Value of spectral computed tomography in the differential diagnosis of atherosclerotic plaque and intramural hematoma

Abstract Differentiating intramural hematoma (IMH) from atherosclerotic lesions remains a diagnostic challenge. Spectral computed tomography (CT), with its ability to provide advanced tissue characterization, may offer improved diagnostic precision. Given its potential utility in young patients with IMH and/or coronary artery dissection, where atherosclerotic plaques are often non-calcified and difficult to distinguish on conventional imaging, we designed a pilot study to analyze a model of aortic IMH and chronic aortic dissection (CAD). We conducted a retrospective review of all available spectral CT studies of IMH and CAD at our institution. A visual descriptive analysis was performed comparing conventional CT images with new spectral reconstructions. Hounsfield units (HU), iodine density, and effective atomic number (Z-effective) were quantified in regions of IMH/CAD and in areas of non-calcified atherosclerotic plaque within the same patient, with at least three measurements per region for comparison. The study included 10 patients (20% female, mean age 57±14 years), comprising 9 cases of CAD (5 Type A and 4 Type B, either partially or fully thrombosed) and 1 case of IMH. The mean time from event to CT was 32.5 months [IQR 11.25–100.5]. Descriptive variables are summarized in Picture 2. Visual analysis revealed that CAD/IMH generally appeared hypointense with greater heterogeneity in contrast enhancement on 40 keV virtual monoenergetic images compared to atherosclerotic plaques. Quantitative analysis of all 35 measurements demonstrated a wide range of HU values for CAD/IMH (56.95 [37.8–110.25]) potentially reflecting their heterogeneity, in contrast to the more homogeneous HU values of atherosclerotic plaques (71.3 [61.55-82]). To specifically assess the value of spectral CT, we selected IMH/CAD segments with attenuation values below the upper HU limit of plaques (82 HU), thus exhibiting similar density to hypodense atherosclerosis on conventional imaging. In this subset (70% of total measurements), iodine density was significantly lower in CAD/IMH compared to plaques (0.4 [0.2–0.85] vs 2.2 [1.4–2.65] mg/ml, p<0.001, respectively), while Z-effective values showed no significant difference. An iodine density threshold of ≤0.93 mg/ml distinguished CAD/IMH from plaque with 81% sensitivity and 100% specificity. Tissue characterization using spectral CT provides valuable information for the diagnosis of CAD/IMH beyond conventional CT assessment. These findings, combined with the improved spatial resolution of spectral CT, suggest its potential value in the non-invasive diagnosis of IMH and dissection of smaller-caliber arteries, including the coronary arteries.Visual characterization of the lesions.  Sample characteristics and measurements.