Midaortic syndrome

Midaortic syndrome is an uncommon entity affecting children and young adults. It is characterised by progressive narrowing of the abdominal aorta and its major branches.

Clinical presentation

The onset of symptoms is usually during childhood or young adulthood ^2. However, cases are occasionally detected in adults. :

• hypertension (most common): 90% of cases, which is commonly unresponsive to pharmacological antihypertensive treatment
• intermittent claudication
• renal failure
• Patients may present with complications from hypertension such as encephalopathy, retinopathy, coronary artery disease, congestive heart failure, or cerebrovascular accidents.
• Weak or absent femoral pulses, a difference in blood pressure between upper and lower limbs, an ejection systolic murmur, and an abdominal bruit.

Pathology

The exact cause is unknown in most cases though it is probably due to an insult during intrauterine life. Whilst intimal and subintimal fibrosis and fragmentation of the elastic media are seen, arteritis and atherosclerosis are characteristically absent in this condition. 

Elastin arteriopathy in Williams syndrome can rarely be a cause ⁵. 

Radiographic features

Ultrasound

Ultrasound is an effective imaging modality which can demonstrate luminal narrowing and altered flow parameters. It is often the first-line imaging investigation requested. Understanding the sonographic features will help to improve detection of this uncommon disease.

On gray‐scale imaging, segmental narrowing or tortuosity can be detected in the distal thoracic and the abdominal aorta. 

Colour Doppler can demonstrate aliasing while spectral Doppler can show elevated peak systolic velocities in the narrowed vessels (often ranging around 230~480 cm/s) ⁹. Tardus‐parvus waveforms can be seen in the vessels distally of the stenosis.

CTA and MRA

CT angiography and MR angiography are now more widely used for evaluation and can define the extent of disease and guide surgical or endovascular management. Radiation exposure from CT and safety issues of gadolinium in MRI are, however, important considerations particularly because MAS most commonly affects children and young adults, many of whom have impaired renal function.

The normal diameter of the abdominal aorta at the level of the celiac trunk ranges from 21 mm to 25 mm.

Angiography (DSA): the gold standard

Whilst involvement of any portion of the abdominal aorta may be seen, the interrenal segment including the origins of the renal arteries is often narrowed. Typically enlarged splanchnic collaterals (e.g. inferior mesenteric artery, arc of Riolan, the marginal artery of Drummond) are noted. The aortic bifurcation and iliac arteries are spared ³.

Treatment and prognosis

Endovascular treatment is the preferred mode as it is a minimally invasive treatment option. Balloon expandable stents / stent-grafts are usually placed to expand the lumen of the aorta. Complex endovascular/surgical options such as fenestrated grafts with re-implantation of the renal arteries will be required if the renal arteries are involved.

Without treatment, life expectancy is dramatically shortened with most dying of ischaemic/hypertensive complications by age 40 ⁴.

Differential diagnosis

Imaging differential considerations include ²:

• Takayasu arteritis
• neurofibromatosis