Atypical ductus diverticulum

A 41-year-old female patient was referred to chest CT following left lower lobe pneumonia that was treated with antibiotics. She complained of mild chest pain and discomfort associated with a week-long cough, all entirely resolved following treatment.  A few months earlier, she tested positive for COVID-19 infection without any significant symptoms. Ten years ago, she was involved in a car accident, and at a time, only mild head trauma and thoracic wall contusion were reported.

Non-contrast CT scan was performed. The scan revealed no acute infiltration within the lungs but did reveal a focal bulging of the aortic wall in the region of the aortic isthmus. Patient was subsequently referred to the cardiologist, and additionally, CT coronarography and angiography of the thoracic aorta were performed. Contrast-enhanced multiplanar reconstructions (MPR’s) confirmed a convex bulging of the aortic wall, with smooth, steeper margin superiorly and more obtuse margin inferiorly, accompanied by mild calcified atherosclerotic plaques within the wall. There were no signs of mediastinal haemorrhage, pleural or pericardial effusion, or any other signs of thoracic trauma.

The Ductus diverticulum presents a remnant of the ductus arteriosum and is considered anatomic variation of aortic arch. [1] MDCT is the diagnostic imaging method of choice for detecting or excluding traumatic aortic injury because it Is noninvasive, fast and widely available. On a CT scan, it occasionally presents as a bulging of aortic wall in the region of aortic isthmus. In the case of thoracic trauma, it may become challenging to differentiate between aortic wall trauma (traumatic pseudoaneurysm) and ductus diverticulum, as both are commonly seen in the isthmic region. This may become particularly difficult in case of an atypical form of ductus diverticulum, as shown in this case.

When compared to traumatic pseudoaneurysm on multiplanar CT images, ductus diverticulum presents with broader base and forms obtuse angles with the aortic wall. While typical ductus diverticulum has smooth, gentle shoulders, the atypical form is characterized by a shorter, steeper slope superiorly and a gentler slope inferiorly. The direction of ductus diverticulum is also another indication of its origin, point towards the proximal portion of the left pulmonary artery. As such, it has the same orientation as a calcified ligamentum arterosium, which is seen intermittently in routine chest CT. Atheromatous wall calcifications may be present however it is by itself not a discriminatory feature from a post-traumatic aneurysm, and it may not be absent in younger patients. [2–6]

If the ductus diverticulum tends to dilate over time due to hypertension and atherosclerosis, it may be referred as ductus diverticulum aneurysm (DDA). In such cases, according to the literature, surgical intervention with endovascular stent grafting is considered for DDA greater than 3 cm in its largest diameter. [7]

Post-traumatic pseudoaneurysm is usually found in patients with a history of high-velocity trauma, has an irregular shape, forms acute angles with the aortic wall and tends to grow towards the left. Acute aortic injuries may also be associated with mediastinal haemorrhage, sternal or cervicothoracic spine injuries, and intimal flup may be visible. [5-7]

From a clinical perspective, it is important to differentiate these entities, as it significantly affects the therapeutic approach.  A traumatic aortic pseudoaneurysm is a surgical emergency, whereas a ductus diverticulum is a normal anatomic variant. Despite a positive clinical history of trauma, morphologic features of aortic wall bulging described in this case meet the criteria for the atypical ductus diverticulum.