Coronary Artery Involvement in Segmental Arterial Mediolysis: A Case Report

Abstract

Segmental arterial mediolysis (SAM) is an increasingly recognized disorder affecting small- to medium-sized muscular arteries. A patient with SAM involving the visceral arteries who was also found to have multivessel coronary artery involvement is described. The patient underwent a battery of biochemical, imaging, and genetic tests to exclude other vasculitides and connective tissue disorders. The aim is to shed light on the potential for SAM to affect the coronary arteries and recommend screening of the coronary arteries of patients with SAM.

© RSNA, 2019

Summary

Clinicians should be aware of the possibility of coronary artery involvement with segmental arterial mediolysis.

Key Points

• ■ Segmental arterial mediolysis (SAM) is an uncommon but increasingly recognized vasculopathy of the visceral arteries.

• ■ Coronary artery involvement is a heretofore rarely reported manifestation of SAM.

• ■ Coronary involvement in SAM may be underreported because of lack of screening.

Introduction

Segmental arterial mediolysis (SAM) is a rare and curious medium-vessel vasculopathy (1). Histologically, SAM is characterized by spontaneous, sporadic, and heterogeneously distributed lysis of the tunica media of visceral arteries in the absence of inflammation, atherosclerosis, or underlying genetic connective tissue abnormality (2). Lysis of the tunica media in SAM results in various untoward macroscopic effects, including focal dissection, aneurysmal formation, thrombosis, and rupture.

Historically, the invasiveness and impracticability of visceral artery biopsy was an Achilles heel when a diagnosis of SAM was entertained. However, surgical pathology is no longer considered a requirement for diagnosis (2–4). Advances in the technology of CT angiography have expanded the diagnostic imaging criteria for SAM (3). New serologic and genetic tests allow for the exclusion of competing diagnoses, such as Takayasu arteritis, polyarteritis nodosa, or type IV Ehlers-Danlos syndrome (4).

We report an adult patient referred from a tertiary institution, outside of our geographic region, with a diagnosis of SAM. Upon review of the results of the patient’s outside ungated CT angiography, we were surprised to see involvement of the coronary arteries. We decided to confirm and better characterize our findings with gated cardiac CT angiography, which confirmed our suspicion.

Case Report

A 55-year-old man initially presented to a nearby community hospital emergency department with lower extremity trauma and back pain after a fall. His past medical history included rate-controlled atrial fibrillation. In the course of his care, CT angiography of the abdomen and pelvis was performed, results of which demonstrated a superior mesenteric artery dissection and multifocal aneurysms involving multiple vessels, including the splenic, left renal, and bilateral common iliac arteries. These findings were judged to be incidental and unrelated to the patient’s relatively mild traumatic injuries. In light of the vascular pathologic finding revealed at CT angiography, the patient sought and received care at a university hospital outside our geographic region, where he underwent complete vasculopathic evaluation and prophylactic embolization of the splenic artery aneurysm. Although the patient had a family history of lupus, a battery of rheumatologic tests were negative. Genetic testing was also negative for connective tissue disorders. The patient’s social history was noncontributory. On the basis of clinical, imaging, and laboratory data, a diagnosis of SAM was reached.

The patient then presented to our hospital for long-term imaging follow-up. In light of our limited experience with SAM and the lack of surveillance guidelines for SAM, multiple alternatives for imaging follow-up were discussed with the patient and his physician. A decision was made to proceed with MR arteriography of the abdomen and pelvis every 2 years following a baseline MR arteriographic scan, similar to our institutional follow-up schedule for patients with vascular Ehlers-Danlos syndrome (5). During interpretation of the patient’s baseline MR arteriographic results, the postembolization CT angiographic findings from the outside tertiary center were reviewed for the purpose of comparison (Fig 1). The outside examination included the entirety of the aorta within the scan range. We observed what we believed to be an aneurysm and dissection of the left coronary artery. As the outside CT angiography was performed without gating, and because we were not aware that SAM could involve the coronary arteries, we were less than confident in our diagnosis. We elected to proceed with cardiac CT angiography to further characterize our findings.

Figure 1:

(Left) Anterior and (right) lateral projection curved planar reformat images of the superior mesenteric artery (*) demonstrate chronic aneurysm, dissection, and thrombus. A = aorta.

After confirmation of the diagnosis with cardiac CT angiography (Figs 2, 3), the patient was given high-intensity statin therapy. Aspirin was added to his already initiated warfarin therapy.

Figure 2:

Pseudocolored multimasked volume rendering of the aortic root and coronary arteries. The black asterisk demarks an aneurysm and dissection of the left circumflex coronary artery. Other aneurysms and dissections of the coronary arteries can be seen.

