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Yoshihisa Murayama, Kazuhide Sakurama, Koichi Satoh, and Shinji Nagahiro

✓ The carotid artery (CA) dural ring is an important structure in aneurysm surgery of the paraclinoid region. The authors used three-dimensional computerized tomography (3D-CT) angiography to study the CA dural ring.

Three-dimensional computerized tomography angiography was performed in patients with cerebral aneurysms and other cerebrovascular diseases. The paraclinoid segment of the internal carotid artery (ICA) was examined by the shaded surface reconstruction method on targeted 3D-CT angiography. The concavity was recognized in the paraclinoid segment of the ICA. The relationship between the concavity and the dural ring was investigated with anatomical studies and surgical findings.

In anatomical studies, the concavity in the paraclinoid segment of the ICA on 3D-CT angiography coincided with the level of attachment of the dural ring. Using 3D-CT angiography, it is possible to identify the location of the dural ring in patients being considered for aneurysm surgery.

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Kazuhiko Bando, Koichi Satoh, Shunji Matsubara, Minoru Nakatani, and Shinji Nagahiro

✓ The authors report on a patient who underwent percutaneous transluminal angioplasty (PTA) for stenosis of the intracranial vertebral artery (VA). This 67-year-old man's dizziness while walking was caused by infarction of the left cerebellar peduncle. On angiograms, his left VA manifested 90% stenosis at the intracranial portion and his right VA ended at the posterior inferior cerebellar artery. Because single-photon emission computerized tomography (SPECT) showed low perfusion and poor perfusion reserve in the posterior circulation, the authors performed PTA of the left VA, which was only 35% dilated due to stenosis. Although the patient's postoperative course was uneventful, postoperative hemodynamic studies (SPECT and transcranial Doppler [TCD] ultrasonography) revealed the hyperperfusion phenomenon. A 100% increase of regional cerebral blood flow in the posterior circulation was demonstrated on SPECT studies and TCD ultrasonography revealed a doubling of blood flow velocity in the VA compared with preoperative values. Careful control of the patient's blood pressure resulted in resolution of the hyperperfusion phenomenon within 1 week post-PTA. Although hyperperfusion syndrome following carotid endarterectomy is not rare, it is seldom seen after reconstruction of the posterior circulation, and the possibility of its occurrence must be kept in mind when the posterior circulation is reconstructed.

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Mohammad A. Jamous, Shinji Nagahiro, Keiko T. Kitazato, Koichi Satoh, and Junichiro Satomi

Object. The formation of cerebral aneurysms involves complex processes and little is known about the mechanisms by which they originate, grow, and rupture. The purpose of this study was to identify early ultrastructural morphological changes that lead to the formation of experimental cerebral aneurysms.

Methods. Twenty male Sprague—Dawley rats were subjected to cerebral aneurysm induction (renal hypertension and right common carotid artery ligation); 10 intact rats served as the control group. The animals were killed after 2 months, and a vascular corrosion cast of their cerebral arteries was prepared and screened for aneurysm development by using a scanning electron microscope.

Sequential morphological changes observed at the cerebral artery bifurcation in response to hemodynamic shear stress included endothelial changes, intimal pad elevation, and saccular dilation. Endothelial cell changes were the first observed morphological changes; they were followed by various degrees of artery wall dilation. No aneurysmal changes developed in any of the control rats. Of the 20 surgically treated rats, 11 displayed aneurysmal changes. In five of these animals only changes in the endothelial cell imprints could be identified. In the other six rats morphological changes in endothelial cells were associated with different stages of aneurysmal dilation.

Conclusions. This is the first study to demonstrate in vivo early morphological changes that lead to the formation of cerebral aneurysms. The morphological findings indicate the principal role of endothelial cells in the pathogenesis of cerebral aneurysms and suggest that hemodynamic shear stress and blood flow patterns may precipitate these early changes.

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Mohammad A. Jamous, Shinji Nagahiro, Keiko T. Kitazato, Junichiro Satomi, and Koichi Satoh

Object. Estrogen has been shown to play a central role in vascular biology. Although it may exert beneficial vascular effects, its role in the pathogenesis of cerebral aneurysms remains to be determined. To elucidate the role of hormones further, the authors examined the effects of bilateral oophorectomy on the formation and progression of cerebral aneurysms in rats.

