= epithelium-lined dural tube extending from skin surface to intracanalicular space + frequently communicating with CNS / its coverings

Cause: focal point of incomplete separation of cutaneous ectoderm from neural ectoderm during neurulation

Age: early childhood to 3^rd decade; M÷F = 1÷1

• small midline dimple / pinpoint ostium
• hyperpigmented patch / hairy nevus / capillary angioma

Location: lumbosacral (60%), occipital (25%), thoracic (10%), cervical (2%), sacrococcygeal (1%), ventral (8%)

Course: in a craniad direction from skin level toward cord ← ascension of cord relative to spinal canal during embryogenesis

Associated with: epidermoid / dermoid tumors in up to 20%

• 50% of dorsal dermal sinuses end in dermoid / epidermoid cysts!
• 20–30% of dermoid cysts / dermoid tumors are associated with dermal sinus tracts!

CT myelography (best modality to define intraspinal anatomy):

• groove in upper surface of spinous process + lamina of vertebra
• hypoplastic spinous process
• single bifid spinous process
• focal multilevel spina bifida
• laminar defect
• dorsal tenting of dura + arachnoid
• sinus may terminate in conus medullaris / filum terminale / nerve root / fibrous nodule on dorsal aspect of cord / dermoid / epidermoid
• nerve roots bound down to capsule of dermoid / epidermoid cyst
• displacement / compression of cord by extramedullary dermoids / epidermoids
• expansion of cord by intramedullary dermoids / epidermoids
• clumping of nerve roots from adhesive arachnoiditis

Cx:

1. Meningitis (bacterial / chemical)
2. Subcutaneous / epidural / subdural / subarachnoid / subpial abscess (bacterial ascent)
   • Dermal sinus accounts for up to 3% of spinal cord abscesses!
3. Compression of neural structures

DDx: pilonidal sinus / simple sacral dimple (no extension to neural structures)