Aortic Intimal Sarcoma Mimicking Atherosclerotic Plaque: Diagnostic Limitations of Fluorodeoxyglucose-positron Emission Tomography/Computed Tomography and Magnetic Resonance Imaging

Figure 1.. Contrast-enhanced CT showing irregular thickening of the thoracic aortic wall with prominent thrombi or plaques. In the proximal right subclavian artery, a soft tissue density consistent with thrombus or plaque is evident, causing severe stenosis or occlusion (a, b). Non-contrast-enhanced CT reveals a pathological fracture with osteolytic changes in the left 10th rib (c) (white arrow). Similar osteolytic changes are noted in the left acetabulum (d) (white arrow).

Figure 2.. Initial whole-body 18F-FDG PET/CT scan showing an extensive FDG uptake in multiple bones, as well as an uptake in the right adrenal gland and right testis (red arrows) (a). The FDG uptake corresponds to osteolytic lesions identified on non-contrast CT, including the ribs (b) and left acetabulum (c). There is no abnormal accumulation of FDG in the mural thrombus of the thoracic aorta (SUVmax 2.47) (d, e).

Figure 3.. Contrast-enhanced CT shows a prominent mural thrombus in the aortic arch (a). A follow-up 18F-FDG PET/CT scan at 20 months after the symptom onset reveals an increased FDG uptake near the surface of the thickened regions of the aortic arch, despite the SUVmax remaining 3.1 (b) (white arrow). A soft tissue mass is identified in front of the thoracic spine (yellow arrow).

Figure 4.. MRI reveals no diffusion restriction in the mural thrombus of the aortic arch on diffusion-weighted images (a) or ADC maps (b). Gadolinium-enhanced MRI also shows no contrast enhancement in the thickened area of the aortic arch (c).

Figure 5.. Gross pathology of the aortic arch to descending aorta demonstrates approximately 15 cm of luminal narrowing, the most severe stenosis being evident from the origin of the left subclavian artery to the descending aorta (a, b).

Figure 6.. Low-power Hematoxylin and Eosin (H&E) staining shows intimal thickening associated with arteriosclerosis (a). A microscopic examination reveals tumor necrosis, fibrin deposition, and viable tumor tissue on the luminal surface of the aorta (b–d, ×4, ×10, ×20). Immunohistochemistry demonstrates positive staining for keratin AE1/AE3 (e, ×40), vimentin (f, ×40), CD31 (g, ×40), and SMA (h, ×40). The MIB-1 labeling index (i, ×40) is approximately 68%, with regional variation in expression. Metastases on the anterior surface of the lower thoracic spine, shown with H&E staining (j–l), are composed of pleomorphic tumor cells with marked atypia (×4, ×10, ×20). CT: computed tomography, 18F-FDG PET/CT: 18F-fluorodeoxyglucose-positron emission tomography/computed tomography, ADC: apparent diffusion coefficient, SMA: smooth muscle actin, MIB-1: mindbomb homolog-1