Diagnostic Criteria for Occult Dysraphism: Location-Based Risk Stratification
The location of a dimple along the craniocaudal axis is the single most critical diagnostic feature: coccygeal dimples at or below an imaginary line connecting the tops of the gluteal cleft forks are innocent and require no imaging, while lumbosacral dermal sinus tracts located cranially on the flat sacrum are always abnormal and mandate MRI evaluation. 1
Anatomical Distinction Between Innocent and Pathologic Lesions
Innocent Coccygeal Dimples
- Located at or below the line between the tops of the two gluteal cleft forks 1
- Typically lie within 1 centimeter of the coccyx, within the gluteal cleft itself 1
- Usually invisible unless buttocks are parted 1
- A finger placed over the dimple can be rolled over the tip of the underlying coccyx 1
- No imaging is necessary - the tract extends from the pit to the coccygeal tip, well below the end of the thecal sac, and is not connected to the spinal cord 1
- Have no associated cutaneous abnormalities 1
- Not associated with signs or symptoms of tethering 1
- Occur in approximately 4% of the population 1
Pathologic Lumbosacral Dermal Sinus Tracts
- Located cranial to the gluteal cleft on the flat part of the sacrum 1
- Above the imaginary line between the tops of the gluteal cleft forks 1
- Most commonly occur at S2 level 1
- Always abnormal and require surgical correction 1
- May be associated with surrounding cutaneous manifestations including vascular anomalies, tufts of hair, skin tags, or subcutaneous dermoid masses 1
Common Diagnostic Pitfall
The traditional teaching that a dimple is innocent if its base can be visualized is incorrect. 1 The presence or absence of a visible "bottom" has little to do with pathologic nature. Location along the craniocaudal axis is what matters.
Associated Cutaneous Markers Indicating Higher Risk
When evaluating for occult dysraphism, the following cutaneous stigmata warrant imaging:
- Dermal sinus tracts (highest risk marker) 2, 3
- Hairy patches 4
- Subcutaneous lipomas 4
- Capillary hemangiomas 4
- Multiple cutaneous markers present simultaneously (significantly higher risk than single markers) 2, 3
Imaging Algorithm
For Neonates and Infants <4 Months
- Spinal ultrasound is the appropriate initial imaging modality 1, 2, 5
- Ultrasound allows real-time examination and can demonstrate oscillations of the conus, filum, and cauda equina 5
- If ultrasound shows abnormalities (low-lying conus, abnormal cord position, thick filum terminale, intrathecal mass, lipoma, or dermal sinus tract), proceed to MRI 2, 5
For Older Infants and Children with Dermal Sinus Tracts
- MRI of the lumbar spine without IV contrast is the required initial imaging 1
- MRI has high sensitivity and specificity for detecting spinal dysraphism 1
- Must evaluate the conus medullaris, filum terminale, and assess for open or closed spinal dysraphism 1
- Add IV contrast only if there is suspected neoplasm or infected dermal sinus tract 1
- When contrast is used, precontrast images are essential to accurately assess enhancement 1
Clinical Presentations of Pathologic Dermal Sinus Tracts
Lumbosacral dermal sinus tracts present in one of five ways:
- Visible cutaneous tract 1
- CNS infection (meningitis or intraspinal abscess) 1
- Aseptic meningitis from desquamation of epithelial cells from associated dermoid/epidermoid cyst 1
- Spinal cord compression from growth of intra- or extradural dermoid/epidermoid cyst 1
- Neurologic deterioration from tethering 1
Infection is the most feared complication because it generates intradural scarring that makes surgical excision significantly more difficult and increases risk of neurologic deficits 1
Critical MRI Limitation
MRI significantly underreports the true extent of pathology: studies show MRI detects intradural tract extension in only 46% of cases versus 86% found at surgery, and identifies inclusion cysts in only 15% versus 24% found operatively 6. This limitation justifies surgical exploration of all dermal sinus tracts regardless of MRI findings 6.