Nomenclature and Reporting
Reports in uroradiology should be well structured with a systematic description of normal findings and potential pathology. Reports have to be understandable by all physicians who may have to manage children with urologic or nephrologic disorders. To achieve this goal, terms have to be standardized and accepted by the medical community in general. The European Society of Pediatric Radiology uroradiology task force has issued on harmonizing and standardizing uroradiologic terminology in cooperation with European urologists and nephrologists (Vivier PH at al. 2017).
Reports in uroradiology should be well structured with a systematic description of normal findings and potential pathology. Reports have to be understandable by all physicians who may have to manage children with urologic or nephrologic disorders. To achieve this goal, terms have to be standardized and accepted by the medical community in general. The European Society of Pediatric Radiology uroradiology task force is currently working on harmonizing and standardizing uroradiologic terminology in cooperation with European urologists and nephrologists.
Number, location, size
Renal parenchyma morphology
Potential dilatation of urinary cavities
All relevant bladder features including ostia and distal ureters, and (if applicable) the urethra, the perirenal and perivesical space need to be included
2 How to Report
2.1 General Consideration
When referring to the anatomy of the urogenital tract, the natural flow of urine from the kidney to the urethra has to be considered. Proximal means close to the arriving urine unlike distal which means downstream. For example, the proximal ureter is close to the kidney, whereas the distal part is close to the bladder. Furthermore, the terms used in the report should be consistent, and a standardized fashion including relevant measurements should be respected.
2.2 Number of Kidneys
Usually two kidneys are present. In case of a solitary kidney, the term renal agenesis should be avoided as imaging cannot determine the cause of the missing kidney (shrinkage or renal agenesis) or some remnants may not be depictable. The radiological absent kidney may correspond to a real renal agenesis or more often results from an involution of dysplastic kidney tissue or an ectopic renal bud difficult to visualize (Zaffanello et al. 2009). In this context, ipsilateral Müllerian or Wolffian anomalies are frequently associated. Therefore, genital abnormalities have to be screened and reported.
Supernumerary kidneys are exceptional. The supernumerary kidney is a definitive accessory organ with its own collecting system, blood supply, and distinct encapsulated parenchyma. It should not be confused with a duplex kidney which is much more frequent. A duplex kidney corresponds to a renal unit with a single capsule, containing two pyelocalyceal systems associated with either a single or double ureters. In case of two ureters, a complete duplicated (separated) set of ureters can be observed with two ureterovesical junctions and ostia, or the ureters can fuse (anywhere) on its course and drain by a single ostium. The former malformation is called duplicated ureter and is often associated with disease; the latter is called bifid ureter and is often just an anatomic variant. If a parenchymal renal bridge is present without pyelocalyceal dilatation and without vesical abnormality, ultrasound (US) is generally not able to differentiate both entities, except if the two ostia (with two separate urinary inflow jets) can be depicted.
The term double kidney has an unclear meaning and should be avoided.
2.3 Location of Kidneys
Kidneys are normally located in the lumbar fossae. Embryologically, they migrate cephalad from the pelvis to the level of the adrenal glands. An ectopic kidney is defined by its location elsewhere than in the lumbar fossa and results from a failure of the normal migration (see chapters “Urinary Tract Embryology, Anatomy and Anatomical Variants” and “Anomalies of Kidney Rotation, Position and Fusion”). It is generally located below (pelvic kidney, iliac kidney, horseshoe kidney) or on the opposite side (crossed renal ectopia with or without fusion with the other kidney) of its usual position. Exceptionally, the cephalad migration of the kidney can be excessive prior to the diaphragmatic closure or in combination with delayed diaphragmatic closure, then even resulting in an intrathoracic location.
2.4 Renal Size
The size of both kidneys should be reported in every report when kidneys are measurable. Kidney volume is usually correlated with the single kidney glomerular filtration rate. Kidney length is generally considered as a surrogate measurement of kidney volume. The long axis has to be compared to age-related normal values (Dinkel et al. 1985; Kadioglu 2010; Konus et al. 1998; Rosenbaum et al. 1984). Nomograms should be easily accessible when reporting; patient age/size/weight must be available. Normal values are included within the interval range: mean ± 2 standard deviations.
However, it should be kept in mind that the correlation between kidney length and kidney volume is quite poor (Bakker et al. 1999; Emamian et al. 1993; van den Dool et al. 2005). In case of pelvicaliceal dilatation, the kidney often increases in size due to the urine accumulation although the kidney parenchymal volume may be decreased. Moreover, the variability in sonographic measurement of renal length is comparable to the expected annual increase in length during childhood (2–6 mm per year). Also renal length in the same patient may vary in a small amount, up to 4.3 %, with the hydration status (Peerboccus et al. 2013). Therefore, caution is suggested when using sonography to evaluate renal growth in children during a year’s time.
