Synonyms

Congenital anomalies or malformations of the urinary tract

Definition

Urinary tract malformations include congenital anomalies that cause disease and potential sequelae. Differentiation of some anatomic variants from malformations is difficult and seen differently at different centres; in some conditions a clear differentiation of a ‘variation’ versus a ‘malformation’ can only be established retrospectively, with knowledge of the patient's history. Thus—in addition to ‘real malformations’—a number of conditions and abnormalities have to be listed that may partially present as a non‐symptomatic variants such as duplex kidneys (Table 1). These and rotational, positional as well as fusion anomalies of the kidneys have been addressed in the chapter Urinary Tract-anatomic variants, though some forms rather represent a malformation such as the rare ‘cross fused ectopic duplex kidney’. Other variants may eventually cause disease and thus need to be mentioned here, such as an unusual course of the left renal vein (retro‐aortal left renal vein with nutcracker syndrome) or a prominent or accessory (segmental) renal artery obstructing the ureter, the uretero‐pelvic junction or the calyceal neck causing a (disproportional) dilatation of the affected part. Malformations of the renal parenchyma include cysts (see entry Cystic Renal Disease, Childhood), dysplasia of various degrees as well as some syndromal or inherited conditions (Table 1). Furthermore, some variants may cause impaired urinary drainage and hydronephrosis such as an abnormal course and position of the ureter (i.e. in retro‐caval ureter or compression of the ureter by a horseshoe kidney).

Table 1 List of common renal malformations
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In the lower urinary tract, a number of conditions must be mentioned such as malformations of the uretero–vesical junction, an ureterocele, ectopic ureteral insertion, a persisting urachus, bladder diverticula, bladder septation and—in rare cases—duplication (Table 2). The most severe bladder malformation is bladder exstrophy. The urethra as well has a number of malformations, the most common and most dreadful malformation being congenital posterior urethra valves (Table 2). Furthermore there are urethral diverticula as well as pathologic opening and fusion of the urethra leading to various degrees of hypospadia and epispadia. Other rare conditions which need to be mentioned are the prune belly syndrome, the megacystis–megaureter–hypoperistalsis syndrome and urinary tract malformations associated with other systemic or syndromal disease.

Table 2 List of most important lower urinary tract malformations
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Embryology and pathogenesis: The embryology of the urinary tract is described in the entry Urinary Tract, Normal Anatomy and Variations. The various malformations mostly are caused by disruption of the physiological development, and cannot be defined in detail for all these conditions. Due to the common development of the genital and the urinary tract, urinary tract malformations are frequently associated with genital anomalies, typically presenting on the same side as the urinary tract pathology (for more details see entry Genital tract, Childhood). This association needs to be remembered and properly addressed by imaging, particularly as the female genitalia may be difficult to image after the initial months of life until late childhood. Typical anomalies are cystic seminal vesicles, vaginal and uterine duplications, uterine hypo‐ or aplasia, ovarian hypo‐ and dysplasia or agenesis and cystic remnants of the Wolffian and Müllerian duct. The most complex entity of these is the cloacal malformation, which usually involves not only the urinary, but also the genital and the anorectal tract, often associated with lower spinal malformations and neurological impairment, which are beyond the scope of this chapter to describe.

Imaging

Depending on the level and severity of the malformation, different modalities will become indicated. Ultrasound (US) in general constitutes the basic imaging tool that then helps to decide on further imaging needs. Depending on the underlying condition nearly all imaging modalities may become indicated and are used for complete—particularly pre‐operative—workup of children with (complex) urinary tract malformations.

Imaging modalities: In mild forms and for pre‐natal examinations imaging consists simply of US; post‐natally this maybe complemented by voiding cystourethrography (VCUG) and scintigraphy. In more complex cases a more detailed renal imaging by intravenous urography (IVU) in former times and MR‐urography (MRU) today commonly becomes necessary. Renal scintigraphy provides an excellent assessment of renal function and drainage and can be particularly useful for follow‐up comparison. If associated skeletal anomalies need to be assessed and evaluated for planning surgical procedures like in complex bladder exstrophy, plain films (to look at the spine, pelvis) and a pelvic CT may become valuable, particularly using 3D reconstruction and viewing techniques of modern multi‐slice CT. Interventional radiology may offer treatment options in severe obstruction—particularly as a bridging measure—till completion of diagnoses and definite surgery, or may serve as a tool for managing post‐operative complications. While these interventional procedures were more frequently performed some decades ago, the change in paradigms based on modern insights in development and prognosis of urinary tract malformations has significantly reduced indication for these procedures, which today are considered helpful mostly for severe bilateral obstruction or intractable infection in an obstructed system. Today measures for remodelling the collecting system without impact on future renal development are deemed less important; the final goal of treatment is preservation of renal function. Therefore—in all these malformations—this final goal becomes the only evidence based driving force that indicates imaging and allows deciding on an individually adapted imaging algorithm.

Imaging algorithms: The task of imaging is often to confirm a pre‐natally suspected condition and then to identify the entity. A thorough investigation of the entire genito‐urinary tract for depiction of or ruling out associated malformations and dysfunctions needs to be performed in more severe findings such as severe dilatation (e.g. uretero‐pelvic—and uretero‐vesical junction obstruction, posterior urethral valve), cystic and dysplastic kidneys, duplex systems with disproportional widened moieties or focal dysplasia, ureteroceles, ectopic kidneys and ureters, severe hypo‐/epispadia and bladder exstrophy. Finally imaging must provide some grading, not only for initial estimation of the severity of the disease and consecutive implications on treatment, but also for comparison during follow‐up, particularly in the increasing number of patients who are treated conservatively. And imaging should provide the pre‐operative anatomic information as necessary for the surgeon.

Taking all these tasks into consideration imaging usually starts with a detailed US in a well hydrated child. US not only provides a basic information and overview, but very often is able to establish a definite diagnosis and—to a certain extent—rate the degree of disease. Further imaging is defined by these initial US findings: In a neonatal boy with significant urinary tract dilatation or bladder anomaly, an additional VCUG is recommended for assessment of urethral pathology. (Delayed) renal scintigraphy is usually performed for a baseline assessment of renal function and potential scarring. Diuretic renal scintigraphy and MRU are performed in obstructive and dilative uropathy that potentially need surgery. IVU is rarely used today, sometimes—if MR is unavailable—for pre‐operative imaging (to provide basic anatomic information or to rule out a duplex system) and in the post‐operative setting for diagnosing post‐operative complications. Note, that these investigations should be tailored to the individual query with an adapted imaging protocol (contrast‐ and X‐ray‐dose, adapted timing of the individual exposures …). For follow‐up, US supplemented by VCUG or contrast‐enhanced cystosonography (for refluxing disease) or by diuretic renography and functional semi‐quantitative MRU (for obstructing uropathy) are generally recommended.

Diagnosis

Diagnosis is made by imaging as described above, using the criteria listed in the definition and imaging sections.