(Stroke. 1997;28:1278-1282.)
© 1997 American Heart Association, Inc.
Articles |
Ruptured Dissecting Aneurysm as a Cause of Subarachnoid Hemorrhage of Unverified Etiology
From the Department of Neurosurgery, Showa General Hospital, Tokyo, Japan.
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Abstract |
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Background and Purpose The clinical features of "aneurysmal" subarachnoid hemorrhage (SAH) of angiographically unverified etiology were reviewed to clarify the incidence and natural history of dissecting aneurysms as the hemorrhagic source of SAH.
Methods We reviewed 30 patients with SAH of unverified etiology in whom initial CT scan showed a diffuse or anteriorly distributed subarachnoid blood clot. Ten of the patients had stenotic or occlusive lesions (SOCL) on initial angiography, and these were the main focus of this study.
Results Among the 10 patients with SOCL on initial angiography, the lesions were located on the anterior circulation in 6 and on the posterior circulation in 4. Ruptured dissecting aneurysms were confirmed by exploratory surgery or autopsy in 6 patients. Subsequent rupture occurred in 6 of the 10 patients (60%), and all 6 of these patients died as a result.
Conclusions The incidence (6/30) of dissecting aneurysms as the cause of SAH of unverified etiology was unexpectedly high, especially when initial angiography disclosed SOCL (6/10). The moribund patients with SOCL showed a high rate of rebleeding, and the untreated recurrent hemorrhages were fatal. Further MRI study is indicated for these patients to demonstrate the intramural hematoma. Compared with the devastating mortality caused by the subsequent ruptures, the extent of surgical morbidity was minor. Surgical intervention could therefore be justified when the following neuroradiological findings are present: (1) SOCL evident on angiography, (2) distribution of SAH on CT compatible with the location of the SOCL, and (3) intramural hematoma on MRI in the same region as the SOCL.
Key Words: aneurysm • angiography • dissection • occlusion • stenosis • subarachnoid hemorrhage
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Introduction |
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Approximately 13% to 22% of patients suffering from spontaneous subarachnoid hemorrhage (SAH) are diagnosed as having SAH of unverified etiology when the source of bleeding cannot be determined despite extensive neuroradiological investigation.1 Several causes of bleeding can be considered in patients with normal angiograms who show diffuse or anteriorly located hemorrhages in the basal cisterns: tiny or thrombosed aneurysm, dural arteriovenous malformation (AVM), spinal AVM, or trauma.1 Some reports indicate that vertebral or carotid dissecting aneurysms could cause such bleeding; dissecting aneurysms often demonstrate subtle angiographic features in the acute stage without any presentation of typical double lumen or pearl and string signs.1 Although identification of a double lumen is the main diagnostic feature of dissecting aneurysms, some ruptured dissecting aneurysms appear only as stenotic or occlusive lesions (SOCL). Here we discuss the significance, incidence, and natural course of dissecting aneurysms among SAH cases of unverified etiology, particularly those in which initial angiography disclosed nonatherosclerotic SOCL.
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Subjects and Methods |
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During an 11-year period from April 1984 through August 1995 at Showa General Hospital, the authors reviewed and evaluated 767 patients with nontraumatic SAH, 648 of whom underwent thorough angiographic investigation to determine the source of the SAH within 48 hours after onset. All the patients showed the typical clinical symptoms and signs of SAH, which was confirmed by CT scan and/or lumbar puncture. Among these patients, 594 had saccular aneurysms and 14 had vertebrobasilar dissecting aneurysms. In the remaining 40 patients with negative initial angiographic findings, other neuroradiological modalities disclosed 1 dural AVM, 2 spinal AVMs, and 1 giant thrombosed aneurysm as the source of hemorrhage. Of the remaining 36 patients, 6 with a perimesencephalic pattern of hemorrhage had an invariably good prognosis. The remaining 30 patients with diffuse or anteriorly located subarachnoid blood clots on early CT scan were divided by the presence or absence of SOCL on initial angiography. It was hypothesized that patients with SOCL would be more likely to have dissecting aneurysms. In total, 10 patients had SOCL (5 men and 5 women ranging in age from 41 to 78 years, with a mean age of 53.0 years) (Table 1
). Patients with positive signs of subtle
abnormality at the arterial bifurcation and those with SOCL
were considered as candidates for surgery. For the latter group,
further MRI study focused on the region of angiographically evident
SOCL is indicated to visualize the intramural hematoma along the
arterial flow void. Exploratory surgery disclosed four
semifusiform aneurysms in the former group and three dissecting
aneurysms in the latter group. Sixteen patients without SOCL
and subtle angiographic signs at arterial bifurcation
underwent serial angiography, which disclosed saccular
aneurysms in 9 patients. The initial status of patients was
evaluated according to World Federation of Neurological Surgery grade,
and the Glasgow Outcome Scale was used for assessment of the patients'
condition at 6 months after the initial hemorrhage.
