Segmental arterial mediolysis

Last revised by Igor Vlašiček on 26 Sep 2023

Segmental arterial mediolysis (SAM) is an increasingly recognized vascular disease of the middle-aged and elderly and a leading cause of spontaneous intra-abdominal hemorrhage. It is characterized by fusiform aneurysms, stenoses, dissections and occlusions within splanchnic arterial branches. Imaging is not only the key to the diagnosis of this condition, but can also facilitate life-saving endovascular therapy.

Segmental arterial mediolysis was first described as a discrete entity in 1976 1, and was initially thought to be very rare 2. Only 14 cases were reported over 20 years to 1997, but in the last decade reports have become much more frequent 3, and this is thought to be a combination of increased use of thin slice computed tomographic angiography (CTA) and increased awareness in the radiological community. The incidence may be as high as 1 per 100,000 per year 4

Segmental arterial mediolysis most commonly presents as spontaneous intra-abdominal hemorrhage in patients aged 50 to 80. Bleeding may occur into the mesentery or peritoneum, or less commonly, into the bowel lumen. Abdominal pain, distension, shock, and falling hematocrit are typical. Bowel ischemia, hematuria, or hemobilia are also described 3. For middle-aged patients with non-traumatic spontaneous mesenteric hemorrhage, segmental arterial mediolysis is the most likely underlying cause. Mortality has been described as high as 50% 5.

Segmental arterial mediolysis is an uncommon arteriopathy, which is not atherosclerotic or inflammatory. The underlying histological process is lysis of the smooth muscle of the outer media of the arterial wall 5, resulting in intramural hemorrhage, saccular or dissecting aneurysms, thrombosis and hemorrhage. It affects the visceral arteries of the abdomen in a skip pattern 6, most commonly affecting the medium size branches of the superior mesenteric artery. The etiology is unknown, but an association with episodes of splanchnic vasoconstriction has been observed (e.g. shock, hypoxia, recent major operation, vasopressor infusion) 5,7. There is some histological similarity to fibromuscular dysplasia, which is a differential diagnosis, but the clinical features and lesion distribution are usually characteristic.

The hallmark of the disorder is multiple abdominal splanchnic artery aneurysms. CT is the modality of choice 6.

CT typically shows mesenteric or intraperitoneal hemorrhage, and CT angiography reveals a range of arteriographic abnormalities of the branches of the visceral arteries 5,6, including:

  • fusiform aneurysms

  • stenosis

  • dissections

  • occlusions

A pattern of aneurysms and stenoses in series is characteristic; the "string-of-beads" appearance. The aneurysms have a random distribution, in contrast to mycotic aneurysms which show a predilection for bifurcations 6. Dissections may occur but are rare in splanchnic branches.

The severity of the presenting illness is variable, and conservative therapy may be appropriate. Importantly, immunosuppression by steroids or other drugs is thought to be counterproductive, as the arteriopathy is not inflammatory or autoimmune. Generally, the prognosis after the presenting episode appears to be good.

For incidentally discovered lesions, the natural history of segmental arterial mediolysis is poorly understood. Cases of segmental arterial mediolysis have been described in which there is an abrupt onset of arteriographic abnormalities, followed by a symptomatic stage, during which hemorrhage carries significant mortality. After this, the arteriopathy may either resolve, remain in status quo, fluctuate, or move from some segments to others. This unpredictable natural history leads most authors to recommend continued surveillance over several years, with prophylactic endovascular treatment performed for enlarging aneurysms, especially if >10 mm in size 8-10.

Significant abdominal hemorrhage requires urgent treatment. Coil embolization is most frequently advocated, and this is usually straightforward where the affected artery can be sacrificed without causing significant distal ischemia. As typical in visceral arteries, complete exclusion often requires vessels to be occluded both proximal and distal to the bleeding site. Glue embolization can also be performed 11.

If embolization is not available or contraindicated, surgical exploration, ligation, and resection of the affected gut segments and viscera may be necessary.

Conditions to consider include 12:

ADVERTISEMENT: Supporters see fewer/no ads