend dorsally through spina bifida
  - LM = tethered cord and junction between placode and lipoma within spinal canal, lipoma through bony defect
  - Lipoma attached to dorsal aspect of neural placode and contiguous with SQ fat
  - Dorsal and ventral nerve roots exit from ventral surface of placode
  - ± segmentation anomalies, sacral anomalies, syrinx, diastematomyelia, anorectal and GU abnormalities
Diastematomyelia
- Key facts: Majority between T9 and S1
- Imaging
  - Split cord malformation (SCM) = sagittal split into 2 hemicords ± fibrous, osteocartilaginous, or osseous spur
  - Pang type 1 SCM = separate dural sac, arachnoid space around each hemicord, separated by fibrous/osseous spur
  - Pang type 2 SCM = single dural sac and arachnoid space without spur ± adherent fibrous bands tethering cord
  - Nearly all reunite below split
  - ± thick filum, tethered cord, syringohydromyelia in 1 or both hemicords, myelocele, or MM
  - ± intersegmental laminar fusion ≈ pathognomonic for diastematomyelia

Helpful Clues for Less Common Diagnoses

Dorsal Dermal Sinus
- Key facts
  - Midline or rarely paramedian dimple or pinpoint ostium ± pigmented patch, hairy nevus, or cutaneous hemangioma
  - Differentiate from simple sacral dimple (< 2.5 cm from anus, extends inferiorly toward coccyx) and pilonidal sinus (low ostium, does not enter spine)
  - High suspicion if dimple above intergluteal fold
- Imaging
  - ↓ curvilinear tract through ↑ SQ fat May end in SQ tissue or extend into canal, terminating in conus medullaris, subarachnoid space, filum terminale, nerve root, fibrous nodule on surface of cord, or dermoid/epidermoid cyst
  - Dural “tenting” at dural penetration
  - LS > occipital > T > C spine
  - ± varying degrees of dysraphism; incomplete posterior element fusion → multilevel dysraphism
  - ± dermoid/epidermoid, abscess, or arachnoiditis
  - ± cord tethering in lumbosacral lesions

Helpful Clues for Rare Diagnoses

Meningocele, Dorsal Spinal
- Key facts: Skin covered
- Imaging
  - Meninges protrude through dysraphism into SQ fat
  - Cord tethering and syrinx rare
Terminal Myelocystocele
- Key facts: Large skin-covered mass, usually sacral/coccygeal
- Imaging
  - Hydromyelic tethered cord traverses dorsal meningocele, terminates in dilated terminal ventricle
Segmental Spinal Dysgenesis
- Key facts: Focal dysmorphic/hypoplastic vertebrae, meninges, and spinal cord with normal spine above and below
- Imaging
  - Dysplastic vertebrae → severe focal kyphosis
  - Thecal sac narrows and then terminates; spinal cord narrows and disappears rostral to thecal sac
  - Thecal sac reappears below dysplastic segments
  - Spinal cord reappears below reappearance of thecal sac