Sadaf T. Bhutta M.B.,B.S.

University of Arkansas for Medical Sciences

Arkansas Children’s Hospital

No financial disclosures

Gadolinium chelates for contrast enhanced MRA

Pediatric Hypertension Definition Hypertension is defined as average systolic blood

pressure (SBP) and/or diastolic blood pressure (DBP) that is ≥ 95th percentile for gender, age and height on ≥ 3 occasions

Pre-hypertension is defined when the child’s average BP is between 90th and 95th percentile.

Adolescent with BP > 120/80 is considered hypertensive, even if it is below 90th percentile for that child

[Guideline] NHLBI. National High Blood Pressure Education Program Working Group on High Blood Pressure in Children and Adolescents. The fourth report on the diagnosis, evaluation, and treatment of high blood pressure in children and adolescents.

Pediatrics. Aug 2004;114(2 Suppl 4th Report):555-76.

Epidemiology True incidence of pediatric hypertension is unknown

in this country.

No race predilection

No gender difference under 6 yrs of age, higher in girls from 6yrs till puberty and higher in boys after puberty

Height and weight affect BP

Factors affecting BP include Cardiac output Baroreceptors Extracellular volume Effective circulating volume

Atrial natriuretic hormones Mineral corticoids Angiotensin

Sympathetic nervous syndrome Vascular resistance Pressors

Angiotensin II Calcium (intracellular) Catecholamines Sympathetic nervous system Vasopressin

Depressors Atrial natriuretic hormones Endothelial relaxing factors Kinins Prostaglandin E 2 Prostaglandin I 2

Causes Primary

Generally found after puberty

Secondary Renal parenchymal disease (>70%)

Coarctation of Aorta (CoA)

Renal Artery Stenosis

Pheochromocytoma

Vasculitides

Other tumors and endocrine causes

Coarctation of Aorta

Edwards J.E.: Aortic arch system. In: Gould S.E., ed. Pathology of the Heart and Blood Vessels, 3rd ed. Springfield, IL: Charles C Thomas; 1968:416-454.

Waist lesion

Tubular hypoplasia

Associated Disorders High association with Turner’s syndrome and other

structural anomalies of X chromosome, bicuspid aortic valve and abnormal mitral valve

Coarctation complex in neonates

Coexisting vascular disorders: abnormal proximal and distal para-coarctation aortic media, aneurysms of circle of Willis, aneurysms of left subclavian and intercostal arteries, tortuous retinal arterioles, vascular rings and interruption of aortic arch

Retinal arterial tortuosity in a young adult with coarctation of aorta

Eye London 1996;10 (pp4):525-27

Berry aneurysm at circle of Willis

Double Outlet LV with CoA

Pathophysiology “Despite successful surgical repair, aortic coarctation is

associated with unfavourable prognosis mainly due to cardiovascular disease. Late timing of repair and arterial hypertension represent adverse prognostic factors. Arterial hypertension can recur after coarctation repair, despite the absence of residual obstruction, with a prevalence of up to 45%.”

Arterial hypertension and cardiovascular prognosis after successful

repair of aortic coarctation: a clinical model for the study of vascular function. deDivitiis M, Rubba P, Calabro R. Nutr Metab Cardiovasc Dis. 2005 Oct;15(5):382-94

Role of Imaging Echocardiography

CT Angiography

MR Angiography

Algorithm

Echocardiography

CTA MRA

Echocardiography Trans-thoracic vs. Trans-esophageal echocardiography

Suprasternal notch window with color flow

Localized zone of accelerated flow

Peak systolic velocity gives estimation of systolic gradient

Diastolic run-off with decreasing high-velocity forward flow during elastic recoil of ascending aorta suggests hemodynamic significance

Echocardiography

Echocardiography Post repair evaluation determines residual or recurrent

obstruction or para-coarctation aneurysm formation

Post-op exercise echo-Doppler is useful for gradients and ventricular function

Doppler peak systolic velocity has a better correlation with residual narrowing than the SBP gradient between the upper and lower extremities

CT Angiography (CTA) Pros

High spatial resolution….important for assessing collaterals

Easier technique with a shorter scan time

Decreases anesthesia/sedation use and time

Cons Radiation risk

Limited functional analysis

CTA protocol Peripheral IV line large enough to sustain a contrast

flow rate of at least 1 ml/sec, given by power injector

Except for infants, our usual flow rate is 3-4 ml/sec

Saline chaser at same rate

80 kVp uptil 50 kg. weight, increase to 100 kVp for higher weight patient

MAs modulated

CTA protocol Bolus tracker in descending aorta

Slice thickness= 0.5 mm, reformatted at 1-2 mm

Non-gated, breath-hold vs. free breathing

Z-axis= thoracic inlet to diaphragm

Post-processing for 2-D multi-planar reformatted (MIP) and 3-D volume rendered images on a separate workstation

