Observing a small depression at the bottom of your baby's back can raise legitimate questions. The sacro coccygian dimple is a common characteristic, affecting about 2 to 5% of newborns, and is often completely benign. This complete guide will accompany you to better understand this particularity through:
- The precise definition and anatomy of this small cutaneous indentation.
- Clinical signs that differentiate a typical dimple from an atypical form.
- Diagnostic methods used by healthcare professionals.
- Behaviours to be adopted on a daily basis for appropriate monitoring.
- Situations requiring urgent consultation in paediatrics.
This guide offers you to explore the various reassuring aspects and those that call for vigilance. Thus, you will know when you can simply observe your baby's follow-up, and when it becomes necessary to intervene to ensure his/her infant health.
Definition and location of the sacro coccygian dimple in the baby: essential baby anatomy
The sacro coccygian dimple is characterized by a small hollow-shaped skin depression, located just above the interfessory fold, at the level of the sacrum and the coccyx. When you gently spread your baby's buttocks, it often appears as a small point or a superficial indentation. Anatomically, this dimple is located on the back centreline, which is a reassuring first criterion because off-axis variants can be associated with anomalies.
This skin characteristic reflects an embryonic residual. During the formation of the spinal column, the skin may slightly invagrate without communication with the underlying tissues. This explains why the dimple is often neither painful nor disturbing to the infant. For example, in 3 per cent of births in 2026, the paediatrician noted the presence of typical dimple Without worrying signs at maternity.
Here are the characteristics of a typical dimple, on which we support our monitoring:
- Diameter less than 5 mm with a visible base at the bottom of the hollow.
- Strictly median locationless than 25 mm of anus.
- Absence of any associated skin signs such as hair, mass, redness or discharge.
- Unique dimple, without other skin markings around.
These simple but precise features allow the majority of parents to be serene, because a smaller hollow, placed in the right area and without inflammatory signs remains a classic and safe pattern for babies.
Differentiating a typical dimple of an atypical form: visual and clinical criteria to monitor
Discern if sacro coccygian dimple is a normal variation or a sign requiring consultation is the main issue in the first days and weeks after birth. Paediatricians rely on several visual criteria that you can observe carefully:
- Size and depth: a dimple exceeding 5 mm in diameter or very deep, with a base not visible, requires increased vigilance.
- Location: a dimple more than 25 mm above the anus or outside the centreline is atypical.
- Associated skin signs: The presence of hair, pigmented stains, a button, a small appendix or redness are all alert.
- Number: multiple dimples are rare and can signal an underlying disorder.
- Other symptoms: dry or purulent discharge, abnormal smell, pain in touch.
In these atypical cases, the risk of spinal dysraphism — spinal cord closure abnormality — is a possibility that needs to be eliminated quickly. We met Anna, baby mom Emilia, worried about a dimple wider than expected. After an examination and a spinal cord ultrasound, the doctors were able to confirm the absence of a serious abnormality, which illustrates that rapid management is reassuring.
This table summarizes the main differences between typical and atypical dimples:
| Characteristics | Typical dimple | Atypical dimple |
|---|---|---|
| Size / depth | Less than 5 mm, visible base | More than 5 mm, deep or non-visible base |
| Location | Fold medium, less than 25 mm of anus | Above 25 mm, excluding centreline |
| Associated signs | No skin signs | Hair, stains, masses, flows |
| Number | Unique | Multiple dimples |
| Need for review | Simple monitoring | Recommended Consultation and Imaging |
The medical diagnosis of the sacro coccygian dimple in the baby: essential examinations and methods
The diagnosis always begins with a rigorous clinical evaluation. The doctor takes the time to examine the dimensions, depth, precise position and nature of the surrounding skin. Particular attention shall be paid to warning signs referred to above. This preliminary sorting allows to identify cases that require further investigation.
In babies under three months of age with an atypical dimple, the spinal cord ultrasound is the preferred examination. The technical reason is simple: the weak bonesification of the spine at this age makes it possible to visualize the marrow and its surroundings without recourse to X-rays or anesthesia. This examination is painless, fast and very reliable to detect anomalies such as cord attached or a dermal sinus.
After this age, lombo-sacred MRI becomes the reference. It provides a more accurate picture of nerve structures and soft tissue. Although it sometimes requires mild sedation, it is reserved for situations where ultrasound is insufficient or for the presence of evocative neurological signs.
A good follow-up can thus be organised by means of these tools: hence the crucial importance of the first clinical examination and compliance with the imaging criteria in order to avoid unnecessary costly and anxiety checks. A 2025 study showed that the use of ultrasound before 3 months reduced unnecessary MRI by 40%, thus relieving families and hospital services.
Daily care and supervision of the sacro coccygian dimple: parent child health advice
For daily care, the sacro coccygian dimple requires a simple focus on hygiene and infection prevention. The following are key practical guidelines:
- Use lukewarm water to gently clean without rubbing or inserting object into the dimple.
- Dry the area carefully by buffering.
- Regularly change layers to avoid moisture that promotes maceration.
- Do not try to remove the hair or manipulate the dimple at the risk of irritating the skin.
- Observe possible redness, pain or discharge.
- Take a regular photo if you notice changes to track it with your pediatrician.
In most cases, this caution avoids any local complication. When a dimple remains stable and shows no signs of inflammation, parents can reassure their loved ones and focus on the overall well-being of the baby.
A telling example is Sophie, a young mother in Île-de-France, who has been able to ease her concerns thanks to this simple type of surveillance. His pediatrician accompanied him by explaining that most dimples became less visible by growing up without the need for intervention.
Regular paediatric follow-up complements this care and allows rapid detection of any progressive anomaly that may require further assessment. Parents' awareness of this monitoring is a fundamental foundation for ensuring that the child health remains at the heart of priorities without generating disproportionate stress.
Risks and complications of the sacro coccygian dimple in the baby: congenital malformation to detect
Although rare, some complications associated with sacro coccygian dimple to know when to act without delay. The underlying anomalies, grouped under the term spinal dysraphism, include:
- The spina bifida occulta, an incomplete closure of the spine, usually silent at the beginning but which may cause progressive neurological disorders.
- The cord syndrome attached, where the marrow is abnormally fixed, causing back pain, motor or urinary disorders as the child grows.
- The deep dermal sinusan abnormal channel between the skin and deep tissue that can cause recurrent infections.
- Other rare malformations such as dermoid cysts or diastematomyelia (partial division of the marrow).
In the face of these risks, clinical examination and imaging provide accurate responses. The crucial point is early detection in order to offer suitable treatment. A pediatric neurosurgeon may then be involved, often to discuss an intervention to release the marrow or close an abnormal channel. Surgery generally uses multidisciplinary expertise, including specialists in paediatric rehabilitation and neurology, to optimize long-term development.
All this may seem worrying to hear, yet it must be borne in mind that the vast majority of babies wearing a typical sacro coccygian dimple do not develop any complication. Vigilance is therefore based on appropriate surveillance, combined with clear communication between parents and health care professionals.
To accompany this statement, here is a list of signs that require immediate consultation:
- Very wide or deep dimple with invisible base.
- Abnormal location outside the centreline.
- Presence of hair, mass or skin appendage.
- Redness, local heat, purulent discharge or pain.
- Neurological symptoms (weak legs, urinary control disorders).
- Fever associated with an inflammatory sign.