Some authors have reported the use of the ellipsoid formula (kidney volume = length × width × thickness × 0.5) to estimate kidney volume. However, the volumes are underestimated by the ellipsoid formula to up to 20 % with a large variability that does not allow a systematic correction (Bakker et al. 1999). The inaccuracy occurs because the kidney is not a true ellipsoid and because errors in measurements in the three dimensions can be additive (Emamian et al. 1995).
Other authors proposed to measure renal parenchymal area (Cost et al. 1996) on an oblique coronal view or the parenchymal thickness (Emamian et al. 1995). Both methods have shown to have a poor reproducibility and are considered unwieldy in a clinical setting (Brandt et al. 1982; Jeon 2013).
Semiautomatic renal volume measurement techniques have been developed with (3D) US, CT, and MRI (Breau et al. 2013; Riccabona et al. 2005; Vivier et al. 2008). The results are promising, but these algorithms are time consuming or not widely available and not used for routine examinations.
Despite its limitations, kidney length is the most important measurement in daily practice. Comparison of measured values with the previous ones is key when reporting.
2.5 Renal Parenchymal Morphology
Thickness: This parameter is also an indirect estimate of kidney volume. Age-related renal parenchymal thickness values have been published (Kadioglu 2010). However, in case of pelvicaliceal dilatation, the thickness can be decreased due to a tissular stretching rather than to a real parenchymal volume shrinkage.
Corticomedullary differentiation: US and MRI allow for observing the corticomedullary differentiation without contrast injection. For consistency, the echogenicity of the cortex has to be compared to the adjacent spleen and liver. It should be mentioned in every report, even if normal.
Note that a transient increase in the echogenicity of the pyramids is commonly seen in neonates and is the result of physiologic events in the postnatal period. The maximal hyper-echogenicity is located at the apex of the pyramids near/in the papillae. This increased echogenicity is transient and usually resolves in a few days when the infants have been hydrated and urine output reaches the standard rate. The cause of this transient increase in echogenicity in neonates remains uncertain, but seems to be independent from the deposition of Tamm-Horsfall protein as suggested formerly.
Corticomedullary differentiation can be increased (for instance, in the neonatal period and in hemolytic and uremic syndrome or in acute cortical necrosis) (Kraus et al. 1990), decreased, or reversed. A decreased differentiation is often but not always suggestive of a poor single kidney function (Mercado-Deane et al. 2002). In this case, the term renal dysplasia should be avoided by radiologists as it is a histological term corresponding to undifferentiated and metaplastic tissues (see chapter “Imaging in Renal Agenesis, Dysplasia, Hypoplasia and Cystic Diseases of the Kidney”). The simple description of loss of corticomedullary differentiation is recommended. A reversed corticomedullary differentiation is seen, for example, in medullary nephrocalcinosis (see chapters “Urolithiasis and Nephrocalcinosis” and “Imaging of Urolithiasis and Nephrocalcinosis”).
Scarring: Visualization of cortical scarring is common with MRI and CT, but it can be observed also with US. It should not be confused with junctional parenchymal defect or line (corresponding to the fusion of fetal lobulations) that appears as a triangular echogenic focus peripherally without cortical loss and between pyramids, unlike scarring that develops in front of pyramids.
Cysts: They can be sporadic, acquired, or inherited. Their absence at birth does not preclude their appearance during childhood. The number, size, features, and location of cysts should be described. They can be located in the cortex (mainly subcapsular or not) or medulla, at their junction, or in all of these and parapelvic. In case of renal cysts, the liver, spleen, and pancreas have to be evaluated for cysts. For proper interpretation of these findings, the medical history of the patient and the knowledge of a family history of cystic disease are of utmost importance (see chapters “Renal Agenesis, Dysplasia, Hypoplasia and Cystic Diseases of the Kidney” and “Imaging in Renal Agenesis, Dysplasia, Hypoplasia and Cystic Diseases of the Kidney”).
Tumors/space occupying and other focal lesions: The size, location, content (tissue, calcifications, fat, liquid, or necrosis), vascularization, borders, local and distal extension, as well as relation to surrounding structures have to be described. Differentiation against a parenchymal bridge needs to be considered as well as other pseudotumoral (inflammatory) lesions; a potential membrane-like containment may indicate an abscess. Patency of the renal vein and inferior vena cava has to be systematically imaged. Note that nonhemorrhagic peritoneal effusion is often present without peritoneal rupture (Brisse et al. 2008) (see chapter “Neoplasms of the Genitourinary System”).
