Mega-aorta syndrome development in giant cell arteritis. A same entity?

The megaaortic syndrome: Progression of ascending aortic aneurysm or a disease of distinct origin?

BACKGROUND

Thoracic aortic aneurysm (TAA) is an often asymptomatic disease with fatal outcome, such as dissection or rupture. The megaaortic syndrome (MAS) is an extensive dilatation of the whole aorta with low incidence but high lethal outcome with unknown pathophysiology so far.

METHODS AND RESULTS

We compared aortic tissue of patients with sporadic TAAs and MAS of the ascending aorta with non-aneurysmal control tissues. Specimens of MAS patients showed a significantly reduced thickness of the media but an increased thickness of the intima compared to control tissue and TAAs with moderate dilatation. Advanced media degeneration however was detectable in both, TAAs with enhanced luminal diameter and MAS specimens, accompanied by reduced medial smooth muscle cell-density. Further specimens of MAS were characterized by massive atherosclerotic lesions in contrast to specimens of sporadic TAA patients. Infiltrations of macrophages in atherosclerotic lesions but also in the media adjacent to the adventitia were significantly elevated in tissue of TAAs with dilatation ≤6cm. Of note, atherosclerotic plaque-associated macrophages as well as those in the external media produce huge amounts of MMP-9 which is possibly involved in media degeneration and tissue destruction.

CONCLUSIONS

Taken together these results demonstrate that the pathology of MAS shows similarities with that of TAAs but pathological differences in the ascending aorta, suggesting that MAS might be a disease of different origin.

Imaging in Giant Cell Arteritis

Much progress has been made in the use of imaging as a diagnostic tool in giant cell arteritis (GCA), which assists in the management of patients where the initial diagnosis is unclear. This includes patients with atypical cranial symptoms, or with predominantly systemic, constitutional or limb symptoms. Ultrasound and magnetic resonance imaging are capable of visualising both the cranial and extracranial large vessel circulation, with vessel wall thickening and stenotic lesions being visualised. Computed tomographic angiography is helpful in visualising the aorta for aneurysm complicating GCA but can also detect vessel wall thickening in established large vessel vasculitis. PET-CT is a very sensitive test for early vascular inflammation in extracranial large vessel vasculitis, before aneurysmal or stenotic lesions have developed, of use in the patient with unexplained constitutional symptoms. The place of imaging in the follow-up of GCA is being investigated, and repeated imaging may be useful in select cases. Generally, vascular abnormalities become less defined once glucocorticoid treatment has been started, and therefore, imaging studies must be conducted early as part of a GCA fast-track assessment.