CTA

MR Angiography Pros

Less invasive than catheter angiography

No ionizing radiation

Morphology AND function

Cons

Contra-indications

Sedation/anesthesia risk

Longer acquisition and post-processing time

MRA protocol Primary Coarctation

Axial black blood sequence

3D SSFP (non gadolinium MRA)

Gadolinium enhanced MRA

Flow analysis

Pre-coarctation

Coarctation

Aorta at diaphragm

MRA Protocol Follow-up Coarctation

Axial black blood Cine imaging

Vertical long axis LV Outflow Short axis

3D SSFP (non gadolinium MRA with emphasis on heart) Gadolinium enhanced MRA Flow Analysis

Aorta Pulmonary artery Atrio-ventricular valves

Delayed enhancement (optional)

MRA

Non-Gd MRA Gd enhanced MRA

At coarctation

Post coarctation

At diaphragm

Renal Artery Stenosis Renovascular hypertension (RVHT) denotes secondary

hypertension in which a causal relationship exists between anatomically evident arterial occlusive disease and elevated blood pressure

Renal artery stenosis (RAS) is a major cause of RVHT

Pediatric causes Systemic disease (Arteritis or diffuse vasculitis)

Compression/mass effect (e.g. tumor)

Aneurysm/pseudoaneurysm

Thrombo-embolic disease

RAS of transplant kidney

Fibromuscular dysplasia

Pathophysiology Renin-angiotensin-aldosterone mechanism

Physiologic testing to assess R-A-A system

Plasma renin levels (stimulated or unstimulated)

Assess renal function (nuclear studies)

Perfusion studies to assess relative renal blood flow

Vascular studies to directly image renal arteries (DSA, CTA, MRA)

Imaging in RAS Digital Subtraction Angiography (DSA)

Ultrasonography

CTA

MRA

Nuclear Renogram/split function scans

DSA-Gold standard Hypertensive children without co-morbid conditions

who have RAS usually have single, focal branch artery stenosis. This distribution supports angiography in these patients because of its superior sensitivity in detecting branch vessel disease and its therapeutic role in percutaneous transluminal renal angioplasty.

Vo NJ, Hammelman BD, Racadio JM, Strife CF, Johnson ND,

Racadio JM. Anatomic distribution of renal artery stenosis in children:

implications for imaging. Pediatr Radiol 2006 Oct;36(10):1032-6. Epub

2006 Jul 4.

DSA Not a screening tool!!

Renal artery stenosis

Ultrasonography (USG) Safe, inexpensive, widely used (sens= 60-97%, spec=

85-99%)

Renal size assessment

Imaging of renal arteries and color flow

Measurement of blood flow velocity and pressure waveforms

Spectral sampling proximal to stenosis shows spectral widening and increased velocity

USG criteria Ratio of peak systolic velocity between main renal

artery and aorta is indicative of luminal narrowing

Magnitude of peak systolic velocity at the narrowed segment correlates with degree of luminal narrowing

Turbulent flow in post-stenotic segment

If renal arteries are visualized but no doppler signal, “total occlusion” should be suspected

USG criteria Tardus-Parvus phenomenon

Loss of early systolic peak

Acceleration rate <3 m/s²

Acceleration index >4

Acceleration time to systolic peak >0.07 s

Pulsatility index >0.12

CTA Protocol Similar protocol as Coarctation of aorta except scan

extends from diaphragm to below aortic bifurcation

2-D MIP images and 3-D volume rendered images

Size, shape of kidneys and accessory renal arteries

Degree and location of stenosis

Metal stents

Left ICA lat view Right ICA frontal view

MRI/MRA T-1 weighted contrast enhanced MRA acquisitions

have increased sensitivity (from 88-100%) and specificity (from 71-99%) for diagnosing RAS (caveat)

Fain SB, King BF et al. High spatial resolution contrast enhanced MR angiography of

the renal arteries: a prospective comparison with digital substraction angiography. Radiology.

2001;218(2):481-90

Volk M, Strotzer M et al. Time-resolved MR angiography of renal artery stenosis:

Diagnostic accuracy and interobserver variability. Am J Roentgenol. 2000;174(6):1583-88

Shorter acquisition times and higher spatial and temporal resolution

Williams syndrome

Conclusion Imaging in pediatric hypertension is useful for

vascular causes

Diagnostic (therapeutic) and follow-up

Look for associated findings