In the medical examiner's office, rupture of a berry aneurysm is the most common cause of nontraumatic subarachnoid hemorrhage. Berry aneurysms per se are not uncommon — unruptured aneurysms have been reported in 4.9% of all routine autopsies when searched for.46 While Berry aneurysms are rare in children, they increase in frequency with age. They are located, for the most part, at the point of bifurcation and branching of the cerebral arteries, with approximately 90% found in the anterior cerebral, middle cerebral and internal carotid arteries. Berry aneurysms are thought to be the result of developmental weakness of the vessel walls. This abnormality generally consists of a defect in the formation of the media at the branching point. The intimal elastic lamina and the muscularis terminate at the neck of the aneurysm, with the wall of the sac made up of thickened hyalinized intima and the adventitia. Persistence of incomplete involuted embryonic arteries with residual medial weakness is the explanation proposed for aneu-rysms away from the point of bifurcation.
Hypertension and cigarette smoking are predisposing factors. Atherosclerosis may also play a secondary role, leading to focal destruction and weakening of the vessels walls. Multiplicity of aneurysms is quite common, multiple aneurysms being reported in anywhere from 12 to 31.4% of cases.47
Berry aneurysms almost invariably rupture at the apex. When rupture occurs, there is generally hemorrhage into the subarachnoid space. Hemorrhage may also occur into the substance of the brain. The patient usually complains of an excruciating headache and loses consciousness almost immediately. Death is due to generalized vasospasm triggered by the subarachnoid hemorrhage, with resultant ischemic injury to the brain. Minor leakage from the aneurysm may precede rupture. In such cases, the patient often complains of headache for days or weeks prior to rupture.
Most of the statistical data on ruptured intracranial aneurysms are based on hospital cases, that is, those individuals who survive a rupture long enough to be admitted to a hospital. There are, however, two studies in the literature that include large numbers of individuals who died prior to or on arrival at a hospital.47,48 These studies more accurately represent the cases seen in the medical examiner system. In both reports, 60% of the patients died immediately after rupture. Of those who survived the initial insult, more than half died less than 24 h after admission to a hospital.
In Freytag's study, the ages of the individuals ranged from 14 to 77, with a mean age of 46 years.47 Eighty-four percent of the aneurysms were located in the anterior portion of circle of Willis and 16% in the posterior portion; 27% were present in the middle cerebral artery, 25% in the internal carotid artery, 24% in the anterior communicating artery, and 10% in the basilar artery. Patients with aneurysms of the posterior circle of Willis or the internal carotid artery showed a greater tendency (69-79%) to die at the time of rupture than those in other areas (49-53%). Of the 24 aneurysms in the basilar artery, 20 were present at the branching point of the posterior cerebral arteries. Evidence of previous bleeding from the aneurysms was present in 13% of the cases.
In ruptured berry aneurysms, massive subarachnoid hemorrhage was present in 96% of the cases, subdural hemorrhage in 22%, and intracerebral hemorrhage in 43%. Subarachnoid hemorrhage was the only lesion in 49% of the cases, with intracerebral hemorrhage and subdural hemorrhage alone in 1% of each of the cases. Intracerebral hemorrhage was present in 24% of those who died immediately, but in 71% of those who survived some time, thus indicating a better chance of survival if the aneurysm had ruptured into the brain tissue. Hemorrhage into the ventricular system occurred in 17% of the cases with intracerebral hemorrhage. Such hemorrhage into the ventricular system may be as rapidly fatal as bleeding into the subarachnoid space. Twenty-two percent of the cases showed hemorrhage in the subdural space. Only 5% of the cases, however, were space-occupying (over 50 mL).
In deaths due to subarachnoid hemorrhage from a ruptured berry aneu-rysm, the largest quantity of blood is on the ventral surface of the brain, with lesser amounts laterally and dorsally (Figure 3.9A). Large pools of blood on the ventral surface of the brain often make it difficult to locate the aneurysm if the brain is not examined when fresh. The arachnoid membrane should be removed with forceps and the ventral surface of the brain flushed with
running water. This will allow inspection of the circle of Willis for aneurysms (Figure 3.9B). In approximately 10% of all cases in which subarachnoid hemorrhage is present and in which the presentation is that of a ruptured berry aneurysm, no aneurysm can be found. If we exclude all other causes of the subarachnoid hemorrhage, then, in all probability, the cause is a rupture of a small aneurysm that has been completely obliterated by the blowout of the vessel.
A small percentage of the cases of nontraumatic subarachnoid hemorrhage are due to bleeding from an arteriovenous (AV) malformation. These are complex tangles of abnormal arteries and veins linked by one or more fistulas.49 They lack a capillary bed and the small arteries have a deficient muscularis. They range from small to large; cortical to deep. Most of these lesions are visible on the surface of the brain, appearing as a wedge of arteries and veins extending into the subcortical white matter. Deep arteriovenous malformations may lie in the white matter, basal ganglia, thalamus or brain-stem. The majority of arteriovenous malformations of the brain involve the central parietal cortex.
Most arterio-venous malformations derive part of their blood supply from at least one branch of the middle cerebral artery. There may be severe bleeding from these lesions into the subarachnoid space or into the substance of the brain, presenting as a massive intracerebral hemorrhage. It is estimated that 0.1% of the population have AV malformations with 12% of these symptomatic.49 Sturge-Weber syndrome is characterized by multiple arteri-ovenous malformations of the cerebral hemispheres associated with vascular nevi of the face and/or neck and epilepsy. The most common clinical presentations are intracranial hemorrhage (30-82%); seizures (16-53%); headache and focal neurological deficits.49 Two percent of all strokes are due to AVs. The death rate from hemorrhage is 10-15%.
A rare cause of subarachnoid hemorrhage is sickle cell disease. At autopsy, there is diffuse subarachnoid hemorrhage distributed evenly over the convexities of the cerebral hemispheres, as well as on the ventral surfaces of the brain. The marked concentration of subarachnoid hemorrhage on the ventral surface of the brain seen in rupture of a berry aneurysm is not present. The brain must be carefully examined to rule out the presence of arterio-venous malformations or berry aneurysms.
Whatever the cause of the nontraumatic subarachnoid hemorrhage, as soon as blood enters the subarachnoid space, it causes a mild inflammatory reaction in the meninges.509 Fibrosis subsequently develops in many cases. Following hemorrhages into the subarachnoid space, a meningeal reaction is generally not seen for at least 2 h, when there are small accumulations of polymorphonuclear cells around pial blood vessels. By 4-16 h, a more intensive polymorphonuclear reaction is seen. Lymphocytes begin to accumulate around the pial vessels. After 16-32 h there are large numbers of polymorphonuclear cells and lymphocytes. Reaction of the mesothelial cells lining the subarachnoid space and arachnoid trabeculae appears 24 h after the subarachnoid hemorrhage. Breakdown of the erythrocytes can be seen as early as 16-32 h after subarachnoid hemorrhage. By the third day, the poly-morphonuclear reaction has reached its peak. Because of a rapid increase in lymphocytes and macrophages, however, it accounts for only half of the cells present. Hemosiderin granules can be seen inside macrophages. By 7 days, no more polymorphonuclear reaction is present. At this time, lymphocytic infiltration is most prominent, with macrophages and hemosiderin. Some intact red blood cells are still present. Fibrosis of the pia matter develops in about 10 days. Since slight fibrosis of the pial and arachnoid membranes may be present as a "normal" aspect of these membranes, especially with advancing age, interpretation of minimal fibrosis is difficult.
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