Giant Coronary Aneurysm Causing Ostial Occlusion of Coronary Artery by Mass Effect: A Case Report

Coronary atherosclerosis can rarely lead to complications like giant coronary aneurysm (GCA), and acute myocardial infarction (AMI) due to thrombosis in the GCA is even rarer. Multimodality imaging is preferred over relying solely on selective coronary angiogram in such cases due to the limitations of invasive coronary angiogram in visualizing thrombosed aneurysms. We report a rare case of a patient with ST-elevation myocardial infarction caused by ostial occlusion of a right coronary artery (RCA) due to mass effect created by thrombosis in a GCA, thereby highlighting a mechanism of AMI that has not been previously described in GCA. Multimodality imaging led to the correct diagnosis and detection of the underlying mechanism, which had been completely missed by invasive coronary angiography (ICA). We also discuss the utility of multimodality imaging in such cases.


Introduction
Aneurysmal dilatation of coronary artery and giant coronary artery aneurysm (GCA) are rare findings during angiography [1,2]. There is no clear definition of GCA, but in the context of Kawasaki disease, large or giant aneurysms are defined as those with an internal lumen diameter >8 mm [3], and some experts consider atherosclerotic aneurysms >2 cm as GCA [4]. Although invasive coronary angiography (ICA) is the gold standard imaging technique in such cases, it may fail to detect coronary artery aneurysm (CAA) in the presence of luminal thrombi. In this report, we present a case of GCA involving left anterior descending artery (LAD) and right coronary artery (RCA) presenting as acute myocardial infarction (AMI) due to the occlusion of RCA ostium caused by the mass effect of thrombosed GCA of RCA. In this case, multimodality imaging led to the correct diagnosis and the detection of the underlying mechanism, which had been completely missed by ICA. To the best of our knowledge, GCA causing AMI due to mass effect has not been previously reported in the literature.

Case Presentation
A 60-year-old male non-smoker, non-diabetic, and normotensive patient was referred to our center with a history of retrosternal chest pain and dyspnea [New York Heart Association (NYHA) class IV] for two days. The patient had a history of exertional dyspnea and angina (NYHA class II) for the past year, but he was neither on any sort of medication and nor had consulted any physician for the same. The patient denied any past history of fever, joint pain, limb claudication, trauma to the chest. He was a farmer by occupation, and prior to this visit, there was no history of any medication or procedure done on him. On physical examination, his blood pressure was 100/70 mmHg, pulse was 100/minute, and regular in rhythm. The rest of the cardiovascular examination was unremarkable. An electrocardiogram at admission showed sinus rhythm with ST elevation in inferior leads (lead III/aVF) along with reciprocal ST depression in lead I, aVL, and V5-V6 ( Figure 1A). The cardiac biomarkers were significantly elevated. Initial imaging with chest X-ray revealed cardiomegaly with enlarged right heart border ( Figure 1B), and 2D-echocardiogram demonstrated inferior wall hypokinesia with mildly reduced left ventricular systolic fraction and a well-circumscribed cystic mass adjacent to the right ventricle ( Figures 1C, 1D). The routine biochemistry findings are provided in Table 1.   Angiogram of the left coronary system (Figures 2A-2D; Videos 1, 2) showed significant left main stenosis with a GCA arising from proximal LAD (Figures 2A-2C) with Thrombolysis in Myocardial Infarction (TIMI) grade II flow distal to the aneurysm. Diffuse significant lesions in the proximal left circumflex artery and its major branches were also observed. The ostium of RCA could not be engaged selectively despite several attempts, and a nonselective angiogram revealed occlusion of RCA from the ostium with mild disease in the conal branch of RCA arising from a separate ostium ( Figure 2D, Video 3).  The patient was counseled on the need for surgical intervention for his treatment, but he opted for medical management only. He was treated with guideline-directed medical therapy including anticoagulation and was discharged in a hemodynamically stable condition. The follow-up data was not available at the time of writing this case report.

Discussion
Giant aneurysms are very uncommon and are found in only 0.02-2% of the general population [5]. The majority of GCA in adults is attributed to atherosclerosis. Other causes of GCA include congenital malformation, Takayasu's arteritis (<40 years of age), connective tissue disease, other forms of vasculitis, infections, drugs, chest trauma, cardiac lymphoma, and trauma during angioplasty [6]. The most common affected artery is RCA, and concomitant involvement of other coronary arteries is uncommon [7].
The clinical presentation of GCA may range from asymptomatic to life-threatening complications. Although rare, an aneurysm could undergo thrombotic changes and may lead to AMI, but the exact incidence of AMI in GCA remains unknown [8]. Forte et al., in a study from Italy, have reported that 66.7% of CAA developed intraluminal thrombosis, out of which only 22.3% presented with atypical chest pain [9].
Besides providing information about the morphology of aneurysm, MSCT-CA helps to capture complex anatomy and detect intraluminal thrombi. Furthermore, maximum intensity projections (MIP), curved multi-planar reformations (c-MPR), and 3D volume clearly display the anatomical relationships of the aneurysm to the surrounding structures [9]. Therefore, it is wise and logical to incorporate multimodality imaging, especially CT scan, when GCA is detected in ICA.
Currently, there are no proper guidelines regarding the management of AMI caused by GCA. Treatment options include percutaneous coronary intervention (PCI) using a covered stent and surgical intervention on the background of medical therapy [11]. One study recommends surgical treatment for all CAAs that are >3 cm because of the risk of rupture [10]. The Coronary Artery Aneurysm Registry (CAAR) [12], the largest multicentre registry (including >1500 patients) of such cases, found the mortality and major adverse cardiac events (MACE) rates to be 15.3% and 31%, respectively, in such cohorts, and hence timely treatment is of utmost importance.
The main aim of the current case report is to highlight the importance of multimodality imaging in the diagnosis and characterization of GCA. Although selective invasive coronary angiogram remains the gold standard to diagnose GCA, an initial noninvasive test may provide a clue to its diagnosis by the detection of mass-like appearance on chest X-ray and echocardiogram. Moreover, the major limitation of ICA is the failure to detect aneurysms in the presence of intraluminal thrombi and its relationship to the surrounding structures, as it is a luminogram only [8]. In our case, thrombosis of RCA aneurysm led to compression of the proximal segment of RCA due to mass effect causing AMI. This was missed by ICA, which gave an impression of ostial occlusion. Also, the RCA aneurysm was not visualized on ICA.

Conclusions
GCAs are very uncommon and are found in only 0.02-2% of the general population. AMI caused by thrombus formation is an uncommon complication of GCA. We described a case of AMI due to compression of a coronary artery due to mass effect, which has not been described before. Noninvasive tests may provide a clue to the diagnosis of GCA, and relying solely on invasive selective coronary angiogram may fail to detect thrombosed GCA; hence, it is prudent to incorporate multimodality cardiac imaging when GCA is encountered. Besides providing information about the morphology of aneurysm, MSCT-CA also helps to capture complex anatomy and detect intraluminal thrombi.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.