Background: Giant thoracic aortic aneurysms involving the supra-aortic branches are rare and may present with unusual compressive, thromboembolic, and erosive complications. Extensive osseous erosion of the anterior chest wall is particularly uncommon and may mimic an aggressive cervicothoracic mass.

Case Presentation: A 79-year-old man with a history of arterial hypertension presented with a progressively enlarging painless right supraclavicular mass. Computed tomography angiography (CTA) demonstrated a complex multisegmental aneurysmal disease involving the ascending aorta (57 mm), aortic arch (75 mm), and brachiocephalic trunk, with a giant saccular cervicothoracic aneurysmal component measuring 127 × 89 × 73 mm and extending to the C5 level. The aneurysm caused marked erosion and scalloping of the posterior manubrium and medial right clavicle, together with leftward tracheal deviation and compression of adjacent cervicomediastinal structures. A large mural thrombus within the brachiocephalic component was associated with complete occlusion of the right subclavian artery, while the right common carotid artery remained patent.

Conclusion: This case illustrates an unusual presentation of a giant multisegmental thoracic aortic aneurysm as a cervicothoracic mass with sternoclavicular bone erosion and thromboembolic complications. CTA is essential for establishing the vascular origin of such lesions, identifying potentially misleading osseous changes, assessing associated complications, and providing the detailed anatomical mapping required for therapeutic planning.

Keywords: Thoracic Aortic Aneurysm; Brachiocephalic Trunk; Bone Erosion; Computed Tomography Angiography; Cervicothoracic Mass; Subclavian Artery Occlusion

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