Pediatr Nephrol (2008) 23:541–551 36]. When findings are abnormal, partial denervation in the urethral sphincter muscle or failure of the sphincter to relax during a detrusor contraction are the most common findings in infancy, while extensive denervation of the sphincter and/or an acontractile detrusor combined with changes in lower extremity function are the most common abnormal- ities in an older child [37]. As noted previously for myelomeningocele in children, a voiding cystourethrogram is warranted only when the urodynamics parameters suggest risk to the upper urinary tract from increased bladder outlet resistance or poor detrusor compliance. Vesicoureteral reflux, hydronephrosis and urinary inconti- nence are all managed in the same fashion as one would treat children with similar neurologic impairment due to an open spinal abnormality. The abnormal condition tends to improve following spinal cord de-tethering in the infant, but this normalization is unlikely when an older child is operated on [33, 37–39]. Therefore, specific urologic therapy is not instituted following delineation of an abnormality in infants until urodynamics studies have been repeated 3 months after the condition has been repaired. If the findings have not changed, or the child is older (when the chance that the neurologic abnormality will not improve), treatment based on principles outlined in the section on open spinal lesions is instituted. Thirty percent of children will have secondary spinal cord tethering over time, some as late as puberty or just beyond it, when the last growth spurt occurs [28, 37, 39]. Therefore, careful surveillance and repeated assessment at the first sign of incontinence or changing lower extremity function is warranted. No child is considered risk free until he or she has reached full adult height. Sacral agenesis Partial or complete absence of the lowermost vertebral bodies is labeled sacral agenesis. The condition can range from the absence of just the last two or three sacral bodies to the absence of sacral and several lumbar bones as well (sirenomyelia). This can be seen in offspring of insulin- dependent diabetic mothers (1%) [40], but it may be part of a genetic disorder due to a deletion of part of chromosome 7 (7q36), leading to absence of an important transcription factor that plays a role in the development of the caudal end of the spinal cord and vertebral column [41]. In familial cases of sacral agenesis associated with the Currarino triad syndrome (presacral mass, sacral agenesis and anorectal malformation), deletions in chromosome 7 (7q) resulting in HLXB9 genetic mutations have been found [42]. A mutation in HLXB9, a homeodomain gene of a 403 amino acid protein, which appears to be responsible for neural 545 plate infolding, has been identified in 20 of 21 patients with familial Currarino triad syndrome and in two of seven sporadic cases of this syndrome [43, 44]. Heterozygote carriers within these families have also been identified [45]. Thus, sacral agenesis may represent one point on a spectrum of abnormalities that encompass a sacral menin- gocele and ano-rectal malformations [46]. In the newborn period (and even afterwards) these infants appear normal, with no lower extremity abnormal- ity. Unless it is thought of during the examination of a newborn of a diabetic mother, such babies often go undiagnosed. With time, as they have difficulty in toilet training or have urinary infection, it becomes evident that there is a problem [40, 47]. The pathognomic sign is absence of the upper end of the gluteal cleft, with flattened buttocks. When the diagnosis is considered a lateral spine film (or a spinal ultrasound in infants) will confirm the abnormality. A spinal MR reveals a sharp cut off to the cord at about T-12, with nerve roots streaming from it. Approximately 90% of children develop neurogenic blad- der dysfunction [48]. An equal number of children have an overactive detrusor with sphincter dyssynergy or an acontractile detrusor with complete denervation in the urethral sphincter [47, 49]. The former is often associated with recurrent urinary infection and vesicoureteral reflux, whereas the latter produces continuous incontinence. The type of neurologic impair- ment affecting the lower urinary tract cannot be predicted from the level of absent or abnormal vertebral bones [47]. Obviously, management depends on the type of dysfunction present. CIC, anticholinergic medication and antibiotics are instituted in those with an upper motor neuron type lesion, while surgical measures with CIC are needed in those with an incompetent sphincter mechanism. Associated conditions Imperforate anus Failure of the lowermost portion of the developing colon in the fetus to canalize fully, resulting in a closed rectum that does not open onto the anal skin verge, is a rare anomaly, but one that needs immediate attention after delivery. In boys there is a fistula from the end of the rectal canal to the posterior urethra, whereas a stenotic, anteriorly placed anal canal that ends at the posterior aspect of the vestibule, may be noted in girls (Table 3). Usually, a colostomy is performed, or, more recently, definitive repair is undertaken in the first 24 h of life in boys, while anal dilatation is begun in girls. From a urologic standpoint, this condition is often part of a constellation of abnormalities known as the VATER or