Cerebral aneurysm

The spontaneous disappearance and reappearance of a ruptured cerebral aneurysm is generally assumed to be a rare phenomenon although the actual incidence is unknown. Among 39 consecutive cases of acute subarachnoid hemorrhage (SAN), 33 were studied by three-dimensional computed tomographic angiography (CTA) within 6 h after the onset of SAH, followed by digital subtraction angiography (DSA) within 24 h after the ictus. Of those patients, one, a 58-year-old woman, had a saccular aneurysm at the distal anterior cerebral artery; the aneurysm was clearly demonstrated by CTA 2.5 h after the SAH onset, but was not shown by a subsequent DSA performed 8.5 h after the ictus. A follow-up DSA detected the neck of aneurysm on day 11, and the whole aneurysm was visualized on day 19. The observations in this particular case suggest that the spontaneous disappearance of a ruptured cerebral aneurysm may occur during the ultra-early stage of SAH and that reappearance may follow during the next few weeks. The patient did not suffer complications such as vasospasm or systemic hypotension nor was she treated with antifibrinolytic agents. The aneurysmal shape and the surrounding clot are considered as putative factors possibly related to the intermittent appearance of the aneurysm. [Neurol Res 2000; 22: 583-587]

Keywords: Cerebral aneurysm; angiography, computed tomography; thrombosis; subarachnoid hemorrhage; three-dimensional reconstruction

INTRODUCTION

Although most neurosurgeons agree that the spontaneous disappearance and reappearance of a ruptured cerebral aneurysm does occur, this belief is mostly based on sporadic, incidental findings in uncontrolled clinical settings',z. The incidence and the natural course of such intermittent appearances are largely unknown.

The recently developed, three-dimensional computed tomographic angiography (CTA) is a good tool for studying patients with acute subarachnoid hemorrhage (SAN) because it is non-invasive3-5. In the present series of 33 consecutive cases of ultra-early stage SAH, each patient was first studied with CTA for screening of the ruptured aneurysm and then with digital cerebral angiography (DSA) a few hours later for pre-surgical evaluation. Among those patients, we found one in whom the initial CTA clearly demonstrated an aneurysm but the follow-up DSA failed to show it. The aneurysm gradually re-appeared on follow-up DSAs performed over the next few weeks. We examined the angiographic features and possible mechanisms of this supposedly rare phenomenon, taking into consideration the lack of data concerning its actual incidence.

MATERIALS AND METHODS

The subjects of this study were 39 consecutive patients who were admitted to our institution between October 1994 to October 1996 and who had a ruptured saccular aneurysm detected by initial CTA performed within 6 h after the onset of SAH. Nicardipine hydrochloride (Perdipine(R), Yamanouchi Pharmaceutical Co. Ltd., Tokyo, Japan) was administered intravenously to control blood pressure, and buprenorphine hydrochloride (Lepetan(R),, Otsuka Pharmaceutical Co. Ltd., Tokyo, Japan) was used for sedation when necessary. Five patients who were transferred to our institution while in cardiopulmonary arrest (CPA) were studied with CTA after resuscitation. The patients' clinical status and CT findings on admission were evaluated according to the World Federation of Neurological Surgeons grading scaleb and Fisher's grading system7, respectively. After confirmation of SAH by initial conventional CT study, they were examined with CTA to screen for aneurysm. The details of the method are described elsewheres.

Briefly, the volume data were obtained with a Hitachi W-3000 CT scanner (Hitachi Medical Corp., Tokyo, Japan) after injection of 80 ml of iopamidol (lopamiron 300(R), 300 mg ml-1; Nihon-Schering, Tokyo, Japan). Prior to the volume scan, we employed a single slice dynamic CT prescan which optimally visualizes contrast enhancement in arterial phase of the first circulation of contrast material in order to reduce the artifact caused by venous enhancement. The volume data were transferred to the workstation, which generated the angiographic images at a 1-mm reconstruction pitch using a voxel transmission method. When surgical indication was suggested by the patient's condition and CTA, DSA was performed with a Philips Integris V3000 angiographic unit using four-vessel angiography with optional use of the rotational techniques8.

RESULTS

Five patients resuscitated from CPA were studied by CTA but not by DSA because they were not indicated for craniotomy. Another patient was not examined with DSA because of rebleeding during angiography. In the remaining 33 patients, CTA was performed within 60 to 351 min (190 +/- 74 min, mean +/- SD) and DSA within 85 to 1336 min after SAN (555 +/- 392 min). The clinical parameters of 33 patients studied with both CTA and DSA are summarized in Table 1. In 32 patients, DSA confirmed the aneurysms, which were clipped on the same day. In one patient, CTA demonstrated an aneurysm but the subsequent DSA failed to detect it. The details of this particular patient are described below.

Case presentation

A 58-year-old, right-handed woman was admitted to our institution because of sudden onset of severe headache. On admission, she was lethargic and complaining of extremely severe headache. She had been suffering from a hemiweakness of the right side of the body and motor dysphasia for eight years due to the hemorrhagic infarction in the left hemisphere.

A CT scan on admission demonstrated a diffuse SAH and a dense clot around the anterior genu of the corpus callosum (Figure 1). CTA performed 2.5 h after SAH onset, demonstrated a 5-mm saccular aneurysm with a small bleb located at the A2-A3 junction of the right anterior cerebral artery (Figure 2). The neck of the aneurysm appeared to be rather narrow and long. She was treated in the intensive care unit under mild sedation and her blood pressure was controlled with systolic pressure maintained from 100 to 120 mmHg. A

DSA including rotational technique performed 8.5 h after SAH disclosed no aneurysms (Figure 3, left). There was no angiographic evidence of vasospasm. A followup DSA performed on day 11 showed that the neck of the aneurysm had reappeared (Figure 3, center). The entire aneurysm had reappeared by day 19 (Figure 3, right). Craniotomy performed on day 19 disclosed the aneurysmal dome buried in the intracerebral hematoma at the anterior genu of the corpus callosum. The rather narrow, long neck of the aneurysm was readily identified and successfully clipped. She was discharged in good condition after an uneventful post-operative course.

