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1999-05-17-18 Caudal regression syndrome © Silva
Caudal regression syndrome 

Updated 2006-01-18 by Juliana Leite, MD

Original text 1999-05-17 Philippe Jeanty, MD, PhD & Sandra R Silva, MD

Definition: Caudal regression syndrome is a rare congenital defect, characterized by the absence of the sacrum, and defects of variable portions of lumbar spine, associated with anomalies from different systems. 

Synonyms: Caudal dysplasia sequence, sacral agenesis.

Prevalence: 0.1-0.25:10,000 in normal pregnancies and 200-250 times higher in diabetic pregnancies[1].

Etiology: Unknown, but associated with maternal diabetes in 16% of the affected[2].

Recurrent risk: This anomaly is not thought to be hereditary, and the recurrent risk is very small, although higher in diabetics.

Diagnosis: The sonographic findings are variable, and depend on the extent and severity of the defect. It ranges from complete absence of the sacrum associated with abnormalities of the lumbar spine (fig. 1-2) and lower extremities (such as clubbed feet and contractions of the knees (fig. 3) and hips) to abnormalities of the sacrum, without associated defects[3].  The most typical findings are the absence of a few vertebrae, the shield like appearance of the fused or approximated iliac wings (fig 4) and the decrease interspace between the femoral heads. Some section will intersect the fetus at such an angle that no spine is visible, a very striking and probably pathognomonic finding (fig 5). Decreased movement of the legs is frequently observed. First trimester diagnosis may be hard to accomplish because of the incomplete ossification of the sacrum at that time. A short crown-rump length and abnormal appearance of the yolk sac have been proposed as early sonographic signs of caudal regression syndromes3.


Figure 1: Although on superficial examination this image might pass for normal, note that on the caudal side of the image (on the right, since the ribs can be seen on the left side of the image) the spine terminates without the usual landmark of the iliac wings and sacrum.

Figure 2: This same finding is even more striking on the sagittal view of the spine where the distal end appears to have been “erased”. This is actually the finding that caught the eye of one of my astute sonographer: she was puzzled by the spine “looking too short”.


Figure 3: Webbing of the popliteal joint is very typical too, but difficult to capture on a frozen image. By scanning meticulously over the popliteal region, the arciform shape of the soft-tissue can be recognized.


Figure 4: The lack of sacrum allows the iliac wings to be approximated, giving them a “shield” like appearance.

Figure 5: The spinal cord of this fetus is about at 2:00 (compare with the position of the iliac wing on fig. 4). I do not know of any other condition that can provide this same image of a cross-section though a fetal abdomen with no visible spine. All the other differential diagnoses such as achondrogenesis and the severest forms of OI would not present with the localized anomaly seen here.

Genetic anomaly: unknown

Pathogenesis: Disruption of the maturation of the caudal portion of the spinal cord complex prior to 4 weeks gestation, leading to motricity deficits and neurologic impairment, varying from incontinence of urine and feces to complete neurologic loss.

Associated anomalies: Anomalies of the central nervous, musculoskeletal, genito-urinary, cardiac, respiratory and gastrointestinal systems may be found in association with caudal regression syndrome.

Differential diagnosis: Sirenomelia, which was thought to be the most severe form of caudal regression syndrome (today it is considered a different entity)3, is the main differential diagnosis. Fusion of the lower extremities is a typical finding of sirenomelia.

Prognosis: Depends on the severity of the spinal defect and associated anomalies, but the vast majority of survivals requires urologic and orthopedic interventions. Severe forms are commonly associated with cardiac, renal and respiratory problems, which are responsible for early neonatal death.

Management: If detected early, pregnancy termination can be offered. Standard prenatal care is not altered if continuation of pregnancy is opted for. If born alive, extensive surgery in tertiary center is usually needed to repair the defects.



[1] Jaffe R, Zeituni M, Fejgin M. Caudal regression syndrome. Fetus, Spinal anomalies, 1991, 7561: 1-3

[2] Jones KL. Caudal dysplasia sequence in Smith’s recognizable patterns of human malformation. WB Saunders Company – Philadelphia – 1998, pp 635.

[3] Benacerraf BR. Caudal regression syndrome and sirenomelia in ultrasound of fetal syndromes -  Churchill Livingstone – New York – 1998, 250-254.

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