A 30-minute old, full-term, female infant was born by normal spontaneous vaginal delivery after an uncomplicated pregnancy and delivery. The family history was notable for heart disease and obesity.
The pertinent physical exam showed a normal appearing female with normal vital signs, weight of 3368 grams (25-50%), length of 51 cm (50%), and head circumference of 37 cm (90%). Ballard examination was consistent with a 39 week female. Her examination was normal except that the intern noted a small sacral dimple within the midline of the gluteal cleft. The base could be seen with mild retraction. It was estimated to be 3 mm deep and in diameter. It was approximately 2 cm from the anus. There were no other cutaneous abnormalities noted.
The diagnosis of of a healthy full-term female with a simple sacral dimple was made. The intern said that she knew that if you could see the bottom of the dimple, then it was okay but wanted to know if there were other abnormalities she should worry about. The attending said that generally if the dimple is small, within the gluteal cleft near the anus and the bottom can be seen and there are no other abnormalities then it should be fine. She said, “If the dimple seems too big, seems far away from the anus or is outside the gluteal cleft then I start to get concerned. Also if it isn’t midline, or has other skin lesions or spine problems, or the baby has other malformations then you need to measure and evaluate the dimple more. It may not be something that is simple and could be a spinal defect.” She went on, “If you aren’t really sure you can always ask someone else to look at the baby too. That is why you are still learning and we all still learn as we continue to practice over the years.”
Neural tube defects are a group of disorders that arise during embryogenesis. They include anenephaly, exencephaly, meningmyelocoeles and encephalocoeles and other malformations including occult spinal dysraphism. Occult spinal dysraphism (OSD) has incomplete fusion of the midline elements of the spine including the bony, neural, and mesenchymal tissues but the abnormalities are covered by skin (ectodermal tissues) and therefore are not obvious. OSD has a higher risk of tethered spinal cord syndrome or other neurological/neurosurgical problems.
Normally the caudal end of the spinal cord, the conus medullaris, hangs freely within the spinal column but is stabilized by the filum terminale. As the spinal column grows faster than the spinal cord, there is relative ascension of the conus medullaris during embryogenesis, reaching the adult level from birth to 2 months of age. The adult level is L2 to L3 for 98% of the population. Tethering occurs when a thickened filum terminale or mass does not allow normal ascension and damage to the spinal cord can occur because of ischemia or the mechanical traction. Tethered cord can produce a number of symptoms including bowel or bladder problems, back or leg pain, numbness or tingling, changes in leg strength or gait, muscle spasms, leg deformities, scoliosis, etc. Developmental regression of milestones previously obtained also can occur in children as a sign of tethered cord syndrome. Treatment is by freeing the conus medullaris. Unfortunately retethering can occur after treatment.
In OSD, the cutaneous lesions are usually midline (~70%) but if there is a laterality it is usually left-sided. Obviously it is possible to have OSD and not have any cutaneous abnormalities or have subtle abnormalities which potentially can lead to delayed diagnosis.
There is an increased risk of having OSD with more than 1 cutaneous finding. Also if anogenital malformations, lower extremity deformities, or problems consistent with tethered cord syndrome are present, OSD should be considered.
Cutaneous signs of potential OSD include:
- Cutis aplasia
- Dermal sinus
- Deviation of the gluteal furrow (DGF)
- Fibroma penculum
- Port wine stain
- Subcutaneous lipomas
One paper says that in “.. patients with isolated lesions that are not usually associated with OSD: [port wine stain], hemangioma, hypertrichosis, simple dimple, pigmentary nevus, and mongolian spot[congenital dermal melanocytosis]…. a radiologic investigation does not seem to be appropriate…. Nevus flameus [also] has no pathologic significance.”
Simple dimple is not a sign of OSD. “…[S]imple dimple, or coccygeal pit, as an insolated small dimple (≤ 5 mm in diameter) 2.5 cm or closer to the anus and localized just above the gluteal furrow.” Atypical dimples are potential signs of OSD. “…Atypical dimples seemed to be large (≥ 5 mm), high on the back (≥ 2.5 cm from the anus, and appears in combination with other lesions.” DGF is classically taught that it is not a sign of OSD, but in some studies it can be a sign of lipoma. These studies are small, and larger studies are needed to better define the potential problem.
Test of choice for OSD is magnetic resonance imaging to detect the underlying lesion and also the conus medullaris. Spinal ultrasound can also be appropriate for newborns to age 5-6 months before the spinal bony elements are ossified.
Questions for Further Discussion
1. How is a suspected fetal meningomyelocoele treated during birth and in the immediate neonatal period?
2. Why are latex precautions indicated for patients with meningomyelocoele?
- Symptom/Presentation: Minor Congenital Anomaly
- Age: Newborn
To Learn More
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Guggisberg D, Hadj-Rabia S, Viney C, Bodemer C, Brunelle F, Zerah M, Pierre-Kahn A, de Prost Y, Hamel-Teillac D.
Skin markers of occult spinal dysraphism in children: a review of 54 cases.
Arch Dermatol. 2004 Sep;140(9):1109-15.
Hertzler DA 2nd, DePowell JJ, Stevenson CB, Mangano FT. Tethered cord syndrome: a review of the literature from embryology to adult presentation.
Neurosurg Focus. 2010 Jul;29(1):E1.
Zerah M, Kulkarni AV. Spinal cord malformations. Handb Clin Neurol. 2013;112:975-91.
Bellet JS. Developmental anomalies of the skin. Semin Perinatol. 2013 Feb;37(1):20-5.
Sewell MJ, Chiu YE, Drolet BA. Neural tube dysraphism: review of cutaneous markers and imaging.
Pediatr Dermatol. 2015 Mar-Apr;32(2):161-70.
Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa
January 8, 2018