Doppler US assessment of maternal kidneys: analysis of intrarenal resistivity indexes in normal pregnancy and physiologic pelvicaliectasis

Management of ureteric stone in pregnancy: a review

Background

Urolithiasis in pregnancy is a major health concern and is one of the most common causes for non-obstetrical abdominal pain and subsequent hospital admission during pregnancy. The incidence of urinary calculi during pregnancy varies in the range of 1/200 to 1/2000. Acute ureteric colic in pregnancy is associated with significant potential risks to both mother and fetus. Significant anatomic and functional changes occur in pregnancy which not only lead to stone formation but also create diagnostic dilemma. The diagnosis of ureteric calculi can be incorrect in about 28% of pregnant patients.

Main body

Management of ureteric stone during pregnancy is remaining to be a challenge for the treating urologist. Because of the inability to use good imaging options for the diagnosis confirmation and more invasive approach for the treatment, management continues to be difficult. The main threats are preterm labor with delivery and premature rupture of membranes. Other pregnancy complications are obstructive uropathy, gestational diabetes mellitus, recurrent abortions and pre-eclampsia. Management of diagnosed ureteric stone is unique in the pregnant population and requires multi-disciplinary care. It should be individualized for each patient and moves preferably from conservative to invasive approaches sequentially. With continued advancements in endourological techniques, few definitive treatment options are also available for such patients.

Conclusion

There are several lacunae related with the diagnostic imaging, medical expulsive therapy, reliability of ureteral stent/percutaneous nephrostomy insertions and safety of ureteroscopy during pregnancy. Herein, we review the management of ureteric stone during pregnancy, the various diagnostic modalities and treatment options with their advantages and disadvantages. We also proposed our management algorithm to deal with such clinical scenario in this particular population.

Kidney Imaging and Biopsy in Pregnancy

Physiologic glomerular, tubular, and structural changes related to pregnancy may complicate the detection of underlying kidney disease in pregnant patients. Imaging studies may provide important clinical information to assist in the diagnosis and treatment of kidney disease during pregnancy. Furthermore, in select patients who develop new or worsening kidney disease in pregnancy, kidney biopsy may be essential to ensure the accuracy of diagnosis and guide treatment choices. This review article will discuss the risks and benefits of various modalities used to image the kidneys and urinary tract during pregnancy to aid in the judicious selection of appropriate imaging studies that are likely to maximize clinical benefit while minimizing fetal risk. It will also highlight the potential benefits and harms associated with antepartum kidney biopsy and will offer strategies for identifying patients who are most likely to benefit from kidney biopsy during pregnancy.

Anatomical and physiological alterations of pregnancy

The extensive metabolic demands of pregnancy require specific physiological and anatomical changes. These changes affect almost all organ systems, including the cardiovascular, respiratory, renal, gastrointestinal, and hematologic system. The placenta adds another layer of complexity. These changes make it challenging for clinicians to understand presenting signs and symptoms, or to interpret laboratory and radiological tests. Furthermore, these physiological alterations can affect the pharmacokinetics and pharmacodynamics of drugs. Drug safety in lactation is only supported by limited evidence. In addition, the teratogenic effects of medications are often extrapolated from animals, which further adds uncertainties. Unfortunately, pregnant women are only rarely included in clinical drug trials, while doses, regimens, and side effects are often extrapolated from studies conducted in non-pregnant populations. In this comprehensive review, we present the changes occurring in each system with its effects on the pharmacokinetic variables. Understanding these physiological changes throughout normal pregnancy helps clinicians to optimize the health of pregnant women and their fetuses. Furthermore, the information on pregnancy-related physiology is also critical to guide study design in this vulnerable 'orphan' population, and provides a framework to explore pregnancy-related pathophysiology such as pre-eclampsia.

Ultrasonographic study and Doppler flow velocimetry of maternal kidneys and liver in low-risk pregnancy

OBJECTIVE

Longitudinal study with B-mode ultrasonography and Doppler ultrasonography of maternal kidneys and liver in low-risk pregnancy, to establish and quantify normality parameters, correlating them with physiological changes.

