542 Urodynamic studies A urodynamic study consists of the following components. The child is catheterized with a triple-lumen urodynamic catheter after a small amount of liquid lidocaine (1%) has been injected into the urethra and held in place for a moment or two. First, intravesical pressure is recorded; then, the bladder is drained and the residual urine carefully measured, yielding a pressure at residual volume (this helps determine detrusor compliance at natural filling and is more accurate than cystometric compliance measured during even slow filling of the bladder). A small balloon catheter is passed into the rectum to measure intra-abdominal pressure during the cystometrogram to identify artifacts of motion and monitor increases in abdominal pressure during the filling and emptying phases of the study. The side-hole port of the urethral pressure channel is positioned at the highest point of resistance in the urethra and kept in place, measuring this resistance throughout bladder filling and emptying to determine the leak point pressure. External urethral sphincter electromyography (EMG) is performed using a 24-gauge concentric needle electrode inserted perineally in boys or para-urethrally in girls and advanced into the skeletal muscle component of the sphincter until individual motor unit action potentials are seen or heard on a standard EMG recorder. The characteristics of the individual motor unit potentials at rest, in response to various sacral reflexes (i.e. bulbocavernosus, anocutaneous, Valsalva and Credé maneuvers) and bladder filling and emptying are recorded to detect degrees of denervation. Next, the bladder is filled through the second port while intravesical pressure is monitored via the third port of the tri-lumen urodynamic catheter. The rate of filling is set at 10% of expected capacity for age [age (in years) +30 × 30= expected capacity in milliliters] [6]. Detrusor pressure measurements are continuously recorded throughout filling to calculate compliance, and during voiding or leaking to denote emptying pressure. Detrusor overactivity is defined as any short-lived pressure rise of >15 cm H2O from baseline before capacity is reached [6]. Sometimes, the urodynamics study is combined with fluoroscopic video- imaging using a dilute radio-opaque contrast agent to visualize the appearance of the bladder wall and bladder neck or to detect the presence of vesicoureteral reflux during the test. Alternatively, a radionuclide agent is instilled, with the patient lying above a nuclear camera, to determine at what pressure reflux occurs, when it is known to be present beforehand. The study is not considered complete until the child actually urinates or leaks and the ‘voiding’ pressure is measured. The small size of the urodynamic catheter does not seem to affect the voiding pressure adversely, even in very young children. The normal end filling pressure should be <10 cm H2O, while Pediatr Nephrol (2008) 23:541–551 the normal voiding pressure varies from 55 cm to 80 cm H2O in boys and from 30 cm to 65 cm H2O in girls [5]. Detrusor overactivity is considered an abnormal finding at any time [6]. The examination findings are considered normal when there is an appropriate capacity, good compliant bladder, with no overactivity, and normal innervation of the sphincter with normal sacral reflexes, and an increase in sphincter activity during filling and complete silencing during emptying. An upper motor neuron lesion is present when there is detrusor overactivity and/or hyperactive EMG responses to sacral reflexes and/or a failure of the sphincter muscle, on EMG, to relax (either partially or completely) with a bladder contraction or leaking at capacity. A lower motor neuron lesion is noted when there are no contractions of the detrusor muscle and/or there is a degree of denervation, either partial or complete, in the sphincter muscle, with characteristic EMG changes in the motor units or no motor unit activity at all, respectively, and little or no response in the sphincter to sacral reflexes and/or bladder filling or emptying [7]. Neurospinal dysraphism Myelomeningocele With regard to embryology, the developing spinal canal begins on the 18th day of gestation and is completed by day 35, closing in a caudad direction from the cephalic end of the body. Failure of mesodermal in-growth over the developing spinal cord results in an open lesion, most commonly seen in the lumbo-sacral area and, with decreasing regularity, in the thoracic and cervical areas (Table 1). The exposed spinal cord and its nerve roots, some of which may protrude into the meningocele sac, and tension on the spinal cord as the cord ‘rises up’ the canal with elongation of the fetus (from L2, L3 in mid- to late fetal life, to L1 at birth), contribute to a variable picture of neural injury to the lower urinary tract and lower extremities [8]. Coupled with obstruction of the aqueduct to the fourth ventricle (Chiari malformation), with possible Table 1 Spinal bony level of myelomeningocele (uppermost vertebral abnormality) Location Cervical-high thoracic Low thoracic Lumbar Lumbosacral Sacral Incidence (%) 2 5 26 47 20