Teaching Case

A 24-year-old man presenting to the emergency department following a motorcycle accident.

Contrast-enhanced CT of thorax and abdomen was performed considering the high-velocity nature of the trauma. Non-contrast images of chest showed an intramural haematoma. Contrast-enhanced CT of thorax demonstrated a saccular pseudoaneurysm arising from the aortic isthmus with a visible intimal tear at the neck of the pseudoaneurysm. Three-dimensional volume-rendered images showed the aneurysm making an acute angle with the normal aortic contour, hence ruling out the possibility of a normal variant, namely ductus diverticulum.

Thoracic aortic injury secondary to blunt chest trauma is a life-threatening emergency with very high mortality and morbidity rate if left undiagnosed or untreated [1]. The mechanism of injury is postulated to be a deceleration injury in which there is displacement of the heart anteriorly in combination with the torsion and shearing forces acting on the immobile aorta [2,3].

The CT angiography findings of acute traumatic aortic injury have been categorized into direct and indirect findings. Direct findings include hyper attenuating intramural haematoma, pseudoaneurysm with visible intimal flap. Indirect findings like periaortic haematoma, changes in normal calibre and contour of the aorta, especially the aortic isthmus warrants concern for aortic injury. Intramural haematoma appears as a focal crescentic, hyperattenuating region of eccentrically thickened aortic wall with inward displacement of intimal calcifications on non-contrast CT in distinction to a periaortic haematoma which is ill-defined and does not take a crescentic shape. The high attenuation appearance and inward displacement of intimal calcification are best appreciated in non-contrast phase, hence non-contrast phase should be included in CT imaging of aorta. A classic aortic dissection with thrombosed false lumen can closely resemble an intramural haematoma. Unlike the intramural haematoma which maintains a constant relation with aorta, the thrombosed false lumen in a classic dissection spiral longitudinally around the aorta. Intramural haematoma can coexist in a classic dissection as both conditions primarily involve the aortic media [4].

Aortic isthmus is the most common site of injury due to the tethering effect of ligament arteriosus [3-7]. Traumatic aortic lesions are classified into three grades by Goarin et al [8]. Grade 1 refers to isolated intramural hematoma. Grade 2 lesions are the cases in which both intima and media are involved and the resultant pseudoaneurysm formation. Grade 3 lesions involve all three layers of aortic wall and result in fatality from rapid extravasation of blood.

Multiplanar reconstructions and curved reformats are necessary to rule out aortic injuries. The diagnostic challenges are more in non-cardiac gated studies due to artefacts related to aortic pulsations which degrade image quality in aortic sinus and ascending aorta. Ductus diverticulum is an anatomical variant that mimics a traumatic pseudoaneurysm of aortic isthmus. This entity can be identified with confidence by noting the obtuse angle made with aortic wall in contrast to the acute angle made by pseudoaneurysm [9].

Treatment options include open surgical repair, endovascular repair and medical management. Open surgical repair is preferred for injuries involving the aortic root and ascending aorta. Endovascular repair has become the procedure of choice for injuries to aortic isthmus and descending aorta. Surgery is the primary treatment for injuries of ascending aorta. Medical management with frequent imaging follow-up is regarded safe in grade 1 aortic injuries.

As the patient was hemodynamically stable, imaging follow-up with plan for endovascular repair in the future was considered.

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