MATERIALS AND METHODS

Twenty-five pregnant women were assessed and selected to participate in the study, each of them undergoing four examinations at the first, second, third trimesters and postpartum.

RESULTS

Findings during pregnancy were the following: increased renal volume, pyelocaliceal dilatation with incidence of 45.4% in the right kidney, and 9% in the left kidney; nephrolithiasis, 18.1% in the right kidney, 13.6% in the left kidney. With pyelocaliceal dilatation, mean values for resistivity index were: 0.68 for renal arteries; 0.66 for segmental arteries; 0.64 for interlobar arteries; 0.64 for arcuate arteries. Without pyelocaliceal dilatation, 0.67 for renal arteries; 0.64 for segmental arteries; 0.63 for interlobar arteries; and 0.61 for arcuate arteries. Portal vein flow velocities presented higher values in pregnancy, with mean value for maximum velocity of 28.9 cm/s, and 22.6 cm/s postpartum. The waveform pattern of the right hepatic vein presented changes persisting in the postpartum period in 31.8% of the patients. Cholelithiasis was observed in 18.1% of the patients.

CONCLUSION

Alterations in renal volume, pyelocaliceal dilatation, nephrolithiasis, cholelithiasis, changes in portal vein flow velocity, alterations in waveform pattern of the right hepatic vein, proved to be significant.

Stone disease in pregnancy: imaging-guided therapy

Renal colic is the most frequent nonobstetric cause for abdominal pain and subsequent hospitalization during pregnancy. The physio-anatomical changes in the urinary tract and the presence of the fetus may complicate the clinical presentation and management of nephrolithiasis. Ultrasound (US) is the primary radiological investigation of choice. Magnetic resonance urography (MRU) and low-dose computed tomography (CT) have to be considered as a second- and third-line test, respectively. If a study that uses ionizing radiation has to be performed, the radiation dose to the fetus should be as low as possible. The initial management of symptomatic ureteric stones is conservative during pregnancy. Intervention will be necessary in patients who do not respond to conservative measures. Therefore, it is crucial to obtain a prompt and accurate diagnosis to optimize the management of these patients. Teaching Points • In pregnancy, renal colic is the most frequent nonobstetric cause for abdominal pain and hospitalization. • Magnetic resonance urography should be considered when ultrasound is nondiagnostic. • Low-dose CT should be considered as a last-line test during pregnancy.

Use of renal resistive index and semi-rigid ureteroscopy for managing symptomatic persistent hydronephrosis during pregnancy

PURPOSE

The aim of this study was to evaluate the use of Doppler ultrasonography (DUS) and semi-rigid ureteroscopy (URS) for managing symptomatic persistent hydronephrosis during pregnancy.

MATERIALS AND METHODS

The study included 19 pregnant patients with unilateral symptomatic persistent hydronephrosis. All pregnant patients were assessed with conventional ultrasonography (US) followed by DUS for both kidneys.

RESULTS

The mean patient age was 26 years (range 19-40), and the gestational period was 24 weeks (range 16-33). There was a significantly higher mean resistive index in the kidneys with ureteral obstruction than in the contralateral normal kidneys. Spinal anesthesia was performed on 18 patients, while general anesthesia was performed on 1 patient. Endoscopically stones were found in 17 patients (89.5%), while no stone was found in 2 patients (10.5%). The stones were fragmented by holmium laser and retracted with forceps. After lithotripsy, a ureteral JJ stent was inserted in 8 of 17 (47%) patients with ureteral stones. Intraoperatively, there were no obstetric complications, while ureteral perforation was seen in one patient. Two patients are still pregnant at the time of this writing, and 17 babies were born normally.

CONCLUSIONS

Both RI and ΔRI increase in unilateral symptomatic persistent hydronephrosis during pregnancy. Semi-rigid URS can be used successfully for diagnosis and treatment in these patients.

