Evaluation and Imaging of Sacral Dimples in Newborns
Anatomical Criteria for Imaging
- Dimples located at or below an imaginary line connecting the tops of the two gluteal folds are considered benign and do not require imaging, whereas dimples above this line on the flat sacrum are pathologic and warrant imaging. 1, 2
- The traditional teaching that a dimple is benign if its base is visible is incorrect; the craniocaudal position along the spine, not base visibility, determines clinical significance. 1, 2
Benign Coccygeal Dimples (No Imaging Required)
- These dimples are typically within 1 cm of the coccyx, situated in the gluteal cleft, and are often invisible unless the buttocks are separated. 1, 2
- They occur in approximately 4 % of healthy infants. 1, 2
- The associated tract ends at the coccygeal tip, well below the thecal sac, with no connection to the spinal cord. 1, 2
Pathologic Sacral Dimples (Imaging Required)
- Dimples cranial to the gluteal cleft on the flat portion of the sacrum are considered abnormal. 1, 2
- Their incidence is about 1 in 2,500 live births. 1
- They represent dermal sinus tracts, which are always abnormal and require surgical correction. 1, 2
High‑Risk Cutaneous Markers Mandating Imaging
- Hypertrichosis (faun tail) – focal tuft of hair over the sacrum. 3
- Midline infantile hemangioma in the lumbosacral region. 3
- Subcutaneous mass or lipoma over the sacrum. 3
- Capillary malformations (e.g., port‑wine stain or salmon patch) in the midline. 3
- Caudal appendage or large skin tags over the sacral area. 3
- Atretic meningocele – scar‑like “cigarette‑paper” skin lesion. 3
Imaging Modality Recommendations
- Spinal ultrasound is the first‑line modality for newborns with concerning dimples or any of the high‑risk cutaneous markers.
- Ultrasound should ideally be performed after 31 days of age (preferably when corrected age > 42.5 weeks and weight > 4.6 kg) to improve diagnostic accuracy.
- MRI is indicated when ultrasound reveals abnormalities or when the infant is older and ultrasound is technically limited; MRI provides superior visualization of neural tissue, conus level, filum terminale thickness, and intraspinal masses. 3
Pitfalls to Avoid
- Do not rely on visibility of the dimple base to decide on imaging; this criterion is outdated. 1, 2
- Do not image isolated coccygeal dimples, as this leads to unnecessary cost and parental anxiety. 1, 2
- Do not dismiss dimples accompanied by high‑risk cutaneous markers, because they carry a significantly elevated risk of occult spinal dysraphism. 3
Evaluation and Management of Sacral Dimples in Infants
Classification by Location
- The anatomical location of a sacral dimple determines whether it is benign (coccygeal) or warrants further evaluation (sacral) 4, 5.
- A dimple that lies at or below an imaginary line joining the upper edges of the two gluteal folds is considered a normal (benign) finding 4, 5.
- A sacral dimple located on the flat portion of the sacrum, well above the upper edge of the gluteal fold, is classified as potentially pathologic 4, 5.
Epidemiology
- Benign coccygeal dimples are present in approximately 4 % of the general infant population 4, 5.
- Pathologic sacral dimples occur in roughly 1 in 2,500 live births 4.
Clinical Features and Management of Benign Dimples
- Benign coccygeal dimples are usually invisible unless the buttocks are separated and do not require any imaging studies or therapeutic intervention 6.
Indicators for Spinal Ultrasound (Imaging)
- Spinal ultrasound is recommended when a sacral dimple is accompanied by any of the following cutaneous markers:
Evidence‑Based Guideline Statements
- The traditional teaching that a dimple is harmless if its base is visible is inaccurate; the craniocaudal location of the dimple is the critical determinant of its clinical significance 4, 5, 6.