Role of magnetic resonance urography in pediatric renal fusion anomalies

Unique Variants of Megacalycosis on Magnetic Resonance Urography

OBJECTIVE

To present a unique set of patients diagnosed with megacalycosis by magnetic resonance urography (MRU) to re-evaluate the definition of megacalycosis and provide a new perspective on diagnosis and treatment.

MATERIALS AND METHODS

A retrospective chart review of patients with megacalycosis as diagnosed by MRU was conducted. MRU was performed to determine the presence of obstruction, further visualize renal anatomy, and clarify the presence of megacalycosis. Patients who were asymptomatic and demonstrated no evidence of obstruction were managed with long-term observation through renal bladder ultrasonography, and symptomatic patients who showed evidence of obstruction (crossing vessels, abnormal renal transit time, or disparity in differential renal function of <40%) were treated surgically with a dismembered Anderson-Hynes pyeloplasty.

RESULTS

Thirteen cases of megacalycosis were identified as diagnosed by MRU at our institution between 2007 and 2020. In 7 patients (54%), MRU revealed the simultaneous occurrence of obstruction and megacalycosis. In patients with obstruction (N = 7), surgical intervention was required to correct the obstruction via robotic pyeloplasty. In patients without obstruction (N = 6), conservative management was performed to monitor megacalycosis through long-term follow-up via routine ultrasounds.

CONCLUSION

While megacalycosis has historically referred to the non-obstructive dilatation of the renal calyces, our study presents 7 cases of obstruction occurring simultaneously with megacalycosis as diagnosed by MRU. By expanding the designation of megacalycosis to include patients with obstruction, surgical treatment can be explored to prevent future renal colic and/or renal deterioration in those patients.

Feasibility and Implementation of a 4D Free-Breathing Variable Density Stack-of-Stars Functional Magnetic Resonance Urography in Young Children Without Sedation

BACKGROUND

Functional magnetic resonance urography (MRU) is well established in the diagnostic workup of urinary tract anomalies in children, providing comprehensive morphological and functional information. However, dynamic contrast-enhanced images acquired in the standard Cartesian k-space manner are prone to motion artifacts. A newly introduced 4D high spatiotemporal resolution dynamic contrast-enhanced magnetic resonance imaging based on variable density elliptical centric radial stack-of-stars sharing technique has shown improved image quality regarding motions under free breathing.

OBJECTIVE

The aims of this study were to implement this 4D free-breathing sequence for functional MRU and to compare its image quality and analyzability with standard breath-hold Cartesian MRU.

MATERIALS AND METHODS

We retrospectively evaluated all functional 4D MRU performed without general anesthesia between September 2021 and December 2022 and compared them with matched pairs (age, affected kidney, diagnosis) of standard Cartesian MRU between 2016 and 2022. Image analysis was performed by 2 radiologists independently regarding the following criteria using a 4-point Likert scale, with 4 being the best: overall image quality, diagnostic confidence, respiratory motion artifacts, as well as sharpness and contrast of aorta, kidneys, and ureters. We also measured vertical kidney motion due to respiratory motion and compared the variance for each kidney using F test. Finally, both radiologists calculated the volume, split renal volume (vDRF), split renal Patlak function (pDRF), and split renal function considering the volume and Patlak function (vpDRF) for each kidney. Values were compared using Bland-Altman plots and F test.

RESULTS

Forty children (20 for 4D free-breathing and standard breath-hold, respectively) were enrolled. Ten children of each group were examined using feed-and-sleep technique (median age: 4D, 3.3 months; standard, 4.2 months), 10 were awake (median age: 4D, 8.9 years; standard, 8.6 years). Overall image quality, diagnostic confidence, respiratory motion artifacts, as well as sharpness and contrast of the aorta, kidneys, and ureters were rated significantly better for 4D free-breathing compared with standard breath-hold by both readers ( P ranging from <0.0001 to 0.005). Vertical kidney motion was significantly reduced in 4D free-breathing for the right and the left kidney (both P < 0.001). There was a significantly smaller variance concerning the differences between the 2 readers for vpDRF in 4D MRU ( P = 0.0003). In contrast, no significant difference could be demonstrated for volume ( P = 0.05), vDRF ( P = 0.93), and pDRF ( P = 0.14).

CONCLUSIONS

We demonstrated the feasibility of applying a 4D free-breathing variable density stack-of-stars imaging for functional MRU in young pediatric patients with improved image quality, fewer motion artifacts, and improved functional analyzability.

Imaging features of renal ectopia and fusion in 13 cats

CASE SERIES SUMMARY

A retrospective multicenter case series of renal fusion anomalies in cats was investigated. The aim of this study was to describe the imaging characteristics (radiography, ultrasonography and CT) of renal ectopia and fusion in cats. A total of 13 feline patients (median age 9 years) were included in this multicentric retrospective study. Ultrasound was available in 12/13 cases, radiographs in 4/13 cases and CT in 3/13 cases. Of the 13 cases, seven were left to right fusions, four were right to left fusions, one was on the midline and one was in the pelvic inlet. Adopting a human classification system, there were five lump kidneys, four disc kidneys, one horseshoe kidney, one caudal ectopia, one L-shaped kidney and one pelvic kidney. In 2/13 cases, additional congenital malformations were noted, including an azygous continuation of the caudal vena cava and a peritoneal-pericardial diaphragmatic hernia.