Imaging of pregnant and lactating patients: part 2, evidence-based review and recommendations

OBJECTIVE

The objectives of this article are to discuss the current evidence-based recommendations regarding the use of diagnostic imaging in the evaluation of pulmonary embolism, appendicitis, urolithiasis, and cholelithiasis during pregnancy.

CONCLUSION

Diagnostic imaging should be performed during pregnancy only with an understanding of the maternal and fetal risks and benefits, the comparative advantages of different modalities, and the unique anatomic and physiologic issues associated with pregnancy.

Imaging the pregnant patient for nonobstetric conditions: algorithms and radiation dose considerations

Use of diagnostic imaging studies for evaluation of pregnant patients with medical conditions not related to pregnancy poses a persistent and recurring dilemma. Although a theoretical risk of carcinogenesis exists, there are no known risks for development of congenital malformations or mental retardation in a fetus exposed to ionizing radiation at the levels typically used for diagnostic imaging. An understanding of the effects of ionizing radiation on the fetus at different gestational stages and the estimated exposure dose received by the fetus from various imaging modalities facilitates appropriate choices for diagnostic imaging of pregnant patients with nonobstetric conditions. Other aspects of imaging besides radiation (ie, contrast agents) also carry potential for fetal injury and must be taken into consideration. Imaging algorithms based on a review of the current literature have been developed for specific nonobstetric conditions: pulmonary embolism, acute appendicitis, urolithiasis, biliary disease, and trauma. Imaging modalities that do not use ionizing radiation (ie, ultrasonography and magnetic resonance imaging) are preferred for pregnant patients. If ionizing radiation is used, one must adhere to the principle of using a dose that is as low as reasonably achievable after a discussion of risks versus benefits with the patient.

Resistance and pulsatility index increase in capsular branches of testicular artery: indicator of impaired testicular microcirculation in varicocele?

PURPOSE

To evaluate the effect of clinical varicocele on testicular microcirculation using spectral Doppler analysis.

METHODS

Forty-nine young and healthy volunteers were enrolled in this prospective study. Varicocele grades were determined according to sonographic parameters. Patients with left-sided clinical varicocele were classified as the patient group (n = 15), while the remaining patients served as controls (n = 34). Spectral Doppler measurements of testicular arteries (peak systolic/end diastolic velocity, resistance index, pulsatility index) were measured from capsular and intratesticular branches.

RESULTS

No statistically significant difference was found between the Doppler parameters obtained from the intratesticular branches of both testes and the capsular branches of the right testis. On the other hand, in left-sided clinical varicocele cases, the average resistance index (RI) and pulsatility index (PI) of capsular branches of the left testes (RI, 0.68 +/- 0.04; PI, 1.22 +/- 0.15) were significantly greater than in the control group (RI, 0.64 +/- 0.06; PI, 1.07 +/- 0.18) (p < 0.05 and p < 0.01, respectively).

CONCLUSIONS

Increased RI and PI of capsular branches of testicular arteries on spectral Doppler examination may be an indicator of impaired testicular microcirculation in patients with clinical varicocele. Further studies addressing the correlations with sperm counts are needed to determine the cut-off values for these indices.

Urologic Radiology During Pregnancy

The pregnant patient presents a unique diagnostic challenge to the urologist because the well-being of both the mother and fetus must be considered. Radiation exposure to the fetus during gestation presents risks such as cell death and teratogenic effects, carcinogenesis, and genetic effects, which must be considered when selecting diagnostic tests. However, with the exercise of good clinical judgment and the use of the armamentarium of diagnostic imaging modalities available, the pregnant patient can be managed with minimal, if any radiation exposure to the fetus.

Ureteroscopy and Holmium Laser Lithotripsy in Pregnancy: Stents Must Be Used Postoperatively

PURPOSE

To present our experience with ureteroscopy and holmium laser lithotripsy in pregnant patients and discuss the need for stents postoperatively.

PATIENTS AND METHODS

A retrospective analysis was performed on seven consecutive pregnant patients presenting with renal colic necessitating intervention between 1997 and 2003. One patient presented during the first, five in the second, and one in the third trimester. Abdominal ultrasonography was the primary diagnostic test. If the stone could not be seen with a rigid ureteroscope, flexible ureteroscopy (f-URS) was performed. Stones were fragmented with a holmium laser, and large fragments were taken out. Ureteral stents were placed routinely in all but the first two patients.

