A sacral dimple is a common indentation found on the lower back, above the crease of the buttocks. This small mark is present at birth and is usually harmless. It is a normal variation in development for many babies.
What is a Sacral Dimple?
A sacral dimple appears as a small depression or pit in the skin, located directly over the sacrum, the triangular bone at the base of the spine. These dimples are shallow and small, often measuring less than 5 millimeters across. They are positioned in the midline, within 2.5 centimeters of the anus.
Simple sacral dimples have a visible base and no other associated skin changes, such as hair tufts or discoloration. They are considered benign. However, their characteristics can vary in size and depth.
How Do Sacral Dimples Form?
Sacral dimples are congenital, meaning they are present from birth. They form during early embryonic development when the neural tube, which eventually develops into the brain and spinal cord, undergoes a process of closure. Sometimes, a minor variation occurs in this closing process at the very bottom of the spine, resulting in a tiny indentation in the skin.
This developmental variation occurs in 2% to 4% of newborns. The exact reasons why some individuals develop sacral dimples are not fully understood, and they are not linked to actions during pregnancy.
When a Sacral Dimple Might Be a Concern
While most sacral dimples are harmless, certain characteristics can indicate a potential connection to underlying spinal issues. A dimple might warrant further evaluation if it is large, deep, or located higher up on the back, away from the gluteal crease. Other concerning features include a tuft of hair growing from or around the dimple, a skin tag, a fatty lump, or an area of discolored skin nearby.
These associated signs can suggest a link to conditions like spina bifida occulta or tethered cord syndrome. Spina bifida occulta is a mild form of spina bifida where the spine does not close completely around the spinal cord, though the cord remains within the spinal canal. Tethered cord syndrome occurs when the spinal cord is abnormally attached to surrounding tissues, limiting its movement and potentially causing tension as a child grows. These indicators prompt further investigation.
What Happens If a Sacral Dimple Is a Concern?
If a sacral dimple presents with concerning features, a healthcare provider will recommend further evaluation. A physical examination is the first step, where the doctor assesses the dimple’s size, location, and any associated skin abnormalities. Depending on these findings, imaging tests may be ordered to check for underlying spinal abnormalities.
For infants under a few months old, an ultrasound is the initial imaging choice due to its non-invasive nature. If ultrasound results are inconclusive or suggest an issue, or if the child is older, a Magnetic Resonance Imaging (MRI) scan is recommended for a more detailed view of the spinal cord. These diagnostic steps help determine if any intervention is needed, though many concerns turn out to be minor and manageable.