Pediatric applications of abdominal vascular Doppler: Part II

Renovascular hypertension in pediatric patients: update on diagnosis and management

Renovascular hypertension (RVH) is defined as an elevated blood pressure caused by kidney hypoperfusion, generally as a result of anatomic stenosis of the renal artery with consequent activation of the Renin Angiotensin-Aldosterone System. The main causes include genetic and inflammatory disorders, extrinsic compression, and idiopathic alterations. RVH is often asymptomatic and should be suspected in any child with refractory hypertension, especially if other suggestive findings are present, including those with severe hypertension, abdominal bruit, and abrupt fall of glomerular filtration rate after administration of angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers. There is a consensus that digital subtraction angiography is the gold standard method for the diagnosis of RVH. Nevertheless, the role of non-invasive imaging studies such as Doppler ultrasound, magnetic resonance angiography, or computed tomographic angiography remains controversial, especially due to limited pediatric evidence. The therapeutic approach should be individualized, and management options include non-surgical pharmacological therapy and revascularization with percutaneous transluminal renal angioplasty (PTRA) or surgery. The prognosis is related to the procedure performed, and PTRA has a higher restenosis rate compared to surgery, although a decreased risk of complications. This review summarizes the causes, physiopathology, diagnosis, treatment, and prognosis of RVH in pediatric patients. Further studies are required to define the best approach for RVH in children.

Recommendations for ultrasonographic assessment of renal arteries

The present clinical practice recommendations are addressed to physicians of all specialties, who perform Doppler ultrasound examinations of the kidneys on a daily basis, and in particular to specialists in radiology and imaging diagnostics. The recommendations were based on the Ultrasonography Standards of the Polish Ultrasound Society and current scientific reports consistent with Evidence Based Medicine. The paper discusses patient preparation protocol, examinat ion technique with particular emphasis on patient’s position allowing to obtain proper Doppler angle of insonation, as well as diagnostic limitations of the technique. Normal blood flow parameters as well as those indicating hemodynamically significant stenosis are also presented. Although the 2013–2014 American guidelines for renal artery duplex sonography (AIUM Practice Parameter for the Performance of Native Renal Artery Duplex Sonography and AIUM Practice Guideline for the Performance of an Ultrasound Examination of Solid-Organ Transplants), which were the basis for many national recommendations, have not been significantly updated to date, a large body of scientific research indicates the need for revision of current Doppler ultrasound standards and parameters, particularly for patients receiving endovascular treatment due to renovascular hypertension. Therefore, the paper refers to the current issue of ultrasound scan interpretation in patients receiving endovascular stenting, after transplantation of kidney, as well as in pediatric patients.

Renal sonography with Doppler for detecting suspected pediatric renin-mediated hypertension - is it adequate?

BACKGROUND

Renal Doppler US is used to evaluate suspected vascular causes of hypertension in children, despite mostly unknown diagnostic performance characteristics.

OBJECTIVE

To evaluate renal Doppler US for detecting vascular causes of hypertension in children with high clinical suspicion of aortic or renal artery narrowing.

MATERIALS AND METHODS

We identified pediatric renal Doppler US examinations performed for hypertension between January 1995 and June 2010 at our institution. We excluded children without follow-up angiography (CT-, MR-, or catheter-based). Two pediatric radiologists reviewed imaging studies and documented relevant findings. Intrarenal spectral Doppler resistive index measurement <0.5 or tardus parvus waveform constituted a positive examination.

RESULTS

Thirty-five boys and 13 girls underwent renal Doppler US and confirmatory imaging (mean age  =  9.0 years). Nineteen US examinations were truly negative, two were falsely negative, 18 were truly positive (16 involved narrowing of the aorta or main renal artery) and nine were falsely positive. Sonography had a sensitivity and specificity of 90% and 68%, respectively, for detecting a vascular cause of hypertension.

CONCLUSION

Renal Doppler sonography reliably detects renin-mediated hypertension caused by aortic or main renal artery narrowing in children. More studies are needed to determine its ability to detect intrarenal and accessory renal artery stenoses.

Renal relevant radiology: use of ultrasonography in patients with AKI

As judged by the American College of Radiology Appropriateness Criteria, renal Doppler ultrasonography is the most appropriate imaging test in the evaluation of AKI and has the highest level of recommendation. Unfortunately, nephrologists are rarely specifically trained in ultrasonography technique and interpretation, and important clinical information obtained from renal ultrasonography may not be appreciated. In this review, the strengths and limitations of grayscale ultrasonography in the evaluation of patients with AKI will be discussed with attention to its use for (1) assessment of intrinsic causes of AKI, (2) distinguishing acute from chronic kidney diseases, and (3) detection of obstruction. The use of Doppler imaging and the resistive index in patients with AKI will be reviewed with attention to its use for (1) predicting the development of AKI, (2) predicting the prognosis of AKI, and (3) distinguishing prerenal azotemia from intrinsic AKI. Finally, pediatric considerations in the use of ultrasonography in AKI will be reviewed.

Normal Doppler spectral waveforms of major pediatric vessels: specific patterns

Every major vessel in the human body has a characteristic flow pattern that is visible in spectral waveforms obtained in that vessel with Doppler ultrasonography (US). Spectral waveforms reflect the physiologic status of the organ supplied by the vessel, as well as the anatomic location of the vessel in relation to the heart. In addition, the waveforms may be affected by age- and development-related hemodynamic differences. For example, adults tend to have higher flow velocities, whereas neonates, particularly those born prematurely, have higher resistance to flow, especially in the cerebral and renal vascular beds. As Doppler US is performed with increasing frequency for vascular evaluation in children, the recognition of normal flow patterns has become imperative. Familiarity with the waveforms characteristic of specific veins and arteries in children is important. In addition, an understanding of the hemodynamic factors involved provides a useful basis for interpreting waveform abnormalities.