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Articles » Magnetic Resonance Imaging
2005-11-06-16 MRI, sacral agenesis © Werner

Sacral agenesis

 Heron Werner, MD*, Pedro Daltro, MD*, Dorothy Bulas, MD #

* Heron Werner, MD & Pedro Daltro, MD*
Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZ
Rio de Janeiro – Brazil

# Dorothy I. Bulas M.D.
Professor of Radiology and Pediatrics
Children"s National Medical Center
George Washington University Medical Center
111 Michigan Ave, NW,   Washington D.C. 20010


Caudal aplasia is the total or partial agenesis of the distal neural tube resulting in sacral agenesis. It is characterized by absence of the sacrum and coccyx, whereas the vertebral abnormalities of the caudal regression syndrome vary from partial sacral agenesis to complete absence of the lumbosacral spine.  Sirenomelia is the most severe form of the caudal regression syndrome in which there is fusion of the lower extremities. 

It can be associated with abnormalities such as gastrointestinal, cardiovascular, lower extremities (clubfoot, scoliosis, hip dislocation and pelvic deformities), central nervous systems and genitourinary. It is rare, but can be increased 200-fold in infants of diabetic women. The prognosis is good when isolated sacral agenesis, but can be worse if associated with others abnormalities. The diagnosis is done by ultrasound, but can be difficult before 19 weeks because the sacrum is not enough calcified.

Case Report

This is a twin pregnancy after IVF in a woman with 40 years-old. We performed the diagnosis of sacral agenesis in the one of the fetus by ultrasound examination the 21th week gestation. The pregnancy was terminated in the 37 weeks by C-section and the babies are well.




1. Sonek JD, Gabbe SG, Landon MB.: Antenatal diagnosis of sacral agenesis syndrome in a pregnancy complicated by diabetes mellitus. Am J Obstet Gynecol 1990; 162: 806-808.
2. Benacerraf BR: Caudal regression syndrome and sirenomelia in ultrasound of fetal syndromes. Churchill Livingstone – New York 1998; 250-254.

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