Segmental arterial mediolysis

Abstract

Segmental arterial mediolysis (SAM) is a nonatherosclerotic, noninflammatory arteriopathy, which is characterized by dissecting aneurysms resulting from lysis of the outer media of the arterial wall. The most common presentation is abdominal pain and hemorrhage in the elderly. Computed tomography (CT) and angiography imaging findings overlap with various vasculitides and include segmental changes of aneurysm and stenosis. A key distinguishing feature is the presence of dissections, the principle morphologic expression of SAM. Differentiation and exclusion of an inflammatory arteritis is crucial in appropriate management, as immunosuppressants generally used for treatment of vasculitis may be ineffective or even worsen the vasculopathy. Although the disease can be self-limiting without treatment or with conservative medical therapy, the acute process carries a 50% mortality rate and may necessitate urgent surgical and/or endovascular therapy. Prompt recognition and diagnosis are therefore of utmost importance in appropriate management of this rare entity.

Keywords: Segmental arterial mediolysis; imaging findings.

Figure 1

(A) Pathogenesis of segmental arterial mediolysis (SAM). Vacuolization and lysis of the outer arterial media leads to formation of arterial gaps and patchy transmural loss of the external elastic lamina. (B) Pathogenesis of SAM. Dissecting hematomas (asterisk “*”) and aneurysms occur at the arterial gaps with separation of the media from the adventitia.

Figure 2

(A) Multiple simultaneous visceral arterial lesions in segmental arterial mediolysis (SAM). Axial contrast-enhanced computed tomography (CT) scan demonstrates focal pseudoaneurysm of the celiac artery (arrow). (B) Multiple simultaneous visceral arterial lesions in SAM. Axial contrast-enhanced CT scan demonstrates a dissecting aneurysm of the common hepatic artery (arrow). (C) Multiple simultaneous visceral arterial lesions in SAM. Axial contrast-enhanced CT scan demonstrates a fusiform dissecting aneurysm of the distal right renal artery (arrow). (D) Multiple simultaneous visceral arterial lesions in SAM. Axial contrast-enhanced CT scan demonstrates a right common iliac dissection and saccular aneurysm of the left common iliac artery (arrows). (E) Multiple simultaneous visceral arterial lesions in SAM. Coronal maximal intensity projection (MIP) image better demonstrates the multiplicity of dissecting aneurysms throughout the abdomen and pelvis (arrows). (F) Multiple simultaneous visceral arterial lesions in SAM. Axial MIP image better demonstrates the multiplicity of dissecting aneurysms throughout the abdomen (arrows).

Figure 3

(A) Angiographic appearance of segmental arterial mediolysis (SAM). Catheter angiography demonstrates segmental alternating fusiform and saccular appearance of the distal left renal artery, representing dissecting aneurysms. (B) Angiographic appearance of SAM. Catheter angiography demonstrates segmental stenoses and irregularity of the distal right renal artery with resultant occlusion of the interlobar and interlobular arteries. (C) Angiographic appearance of SAM. Catherter angiography demonstrates fusiform enlargement of the right renal artery, representings a dissecting aneurysm.

Figure 4

Endorgan injury in segmental arterial mediolysis (SAM). Coronal maximal intensity projection image demonstrates a wedge-like area of nonenhancement of the left renal lower pole, consistent with renal infarction. Note the associated irregularity and dissecting aneurysms involving the distal bilateral renal arteries, better seen on corresponding angiographic exam (Fig. 3).

Figure 5

(A) Dissecting hematomas in segmental arterial mediolysis (SAM). Axial contrast-enhanced computed tomography (CT) scan demonstrates a dissecting aneurysm involving the celiac artery. (B) Dissecting hematomas in SAM. Axial contrast-enhanced CT scan is more sensitive for depiction of diffuse arterial wall thickening in the common hepatic and splenic arteries representing dissecting hematomas. (C) Dissecting hematomas in SAM. Coronal three-dimensional reconstructed image in the same patient demonstrates additional saccular aneurysms in the splenic and superior mesenteric arteries as well as fusiform aneurysms involving the bilateral common iliac arteries.

Figure 6

(A) Surgical treatment of segmental arterial mediolysis (SAM). Catheter angiography reveals a segment of severe stenosis involving the proximal right renal artery. Clinical and radiologic findings were consistent with SAM. (B) Surgical treatment of SAM. Catheter angiography performed after autologous vein bypass grafting of the segment of stenosis demonstrates a widely patent right renal artery.