What is a sacral dimple?

Definition of Sacral Dimple

A sacral dimple is a midline congenital depression or pit in the skin that can be either an innocent finding (when located at or below the gluteal cleft near the coccyx) or a pathologic finding (when located on the flat portion of the sacrum above the gluteal cleft) that may indicate underlying spinal abnormalities. 1, 2

Types of Sacral Dimples

Innocent Coccygeal Dimple

• Found in approximately 4% of the population 1
• Located at or below an imaginary line connecting the tops of the gluteal cleft
• Usually within 1 cm of the coccyx within the gluteal cleft
• Often invisible unless buttock cheeks are parted
• Can be palpated with a finger that can roll over the tip of the underlying coccyx
• No associated skin abnormalities
• Not associated with tethering signs or symptoms
• Does not require further investigation 1, 2

Pathologic Lumbosacral Dermal Sinus Tract (DST)

• Occurs in approximately 1 in 2500 live births 1
• Located on the flat portion of the sacrum above the upper end of the gluteal cleft
• Has an underlying tract of epithelial and fibrous tissue that pierces the skin
• May connect to deeper neural structures
• Requires further investigation and possible intervention 1, 2

Clinical Significance and Evaluation

High-Risk Features Requiring Investigation

• Location above an imaginary line connecting the tops of the gluteal cleft
• Associated cutaneous markers:
  • Hypertrichosis (tuft of hair)
  • Vascular anomalies or infantile hemangiomas
  • Subcutaneous lipomas or masses
  • Skin tags
  • Deviated or forked gluteal cleft 2

Potential Associated Conditions

• Spinal dysraphism
• Tethered cord
• Fibrolipoma of the terminal filum (found in 16.7% of patients with sacrococcygeal dimples in one study) 3
• Intraspinal lesions (more common with deep dimples where the bottom cannot be visualized) 3
• Congenital dermal sinus tract potentially leading to infection or neurological complications 4

Diagnostic Approach

Evaluation Algorithm

1. Determine the location of the dimple relative to the gluteal cleft

   • Below the gluteal cleft line: likely innocent
   • Above the gluteal cleft line: potentially pathologic 1, 2

2. Assess for high-risk features

   • Associated cutaneous markers
   • Deep dimple where bottom cannot be visualized
   • Neurological symptoms 2

3. For high-risk dimples:

   • Refer for imaging (ultrasound for infants <6 months, MRI for older children)
   • Neurosurgical consultation 2

4. For low-risk dimples:

   • Routine well-child care
   • No imaging necessary 2, 5

Common Pitfalls

• Incorrect Assessment of Risk: The traditional teaching that a dimple is innocent if its base can be visualized is incorrect. The location along the craniocaudal axis is the most important feature 1

• Unnecessary Imaging: Studies show that nearly one-third of infants who undergo spinal ultrasonography have simple sacral dimples with low likelihood of spinal dysraphism 6

• Delayed Diagnosis: Failure to recognize high-risk features can lead to delayed diagnosis of serious conditions like tethered cord or intraspinal infection 4

• Overdiagnosis: Not all imaging findings require intervention. Many minor abnormalities like echogenic filum terminale or filar cysts often normalize or remain clinically insignificant 7

The proper identification and management of sacral dimples is important for preventing unnecessary investigations while ensuring that potentially serious underlying conditions are not missed.