Introduction

Porcelain aorta (PA) is a structural aortic wall disease characterized by extensive heavy calcification of the ascending thoracic aorta extending to the aortic arch and descending aorta. The calcification occurs in a diffuse complete or near-complete circumferential pattern involving, predominantly, the ascending aorta's anterior wall and the aortic arch's superior wall.[1][2] 

The definition of porcelain aorta is not clear or standard, and it varied between authors who described it. The common denominator that best describes the clinical problem is aortic calcification that interferes with aortic cannulation, aortic clamping, aortotomy, or central coronary bypass anastomosis, necessitating modification of the surgical technique to avoid complications.[1] The presence of PA complicates the successful performance of surgical and interventional procedures, and the aortic calcification has been associated with an increased risk of periprocedural complications and is an independent predictor of mortality in surgical patients.

Classification

Calcium deposition in porcelain aorta can be located in the tunica intima, starting at the base of atherosclerotic plaques, known as the atherosclerotic type. While in the non-atherosclerotic type, calcification usually occurs in the tunica media of the aortic wall.[2]

Furthermore, porcelain aorta can also be classified into two main types based on the site of calcification in the thoracic aorta as follows:

• Type I - implies the localization of circumferential calcification of the ascending aorta independent of further extensions. This type is subdivided into two subtypes according to assessing the aorta's clamping possibility during cardiac surgery by a calcification score proposed by Nishi et al.[3] and defined as the ratio of the circumferential length of calcification to the entire ascending aortic circumference.[2]
• Type IA in which the calcification score is above 75%, impeding the possibility of aorta clamping during cardiac surgeries[2]
• Type IB shows a calcification score below 75%, allowing the option to clamp the aorta but with increased risk[2]
• Type II - refers to the calcification localized only in the aortic arch and descending aorta.[2]

Etiology

Porcelain aorta is associated with several disease processes, including chronic kidney disease, mediastinal radiation, chronic systemic inflammatory diseases such as Takayasu arteritis, systemic lupus erythematosus, and rheumatoid arthritis. Multiple risk factors have been deemed responsible in PA in literature reviews. The factors commonly involved in both types are a familial factor, aging, diabetes mellitus, radiation, uremia, and Takayasu arteritis. The atherosclerotic type is associated with additional factors such as hypertension, hyperlipidemia, smoking, alcoholism, sedentary lifestyle, obesity, systemic lupus erythematosus, and rheumatoid arthritis.[1]

Epidemiology

Porcelain aorta is a relatively rare entity in the general population, but recently it has been increasingly recognized in patients 60 years and older, particularly those with coronary artery disease, chronic renal disease, and calcific aortic stenosis (AS). The reported incidence rate ranges from 1% to 20% based on different studies. Leyh et al. found that 23 out of 1861 (1.2%) patients who underwent coronary artery bypass grafting (CABG) had porcelain aorta.[4] PA was also detected in 15.1% (54 of 358) of patients enrolled in an inoperable cohort of PARTNER (placement of aortic transcatheter valves) trial.[5] PA was present in 18% (61 of 339) patients undergoing transcatheter aortic valve replacement (TAVR).[6] The FRANCE-2 TAVI registry and German TAVI registry published porcelain aorta incidence rates of 5% and 11%.[7][8] Faggiano et al. also evaluated 240 patients for AS and noted that 7.5% (18/240) had porcelain aorta.[9]

Several studies have reported discordant results for gender differences in the prevalence of porcelain aorta. The evaluation of PA among the heterogenic population has revealed some sex distribution discrepancies, showing a male predominance in some[10][11] and a female predominance in others.[12][13][14] Moreover, a series of patients with PA who underwent transaortic valve replacement (TAVR) for severe aortic stenosis demonstrated a female predominance (52.8% to 75.4%).[6][8][15] On the other hand, there is a male predominance in porcelain aorta prevalence among patients who underwent coronary revascularization surgery.[16]

Pathophysiology

The exact cause of porcelain aorta is still elusive, but two pathophysiological processes have been described in the pathogenesis of this condition. These mechanisms allowed us to divide porcelain aorta into the following two entities:

Atherosclerotic Porcelain Aorta

It is characterized by calcification of tunica intima of the aortic wall due to atherosclerotic plaques development. These atheromatous lesions are induced by an inflammatory endothelial injury that activates the endothelial cells to express adhesion molecules that attract inflammatory cells, mainly monocytes and T lymphocytes, into the subendothelial intima. These monocytes undergo a specific differentiation into macrophages, which phagocytose the modified lipoproteins producing foam macrophages. The activated macrophages secrete cytokines to recruit more inflammatory cells and growth factors that induce the proliferation of inflammatory cells and vascular smooth muscle cells (VSMCs) and endothelial cells. In turn, these factors stimulate the migration of VSMCs from the tunica media into the tunica intima.

