What is a sacral dimple?

Sacral Dimple: Diagnosis and Description

A sacral dimple is a midline congenital depression or pit in the skin that occurs in approximately 4% of the population, which can be either an innocent finding or a pathologic finding that may indicate underlying spinal abnormalities. 1

Characteristics and Classification

Sacral dimples can be described based on several key features:

• Location: The most critical factor in assessment

  • Dimples below the gluteal cleft line are likely innocent
  • Dimples above the gluteal cleft line are potentially pathologic 1

• Depth:

  • Shallow dimples (bottom is visible) - lower risk
  • Deep dimples (bottom not visible) - higher risk (34.6% association with fibrolipoma of terminal filum) 2

• Size:

  • Dimples measuring less than 5mm, within 25mm of the anus on the median line, with no other cutaneous anomaly are considered low-risk 3

Associated High-Risk Features

When examining a sacral dimple, look for these high-risk features:

• Cutaneous markers surrounding the dimple:

  • Hypertrichosis (tufts of hair)
  • Infantile hemangioma
  • Subcutaneous lipoma or masses
  • Skin tags
  • Caudal appendage
  • Deviated or forked gluteal cleft 1

• Neurological symptoms that may indicate underlying pathology

Diagnostic Approach

For accurate assessment:

1. For low-risk dimples (below gluteal cleft, <5mm, within 25mm of anus, no other cutaneous anomalies):

   • No imaging necessary
   • Routine well-child care 1

2. For high-risk dimples (above gluteal cleft, deep, or with associated cutaneous markers):

   • Imaging is recommended:
     • Ultrasound for infants <6 months
     • MRI for older children
   • Neurosurgical consultation 1

Clinical Significance and Complications

Sacral dimples may be associated with:

• Fibrolipoma of terminal filum (16.7% of patients with sacral dimples) 2
• Congenital dermal sinus tract - a rare but serious complication that can lead to:
  • Local infection
  • Meningitis
  • Abscess formation
  • Neurological deficits 4
• Low-lying conus medullaris (8.9% of patients with simple sacral dimples) 5
• Filar cyst (10.6% of patients with simple sacral dimples) 5

Management Considerations

• Surgical intervention is recommended for high-risk dimples with confirmed underlying pathology, ideally within 24-72 hours of birth to prevent complications 1

• Follow-up: For high-risk dimples with normal imaging:

  • Yearly neurological assessment until age 3
  • Or follow neurosurgical recommendations 1

Common Pitfalls

• Underestimating simple-appearing dimples: Even simple sacral dimples can be associated with fibrolipoma of terminal filum, though most have benign outcomes 6

• Delayed diagnosis: Failure to recognize high-risk features can lead to delayed intervention and increased risk of complications, including permanent neurological sequelae 3

• Over-investigation: Not all sacral dimples require imaging; understanding the risk stratification prevents unnecessary testing 1, 3