Stanford type B aortic dissection

Case contributed by Dr Ammar Ashraf

Presentation

RTA (run over by the car) with chest pain and backache. No history of external bleeding, vomiting, or loss of consciousness.

Patient Data

Age: 50 years
Gender: Male

Fractured right 5th -8th ribs posteriorly. Fractured left 3rd -6th ribs posteriorly.  The haziness of bilateral lower zone lung fields, likely representing lung contusions in this patient with a history of trauma. Small bilateral pleural effusions. 

FINDINGS: A small well-defined outpouching having a small mural calcification, is seen at the anteromedial aspect of the thoracic aorta at the site of the aortic isthmus, which is likely a ductus diverticulum. Aortic dissection with intimal flap is noted in the thoracic aorta commencing at the T8 level and extending inferiorly along the right anterolateral aspect of the whole abdominal aorta into the right common iliac artery, it’s both external and internal branches as well as the scanned proximal right femoral artery. It has a smaller false lumen and a larger true lumen; both of which are well-opacified. The celiac trunk, superior mesenteric, right renal, and right common iliac arteries are arising from the false lumen. Partial occlusion of the right common iliac, external iliac, and scanned right femoral arteries and near-complete occlusion of the right internal iliac arteries are noted. A clear discrepancy is seen in the enhancement pattern of both kidneys (hypoperfused right kidney), which needs close follow-up. No gross solid abdominal visceral injury, intra-abdominal free fluid, or pneumoperitoneum is seen. Incidental finding of multiple diverticula along the descending colon without any radiological evidence of diverticulitis. 

Mild fat stranding or soft tissue thickening is seen around the distal descending thoracic and proximal abdominal aorta. Bilateral lung contusions (more evident in the left lower lung), bilateral minimal pneumothoraces, mild bilateral pleural effusions, mild surgical emphysema in the left chest wall. Changes of partial collapse/consolidation are seen in the dependent portions of both lungs. Multiple bilateral posterior rib fractures (right 5th -8th and left 3rd -6th ribs). Slightly displaced fractures involving the spinous processes of T4-T8 vertebrae. Mild degenerative changes are seen in the thoracolumbar spine.

CONCLUSION: These findings are in keeping with post-traumatic Stanford type B aortic dissection.

Case Discussion

  • Ductus diverticulum is a developmental smooth focal bulge/outpouching at the site of aortic isthmus. Unfortunately, it is also a site of ~90% of post-traumatic aortic pseudoaneurysms. In the trauma setting, particularly those cases with positive findings in the chest (like our case with Stanford type B aortic dissection & multiple bilateral rib fractures), the distinction between a ductus diverticulum and an aortic pseudoaneurysm is critically important because of paramount difference in their management. Post-traumatic aortic pseudoaneurysm is a surgical emergency whereas a ductus diverticulum is a normal anatomical variant. Mural calcification, seen in ductus diverticulum, is an important imaging feature, if present (like our case), in differentiating it from pseudoaneurysm, even in the setting of acute trauma. Absence of intimal flap or mural/mediastinal hematoma, are other supportive findings.

  • Stanford type B aortic dissection is managed conservatively/medically with blood pressure control.

  • The patient was hemodynamically stable but had weak right popliteal, and dorsalis pedis pulses and mild numbness in the right lower extremity. The right lower leg and foot were relatively cold as compared to the left side. Due to a lack of vascular surgery and interventional radiological services in our setup, the patient was transferred to the local interventional cardiothoracic center in a stable condition for further evaluation/expert opinion.

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