Pediatric Urologic Advanced Imaging: Techniques and Applications

Imaging of ureter: a primer for the emergency radiologist

In this review article, we will discuss the gamut of abnormalities involving the ureters. In the emergency department, ureterolithiasis is the most common indication for imaging abdomen and pelvis. However, spectrum of ureteral abnormalities including congenital, infectious and inflammatory, primary and secondary ureteral malignancies, retroperitoneal fibrosis rare described in this article may be encountered. Thus, we will describe acute subacute as well as chronic conditions that may affect ureter. Knowledge of common, as well as rare entities and their imaging features, is of utmost importance to enable appropriate management.

Pilot study on renal magnetic resonance diffusion tensor imaging: are quantitative diffusion tensor imaging values useful in the evaluation of children with ureteropelvic junction obstruction?

BACKGROUND

Ureteropelvic junction (UPJ) obstruction is a common cause of renal injury in children. Indications for surgery are still controversial. Currently, there is no threshold to differentiate patients with suspected UPJ obstruction requiring surgery from the ones that do not, or to predict renal outcome after surgery. Several studies have demonstrated that diffusion tensor imaging (DTI) results may correlate with microstructural changes in the kidneys.

OBJECTIVE

To evaluate the feasibility of using DTI to identify UPJ obstruction kidneys.

MATERIALS AND METHODS

We analyzed functional MR urography (fMRU) with renal DTI (b=0 and b=400, 20 directions, 1.5 Tesla, no respiratory triggering) in 26 kidneys of 19 children (mean age: 6.15 years) by comparing 13 kidneys with UPJ obstruction configuration that underwent pyeloplasty following the fMRU, and 13 anatomically normal age- and gender-matched kidneys. DTI tractography was reconstructed using a fractional anisotropy threshold of 0.10 and an angle threshold of 55°. User-defined regions of interest (ROIs) of the renal parenchyma (excluding collecting system) were drawn to quantify DTI parameters: fractional anisotropy, apparent diffusion coefficient (ADC), track length and track volume. The failure rate was evaluated.

RESULTS

All DTI parameters changed with age; fractional anisotropy decreased (P<0.032). Track volume and track length increased (P<0.05). ADC increased with age in normal kidneys (P<0.001) but not in UPJ obstruction kidneys (P=0.11). After controlling for age, the fractional anisotropy (UPJ obstruction mean: 0.18, normal kidney mean: 0.21; P=0.001) and track length (UPJ obstruction mean: 11.9 mm, normal kidney mean: 15.4 mm; P<0.001) were lower in UPJ obstruction vs. normal kidneys. There was a trend toward a higher ADC in UPJ obstruction kidneys vs. normal kidneys (P=0.062). The failure rate in UPJ obstruction kidneys due to technical limitations of DTI was 13/26 (50%).

CONCLUSION

We demonstrated that fractional anisotropy is lower in UPJ obstruction than in normal kidneys. It is necessary to improve this technique to increase the success rate and to perform more studies to evaluate if a decrease in fractional anisotropy can differentiate UPJ obstruction kidneys from hydronephrotic kidneys without UPJ obstruction.

Ultrasonography of hydronephrosis in the newborn: a practical review

Widespread use of fetal ultrasonography is accompanied by more frequent detection of antenatal hydronephrosis. Therefore, sonographic evaluation of neonates with a history of antenatal hydronephrosis is becoming more widespread. As an initial postnatal non-invasive imaging modality, ultrasonography is used to screen for persistence of hydronephrosis, determine the level and severity of obstruction, and contribute to appropriate diagnosis and treatment. This review aims to provide a practical overview of the sonographic evaluation of neonatal hydronephrosis and to describe the sonographic findings of conditions associated with hydronephrosis in the newborn.

Detection of crossing vessels in pediatric ureteropelvic junction obstruction: Clinical patterns and imaging findings

BACKGROUND

Pediatric ureteropelvic junction obstruction (UPJO) is caused by congenital intrinsic narrowing and/or a lower pole-crossing renal artery. When a crossing renal vessel (CRV) is missed at the time of pyeloplasty, a redo-pyeloplasty is often required.

OBJECTIVES

The aims were to analyze clinical predictors for the presence of a CRV in UPJO and the utility of functional magnetic resonance urography (fMRU) in preoperative identification of a crossing vessel.

METHODS

Using an Institutional Review Board approved registry database, we identified 166 patients from July of 2007 until January of 2014 who had undergone open, laparoscopic, or robotic assisted laparoscopic pyeloplasty at our institution. We abstracted data including age at surgery, preoperative symptoms, preoperative imaging findings, and whether or not a CRV was identified intraoperatively. Statistical analysis was performed on SPSS using the Mann-Whitney U test.

RESULTS

Of the 166 patients identified, 78 were found to have a CRV at the time of surgery and 88 did not. The surgical approach was distributed as 104 robotic assisted laparoscopic, 51 open, and 11 pure laparoscopic. On univariate analysis, older age at presentation and pain at presentation predicted the presence of a CRV; antenatal hydronephrosis was a negative predictor, though 20 of 68 (25.6%) infants diagnosed with UPJO antenatally did have a CRV. Subgroup analysis of patients undergoing preoperative MRU showed a sensitivity of 88.2% and specificity of 91.7% for the detection of CRVs.

