Perirenal MR high signal--a new and sensitive indicator of acute ureteric obstruction

Perirenal lymphatics: anatomy, pathophysiology, and imaging spectrum of diseases

Despite being rarely discussed, perinephric lymphatics are involved in many pathological and benign processes. The lymphatic system in the kidneys has a harmonious dynamic with ureteral and venous outflow, which can result in pathology when this dynamic is disturbed. Although limited by the small size of lymphatics, multiple established and emerging imaging techniques are available to visualize perinephric lymphatics. Manifestations of perirenal pathology may be in the form of dilation of perirenal lymphatics, as with peripelvic cysts and lymphangiectasia. Lymphatic collections may also occur, either congenital or as a sequela of renal surgery or transplantation. The perirenal lymphatics are also intimately involved in lymphoproliferative disorders, such as lymphoma as well as the malignant spread of disease. Although these pathologic entities often have overlapping imaging features, some have distinguishing characteristics that can suggest the diagnosis when paired with the clinical history.

"Renal emergencies: a comprehensive pictorial review with MR imaging"

Superior soft-tissue contrast and high sensitivity of magnetic resonance imaging (MRI) for detecting and characterizing disease may provide an expanded role in acute abdominal and pelvic imaging. Although MRI has traditionally not been exploited in acute care settings, commonly used in biliary obstruction and during pregnancy, there are several conditions in which MRI can go above and beyond other modalities in diagnosis, characterization, and providing functional and prognostic information. In this manuscript, we highlight how MRI can help in further assessment and characterization of acute renal emergencies. Currently, renal emergencies are predominantly evaluated with ultrasound (US) or computed tomography (CT) scanning. US may be limited by various patient factors and technologist experience while CT imaging with intravenous contrast administration can further compromise renal function. With the advent of rapid, robust non-contrast MRI, and magnetic resonance angiography (MRA) imaging studies with short scan times, free-breathing techniques, and lack of ionization radiation, the utility of MRI for renal evaluation might be superior to CT not only in diagnosing an emergent renal process but also by providing functional and prognostic information. This review outlines the clinical manifestations and the key imaging findings for acute renal processes including acute renal infarction, hemorrhage, and renal obstruction, among other entities, to highlight the added value of MRI in evaluating the finer nuances in acute renal emergencies.

The diagnostic value of magnetic resonance urography for detecting ureteric obstruction: a systematic review and meta-analysis

OBJECTIVE

To evaluate the diagnostic accuracy of magnetic resonance urography (MRU) and determine its value for detecting ureteric obstruction.

METHODS

The electronic databases, including PubMed, Embase and the Cochrane library, were systematically searched for studies published throughout September 2018. The summary of sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR) and receiver operating characteristic (ROC) curves was assessed to evaluate the diagnostic accuracy of MRU. Subgroup analyses were conducted based on the mean age of the included patients (adults or children).

RESULTS

Eight studies with a total of 594 patients were included. The summary of the sensitivity and specificity of MRU for diagnosing ureteric obstruction was 0.94 and 0.87, respectively. Furthermore, the pooled PLR and NLR were 7.33 and 0.07, respectively. The DOR of MRU for detecting ureteric obstruction was 95.12. In addition, the summary of the area under the ROC of MRU was 0.96. Finally, the specificity, PLR and area under the ROC of MRU for diagnosing ureteric obstruction in adults were higher than children, while the sensitivity of MRU in adults was lower than children.

CONCLUSIONS

These findings suggested a relatively high diagnostic value of MRU for detecting ureteric obstruction. Moreover, the diagnostic accuracy of MRU in adults was higher than in children. KEY MESSAGE Magnetic resonance urography (MRU) in detecting ureteric obstruction has relatively better sensitivity, specificity, PLR, NLR, DOR and AUC. The diagnostic value, including specificity, PLR and AUC of MRU in adults, was higher than in children, while the sensitivity of MRU in adults was lower than in children.

The renal resistive index as a predictor of acute hydronephrosis in patients with renal colic

INTRODUCTION

The objective of this study was to determine whether the renal resistive index (RI) can predict hydronephrosis in patients with renal colic (RC) and whether or not its performance is time-dependent.