DISCUSSION AND CONCLUSION

So far, the phenomenon involving the disappearance and reappearance of a ruptured cerebral aneurysm has been documented angiographically in only two patients,1,2. One had a small frontopolar artery aneurysm that was visible on admission but disappeared on day 16 of the hospital stay, and then reappeared on day 21^sup 1^. The other patient had a small left anterior cerebral artery aneurysm that was visualized on an angiogram on day 9, but was only partly visible on day 19, when the patient was in systemic hypotension, and had disappeared by day 23. Follow-up angiography demonstrated the complete re-appearance of the aneurysm by Day 37^sup 2^. These two patients were under antifibrinolytic therapy with epsilon-aminocaproic acid. In both cases, the intermittent appearance of aneurysm was presumed to be possibly due to temporary aneurysmal thrombosis related to the antifibrinolytic therapy, or to vasospasm or systemic hypotension1,2. Several factors have been proposed as relevant to the spontaneous thrombosis of intracranial aneurysm: the aneurysmal shape, especially the ratio of the size of the aneurysmal dome to the orifice9; hemodynamic changes due to vasospasm, systemic hypotension compression of the parent artery by the aneurysm2,10,11,thrombosis of the parent artery' , after a high-flow extra-intracranial bypass surgery intramural hemorrhage associated with parent artery dissection14; antifibrinolytic therapy1,2; and the compression by the surrounding brain edema and clot's. In our present case, the size of the aneurysm was not unusual, and there was no evidence of vasospasm, systemic hypotension, or compression or thrombosis of the parent artery. The patient was not treated with antifibrinolytic agents. Although the factors relevant to the intermittent appearance of the aneurysm cannot be specified in the present case, we found the shape of the aneurysm, which had a rather narrow, long neck, and the presence of a dense clot surrounding the aneurysm interesting. Those factors may have contributed to the thrombosis of the aneurysm.

Although repeat angiography had been regarded as beneficial for detecting an aneurysm that was undetectable on initial angiography 16, a recent report claims that even aneurysms not noted on initial angiograms could be seen by careful retrospective examination of those initial angiograms. They stressed the importance of the initial angiography being performed appropriately and evaluated by experienced physicians17. In the present study, we employed rotational DSA because this technique is good for the detection of a small aneurysm or a partially thrombosed aneurysm, especially one located in the anterior communicating artery aneurysm where an aneurysm is highly likely to be overlooked on an initial angiogram 8,18-20. Among 69 patients with nontraumatic SAH who were transferred to our clinic during the same period as this study, the incidence of SAH of unknown origin on the initial DSA was only 5.8% (4 of 69 cases). This incidence is lower than that previously reported in a cooperative study (14.9%)21. We performed every ..DSA in the same setting following a consistent protocol as far as was feasible. In the patient presented in this study, the initial CTA clearly demonstrated the aneurysm, the first DSA detected no aneurysm, the second DSA disclosed a portion of the aneurysm, and the third DSA demonstrated the whole aneurysm. It is very likely that the intermittent appearance of the aneurysm was due to the obliteration of the aneurysmal sac rather than to technical or diagnostic errors.

We conducted this study to evaluate the visualization of cerebral aneurysms in ultra-early phase of SAH using CTA as a less invasive imaging technique. CTA may detect the aneurysm that DSA failed to present because contrast resolution of CTA is much higher than that of DSA. The CT number (Hounsfield Unit) of the aneurysm in our case was 300-450, which is higher than that of the distal ACA (272). The neck and the whole feature of the aneurysm were clearly demonstrated on subsequent DSA. For these reasons, it seems reasonable to suppose that DSA could demonstrate the aneurysm 2.5 h after SAH if it was performed.

For the first time, the present study demonstrated the spontaneous disappearance and re-appearance of a ruptured cerebral aneurysm in a well-controlled series of consecutive patients. The aneurysm was probably thrombosed in the ultra-early stage of SAH, between 2.5 h and 8.5 h after the ictus, and then gradually reappeared during the following few weeks beginning with the neck portion. It was not associated with vasospasm, systemic hypotension, or the administration of an antifibrinolytic agent. The rather narrow, long neck of the aneurysm and the dense clot surrounding the aneurysm are possible factors in the temporary obliteration of this particular aneurysm.

ACKNOWLEDGEMENTS

We wish to thank Kenji Sagara, RT, and Shigeaki Nishiike, RT, for technical support and Hiroshi Hasegawa, MD, Department of Neurosurgery, Osaka Kosei-Nenkin Hospital, for his encouragement to proceed with this study.

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Yoshikazu Nakajima, Toshiki Yoshimine*, Hiroshi Mori, Kana Nakamuta, Ichiro Fujimura, Keiji Sakashita, Eiji Kohmura*, Toru Hayakawa* and Junichiro Yokota

Osaka Prefectural Senshu Critical Care Medical Center, *Department of Neurosurgery, Osaka University Graduate School of Medicine, Osaka, Japan

Correspondence and reprint requests to: Yoshikazu Nakajima, MD, PhD, Department of Neurosurgery, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Accepted for publication March 2000.

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