False aneurysms, also known as a pseudoaneurysm, requires all three layers of the arterial wall wall to be disrupted, and integrity of the vessel is only maintained by associated hematoma or surrounding connective tissue 1).

In true aneurysms, the adventitia is preserved.

1)
McElroy KM, Malone RJ, Freitag WB, Keller I, Shepard S, Roychowdhury S. Traumatic pseudoaneurysm of the basilar artery. Am J Phys Med Rehabil. 2008;87:690–691. doi: 10.1097/PHM.0b013e31817fbaea.