[Malformations of the human tail bud or: caudal agenesis syndrome. A review].

This study presents radiological and clinical findings in 70 patients with aplasia of caudal spinal segments and associated anomalies of the lower extremities and the inner organs. From a functional point of view 5 different types can be classified--unilateral hemi-aplasia, bilateral aplasia with or without sacral plateau, complex malformations of the caudal spine and medial spinal aplasia. Foot deformities and anomalies of the inner organs are common findings regardless to the extent of spinal aplasia, whereas popliteal webbing is only seen in cases with involvement of the lumbar spine. The lack of osseous junction between the spine and the pelvis leeds to a lumbopelvic kyphosis. Additionally the iliac wings are rotated in the frontal plane with the result of a narrow pelvic outlet and a change in the geometry of the hip joints. Embryologically all types of caudal spinal aplasia can be referred to a damage of the human tail bud. However, the term "Syndrome of Caudal Regression" is misleading; with respect to the presented results it is proposed to call this type of spinal malformation "Syndrome of Caudal Aplasia".