Sacral dimple – Diagnosis and treatment – Mayo Clinic

Sacral dimples are present at birth and are evident during an infant’s initial physical exam. In most cases, further testing is unnecessary. If the dimple is very large or is accompanied by a nearby tuft of hair, skin tag or certain types of skin discoloration, your doctor may suggest imaging tests to rule out spinal cord problems.

https://www.mayoclinic.org/diseases-conditions/sacral-dimple/diagnosis-treatment/drc-20377357