Dissections, another disease process of the descending thoracic aorta, are rare. Aortic dissections are thought to start with a tear or disruption of the intimal lining of the aorta, either due to medial degenerative diseases, trauma or rupture of an ulcerated intimal plaque. Blood at systemic arterial pressures invades the underlying medial layer of the aortic wall, dissecting the layers of the aortic wall, and forming a false lumen. The dissection then propagates for varying distances and in varying directions along the length of the aorta.