MATERIALS AND METHODS

The study population was composed of 54 patients admitted for unilateral RC. At the time of the first observation (time point I, tpI), each patient underwent routine examinations, abdominal ultrasonography, and renal color Doppler ultrasound (CDUS) with measurement of the RI. The two imaging studies were repeated 6, 12, 18, 24, 36, and 48 h later (tpII, tpIII, tpIV, tpV, tpVI, tpVII). In addition, each patient underwent non-contrast urinary tract CT 48-60 h after admission. A mean renal RI of >0.70 (mRI+) for the symptomatic kidney was considered indicative of obstruction. Patients were retrospectively divided into two groups: those who developed dilatation (group A) and those who did not (group B).

RESULTS

A mRI+ on CDUS predicted the onset of hydronephrosis with 100% sensitivity, 84% specificity, 92.6% accuracy, PPV and NPV of 87.9% and 100%, and diagnostic efficiency of 84%. In group A, mRI+ were always observed before onset of hydronephrosis in a time-dependent manner. In group B, mRI+ were observed occasionally in 4/25 patients (16%) and all were recorded at tpII. In these cases, the RI had returned to normal by tpIII.

CONCLUSIONS

In our RC patients, renal RI obtained with CDUS predicted the onset of acute dilatation with higher sensitivity, specificity, accuracy, and diagnostic efficiency than ultrasonography, and it can be used routinely in the emergency department to supplement ultrasound findings.

MR imaging of acute right lower quadrant pain in pregnant and nonpregnant patients

The use of magnetic resonance (MR) imaging in the evaluation of acute abdominal pain is increasing, particularly in those circumstances where computed tomography (CT) is not desirable (eg, pregnancy, allergy to iodinated contrast material). Although ultrasonography (US) is considered the imaging study of choice for evaluation of abdominal pain in pregnant patients, MR imaging is a valuable adjunct to US in evaluation of pregnant patients with acute right lower quadrant (RLQ) pain who have inconclusive US results. MR imaging is also frequently used in patients with renal failure, in whom the use of iodinated contrast material is contraindicated, as well as in cases where CT results are inconclusive. In patients with acute RLQ pain, the breadth of abnormalities visible at MR imaging is very broad, with pathologic conditions potentially originating from multiple organ systems, but most commonly from the gastrointestinal and genitourinary systems. MR imaging is an excellent imaging modality for evaluation of RLQ pain and should be strongly considered in those patients in whom use of iodinated contrast media or radiation is not desirable.

Imaging for kidney stones

Imaging investigations play a vital role in the management of patients with kidney stones. The techniques available include plain x-ray of the abdomen, ultrasound scan, intravenous urogram, computed tomography (CT) and magnetic resonance imaging, amongst others. All of these techniques have their own individual roles to play and also have limitations. CT has been establishing itself as the imaging technique of choice and some exciting developments are on the way. However, renal stone disease is a complex condition. Furthermore, there are a variety of surgical techniques used to treat stones. It is therefore important that the strengths and weakness of each of the modalities are clearly understood and the investigations are tailored to address the problem in hand.

Evaluation of Painful Hydronephrosis in Pregnancy:: Magnetic Resonance Urographic Patterns in Physiological Dilatation Versus Calculous Obstruction

PURPOSE

We evaluated magnetic resonance urography (MRU) appearances in symptomatic hydronephrosis in pregnancy and compared urographic patterns in physiological and calculous disease.

MATERIALS AND METHODS

A total of 24 consecutive pregnant women with symptomatic hydronephrosis underwent MRU, comprising an overview fast T2-weighted examination of the abdomen and pelvis, and thick slab, heavily T2-weighted MRU images, followed by focused, high resolution T2-weighted sequences obtained in an axial and coronal oblique plane through the level of ureteral caliber change.