2.6 Pelvicaliceal Dilatation
In case of acute obstruction, dilatation of the urinary cavities is often absent within the first hours.
Chronic dilatation of the collecting system does not necessarily indicate obstruction. The current definition of chronic obstruction in practice is the one described by Peters and Koff (Koff 1987; Peters 1995) and is based on functional deterioration and loss of growth potential rather than morphologic changes. Based on this definition, none of the terms describing an upper urinary tract dilatation should have an “obstruction” connotation. As a result, the term “obstruction” should be avoided by radiologists in case of chronic dilatation.
Dilatation of the pelvis and calices is sometimes referred to as hydronephrosis. However, this term has been used with different meanings. Depending on physicians and institutions, a notion of chronic obstruction can be included in this term. That is the reason why the use of hydronephrosis should be avoided, and simple and descriptive terms such as pelvicaliceal dilatation should be preferred. This has been also recently addressed by a consensus statement from the USA where a new suggestion for grading urinary tract dilatation has been proposed, in addition to or replacing the existing “hydronephrosis” grading schemes (Nguyen et al. 2014). Furthermore, the ESPR abdominal imaging task force has also changed its terminology and grading of former “hydronephrosis” to “plevicaliceal distentions / dilatation (PCD)” and issued a respective statement (Riccabona et al. 2017).
A ureteral dilatation should not be described as a megaureter as this term may be misleading. It should always be prefaced with the terms primary, secondary, obstructive, or refluxing. Note that a combination of both mechanisms can occasionally coexist. It can be shown by a post-micturition evaluation for “trapped” urine above the ureterovesical junction. When describing a dilated ureter without knowing the etiology, the term megaureter should be avoided. If the cause is unknown, the term ureteral dilatation (or ureteropelvicaliceal dilatation if any) should be used.
2.7 Urinary Bladder
The bladder wall and its content should be described. Mobile debris is sometimes visible and not systematically associated with urinary tract infection.
Urologists sometimes request post-void residual urine measurement. Healthy infants and toddlers have shown not to empty the bladder completely with every micturition, but they do so at least once during a four-hour observation. Normal residual urine volume is zero, while 20 ml or more on repeat measurements is pathological. Values between these two measurements represent a possible clinical relevant amount of residual urine. In older children, an easy and useful definition is the presence of a residual urine volume higher than 10 % of the expected/actual bladder capacity (Jansson et al. 2000; Neveus et al. 2006). In practice, the definition of the expected bladder capacity is the one of the expected maximum voided volume calculated via the formula [30 + (age in years × 30)], in mL. For US measurement of this volume, an individually adapted correction factor has to be applied depending on the bladder shape (Knorr et al. 1990, see also chapter “Normal Values”).
The morphology of the bladder wall should be described, especially if it is regular or not or if there are diverticula, trabeculations, or focal or global thickening. The bladder thickness is difficult to evaluate as it depends on the filling status. The thickness of the bladder wall decreases continuously as the bladder fills. Bladder wall thickness measurement seems to be more reproducible when nearly empty (Jequier and Rousseau 1987; Kaefer et al. 1997).
If applicable, difficulties in catheterization have to be reported, as usually some sort of filling is required for assessing the urethra either fluoroscopically or by perineal and penile US. The entire urethra must be imaged because disease can occur anywhere from the bladder base to the urethral meatus.
In case of opacification, steep oblique imaging is optimal, especially in male to avoid superimposition of penile urethra and posterior urethra.
Precise location of abnormalities has to be described. The male urethra is divided into anterior and posterior portions. The posterior urethra is composed of the prostatic and membranous urethra (through the urogenital diaphragm). The anterior urethra is composed of the bulbar and penile urethra.
2.9 Conclusion of the Report = Interpretation of Findings
A conclusion must be drawn at the end of every report. It should not repeat the previous reported findings but should provide a comprehensive diagnosis deducted from the findings described above. Ideally, the primary abnormality should be mentioned at first with its consequences thereafter. The conclusion should include other data from the clinical history or from other imaging modalities. For example, if unilateral ureteropelvicaliceal dilatation is found at US and that a previous VCUG did not show VUR, the conclusion should suggest a primary megaureter as the diagnosis. Furthermore, any limitations of the study (e.g., some parts not visible, artifacts, etc.) need to be mentioned. And a recommendation on further complementing imaging should be stated if deemed necessary.
Use of rigorous imaging technique, systematic reporting, standardized terminology, and a comprehensive conclusion improves the quality of the examination and avoids potential misunderstandings.
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