Microcalcification and Thoracic Aortopathy: A Window Into Disease Severity

Abstract

Background: Patients with thoracic aortopathy are at increased risk of catastrophic aortic dissection, carrying with it substantial mortality and morbidity. Although granular medial calcinosis (medial microcalcification) has been associated with thoracic aortopathy, its relationship to disease severity has yet to be established.

Methods: One hundred one thoracic aortic specimens were collected from 57 patients with thoracic aortopathy and 18 control subjects. Standardized histopathologic scores, immunohistochemistry, and nanoindentation (tissue elastic modulus) were compared with the extent of microcalcification on von Kossa histology and 18F-sodium fluoride autoradiography.

Results: Microcalcification content was higher in thoracic aortopathy samples with mild (n=28; 6.17 [2.71-10.39]; P≤0.00010) or moderate histopathologic degeneration (n=30; 3.74 [0.87-11.80]; P<0.042) compared with control samples (n=18; 0.79 [0.36-1.90]). Alkaline phosphatase (n=26; P=0.0019) and OPN (osteopontin; n=26; P=0.0045) staining were increased in tissue with early aortopathy. Increasingly severe histopathologic degeneration was related to reduced microcalcification (n=82; Spearman ρ, -0.51; P<0.0001)-a process closely linked with elastin loss (n=82; Spearman ρ, -0.43; P<0.0001) and lower tissue elastic modulus (n=28; Spearman ρ, 0.43; P=0.026).18F-sodium fluoride autoradiography demonstrated good correlation with histologically quantified microcalcification (n=66; r=0.76; P<0.001) and identified areas of focal weakness in vivo.

Conclusions: Medial microcalcification is a marker of aortopathy, although progression to severe aortopathy is associated with loss of both elastin fibers and microcalcification.18F-sodium fluoride positron emission tomography quantifies medial microcalcification and is a feasible noninvasive imaging modality for identifying aortic wall disruption with major translational promise.

Keywords: aneurysm, dissecting; aorta, thoracic; aortic aneurysm; calcinosis; elastin; sodium fluoride; vascular calcification.

Figures

Figure 1.

Study flowchart. A summary of the sample collected, individual experiments, and samples excluded.

Figure 2.

Distribution of microcalcification in the proximal aortic wall of aneurysms. Assessment of the pattern of microcalcification across the aortic wall. A, Representative image of aortic wall stained with von Kossa, demonstrating significant microcalcification in the media, particularly the outer media, but not the intima. B, Across all samples assessed, as a ratio of total sample uptake, there was relatively little microcalcification of the intima, whereas there was significant deposition in the media, particularly the outer media. C through E, This pattern was consistent across aneurysm and control samples, with bicuspid aortic valve demonstrating a particularly strong preponderance for microcalcification in the outer media.

Figure 3.

18F-sodium fluoride is an excellent marker of medial microcalcification. A through D, Visual comparison of samples with minimal (A), mild (B), moderate (C), and severe (D; scale threshold applies to all autoradiography images). There was a good correlation between histologically assessed von Kossa, and 18F-sodium fluoride determined microcalcification in a sample-level analysis (E). In vivo 18F-sodium fluoride positron emission tomography fused with magnetic resonance angiogram in a patient with bicuspid aortic valve and saccular aneurysm of the ascending aorta seen on 3D reconstruction (F). Fused angiogram and 18F-sodium fluoride (G–I). Note reduced 18F-sodium fluoride at sites of aortic wall expansion (green arrows). TBR indicates tissue to background ratio.

Figure 4.

The relationship between aortopathy severity and microcalcification. A, Patients with mild (Wilcox with Bonferroni correction, P=0.00010) or moderate (Wilcox with Bonferroni correction, P=0.042) histopathologic aortopathy severity had more microcalcification than control samples. Those with severe disease had less microcalcification content than either mild (Wilcox with Bonferroni correction, P<0.0001) or moderate (Wilcox with Bonferroni correction, P=0.0030). B, In aortopathy samples, there was an inverse relationship between histopathologic disease severity and microcalcification content (Spearman ρ, −0.51; P<0.0001). C through K, Representative examples of hematoxylin and eosin (C, F, and I), elastin van Gieson (D, G, and J), and von Kossa (E, H, and K) in mild, moderate, and severe histopathologic disease, with minimal microcalcification coinciding with near total elastin loss in severe disease.

Figure 5.

Elastin fiber loss is associated with reduced microcalcification in severe aortopathy. A, Association between microcalcification content and elastin fragmentation/loss subcategory (Spearman ρ, −0.43; P<0.0001). B and C, Scanning electron microscopy from a sample with moderate histopathologic severity (B) with clear microcalcification precipitation on intact elastin fibers (orange arrows) and severe disease (C) demonstrating similar deposition along intact elastin but areas devoid of elastin with no microcalcification. D through G, Representative von Kossa (E and F) and elastin van Gieson (G and H) image from a patient with bicuspid aortic valve, severe elastin fiber loss, and microcalcification content of 0.4% percentage area (minimal). The microcalcification is clearly colocalized with areas of remaining intact elastin fibers (yellow arrows), whereas there is no microcalcification in areas devoid of elastin fibers (red arrows).