The intimal VSMCs proliferate and ingest lipoproteins forming lipid-laden VSMCs. The layers of foam macrophages and lipid-laden VSMCs are collectively known as fatty streaks, which are recognized as an early sign of stable atherosclerosis. The advanced, stable atherosclerosis is characterized by further enlargement of fatty streaks and secretion of extracellular matrix proteins by VSMCs, forming a fibrous cap covering the lesion. This matrix is followed by apoptosis of foam macrophages, leading to necrosis of VSMCs and degradation of extracellular matrix proteins, thus producing a necrotic core associated with the advanced unstable lesion. The destabilization of atheromatic plaques increases the liability of rupture, resulting in platelet accumulation at the site of rupture and the formation of atherothrombosis that occludes the artery.[1]

Nonatherosclerotic Porcelain Aorta

In this type, calcification occurs in the tunica media of the aortic wall in the absence of atherosclerosis. It is induced by vascular inflammation, radiation, and uremia via triggering a metaplastic transformation of VSMCs into osteoblasts leading to the production of bone-associated proteins such as alkaline phosphatase, bone sialoprotein, bone GLa protein, and bone morphogenic protein 2. In cases of vascular inflammation and aging, apoptotic vesicles arising from dead VSMCs, and elastin degradation mediated by matrix metalloprotease will act as a nidus for medial calcification by sending a paracrine osteogenic signal that will provoke the aortic calcium deposition as well as the collagen deposition and loss of the elastic fibers causing an arterial wall stiffness.[1][17]

History and Physical

Pertinent aspects of history and physical examination in patients with porcelain aorta are related to underlying medical conditions and risk factors.

Evaluation

Porcelain aorta is an asymptomatic condition that usually appears as an incidental finding in patients evaluated for cardiovascular or pulmonary diseases.[1] It is commonly identified on chest radiographs or computerized tomographic scans done for other indications.

Different diagnostic tools have been suggested to diagnose porcelain aorta and evaluate its extent and exact location before any cardiac intervention. The most accurate modality is a multislice computed tomography (MSCT). It is used to accurately diagnose porcelain aorta and give valuable information about the exact level and site of aortic calcification, thereby distinguishing PA (circumferential calcification) from a less extensive aortic calcification. Furthermore, a 3-dimensional (3D), volume-rendered reconstructions of MSCT images can be done to allow 3D mapping of the aortic wall, thus providing us with useful information about the three-dimensional distribution of the calcification.[1][2][18][19][20]

Other modalities include:

• A chest X-ray may occasionally reveal a calcification in the thoracic aorta, but it is not accurate in defining PA.
• Fluoroscopy during coronary angiography is somehow sensitive in detecting an aortic calcification that suggests PA; however, it lacks the precision in assessing the distribution and localization of this calcification.

On the other hand, PA is recognizable during the cardiac surgery by performing an epiaortic echocardiographic scanning of the aorta in conjunction with manual palpation after sternotomy and exposure of the aorta. Such testing confirms the presence of PA, as well as its extent and exact location.[1][2][18][19][20]

Pre-operative identification of porcelain aorta is important because the procedural plan often changes if PA is discovered. When porcelain aorta is suspected based on incidental findings on other imaging modalities, pre-procedural computed tomography can evaluate PA.

Differential Diagnosis

Porcelain aorta is a radiographic diagnosis with few or no differential diagnosis. Often, minor forms of thoracic aortic calcification are found in older patients. PA is the most severe form of thoracic aortic calcification.[33]

Prognosis

Porcelain aorta is typically an incidental finding associated with diffuse atherosclerotic cardiovascular disease, chronic kidney disease, or prior chest radiation therapy. General prognosis in patients with PA is usually related to the underlying medical conditions.

Complications

Porcelain aorta is usually an incidental finding in patients being evaluated for cardiovascular or pulmonary diseases.[1] Porcelain aorta is frequently associated with valvular and coronary calcification, thus increasing the risk of stenotic valvular disorders and ischemic heart diseases due to coronary atherosclerosis in these patients. Furthermore, severe calcification of the aorta and resultant luminal narrowing increases the resistance to the blood flow ejected from the left ventricle, resulting in the development of cardiac hypertrophy, congestive heart failure, and arrhythmias over time. A few studies have also linked an elevated risk of long-term mortality and adverse cardiovascular events and stroke in patients with aortic calcification.[1] 

Cardiac surgery is more complicated in patients with porcelain aorta, and their management can be challenging due to the increased risk of perioperative atheroembolism and aortic dissection.[25]Patients with a PA are at high risk for embolic stroke due to manipulating aortic atheroma during surgery.[33]

Pearls and Other Issues

A porcelain aorta finding is important to recognize in the preoperative evaluation of cardiac surgery as it potentially can complicate cardiac surgeries that require cross-clamping or involving the aorta. Modification of surgical technique may be needed with this condition.

Enhancing Healthcare Team Outcomes

Porcelain aorta significantly increases the morbidity and mortality in patients undergoing cardiac surgeries.[18] It is considered a challenging issue for cardiac surgeons and interventional cardiologists because it precludes and complicates aortic cannulation, aortic clamping, aortotomy, and central coronary bypass anastomosis, thereby raising substantially the complexity and the risks associated with cardiac procedures, particularly cardiopulmonary bypass graft and aortic valve replacement procedures.

Careful pre-operative evaluation can help identify the presence of PA in patients planned for interventional and surgical procedures and can aid in pre-operative planning to minimize complications associated with PA.