Figure 3:

Curved planar reformat image of the left circumflex coronary artery. The black asterisk demarks the aneurysm and dissection present.

Discussion

Although first reported in 1949 (6), Slavin and Gonzalez-Vitale (1976) were the first to fully characterize SAM in a case of fatal hemorrhage due to ruptured abdominal aneurysms (1). SAM is an underrecognized medium-vessel vasculopathy that most commonly involves the mesenteric and renal arteries (2). It is often subclinical and can follow a benign course with spontaneous resolution. Unfortunately, in those cases where it becomes symptomatic, it can lead to fatal exsanguination (1).

The etiology of SAM is unclear but repeated vasoconstrictor stimuli have been associated with a SAM-like histologic pattern (7). The histologic hallmark of the disease is the presence of vacuolization and lysis of outer medial layer of the vessel wall (2). The absence of inflammatory and atherosclerotic markers and a random segmental distribution within the peripheral visceral arterial bed are both supportive of a diagnosis of SAM (8). Another rare nonatherosclerotic and noninflammatory entity that often confounds this constellation of diagnostic features is fibromuscular dysplasia (FMD). Histologically, FMD is characterized instead by thickened fibroplastic ridges rarifying or replacing the muscular media. Review of the histopathologic literature related to these two entities reveals more similarities than differences (Fig 4) (7). The plausibility of histologic progression from SAM to FMD, and the lack of evidence to the contrary, has led to speculation that SAM is an early stage or subtype of FMD (9,10).

Figure 4:

Differences between segmental arterial mediolysis (SAM) versus fibromuscular dysplasia (FMD). Diagnosis of either of these uncommon medium-vessel vasculopathies requires exclusion of other pathologic conditions (eg, collagen vascular diseases).

According to our survey of the literature, cases of SAM associated with coronary artery aneurysms and dissections appear to be sparse. Recently, Michael et al and Naidu et al collectively reported more than 100 cases of SAM, all without record of coronary artery involvement (11,12). Our fortuitous recognition of coronary artery involvement during our review of an outside scan highlights the importance of the radiologic practice of observing every corner of the scan’s field of view (13). With advances in CT technology, coronary artery disease can be evaluated in much greater detail even at regular chest and abdominal imaging. Therefore, assessment and reporting of any coronary findings on torso CT scans should be made a part of routine reporting, which has been the practice at our center (14).

Interestingly, consensus statements published by the American Heart Association and the European Society of Cardiology (15,16) advocate for screening patients with another vasculopathy, spontaneous coronary artery dissection (SCAD), with abdominal CT angiography. SCAD, like SAM but more so, is associated with FMD (17), and it is this association that is the basis for these screening recommendations. The histopathology of SCAD, like that of SAM, involves spontaneous hematoma formation within the arterial media that proceeds to dissection and aneurysm formation (16). However, while the consensus statements mentioned previously discuss SCAD in context with a number of other vasculopathies, they make no mention of SAM. At present, there is no consensus recommendation to screen patients with SAM with cardiac CT angiography, so the true prevalence of SAM associated with coronary artery aneurysms and dissections is unknown.

In spite of some differences, foremost among them the female predilection of SCAD (16), the possibility that SAM and SCAD are manifestations of the same disease should be considered. Given that both SAM and SCAD have either epidemiologic or histologic links with FMD, a pathophysiologic association between these three is possible (Fig 5). Given the rarity of these conditions, the formation of a nationwide SAM and SCAD patient registry, similar to the FMD registry (18), could help reveal an interconnection.

Figure 5:

Schematic representation of pathologic association between fibromuscular dysplasia, spontaneous coronary artery dissection, and segmental arterial mediolysis.

Certain limitations in our evaluation of our patient and his imaging results are worth mentioning. We acknowledge our reliance on the exhaustiveness of the diagnostic investigations done at the outside university medical center. PET was not performed in our case. PET has been shown to uncover early disease activity in large-vessel vasculitis that may not be perceptible with current anatomic imaging. However, at present, due to limitations in its spatial resolution, a role for PET in the diagnosis of medium-vessel vasculitis has not been established (19).

Conclusion

Clinicians should be aware of the possibility for SAM to affect the coronary arteries. Cardiac CT angiography screening study of patients with visceral SAM could help identify the true incidence of coronary artery involvement. As patients with SCAD are screened with abdominal CT angiography for FMD, imaging physicians should also search for signs of SAM, as it is possible that all three diseases are part of a pathologic continuum of noninflammatory and nonatherosclerotic vasculopathy.