A sacral dimple is a small indentation or pit located on the skin just above the crease of the buttocks, specifically over the sacrum bone at the end of the spine. These dimples are common, appearing in up to 4% of newborns, and are generally harmless. While most sacral dimples are benign and do not require medical intervention, some can signal an underlying condition that necessitates further evaluation. Understanding the characteristics of a typical dimple versus one that may be atypical is important for parents and caregivers.
Distinguishing Normal from Atypical Dimples
A typical sacral dimple is small, shallow, and located in the midline, within the gluteal cleft. They are less than 5 millimeters in diameter and no more than 2.5 centimeters from the anus. They lack other associated skin features, and their base is visible. If a child has a typical dimple and is otherwise healthy with no family history of spinal cord problems, no testing or specialist referral is needed.
In contrast, an atypical or complex sacral dimple warrants further investigation. These include large dimples (greater than 5 millimeters) or those notably deep, where the bottom cannot be visualized even when the skin is spread. Dimples located significantly higher than the gluteal crease or off to the side, outside the midline, also indicate an atypical presentation.
Other skin abnormalities near the dimple are another indicator. Features include a tuft of hair, skin tag, fatty lump, or discolored skin (e.g., hemangiomas). Discharge or fluid leaking from the dimple, or multiple dimples, also suggests the need for medical attention. Pediatricians often check for these characteristics during routine newborn examinations.
Potential Underlying Conditions
Atypical sacral dimples can indicate underlying spinal cord conditions. One such condition is spina bifida occulta, a mild form of spina bifida where the bones of the spine do not fully close around the spinal cord, but the cord itself remains within the spinal canal. Most individuals with spina bifida occulta do not experience symptoms and may not realize they have it, often discovering it incidentally through X-rays or other imaging.
Another condition associated with an atypical sacral dimple is tethered cord syndrome. Here, the spinal cord abnormally attaches to surrounding tissues within the spinal canal, limiting its free movement. As a child grows, this tethering causes the spinal cord to stretch, leading to neurological issues. Symptoms include difficulty walking, numbness or weakness in the legs, back pain, scoliosis, or problems with bladder and bowel control.
Beyond spina bifida occulta and tethered cord syndrome, atypical dimples can be associated with other rare malformations of the spinal cord, collectively known as occult spinal dysraphism. These conditions involve incomplete closure of the neural tube during early fetal development, leading to various neurological impairments. An atypical dimple does not automatically mean a child has these conditions; it serves as a flag for further investigation to determine if an underlying issue is present.
Medical Evaluation and Treatment
If an atypical sacral dimple is observed, the first step involves consulting a pediatrician. The doctor conducts a physical examination to assess the dimple’s characteristics: size, depth, location, and any associated skin abnormalities. They also evaluate for neurological signs, such as lower extremity weakness or abnormal reflexes, and assess bowel and bladder function.
Imaging tests are recommended to visualize the spinal cord and surrounding structures. For infants younger than 3 to 4 months of age, an ultrasound is the initial investigation because their vertebral arches are not yet fully ossified, allowing clear images of the spinal cord. If ultrasound findings are concerning or inconclusive, or for older infants and children where ossification is more complete, an MRI scan may be performed. An MRI provides more detailed images of the spinal cord, helping confirm conditions like tethered cord syndrome.
Based on imaging results, a healthcare provider refers the child to specialists (e.g., neurosurgeon or neurologist) for further evaluation and management. If an underlying condition is diagnosed, treatment varies. For conditions like spina bifida occulta with no symptoms, observation is sufficient. If tethered cord syndrome is diagnosed and causing neurological symptoms, surgical intervention is considered to release the spinal cord and prevent further damage. Many cases of sacral dimples, even atypical ones, do not require intervention if no underlying spinal abnormality is found.