Paediatric Imaging

Caudal regression syndrome

includes a broad spectrum of findings resulting from disturbance of normal development of the caudal mesoderm. Abnormalities include sirenomyelia (the most severe end of the spectrum with fusion of the lower extremities), sacral agenesis, anorectal stenosis, anal atresia, renal aplasia, renal dysplasia, neurogenic bladder and malformed external genitalia.

Embryologically the caudal mesoderm (including the cloaca) forms the conus, filum terminale, sacral nerve roots and lower genitourinary structures by a process of canalization and retrogressive differentiation which is usually complete by the 4th week of fetal life. The various manifestations of caudal regression result from disturbance of this normal process during week 3 of fetal development. This may reflect a toxic, infective or ischaemic insult and there is a significant association with maternal diabetes.

Radiographs show a variable degree of absence of the lower end of the bony spine (Fig.1); this may involve partial or complete absence of the sacrum or even extend as high as the thoracolumbar spine. On ultrasound or MR imaging the terminus of the spinal cord (Fig.2) may be high and has a characteristic blunted wedge shape instead of the normal tapering appearance of the conus. See sacral agenesis

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Fig.1

Abdominal radiograph of an infant with severe caudal regression syndrome. Note total absence of sacrum and rudimentary lumbar vertebrae with the lowest normal vertebra being T12. The two iliac bones meet in the mid line.
Caudal regression syndrome, Fig.1
Caudal regression syndrome, Fig.2