Sacral Dimples and Diagnostic Imaging

Jun 21

Abnormal physical exam findings are common during newborn and infant visits. The challenge is distinguishing low-risk findings from those that warrant further investigation. How do we decide when reassurance is enough and when additional workup is required?

We’re going to cover the common finding of sacral dimples, and when reassurance vs. further work-up is required.

Case 1: You are seeing a healthy newborn baby in the office. Everything is going well. The exam is normal until you notice a sacral dimple. What do you do next?

An immediate referral is warranted for an obvious neural defect. However, subtle or minor cutaneous findings can be more challenging to interpret.

Sacral Dimples

Why Do We Care About Sacral Dimples?

Sacral dimples may be associated with neural tube defect (NTD) - another term used is spinal dysraphism.

Open spinal dysraphism (spina bifida aperta): The spinal column is open, with meninges and spinal cord herniating through the defect. These are typically obvious at birth.

Closed spinal dysraphism (spina bifida occulta): The vertebral bodies fail to fuse, but the overlying skin remains intact and neural tissue is not exposed. Closed spinal dysraphism may present with subtle cutaneous findings such as dimples, dermal sinuses, hair patches, hemangiomas, tails, or skin discoloration. The clinical task is distinguishing low-risk from high-risk dimples.

How Do You Differentiate Low-Risk From High-Risk Dimples?

A practical rule of thumb: Most infants with sacral dimples located within the gluteal crease are healthy. Know your low-risk criteria:

Low-Risk Criteria

< 0.5 cm deep
< 0.5 cm wide
Located within 2.5 cm superior to the anal verge
No associated cutaneous markers such as excess hair, hyperpigmentation, hemangioma, or tail

Overlying cutaneous markers are found in 50 to 90 % of cases of spina bifida occulta (1).

What Does the Evidence Say?

A 10-year study of 223 infants who underwent lumbosacral spine ultrasound found that all 86 infants with simple sacral dimples, pits, or sinuses had normal imaging (2).

Another study followed 207 infants with cutaneous stigmata of neural tube defects over three years. None of the infants with simple midline sacral dimples, which comprised 74% of the cohort, had spinal dysraphism. When no high-risk criteria were present, the negative predictive value for simple dimples was 100 %. When one high-risk criterion was present, 40% had evidence of spinal dysraphism (3).

When Is No Further Workup Needed?

Simple, single, midline sacral dimples overlying the coccyx, with a visible intact base and measuring less than 0.5 cm in diameter, are common. The reported prevalence is 2 to 5% (4–6). If low-risk criteria are met, these simple dimples are typically benign and have little to no clinical significance. No further investigation is required.

💡Bottom line: sacral dimples are common - low risk criteria includes <0.5 cm deep, <0.5 cm wide, located within 2.5 cm superior to the anal verge, with no associated cutaneous markers.

Diagnostic Imaging for Sacral Dimples

When Should You Order Imaging?

Sacral dimples are higher risk if they are:
Larger th> 0.5 cm
Deep
Located above the superior gluteal cleft, more than 2.5 cm from the anal verge
Associated with other cutaneous markers such as excess hair, hyperpigmentation, hemangioma, or tail.

If any of these features are present, a spinal ultrasound should be performed to screen for an underlying neural tube defect (4–6).

Spinal Ultrasound Test Characteristics for NTD

Sacral ultrasound is the first-line imaging modality for evaluating at-risk sacral dimples in newborns. Why?

No radiation exposure
High sensitivity and specificity, (~96%)
Cost-effective
Readily available in many centers

Ultrasound is most effective in infants younger than 3 to 4 months, before ossification of the posterior vertebral arches limits the acoustic window (7).

Back to the Case: on inspection, the sacral dimple is:

< 0.5 cm deep
< 0.5 cm wide
Located within 1 cm of the anal verge superiorly
No associated concerning cutaneous features

Plan: This is a benign simple sacral dimple. Provide reassurance. No further testing is required.

💡Bottom line: Most infants with sacral dimples that fall within the gluteal creases are healthy. If low risk criteria are met, no imaging is needed.

Prevention Pearl: Neural Tube Defects and Folic Acid

This is a perfect opportunity to reinforce prevention.

For all individuals of childbearing potential planning pregnancy, assess neural tube defect risk and determine the appropriate folic acid dose. According to SOGC and ACOG recommendations:

Average Risk: supplement with 0.4 mg or 400 mcg daily.

Moderate Risk: 1 mg daily. Includes:

Type 1 or type 2 diabetes
Gastrointestinal malabsorption such as gastric bypass, inflammatory bowel disease, or active celiac disease
Advanced liver disease
Dialysis
Alcohol use disorder
Use of antiepileptic or folate-inhibiting medications
Obesity

High Risk: 4 to 5 mg daily. Includes:

Previous pregnancy affected by a neural tube defect
Either parent with a neural tube defect
Either parent with a first-degree relative with a neural tube defect
Sickle cell disease (8,9)

Start folic acid supplementation 2 to 3 months before conception.

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References

Drolet BA. Cutaneous signs of neural tube dysraphism. Pediatr Clin North Am. 2000 Aug;47(4):813-823. doi:10.1016/s0031-3955(05)70241-8.

Robinson AJ, Russell S, Rimmer S. The value of ultrasonic examination of the lumbar spine in infants with specific reference to cutaneous markers of occult spinal dysraphism. Clin Radiol. 2005 Jan;60(1):72-77. doi:10.1016/j.crad.2004.06.004.

Kriss VM, Desai NS. Occult spinal dysraphism in neonates: assessment of high-risk cutaneous stigmata on sonography. AJR Am J Roentgenol. 1998 Dec;171(6):1687-1692. doi:10.2214/ajr.171.6.9843314.

Choi SJ, Yoon HM, Hwang JS, Suh CH, Jung AY, Cho YA, Lee JS. Incidence of occult spinal dysraphism among infants with cutaneous stigmata and proportion managed with neurosurgery: a systematic review and meta-analysis. JAMA Netw Open. 2020 Jul 1;3(7):e207221. doi:10.1001/jamanetworkopen.2020.7221.

McGovern M, Mulligan S, Carney O, Wall D, Moylett E. Ultrasound investigation of sacral dimples and other stigmata of spinal dysraphism. Arch Dis Child. 2013 Oct;98(10):784-786. doi:10.1136/archdischild-2012-303564.

Eun J, Lee KS, Yang SH. Sacral dimple: clinical perspectives of lesions hidden beneath the skin. Clin Exp Pediatr. 2026 Feb;69(2):103-113. doi:10.3345/cep.2025.01802.

Wilson RD, O’Connor DL, et al. Guideline No. 427: Folic acid and multivitamin supplementation for prevention of folic acid-sensitive congenital anomalies. J Obstet Gynaecol Can. 2022;44(6):707-719.e1.

American College of Obstetricians and Gynecologists. Prepregnancy counseling. Committee Opinion No. 762. Obstet Gynecol. 2019 Jan;133(1):e78-e89. Available from: https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2019/01/prepregnancy-counseling

Victoria Sanderson