Imaging description

CT angiography (CTA) provides a non-invasive method for the diagnosis of segmental arterial mediolysis (SAM), a rare non-atherosclerotic and non-inflammatory arterial disease. Smooth muscle degeneration of the outer layer of the media occurs primarily in the visceral branches of the abdominal aorta, leading to intramural hemorrhage and periadventitial fibrin deposition. Contrast-enhanced arterial phase axial CT imaging in combination with multiplanar reconstructions and maximal intensity projections are useful imaging tools. Imaging findings include caliber irregularities of the splanchnic arteries including a “string of beads” appearance, aneurysm formation, or dissection (Figures 79.1, 79.2, 79.3 and 79.4). Conventional angiography may be reserved for equivocal findings seen on CTA or MRA and for treatment.

Importance

Mortality related to SAM is about 26% and may be due to aneurysm rupture and subsequent hemorrhage. Due to the lack of histopathologic confirmation of this disease in most cases, characteristic imaging findings may be the only way to diagnose this entity in patients with otherwise unexplained abdominal pain and gastrointestinal bleeding after excluding other possible etiologies. Axial and multiplanar CTA may help in the diagnosis while catheter angiography may be used for intervention.

Typical clinical scenario

SAM usually affects middle-aged patients and presents with abdominal pain, gastrointestinal hemorrhage, retroperitoneal hemorrhage or intracranial bleeding. Endovascular intervention has a high success rate while open surgical approach with vascular reconstruction may also be performed in select cases.

Differential diagnosis

Fibromuscular dysplasia (FMD), although considered a variant of SAM given the similar imaging findings, affects middle-aged women and involves primarily the renal and carotid arteries. Congenital conditions such as Ehlers–Danlos syndrome generally starts manifesting at a younger age while neurofibromatosis type 1 may cause vascular narrowing by mass effect from the surrounding neurofibromas easily seen on cross-sectional imaging. Mycotic aneurysms have a predilection for arterial bifurcations and will have surrounding inflammatory changes.