RESULTS

Of these 24 pregnant women 15 were found to have physiological hydronephrosis, 7 had calculous disease and 2 had preexisting urinary anomalies. MRU findings in physiological hydronephrosis cases were extrinsic compression of the middle third of the ureter, no filling defect and a collapsed ureter below it. Obstruction by ureteral calculi was seen at points of ureteral narrowing in the ureter, that is at the vesicoureteral junction in 2 cases, in the compressed mid ureter in 3 and at the pelviureteral junction in 1. Nonobstructive renal calculi were seen in another patient. Calculi presented throughout pregnancy but physiological hydronephrosis presented only in the late second and third trimesters. With distal calculi the MRU appearance was the double kink sign with constriction at the pelvic brim and the vesicoureteral junction with a standing column of urine in the pelvic ureter. There was renal edema and perirenal extravasation. Small calculi were only identified using high resolution T2-weighted magnetic resonance imaging.

CONCLUSIONS

MRU is a valuable and well tolerated investigation for evaluating painful hydronephrosis in pregnancy. There are characteristic and differing urographic appearances in physiological and calculous obstruction.

MR imaging in abdominal emergencies

The use of MR imaging in the emergency setting is evolving. Clear indications include situations in need of contrast media when iodinated contrast cannot be administered or to facilitate assessments in pregnant patients and children when exposure to ionizing radiation is considered unacceptable. The availability of rapid, motion-immune sequences now makes MR imaging a feasible study in less cooperative patients extending the range of patients for whom a diagnostic study can be achieved. Capitalizing on the unique benefits of MR imaging there is optimism that MR imaging can eliminate test redundancy and impact patient care in a cost-effective manner. Further investigations are needed to identify the diagnostic algorithms for which this favorable use holds true.

CT urography and MR urography

CT urography and MR urography are an evolving concept and developing technique. As the technology matures, CT urography will combine the ultimate diagnostic capabilities of intravenous urography and CT. In the near future, many intravenous urograms will be replaced by CT urography to evaluate patients with hematuria and other genitourinary conditions. MR urography currently serves as an alternative imaging technique to intravenous urography and CT urography for children and pregnant women and for patients with contraindications to iodinated contrast media.

MR urography in evaluation of acute flank pain: T2-weighted sequences and gadolinium-enhanced three-dimensional FLASH compared with urography. Fast low-angle shot

OBJECTIVE

The aim of this study was to compare the usefulness of breath-hold heavily T2-weighted sequences with gadolinium-enhanced three-dimensional fast low-angle shot (3D FLASH) MR urography in the evaluation of patients with acute flank pain.

SUBJECTS AND METHODS

Forty consecutive patients with symptoms of acute flank pain underwent MR urography followed immediately by excretory urography. Heavily T2-weighted (combined thin-slice half-Fourier acquisition single-shot turbo spin-echo [HASTE] and thick-slab single-shot turbo spin-echo) and 3D FLASH sequences were evaluated separately and independently by two experienced radiologists for the presence, cause, level, and degree of obstruction. Interobserver agreement was calculated using the kappa statistic. Excretory urography and the final clinical diagnosis were used as reference.

RESULTS

Twenty-six patients were found to have unilateral obstruction caused by ureteral stones. Both MR urography methods were excellent for detecting obstruction. In the detection of stones 3D FLASH was superior, with a sensitivity of 96.2% and 100% and specificity of 100% and 100% for observers A and B, respectively, compared with a sensitivity of 57.7% and 53.8% and a specificity of 100% and 100%, respectively, for T2-weighted sequences. The best degree of obstruction was seen with 3D FLASH, and the interobserver agreement was excellent for stone detection (kappa = 0.97).

CONCLUSION

T2-weighted sequences alone are not sufficient for examining patients with acute flank pain. However, the combined use of both T2-weighted and 3D FLASH sequences will ensure better confidence in the evaluation of acute suspected renal colic. MR urography can replace conventional excretory urography when the latter is contraindicated or undesirable.