Methods. Forty-five female, 7-week-old Sprague—Dawley rats were divided into three equal groups. Group I consisted of intact rats (controls). To induce cerebral aneurysms, the animals in Groups II and III were subjected to ligation of the right common carotid and bilateral posterior renal arteries. One month later, the rats in Group II underwent bilateral oophorectomy. Three months after the experiment began all animals were killed and cerebral vascular corrosion casts were prepared and screened for cerebral aneurysms by using a scanning electron microscope. Plasma was used to determine the level of estradiol and the gelatinase activity.

Hypertension developed in all rats except those in the control group. The estradiol level was significantly lower in Group II than in the other groups (p < 0.01). The incidence of cerebral aneurysm formation in Group II (60%) was three times higher than that in Group III (20%), and the mean size of aneurysms in Group II (76 ± 27 µm, mean ± standard deviation) was larger than that in Group III (28 ± 4.6 µm) (p < 0.05). No aneurysm developed in control animals (Group I), and there was no significant difference in plasma gelatinase activity among the three groups.

Conclusions. The cerebral aneurysm model was highly reproducible in rats. Bilateral oophorectomy increased the susceptibility of rats to aneurysm formation, indicating that hormones play a role in the pathogenesis of cerebral aneurysms.

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Koichi Satoh, Junichiro Satomi, Norio Nakajima, Shunji Matsubara, and Shinji Nagahiro

Object. In this study the authors performed a retrospective analysis of five cases in which the patients (three women and two men) were treated for intracranial dural arteriovenous fistulas (AVFs) associated with cerebellar hemorrhage. On the basis of their findings, the authors evaluated the characteristics of this unusual symptom.

Methods. The dural AVFs were located in the right cavernous sinus in one patient, the left transverse—sigmoid sinus in three patients, and the right superior petrosal sinus (SPS) in one patient. All patients presented with severe headache and/or loss of consciousness. Computerized tomography scans revealed a small cerebellar hemorrhage near the fourth ventricle and hydrocephalus in four cases, and a massive hemispheric cerebellar hemorrhage in the remaining case. The four patients with small hemorrhages underwent ventriculostomy and endovascular treatment; all recovered. The patient suffering from a massive hemorrhage because of a dural AVF in the SPS was treated by suboccipital craniectomy, hematoma evacuation, and removal of the vascular anomaly. This patient remains in a persistent vegetative state. In four cases, results of angiography demonstrated retrograde leptomeningeal venous drainage through the SPS to the anastomotic lateral mesencephalic vein (ALMV) and/or to the vein of the lateral recess of the fourth ventricle (VLR4V). Retrograde leptomeningeal venous drainage to the ALMV and/or VLR4V was responsible for cerebellar hemorrhage in these cases.

Conclusions. Thus, it is important to consider dural AVF in cases in which there is even a small hemorrhage near the fourth ventricle accompanied by intraventricular perforation and a decreased level of consciousness.

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Miyuki Kanematsu, Koichi Satoh, Norio Nakajima, Fusamitsu Hamazaki, and Shinji Nagahiro

✓ A 42-year-old woman experienced the sudden onset of a severe headache. Angiograms demonstrated a persistent primitive hypoglossal artery (PHA) originating from the internal carotid artery at the C-2 vertebral level. In addition, a fenestration at the PHA—basilar artery (BA) junction and an aneurysm at the proximal end of this fenestration were revealed. To perform endovascular embolization of the aneurysm, a microcatheter was introduced into the aneurysm sac via the PHA and two Guglielmi Detachable Coils were placed in the aneurysm. The patient's postoperative course was uneventful, and she was able to resume her normal life. Although many clinical cases have been reported in which a ruptured aneurysm was associated with a PHA or a BA fenestration, as far as the authors know there has been no case in the literature in which a ruptured aneurysm associated with both anomalies and no case in which endovascular embolization was used to treat a ruptured aneurysm associated with a PHA. This rare case is discussed and a review of the relevant literature is presented.

