Dimple in the Back
In the womb, a baby is formed much like a sleeping bag that’s zippered from the head to the bottom. Some babies display a tiny hole on the lower back, the result of that “zipper” failing to close all the way. This is called a sacral dimple, and it’s located in or just above the cleft between the buttocks. It’s not uncommon, and it is usually of no importance.
In extremely rare cases, however, these harmless dimples can be associated with spinal abnormalities, especially if there’s a tuft of hair on the area or on the dimple itself, or if it’s located high on the back. In other rare instances, the dimple can extend deeper into the body, forming a small opening that carries a risk of infection. Both of these would prompt your doctor to order tests to assess the dimple and the surrounding anatomy: either an ultrasound (simple but not very reliable) or an MRI (much more conclusive but requiring sedation).