Spontaneous isolated dissection of the superior mesenteric artery and aneurysm formation resulting from segmental arterial mediolysis: a case report

Abstract

Background: Spontaneous isolated dissection of the superior mesenteric artery (SMA) can lead to bowel ischemia, aneurysm rupture, or even death. Studies have suggested that mechanical or hemodynamic stress on the vascular wall of the SMA may be a contributor, but its pathogenesis is unclear.

Case presentation: A 57-year-old Japanese man with a history of untreated hypertension and hyperuricemia was admitted to our hospital with the sudden onset of severe epigastric pain. Laboratory findings showed elevated white blood cell count and C-reactive protein, and contrast-enhanced computed tomography (CT) of the abdomen demonstrated arterial dissection with luminal stenosis and aneurysm formation at the distal portion of the SMA after the branching of the jejunal artery, and intravenous nicardipine was administered. The patient's epigastric pain resolved spontaneously but recurred on day 6 of his hospital stay. Contrast-enhanced abdominal CT revealed an enlarged aneurysm with wall thinning. Because of the risk of aneurysm rupture, the decision was made to perform aneurysmectomy and bowel resection on day 6. Histologic examinations revealed two separate dissecting lesions: one latent and the other resulting in aneurysm formation. Both lesions showed characteristics of segmental arterial mediolysis (SAM) with lack of arterial media, absence of internal and external elastic laminae and intimal proliferation.

Conclusions: Histologic findings in the present case suggest that mechanical or hemodynamic stress on the vascular wall and SAM-related vascular vulnerability may concomitantly contribute to the onset of isolated SMA dissection.

Keywords: Aneurysm formation; Computed tomography; Dissection; Segmental arterial mediolysis; Superior mesenteric artery.

Fig. 1

Contrast-enhanced CT images on admission. a Superior mesenteric artery (white arrow) showing luminal stenosis and concentric intramural hematoma without extravasation. b A small intimal flap (white arrow) can be seen inside the SMA just proximal to the intramural hematoma. c CT angiograph showing two lesions (asterisks) with segmental dilatation proximal to the SMA aneurysm. A blind-sac aneurysm (black arrow) can also be seen. At this point, SMA blood flow distal (S) to the aneurysm is preserved

Fig. 2

Preoperative contrast-enhanced CT images on day 6 and photograph of resected specimen. a Aneurysm (white arrow) became larger in size, and its wall thickness became thinner, compared with the CT findings on admission. b CT angiograph revealed disappearance of SMA blood flow distal to the aneurysm that had been detected on CT angiograph on admission (Fig. 1c), strongly suggesting obstruction of the SMA distal to the aneurysm. Black line indicates the position of the SMA resection stump during bowel resection. c Gross inspection of the resected specimen reveals formation of a pseudoaneurysm in the mesentery

Fig. 3

Histopathologic findings of resected specimen. a CT angiograph of the SMA on Day 6 indicating the origin of each section; letters A through I correspond to Fig. 3a through i (black lines). Red line indicates the position of the SMA resection stump. b Low-power view (LPV) (×100) with Elastica van Gieson (EVG) staining of the SMA adjacent to the proximal resection stump. Internal (white arrow) and external (black arrow) elastic laminae as well as arterial media have partially disappeared and there is prominent intimal proliferation (asterisk). On CT angiography, this region showed only mild vasodilatation but an entry point of latent dissection was seen. “P” indicates pseudolumen filled mainly with fibrin. c High-power view (HPV) (×400) with hematoxylin and eosin (HE) staining shows vacuolization (black arrow) and marked decrease in the number of vascular smooth muscle cells (SMCs). d LPV (×100) with EVG staining of the area slightly distal to the lesion shows latent dissection with preserved internal elastic lamina and eccentric intimal proliferation. e HPV (×400) with HE staining also shows a vacuolization-rich area (ellipse) in the arterial media and disturbed arrangement of medial SMCs. f LPV (×100) of the SMA with EVG staining of the area adjacent to the pseudoaneurysm neck (N) showing remarkable stenosis of the true lumen (T) due to intimal proliferation (asterisks). A small dissection (D) is also observed, but wall rupture and resultant aneurysm formation are predominant. Arterial wall adjacent to aneurysm neck lacks medial SMCs. g HPV (×400) with EVG staining of the SMA adjacent to the neck of the pseudoaneurysm. Arterial media between internal (I) and external (E) elastic laminae shows focal vacuolization (black arrows) and degeneration of vascular SMCs (white arrow). h LPV (×100) with EVG staining of the SMA distal to the pseudoaneurysm. Both internal and elastic laminae are preserved and intimal proliferation is unremarkable. Arterial lumen is occluded with thrombus. i HPV (× 400) of the distal SMA with EVG staining. There is not a great deal of vacuolization, but degeneration and disarrangement of the outer media (asterisks) are visible