RESULTS

The ureteral stones could be seen with ultrasonography in three patients. In four patients, holmium lasertripsy could be done by the rigid ureteroscope. In the remaining patients, f-URS was performed, and two upper-system stones were fragmented. Six patients were rendered stone free. In one patient, both collectingsystem dilation and right perirenal liquid accumulation were present by ultrasonography, but no stones could be detected. Ureteral-stent insertion reduced postoperative pain and analgesic use in the whole group.

CONCLUSIONS

When conservative therapy fails in the pregnant patient with a ureteral stone, ureteroscopy and holmium lasertripsy should be considered. Routine insertion of ureteral stents with pull-out strings for at least 72 hours will reduce the pain and analgesic use postoperatively.

Functional evaluation of the urinary tract by color-Doppler ultrasonography (CDU) in 100 patients with renal colic

INTRODUCTION AND OBJECTIVE

To evaluate if the addition of a renal color-Doppler ultrasonography (CDU) in the setting of acute renal colic improves the sensitivity of conventional sonography.

MATERIALS AND METHODS

Between July 2002 and June 2003, 100 patients (median 49 years) with renal colic have been evaluated. Within 24 h of the admission, a CDU study of the urinary tract was performed using a sonograph GE Logiq 500 PRO with a multifrequency (3-5 MHz) convex probe. The following parameters were evaluated: ultrasonography (US) of both kidneys, ureters and bladder; resistive index (RI) of the arciform arteries of both kidneys in three different parenchymal areas; ureteric jets in response to hydration. A renal RI>0.70 and/or a 10% difference between the kidneys were considered as diagnostic of obstructive uropathy; an asymmetric and/or reduced ureteric jet from the ureteric orifices was an additional indicator of obstruction. All patients underwent a CT scan both with and without the administration of contrast medium.

RESULTS

Enhanced helical CT demonstrated an urinary stone in 90 out of the 100 patients (90%): 29 pyelic, 28 at the pyelo-ureteral junction, 23 lumbo-iliac and 10 juxtavesical stones. Among 90 patients with urolithiasis, the stone was undetectable with US in 11 cases (12.2%); in 8 cases (8.9%) pyelocalicectasis was absent, and in 6 patients (6.6%) a non-obstructive hydronephrosis was present. Median RI in obstructed and non-obstructed kidney was 0.73 (range 0.71-0.87) versus 0.62 (0.50-0.68), respectively; in two, obstructed kidneys RI was <0.70 but greater than 10% compared with normal side. Sensitivity and specificity of US, CDU (RI+ureteric jet), unenhanced helical CT and CDU in association with unenhanced helical CT were 94.8 and 55.5, 98.9 and 90.9, 100 and 100%, respectively.

DISCUSSION AND CONCLUSIONS

CDU in patients with renal colic and/or pelvicalicectasis improves the diagnostic accuracy of US in distinguishing between obstructive and non-obstructive dilatation. Combined with unenhanced CT, CDU has a 100% sensitivity and specificity. Moreover, due to the absence of contraindications and side-effects, CDU is indicated for the follow-up of patients after ESWL, pregnant women and children.

Prospective evaluation of renal artery resistance and pulsatility indices in normal pregnant women

OBJECTIVES

To establish normal values for renal artery resistance index (RI) and pulsatility index (PI) during gestation and, by comparison with non-pregnant controls, to determine if pregnancy affects these indices.

METHODS

This was a prospective longitudinal study involving 36 normal pregnant women who underwent a total of 280 examinations at 4-week intervals from the 6th gestational week to the end of pregnancy. High-resolution ultrasound equipment with 'triplex' Doppler facilities was used. RI and PI were obtained for the main arteries of both kidneys. The same evaluation was performed in 15 non-pregnant women as controls.

