What is Sacral Dimple?
Sacral dimple is malformation present at birth, located at the end of the back, just above the crease of the buttocks. It is a small pit (a depression) in the skin, with benign prognosis. It is a common occurrence among newborns, but the true prevalence is unknown.
In some of the babies this malformation may be a sign of some inner abnormalities, especially if there are some signs that are associated with it. Usually these are different colour of skin or presence of hair follicles.
They can be, but very rarely be associated with spinal dysraphism, which is the only concern regarding this condition. It is important to evaluate the condition of the baby and the look of the dimple. (1)
There are no known causes or risk factors of spinal dimple development, but the development of spinal dysraphism, which is somewhat similar condition, is known.
There is a problem with coalescing of the bones, cartilage, muscles, skin half part sides, which then creates the gaps or a defect between. It can be developed with the same mechanisms, one of them is not enough folic acid which is essential for bone development.
Signs and symptoms
Sacral dimple looks like a small pit on baby’s lower back, above the buttocks in the midline. This condition is completely asymptomatic, some people become aware of it accidentally in young age. It is usually no deeper than a few millimetres.
There could be some hair follicles, hyperpigmentation, swelling, skin tags, lipid tissue, hemangiomas (vascular benign tumours) or accumulation of melanin (nevus). It may be deeper which raises concern about some complicated birth defects. (2)
In most cases the bottom of the dimple can be easily seen. Usually, the sacral dimple is less than 5 mm in depth and approximately 25mm away from the anus. These criteria are specific for uncomplicated sacral dimples.
If they are more than 5 mm in depth and more than 25 mm away from anus, there is a chance for associated abnormalities underneath. There is a risk that spinal dysraphism ocultus is present which is a condition where there are no bone and cartilage tissue that cover the spinal cord, and there is a huge risk of injury in this vulnerable place.
A doctor needs to thoroughly examine the sacral dimple and decide how to proceed. It also good to evaluate position, tone, muscle strength of both legs, and the function of the bladder and bowel discharging.
If the dimple doesn’t seem complicated on clinical exam, there is no need for ultrasound assessment. Ultrasound is only indicated if the sacral dimple is more than 5mm in depth and more than 25 mm from the anus.
Sometimes, babies are subjected to ultrasound assessment in search for abnormalities of inner organs, and if there is a suspicion of spinal dysraphism, but they are usually completely normal.
It is performed sometimes during the first week after birth, which may concern the parents, or after 3-4 months for a routine ultrasound check.
The ultrasound testing is harmless but gives many valuable information about the state of inner organs (some mild abnormalities that are obviously visible can indicate that there is an abnormality somewhere else in the body) and the length of the conus medullaris of the spinal cord, position of the spinal cord and the existence of a completely formed vertebrae.
Some practitioners order MRI, since it is a gold standard in diagnostics of occult spinal dysraphism, if they are very concerned that the condition may be complicated than ordinary sacral dimple. However, it is not routinely performed for its expenses and the need for sedation of a child. (3)
Sacral dimple is a part of group of signs in the lower back. The pit may appear as :
- Pilonidal abscess
- Pilonidal sinus
- Pilonidal cyst
- Small pit, sacral dimple, with or without possible associated signs.
The first three are actually present later in life but at young age in most of the cases, and should be differentiated from each other.
Sacral dimple is often just an aesthetic and cosmetic defect that requires correction. This is necessary if the bulge of tissue is formed above the dimple, but usually the defect becomes unnoticeable. There is no special treatment. The sacral dimple may become infected which than requires treatment.
Possible complications include:
- Tethering to the spinal cord
- Damage to the centres for voiding and bowel discharge
- Compression on the nerves on both sides of the spinal cord
- Infections, meningitis (bacterial and aseptic).
They need to be quickly diagnosed and managed with specific treatment. Any dysraphism needs to be closed to protect the spinal cord. This surgery can’t be done at an early age, but until a certain time passes, and until than the parents should protect the baby from injuring.
- Sacral Dimple–the Role and Yield of Imaging. Sy C, Nyame V, Haridas A. 2014, Austin Neurosurg Open Access 1(4), p. 1016.
- Zywicke HA, Rozzelle CJ. 2011, Pediatrics in review 32, p. 109.
- Management of Sacral Dimples Detected on Routine Newborn Examination: A Case Series and Review. Lee ACW, Kwong NS, Wong YC. 2007, HK J Paediatr (new series)12, pp. 93-5.