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Results |
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Incidence and Outcome of Subsequent Rupture
Among 10 patients with SOCL, the rate of rebleeding of the patients with a severe clinical grade (3 to 5) was significantly higher than that of the patients with a fair clinical grade (1 to 2) (two-tailed P=.00476). The rebleeding rate in 10 patients with angiographically confirmed SOCL was significantly higher than that of the other 20 patients without SOCL (two-tailed P=.030). By Fisher's exact test, this result was statistically significant with 95% confidence (Table 2
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CT Findings
Among 10 patients, 6 had diffuse subarachnoid clots and 3
had focal subarachnoid clots limited to the unilateral sylvian
cistern. The remaining patient was diagnosed as having SAH by lumbar
tap only. In the 9 patients with positive CT scans, the clot was
distributed predominantly in the cisterns adjacent to the SOCL.
Angiographic Findings
All the patients with SOCL met the following conditions: (1)
initial angiography was performed within 48 hours after onset, (2)
angiographic SOCL indicated single subtle luminal narrowing or vascular
occlusion at a point other than a vascular bifurcation, and (3)
adequate four-vessel studies disclosed absence of vasospasm and no
atherosclerotic changes in the other arterial systems. The
SOCL locations are listed in Table 1
(Fig 1).
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MRI Findings
Among the 10 patients with SOCL, MRI findings were unavailable for
the first 4 patients (pre-MRI era.). The other 6 patients were
scheduled for investigation, but 4 with severe clinical grade did not
undergo MRI because of unstable vital signs and subsequent ruptures.
The 2 patients who underwent MRI study showed intramural hematomas (Fig 2A and 2C).
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Surgical Findings
On the basis of high rebleeding rate, exploratory surgery was
considered to be indicated when the following neuroradiological
findings were obtained: (1) SOCL evident on angiography, (2)
distribution of SAH compatible with the location of the SOCL on CT, and
(3) intramural hematoma in the same region as the SOCL on MRI. The
diagnosis of ruptured dissecting aneurysm was confirmed in all
the surgical cases (Fig 2B and 2D). In our series, surgical morbidity
and mortality were minor (0%). Wrapping or clip-reinforced wrapping
procedures were performed in our series. No subsequent ruptures were
observed during the follow-up period (41 to 95 months) (Table 1).
Autopsy Findings
Among 3 autopsied patients, dissecting aneurysms were
verified on the basilar artery, vertebral artery, and internal carotid
artery, respectively. Fragmentation of the degenerated internal elastic
lamina was most commonly recognized on microscopic study. Multiple
intramural hemorrhages without luminal connections were also
observed in all patients (Fig 3A and 3B).
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Despite improvements in neuroradiological techniques, SAH of unverified etiology is not rare.1 Several studies have demonstrated that 4.7% to 8.6% of patients with such SAH eventually succumb to a subsequent hemorrhage.2 3 Some of these patients were later found to have aneurysms that were not detected during initial diagnostic evaluation.3 In contrast, little attention has been focused on dissecting aneurysms as a cause of SAH of unverified etiology.4 In our 11-year experience, the hemorrhagic sources of spontaneous SAH were revealed to be aneurysms in 594 patients and dissecting aneurysms in 20 patients. Among the latter 20, 6 had SOCL only on the initial angiograms. A substantial proportion (30%) of these dissecting aneurysms showed subtle abnormality on initial angiography. We verified a high ratio (6/30) of dissecting aneurysms as the cause of SAH cases in which the etiology was unverified by angiography. We also demonstrated that patients with SOCL of severe clinical grade showed a high incidence of rebleeding and that recurrent hemorrhages were fatal. The same tendency has been described in previous studies of ruptured dissecting aneurysms with negative initial angiographic findings. There have been 12 reported cases of dissecting aneurysm as a cause of SAH with unverified etiology either in the carotid or posterior circulation. Six of the patients with SAH and dissection in the carotid distribution have been reported,4 5 6 7 8 9 and the clinical outcome was devastating in all cases. In vertebrobasilar distribution, there are reports of six cases in which initial angiography failed to reveal the cause of the SAH and the dissecting aneurysm was revealed by subsequent angiography.10 11 12 13 14 15
Angiography does not always permit a definitive diagnosis because
luminal narrowing or vascular occlusion at a site other than a vascular
bifurcation is also seen in atherosclerotic or other vascular diseases.