RELEVANCE AND NOVEL INFORMATION

This study provides further description of the imaging findings in feline patients with fused renal ectopia. The morphologic characteristics of the fused kidneys in cats appear similar to what is published in the human literature. Renal fusion might be an incidental finding in cats, but further investigations are necessary to determine their clinical relevance.

Stimuli-Responsive Zinc (II) Coordination Polymers: A Novel Platform for Supramolecular Chromic Smart Tools

The unique role of the zinc (II) cation prompted us to cut a cross-section of the large and complex topic of the stimuli-responsive coordination polymers (CPs). Due to its flexible coordination environment and geometries, easiness of coordination-decoordination equilibria, "optically innocent" ability to "clip" the ligands in emissive architectures, non-toxicity and sustainability, the zinc (II) cation is a good candidate for building supramolecular smart tools. The review summarizes the recent achievements of zinc-based CPs as stimuli-responsive materials able to provide a chromic response. An overview of the past five years has been organised, encompassing 1, 2 and 3D responsive zinc-based CPs; specifically zinc-based metallorganic frameworks and zinc-based nanosized polymeric probes. The most relevant examples were collected following a consequential and progressive approach, referring to the structure-responsiveness relationship, the sensing mechanisms, the analytes and/or parameters detected. Finally, applications of highly bioengineered Zn-CPs for advanced imaging technique have been discussed.

Unveiling the confusion in renal fusion anomalies: role of imaging

Renal fusion anomalies are common congenital anomalies of the urogenital tract and have their genesis in the early embryonic period. They are classified into partial fusion anomalies (e.g., crossed fused ectopia, and horseshoe kidney) and complete fusion anomalies (e.g., fused pelvic kidney). Horseshoe kidney is the most common renal fusion anomaly and is characterized by the presence of two distinct functioning kidneys on either side of the vertebral column, with fusion occurring at the inferior poles in majority of the cases. Crossed fused ectopia is characterized by the presence of an ectopic kidney that crosses the midline and fuses with the orthotopic contralateral kidney, whereas fused pelvic (pancake) kidney is a complete fusion anomaly characterized by extensive medial fusion of both kidneys in the pelvis. Fusion anomalies are often associated with abnormalities of renal rotation, migration, and vascular supply, which predispose the kidneys to a number of complications and create difficulty during retroperitoneal surgeries and interventions. They are also associated with other congenital abnormalities of the urogenital tract, gastrointestinal tract, cardiovascular system, and skeletal system. Hence, a thorough understanding of the etiopathogenesis and radiological features of fusion anomalies is important for directing patient management. This review summarizes the embryological basis, clinical presentation and imaging approach to renal fusion anomalies, followed by detailed anatomical and radiological description of the morphological types, and the complications associated with these anomalies.

Functional magnetic resonance urography in infants: feasibility of a feed-and-sleep technique

BACKGROUND

Functional magnetic resonance (MR) urography has been well established in the diagnostic workup of congenital anomalies of kidneys and urinary tract, though long acquisition time requires sedation or general anesthesia in infants.

OBJECTIVE

To evaluate the success rate of an optimized functional MR urography protocol in infants carried out in natural sleep.

MATERIALS AND METHODS

We retrospectively evaluated all functional MR urographies performed under general anesthesia or during natural sleep in infants younger than 1 year between 2010 and 2017 and rated image quality in both cohorts using a 3-point Likert scale. We tested the analyzability of functional sequences using a free available software. We also calculated examination time. Finally, we compared examinations in natural sleep and those with general anesthesia using independent t-test for continuous data and Mann-Whitney U test for categorical data.

RESULTS

Functional MR urography could be performed successfully during natural sleep in 38 of 42 (90%) infants younger than 10 months. Four examinations were aborted before contrast medium was administrated. In the same period, 19 functional MR urographies were performed successfully under general anesthesia. Although image quality was significantly better in this group (P<0.0001), image quality was at least diagnostic in all finished examinations in natural sleep, and the functional analyzability was given in all completed examinations. There was a significant saving in examination time during natural sleep (P<0.001).

CONCLUSION

Functional MR urography can be successfully performed in natural sleep in infants younger than 10 months.

Use of MR Urography in Pediatric Patients

PURPOSE OF REVIEW

In this article, we describe the basics of how magnetic resonance urography (MRU) is performed in the pediatric population as well as the common indications and relative performance compared to standard imaging modalities.

RECENT FINDINGS

Although MRU is still largely performed in major academic or specialty imaging centers, more and more applications in the pediatric setting have been described in the literature. MRU is a comprehensive imaging modality for evaluating multiple pediatric urologic conditions combining excellent anatomic detail with functional information previously only available via renal scintigraphy. While generally still reserved for problem solving, MRU should be considered for some conditions as an early imaging technique.