An intimal flap represents a tear in the innermost lining of an artery, fundamentally disrupting the normal flow of blood. This separation in the arterial wall creates a life-threatening medical emergency known as arterial dissection. The flap is a visual marker of the artery’s structural failure and can rapidly lead to catastrophic consequences. Immediate medical attention is necessary because the flap interferes with the delivery of oxygen and nutrients to vital organs.
Defining the Intimal Flap and Arterial Structure
The wall of a large artery, such as the aorta, is composed of three distinct layers. The innermost layer is the tunica intima, a thin lining of endothelial cells that provides a smooth surface for blood flow and regulates blood pressure. This layer is separated from the one beneath it by the internal elastic lamina, a dense membrane of elastic fibers.
The middle layer is the tunica media, which is the thickest layer and contains smooth muscle cells and elastic fibers. These fibers allow the artery to expand and contract with each heartbeat, which is important for maintaining blood pressure and propelling blood forward. The outermost layer is the tunica adventitia, made of connective tissue that provides structural support and anchors the artery to surrounding tissues.
The intimal flap is the torn segment of the tunica intima, often with a thin layer of the inner media attached, that separates from the rest of the arterial wall. This detachment allows blood to push through the tear and wedge itself between the layers. The flap then projects into the vessel’s center, acting like a mobile piece of tissue within the blood stream.
The Mechanics of Arterial Dissection
The intimal flap signals that an arterial dissection has occurred. The process begins when the tear in the intima allows high-pressure blood from the vessel’s main channel, the true lumen, to enter the space within the wall. This forceful entry splits the tunica media layer, creating a new channel for blood flow known as the false lumen.
The intimal flap serves as the septum, separating the true lumen from the newly formed false lumen. The false lumen can extend for a considerable distance along the artery, either closer to the heart (proximally) or further away (distally). This dissection is most frequently associated with the aorta, the body’s largest artery, resulting in an aortic dissection.
In the aorta, high blood pressure within the false lumen causes it to expand. This expansion can lead to the false lumen becoming larger than the true lumen, compressing the normal blood channel and impeding flow. The flap can also have additional tears, called re-entry points, which allow blood to pass back and forth between the true and false lumens.
Physiological Impact of Compromised Blood Flow
The creation of an intimal flap and a false lumen leads to two consequences: malperfusion and rupture risk. Malperfusion describes the condition where blood supply to downstream organs is compromised. The movement of the intimal flap, driven by pressure differences, can dynamically obstruct the openings of branch arteries that supply blood to organs like the kidneys, brain, or limbs.
This obstruction can be static, where the dissection extends into the branch vessel and blocks it directly. It can also be dynamic, where the flap moves like a valve to intermittently cover the branch vessel opening. The resulting lack of oxygen and nutrients can quickly cause organ failure; for instance, mesenteric malperfusion affecting the intestines has a high associated mortality rate.
The risk of rupture arises from the structural compromise of the arterial wall. When the media layer is split to form the false lumen, the remaining outer wall, the tunica adventitia, is thin and fragile. High-pressure flow within the false lumen stresses this weakened wall, making it susceptible to bursting. A complete rupture of the aorta results in massive internal bleeding, or hemorrhage, which is often immediately fatal.
Detection and Medical Management
Diagnosis of an intimal flap and arterial dissection requires medical imaging to visualize the artery’s internal structure. Computed Tomography Angiography (CTA) is the preferred diagnostic tool, as it clearly shows the intimal flap, the true and false lumens, and the extent of the dissection. Magnetic Resonance Imaging (MRI) and echocardiography, particularly transesophageal echocardiography, are also used to identify the flap and assess the impact on surrounding structures.
Treatment is determined by the dissection’s location and stability. The first line of medical management involves controlling blood pressure and heart rate. Reducing the force of blood flow decreases the stress on the arterial wall, limiting the progression of the dissection and lowering the risk of rupture.
For dissections involving the ascending aorta near the heart (Stanford Type A), immediate surgical intervention is required due to the high risk of rupture and complications. Surgical treatment involves replacing the damaged segment of the artery with a synthetic graft, which eliminates the false lumen and restores normal blood flow. For dissections limited to the descending aorta (Stanford Type B), medical management is often sufficient unless complications like malperfusion or impending rupture occur. In these cases, endovascular repair, such as placing a covered stent graft, may be performed to seal the intimal tear.