It has been suggested that the pathognomonic sign for a dissecting
aneurysm is a double lumen, although this is infrequently
demonstrated.5 Angiographic signs may be understood in
terms of the status of thrombosis in the pseudolumen; thus, a double
lumen could result from minimum thrombosis, a pearl and string sign
could result from partial thrombosis, and subtle SOCL could result from
early progression of thrombosis. Although dissecting aneurysms
often demonstrate only subtle abnormalities in the acute stage, early
thrombosis might not necessarily indicate healing of the dissected
pseudolumen. This was demonstrated in our series and in other reported
cases4 5 6 7 8 9 10 11 12 13 14 15 (Table 1). Cerebral vasospasm due to SAH
occasionally has the appearance of a string sign. Cerebral vasospasm
commonly occurs in multiple vessels and is hardly seen at the acute
stage. Differentiating SOCL from incidental atherosclerotic
stenosis may be important. Another definitive
diagnostic feature of arterial dissection is
intramural hematoma. MRI is very valuable when combined with
angiography because MRI can directly demonstrate the intramural
hematoma.16 In case 6 of our patients, a high-intensity
lesion with marked contrast enhancement on T1-weighted imaging along
the C1 portion of the right internal carotid artery was observed at the
subacute stage (Fig 2A). In case 7, an isointense lesion along the
M1 segment of the right middle cerebral artery was observed at the
acute stage on proton-density imaging. In this case, T1-weighted
imaging was not diagnostic because of its inappropriate
slice position (Fig 2C). In both cases, we clearly demonstrated
intramural hematoma, shown as a crescentic (case 6) or curvilinear
(case 7) isointensity to high-intensity structure in the lumen, in the
same region where SOCL were revealed angiographically. In our series,
there was no false-positive MRI demonstration of intramural hematoma in
cases without SOCL. With the use of MRI, we could successfully diagnose
dissecting aneurysms as the hemorrhagic sources among SAHs of
unverified etiology and discriminate them from atherosclerotic
stenosis.
Our experience and review of the literature suggested that these
lesions posed a significant risk of rebleeding if untreated. The
outcome in all patients presenting with a severe clinical grade was
fatal (Table 1).4 5 6 7 8 9 10 11 12 13 14 15 When such lesions are encountered as
the likely cause of SAH, diagnosis with the aid of MRI and obliteration
of the dissected lesions are essential. Early surgery may be justified
to prevent rerupture: our series and a review of the literature
revealed a greater risk of subsequent rupture within the first week
(Table 1).4 5 6 7 8 9 10 11 12 13 14 15 If a diagnosis of dissecting
aneurysm is highly suspected, trapping of the aneurysm
or proximal ligation of the artery with or without
extracranial-intracranial bypass surgery would be the optimal surgical
treatment for prevention of rebleeding, although the best surgical
procedure is still being debated.5
In conclusion, there was an unexpectedly high ratio (6/30) of dissecting aneurysms as the cause of SAH of unverified etiology. A substantial proportion (30%) of dissecting aneurysms showing only subtle angiographic SOCL in the acute stage was noted. There was a high mortality rate (6/10) due to subsequent rupture of such SOCL. We also demonstrated that patients with a severe clinical grade of SOCL showed a high rate of rebleeding and that untreated recurrent hemorrhages were fatal. Further MRI study is indicated for these patients to demonstrate the intramural hematoma. Compared with the devastating mortality caused by the subsequent ruptures, the extent of surgical morbidity was minor. Surgical intervention could therefore be justified when the following neuroradiological findings are present: (1) SOCL evident on angiography, (2) distribution of SAH on CT compatible with the location of the SOCL, and (3) intramural hematoma on MRI in the same region as the SOCL.
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Footnotes |
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Reprint requests to Hirofumi Nakatomi, MD, Department of Neurosurgery, Fuji Brain Institute, 270-12 Sugita, Fujinomiya City, Shizuoka 418, Japan.
Received February 6, 1997; revision received March 21, 1997; accepted March 21, 1997.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Subarachnoid hemorrhage without detectable
aneurysm: a review of the causes.
Stroke. 1993;24:1403-1409.
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