RESULTS

The mean RI in pregnant and non-pregnant women was the same (0.65 +/- 0.03 for controls and 0.65 +/- 0.02 for the pregnant women). For PI, the values were 1.25 +/- 0.12 for non-pregnant women and 1.18 +/- 0.09 for pregnant women. The only statistical difference (P < 0.05) was found between the PI of the left renal artery in the control group (1.29 +/- 0.20) and that in the pregnant group at the 8-12-week interval of gestational age (1.08 +/- 0.14).

CONCLUSIONS

No significant alterations in renal artery RI and PI occur during normal pregnancy, except for in a subgroup of patients between 8 and 12 weeks of gestation.

AAPM/RSNA physics tutorial for residents: topics in US: Doppler US techniques: concepts of blood flow detection and flow dynamics

Techniques of Doppler ultrasonography (US) have been available to clinicians for nearly 40 years. The Doppler effect as developed by sound propagation in human tissues and with the velocities observed for the human vasculature produces shifts in the frequencies of returning echo signals. These signals can be processed in a manner that allows the observer to determine the condition of the blood flow. The instrumentation for Doppler US has evolved to accommodate the expanding clinical use of US. Each development (eg, pulsed-wave Doppler US, color flow imaging) has been motivated by a desire to provide more clinical information about flow in the body. The algorithms used are complex, but increasingly powerful microelectronics have made these methods a reality at a reasonable cost. Users of Doppler US techniques must be aware of the complicated aspects of flow in the body, especially with regard to detection of disease in the human vasculature. The continuing development of US equipment aims to provide a greater understanding of hemodynamics and the relationship between blood flow and various disease processes.

Renal vein Doppler ultrasound of maternal kidneys in normal second and third trimester pregnancy

The flow pattern in intrarenal veins depends on renal parenchymal histology and cardiac physiology. The intrarenal venous impedance index obtained by Doppler ultrasound is related to compliance in vein, and can be helpful in the assessment of renal parenchymal compliance. The purpose of this study was to determine whether normal pregnancy has a significant effect on intrarenal venous blood flow, and assess if the physiological pyelocaliectasis causes a measurable reduction in venous impedance indexes in pregnant women. Doppler ultrasound of intrarenal veins was performed in 35 asymptomatic pregnant women in the second and third trimester of gestation, and in 24 non-pregnant healthy women. After grading the degree of hydronephrosis, venous impedance index was obtained from the interlobar veins. The venous waveforms in pregnant women showed diminished phasic oscillations owing to elevated pre-systolic flow. The mean venous impedance indexes in pregnant women were significantly lower than the values in non-pregnant subjects, 0.30+/-0.10 versus 0.44+/-0.06 in the right (p<0.001), and 0.36+/-0.11 versus 0.41+/-0.07 in the left kidney (p=0.03). There was an inverse correlation between the grade of pelvicalyceal dilatation and the venous impedance indexes in both kidneys in pregnant women (r=-0.62, p<0.001 for the right kidney, and r=-0.38, p=0.05 for the left kidney). An abnormally reduced venous impedance index in pregnant women can at least in part be explained by reduced vascular compliance from increased interstitial pressure subsequent to partial obstruction of ureters by the gravid uterus, and caution should be exercised in interpreting it as a sign of pathological ureteral obstruction.

The current management of urolithiasis during pregnancy

The management of urolithiasis in pregnancy can present complex challenges to the urologist. However, if the principles discussed above are followed, these difficult clinical problems can be approached in a rational manner.

The management of urinary calculi in pregnancy

When a pregnant patient presents with a urinary calculus, the customary investigations and management must change in order to take into account the well-being of the developing fetus. Transabdominal or endovaginal ultrasound should be the initial imaging modality used in order to establish the diagnosis. A plain abdominal X-ray, limited intravenous pyelography, or retrograde pyelography is used secondarily if a definitive diagnosis is lacking. The treatment of first choice for urolithiasis in pregnancy is conservative, because 70-80% of stones will pass spontaneously. If conservative management fails, or in cases of sepsis, obstruction of a solitary kidney, or bilateral ureteric obstruction, then surgical intervention is indicated. Traditional surgical management consists of draining the obstructed collecting system with a ureteral stent or percutaneous nephrostomy tube with definitive treatment of the stone in the post-partum period. Ureteroscopic lithotripsy and stone extraction is another option that has been used safely and reliably with increasing frequency in many centers. Despite recent reports of using extracorporeal shock-wave lithotripsy, this treatment is still considered contraindicated in pregnancy.