DISCUSSION

This study confirmed the importance of looking for a crossing vessel in all cases, with the knowledge that increased age and pain at presentation were more likely to be associated with a crossing vessel. In addition, fMRU is a valuable source of information in the preoperative identification of the presence of a crossing vessel. The study has limitations including being retrospective in nature, and that the sensitivity of fMRU to identify CRVs was based on the read of an experienced uroradiologist who specializes in MRU, so may not correlate with the standard clinical read of an fMRU.

CONCLUSION

This study confirms the need to maintain a high index of suspicion for the presence of a CRV when intervening in a clinically symptomatic older child, although 25% of infants with antenatally detected UPJO did have one too. Our subset analysis demonstrated that MRU is a reliable method of detecting crossing vessels.

Decrease of renal aquaporins 1-4 is associated with renal function impairment in pediatric congenital hydronephrosis

BACKGROUND

Renal aquaporins (AQP1-4) concentration is downregulated and is in proportion to the degree of hydronephrosis graded by ultrasound in pediatric congenital hydronephrosis (CH). However, the relationship between the expression of AQP1-4 with the changes of renal function impairment (RFI) evaluated by (99m)Tc-DTPA renal dynamic imaging is still unclear. This study aimed to investigate the relationship between AQP1-4 expression and degree of RFI in children with CH.

METHODS

The expression of AQP1-4 was evaluated in 45 children with unilateral ureteropelvic junction obstruction (28 boys and 17 girls, average age: 28±10 months) and 15 children undergoing nephrectomy for nephroblastoma (8 boys and 7 girls, average age: 26±8 months) by immunoblotting and immunohistochemistry. Renal function was graded into mild and severe RFI by (99m)Tc-DTPA renal dynamic imaging.

RESULTS

One-way analysis of variance with Bonferonni's correction showed a significantly reduced protein expression of AQP1-4 in the severe RFI group compared with those in both mild RFI group and controls (AQP1: 0.52±0.09 vs. 0.91±0.06 vs. 1.23±0.033; AQP2: 0.68±0.12 vs. 1.09±0.06 vs. 1.52±0.08; AQP3: 0.59±0.16 vs. 0.94±0.08 vs. 1.31±0.07; AQP4: 0.64±0.06 vs. 1.14±0.07 vs. 1.61±0.07; P<0.001, respectively). In kidneys with severe RFI, there was a reduction in the protein concentration of all four AQP isoforms which was more pronounced compared with those seen in kidneys with mild RFI and in the controls.

CONCLUSION

AQP1-4 expression is reduced in proportion with the impairment degree of renal function graded by (99m)Tc-DTPA renal dynamic imaging in human CH.

Multi-detector CT in the paediatric urinary tract

The use of paediatric multi-slice CT (MSCT) is rapidly increasing worldwide. As technology advances its application in paediatric care is constantly expanding with an increasing need for radiation dose control and appropriate utilization. Recommendations on how and when to use CT for assessment of the paediatric urinary tract appear to be an important issue. Therefore the European Society of Paediatric Radiology (ESPR) uroradiology task force and European Society of Urogenital Radiology (ESUR) paediatric working groups created a proposal for performing renal CT in children that has recently been published. The objective of this paper is to discuss paediatric urinary tract CT (uro-CT) in more detail and depth. The specific aim is not only to offer general recommendations on clinical indications and optimization processes of paediatric CT examination, but also to address various childhood characteristics and phenomena that facilitate understanding the different approach and use of uro-CT in children compared to adults. According to ALARA principles, paediatric uro-CT should only be considered for selected indications provided high-level comprehensive US is not conclusive and alternative non-ionizing techniques such as MR are not available or appropriate. Optimization of paediatric uro-CT protocols (considering lower age-adapted kV and mAs) is mandatory, and the number of phases and acquisition series should be kept as few as possible.

Postnatal imaging of neonates with prenatally diagnosed genitourinary abnormalities: a practical approach

The advent of prenatal US and, more recently, fetal MRI has changed our pattern of referrals. In the current clinical algorithms, most neonates evaluated for genitourinary abnormalities are asymptomatic. These infants are referred for multidisciplinary consultation, imaging and surveillance. Evaluation of these children commences following pertinent review of available prenatal studies; this is appropriate, as in certain instances prenatally gathered information of potential prognostic significance can be inferred or can obviate the need for multiple examinations. US remains the first-line imaging modality for diagnosing urinary abnormalities in neonates and young infants, although it offers primarily morphological assessment. However, US coupled with MAG-3 scanning results in a powerful combination that provides anatomical and functional information. Recently, MRI and MR urography have been increasingly regarded as one-stop-shop examinations that can deliver both anatomical and functional information, and play an increasing role in the evaluation of ureteral ectopia and genital anomalies. Fluoroscopic examinations are reserved to exclude vesicoureteral reflux, to delineate urethral obstruction or to provide additional information to support a diagnosis. A practical approach to postnatal imaging of the neonate is discussed and the important genitourinary anomalies in this age group are presented and illustrated.

Acute management of neonatal respiratory failure due to crossed ectopic obstructed megaureter in a duplicated pelvic kidney

Respiratory distress due to urinary tract obstruction can be a urologic emergency. We describe the diagnostic and surgical management of severe respiratory distress in a neonate due to a crossed ectopic obstructed megaureter in a duplicated pelvic kidney.