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Mohammad A. Jamous, Shinji Nagahiro, Keiko T. Kitazato, Tetsuya Tamura, Kazuyuki Kuwayama, and Koichi Satoh

Object. The increased incidence of cerebral aneurysms in postmenopausal women appears to be related to low levels of circulating estrogen. Using a rat model of aneurysm induction, the authors found that oophorectomy increased the incidence of experimental cerebral aneurysms (Part I in this issue). In the current study they examined the effects of hormone replacement therapy (HRT) on the formation of cerebral aneurysms in rats.

Methods. Forty-five female Sprague—Dawley rats were divided into three equal groups. The animals in Groups A and B were subjected to a cerebral aneurysm induction procedure (renal hypertension and right common carotid artery ligation) followed 1 month later by bilateral oophorectomy. After an additional week the rats in Group A received 17β estradiol continuous-release pellets. The rats in Group C served as controls. Three months after the aneurysm induction procedure, all the rats were killed and vascular corrosion casts of their cerebral arteries were prepared and checked for aneurysmal changes. Using a scanning electron microscope, the authors recorded aneurysmal changes as endothelial changes alone (Stage I), endothelial changes with intimal pad elevation (Stage II), and saccular aneurysm formation (Stage III). Aneurysmal changes (Stages I, II, and III) occurred in one third of rats that had undergone oophorectomy and were receiving HRT (Group A), compared with 87% of the rats that had undergone oophorectomy but did not receive HRT (Group B). Although most of the aneurysmal changes identified in Group A rats were limited to Stage I or II, most changes in Group B animals were identified as saccular dilation (Stage III).

Conclusions. The findings demonstrated the significant protective role of estrogen against the formation and progression of cerebral aneurysms. It appears to be related to the beneficial effects of estrogen on the function and growth of endothelial cells, which play a major role in preserving the integrity of the vascular wall.

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Mohammad A. Jamous, Shinji Nagahiro, Keiko T. Kitazato, Tetsuya Tamura, Hani Abdel Aziz, Masayuki Shono, and Koichi Satoh


Intracranial aneurysms are the leading cause of subarachnoid hemorrhage, which is associated with high morbidity and mortality rates. Despite advances in the microsurgical and endovascular treatment of intracranial aneurysms, little is known about the mechanisms by which they originate, grow, and rupture. To clarify the series of early events leading to formation of intracranial aneurysms, the authors compared aneurysmal morphological changes on vascular corrosion casts with parallel pathological changes in the cerebral arteries of rats.


The authors induced cerebral aneurysms by renal hypertension and right common carotid artery ligation in 40 male Sprague–Dawley rats; 10 intact rats served as the controls. The anterior cerebral artery–olfactory artery bifurcation was assessed morphologically by using vascular corrosion casts of Batson plastic reagent and immunohis-tochemically by using antibodies against endothelial nitric oxide synthase, α–smooth muscle actin, macrophages, and matrix metalloproteinase–9.


Surgically treated rats manifested different degrees of aneurysmal changes. Based on these staged changes, the authors propose that the formation of intracranial aneurysms starts with endothelial injury at the apical intimal pad (Stage I); this leads to the formation of an inflammatory zone (Stage II), followed by a partial tear or defect in the inflammatory zone. Expansion of this defect forms the nidus of the intracranial aneurysm (Stage III).


This is the first study to demonstrate the in vivo mechanisms of intracranial aneurysm formation. The inflammatory response that follows endothelial injury is the basic step in the pathogenesis of these lesions. In this study the investigators have expanded the understanding of the origin of intracranial aneurysms and have contributed to the further development of measures to prevent and treat aneurysms.

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Mami Hanaoka, Koichi Satoh, Junichiro Satomi, Shunji Matsubara, Shinji Nagahiro, Osamu Takimoto, and Masaaki Ohbayashi

✓ The authors describe a novel technique involving the use of a gooseneck snare for microcatheterization of isolated sinus dural arteriovenous fistulas (DAVFs). In some patients the inferior petrosal and transverse–sigmoid sinuses, the route of transvenous embolization (TVE) for DAVF, are separated by several channels. Even if a guidewire can be passed over the occluded portion and the affected sinus can be accessed, one may not necessarily be able to insert a microcatheter. The authors report on three patients who underwent successful microcatheterization via a novel pull-up technique, which makes use of a gooseneck snare to perform TVE even in very difficult circumstances.