Renal colic in pregnant women: role of renal resistive index

OBJECTIVES

To investigate the value of the renal resistive index (RI) in the identification of acute renal obstruction in pregnant women.

METHODS

The study included 22 pregnant women with acute unilateral ureteral obstruction due to a stone disease (group A), 71 normotensive pregnant patients without loin pain (group B), and 20 nonpregnant women of child-bearing age with both kidneys normal (group C). All patients underwent Doppler ultrasound (DUS) with determination of the RI and the difference between the RI of the corresponding and contralateral kidney (DeltaRI). The RI and DeltaRI was considered positive for obstruction with a value of 0.70 or greater and 0.04 or greater, respectively. Ureteral obstruction was confirmed by several clinical, radiologic, and endoscopic findings. The sensitivity, specificity, and overall accuracy of RI and DeltaRI for the diagnosis of acute unilateral ureteral obstruction were calculated.

RESULTS

In group A, kidneys with ureteral obstruction (n = 22) had a mean RI of 0.69 +/- 0.03; the contralateral normal kidneys (n = 22) had a mean RI of 0.63 +/- 0.03, a significant difference (P <0.0001). The mean RI of all kidneys in group B (n = 142) and all kidneys in group C (n = 40) was 0.64 +/- 0.05 and 0.62 +/- 0.04, respectively; the difference was not statistically significant. A comparison between the mean RI of the normal kidneys of group A and all the kidneys of groups B and C revealed no significant difference. The mean RI of the obstructed kidneys in group A was significantly higher than the mean RI of all the kidneys in groups B and C. Similarly, the mean DeltaRI of group A was significantly higher than the mean DeltaRI of groups B and C (0.06 +/- 0.01 versus 0.006 +/- 0.003 versus 0.006 +/- 0.004, respectively). The RI was sensitive in 45%, specific in 91%, and accurate in 87%. The corresponding values for DeltaRI were 95%, 100%, and 99%.

CONCLUSIONS

The DeltaRI is a sensitive and specific test that can replace intravenous urography in the diagnosis of acute unilateral ureteral obstruction in pregnant women.

Assessment of acute abdominal pain in the pregnant patient

The request to image a pregnant patient with abdominal pain often leads to concern and frustration for the referring clinician as well as the radiologist. In this report we will review the basic principles of radiation safety when imaging the pregnant woman, consider the diagnostic possibilities for the causes of abdominopelvic pain, and discuss the available imaging modalities to provide a basis for tailoring an imaging plan to the individual patient.

Doppler ultrasound of the kidney

Conventional ultrasound of the kidney is used commonly to depict structural abnormalities. It is limited, however, by a lack of functional and vascular information. Doppler sonography can reduce this limitation of standard sonography quickly and noninvasively. Doppler examinations, although not difficult, must be done property to obtain useful data. Information regarding the presence and direction of flow in renal vessels can be obtained. Vascular stenosis can be identified by several Doppler criteria, although the role of Doppler as a screening measure remains controversial. Assessment of vascular resistance is possible from Doppler waveform analysis, using parameters such as the resistive index. These data may provide hemodynamic and predictive information regarding a dilated collecting system identified by conventional ultrasound. Analysis of the resistive index also may provide helpful clinical information in nonobstructive renal disease. In certain clinical settings, such analysis provides diagnostic data not readily available with other clinical and laboratory assessment methods. Pharmacologically stimulated renal Doppler examinations may lead to even greater benefits in the future. This article reviews renal Doppler ultrasound, including the physiological basis for Doppler examination, the technical principles of renal Doppler sonography, and the clinical applications of Doppler findings.