Genitourinary imaging: the past 40 years

During the past 40 years, there has been a dramatic evolution in genitourinary imaging. This evolution has resulted in fundamental changes in the subspecialty. Uroradiology initially focused on radiographic imaging of the urinary tract and was practiced primarily by urologists. After the development of safe intravenous contrast materials, radiologists who focused on the urinary tract and worked closely with urologists forged major advances in urinary tract imaging and intervention. More recently, imaging of the extraurinary genital organs has been added to the subspecialty. Cross-sectional imaging techniques have supplanted radiographic imaging for both urinary and genital imaging. The emergence of the cross-sectional techniques, however, has blurred the traditional organ system-based distinction between gastrointestinal radiology and genitourinary radiology, as both organ systems are imaged simultaneously, and has resulted in a new amalgamation, abdominal radiology, with roots in both specialties. The challenge for the new generation of abdominal radiologists, trained predominantly in cross-sectional techniques, will be to maintain the close interaction with our clinical colleagues that the traditional organ system orientation fostered.

State-of-the-art magnetic resonance imaging of the kidneys and upper urinary tract

State-of-the-art magnetic resonance imaging (MRI) is an excellent examination in several clinical contexts of interest to endourologists. First, it offers a one-stop imaging examination of prospective renal donors, obviating the need for arteriography and conventional excretory urography. Second, it reliably depicts urinary tract obstruction and can usually distinguish acute from chronic obstruction, although it is not as sensitive as helical CT in detecting small, nonobstructing stones. Third, it is an excellent examination for characterizing renal masses, especially complex cystic masses, and for surgical planning. Because MRI does not use ionizing radiation and because gadolinium contrast agents are essentially non-nephrotoxic, MRI is especially useful in children, women of childbearing age, and patients with renal insufficiency or renal allografts. Future developments will likely include MR "fluoroscopy," which will provide real-time imaging guidance for interventional procedures in the urinary tract.

The diagnostic utility of HASTE MRI in the evaluation of acute cholecystitis. Half-Fourier acquisition single-shot turbo SE

PURPOSE

The purpose of this study was twofold: (a) to determine the significance of high signal intensity surrounding the gallbladder as seen on T2-weighted HASTE (half-Fourier acquisition single shot turbo SE) MR images in patients with acute cholecystitis and (b) to determine the sensitivity of T2-weighted HASTE MR images in detecting gallbladder and common bile duct (CBD) calculi in patients with acute cholecystitis.

METHOD

Seventy-two patients with a suspicion of acute cholecystitis were referred for HASTE MRI over a 2 year period. Forty-one patients underwent MRI after sonography and the remaining 31 patients before sonography. MR images were independently evaluated for the presence of MR pericholecystic high signal and gallbladder and CBD calculi. Findings were correlated with results obtained at sonography and at surgery.

RESULTS

Of the 72 patients imaged with HASTE MRI, 55 had cholecystitis based on clinical, sonographic, and/or surgical findings. Of these, 45 had acute and 10 had chronic cholecystitis. HASTE MRI demonstrated MR pericholecystic high signal in 41 of 45 (91%) of the patients with acute cholecystitis. The sensitivity of HASTE MRI in diagnosing acute cholecystitis was 91%. The specificity was 79%. The positive predictive value was 87%, the negative predictive value was 85%, and the overall accuracy of the test was 89%. Gallbladder stones were seen by HASTE MRI in 38 of 41 (93%) of patients with acute calculus cholecystitis demonstrated at sonography. CBD stones were demonstrated by HASTE MRI in seven of nine (78%) patients and by sonography in five of nine (56%) patients with documented choledocholithiasis on conventional cholangiography.

CONCLUSION

HASTE MRI has a high degree of accuracy in diagnosing acute cholecystitis based on the single finding of pericholecystic MR high signal. A similar level of accuracy is demonstrated in detecting gallbladder stones. Biliary duct calculi are detected with even greater accuracy than with sonography in patients with acute cholecystitis. Invasive preoperative endoscopic retrograde cholangiography may therefore be limited to only those patients with acute cholecystitis and CBD stones demonstrated on HASTE MRI. These features make HASTE MRI and ideal imaging modality in the initial evaluation of acute biliary pain and may ultimately replace sonography in the preoperative evaluation of acute cholecystitis.