One of the principles of managing trauma patients is that of their continuous re-evaluation over the hours and days. Even if the execution of the computed tomography method is classically recommended, especially in the most serious cases and in polytraumas with major dynamics, the clinician can use or request an ultrasound examination, especially in subsequent re-evaluations. Here we report a clinical case demonstrating how an ultrasound re-evaluation after the acute event can lead to a correct diagnosis of a rare complication of thoracic trauma. The findings were suggestive of a pseudoaneurysm of the internal right mammary artery. Subsequently, an ultrasound-guided injection of thrombin was carried out until complete interruption of the flow within the formation. At subsequent follow-up, no arterial or venous blush was highlighted.