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"Aneurysmal rebleeding" is a term that relates to the occurrence of repeated rupture in a previously ruptured aneurysm.

Consider the example of a particular patient with an unruptured aneurysm (i.e., the aneurysm at present has an intact wall, and has never "leaked", "bled" or "hemorrhaged"). In this particular patient, one day the weakened aneurysm wall (usually the "dome" region; take me to Brain Aneurysms right now) suddenly gives way. This event is referred to as a "bleed" or "hemorrhage" or "subarachnoid hemorrhage" (SAH; because the blood typically spills into the subarachnoid space surrounding the aneurysmal artery). Following this event, the aneurysm wall, now surrounded by blood clot, is in a relatively fragile and precarious state. It may once again rupture, causing a second subarachnoid hemorrhage. If it does, this event is referred to as "aneurysmal rebleeding" or "rebleeding".

Even though not all aneurysms rupture, and not all ruptured aneurysms rerupture, aneurysmal rupture and rerupture are still relatively frequent and potentially life-threatening events ( take me to Brain Aneurysms right now). If a patient survives the initial bleed, the chances of surviving a rebleed are even less. Therefore the major problem associated with rebleeding is the lowered likelihood of survival.

2. Why do brain aneurysms rebleed?

Basically, aneurysms rebleed because their thin, ballooned-out walls (which were weak to begin with owing to relatively low amounts of normal elastic and smooth muscle tissue; take me straight to Brain Artery Structure or Brain Aneurysms) are much weaker following the initial rupture (see Figure 1, below). One can imagine that the wall of a recently ruptured aneurysm, which is now surrounded by fresh blood clot, continues to experience "stress" from the normal pounding of blood still flowing in the ("parent") artery from which the aneurysm arose. That hammer-like stress, which amounts to increased pressure on the aneurysm wall, predisposes to rebleeding. It follows that in patients with high blood pressure (hypertension) affecting the brain arteries, the risk of rebleeding can be expected to be higher.

If the flow of blood slows down in the aneurysm lumen (the center portion or "inner cavity" of an aneurysm), a clot (or "thrombus") may form - this event ("thrombosis") can happen before or after the initial rupture. The clot, which is often a hard and craggy mass (i.e., "organized" thrombus), may exert additional stress on the aneurysm wall and make it easier for it to be torn or retorn, particularly if the normal pulsations of blood are transmitted through the mass itself. Another thing that can happen before or after rupture or rerupture is that small channels of blood can form in the thrombus (a phenomenon referred to as "recanalization"). This is also associated with growth, rupture, and rerupture of an aneurysm. Finally, it should be noted that the cells that make up the wall of an aneurysm are also dependent on oxygen and other nutrients for their survival. If their nourishment is cut off (an event known as "ischemia") during growth of an aneurysm or following rupture, then the wall is further weakened as its cells effectively starve and die. This event can also play a role in causing the rupture of a previously unruptured aneurysm, or the rerupture of a previously ruptured aneurysm.

With regard to the chance (or "risk") of rebleeding, three important facts must be noted. First, all ruptured aneurysms, regardless of their original size, are at risk of rebleeding. Second, the presence of blood clot in a ruptured giant or near-giant aneurysm (i.e., an aneurysm whose diameter is greater than 20 mm) does in no way protect the patient from aneurysmal rebleeding. Third, the risk of rebleeding gradually increases with time from the initial rupture (see 3., below) so, as a rule of thumb, the earlier an aneurysm is treated the better.

Why Aneurysms Rebleed:

Figure 1 shows layers of a normal brain artery wall (A.) compared with a much thinner and weaker aneurysm wall before its initial rupture (B.). Both walls are drawn to the same scale. Note the aneurysm wall has (i) only sparse elastic tissue (shown in an orange-yellow color between the endothelial cell layer drawn in light-blue and the smooth muscle layer drawn in red), and (ii) a thinned-out muscle layer ( take me to Brain Artery Structure right now). The aneurysm wall is likely to be even more fragile following a bleed or subarachnoid hemorrhage. Red arrows indicate blood flowing in the lumen (central opening) of the normal artery or aneurysm.

3. When is a brain aneurysm most likely to rebleed?

Regardless of aneurysm size, most studies suggest that the highest incidence (occurrence) of rebleeding from a ruptured aneurysm in fact occurs within 24 hours of the initial hemorrhage. In this period, 4 to 10% of patients with a ruptured aneurysm will experience a repeated hemorrhage. The daily rate of rebleeding then drops to about 1 - 2% for the first two weeks. Therefore, a patient has an overall (approximately) 20-25% chance of experiencing a rebleed within 2 weeks of the initial hemorrhage. This is illustrated in Figure 2, below.

Pattern of Aneurysmal Rebleeding:

Figure 2 shows the incidence of aneurysmal rebleeding from the day of the initial hemorrhage ("Day 0") to 2 weeks after this event (A.), and the cumulative rate of rebleeding during the first two weeks (B.) following the first hemorrhage. Here, incidence refers to the percentage of patients experiencing a rebleed event on any given day after the initial bleed (Day 0); on the other hand, cumulative rate refers to the overall percentage of patients experiencing a rebleed by a given day after the initial bleed (Day 0). Note that (i) the peak incidence of rebleeding is within the first 24 hours of the initial bleed (i.e., approx. 5% of all patients with a ruptured aneurysm will rebleed within 24 hours), and (ii) the cumulative rate of rebleeding is about 20 - 25% by 2 weeks after the initial bleed [i.e., up to 1 in 4 (25%) patients will have rebled within 2 weeks].

4. What are the complications of brain aneurysm rebleeding?

The main complications (i.e., feared consequences) of aneurysmal rebleeding are death and serious disability. Clinical studies have found that 4 in 10 patients who suffer a rebleed from a previously ruptured brain aneurysm will not survive. Many of those who do survive are left with serious neurological impairments. Given that even a first aneurysmal bleed carries a high risk of death and permanent disability, the overall chance of any given patient surviving two bleeds from the same aneurysm is low. It cannot be overstated that early diagnosis (and early referral if appropriate), in addition to thorough planning and early treatment in an experienced neurosurgical / neuroradiological center are key recommendations for patients with ruptured brain aneurysms.