Surgical approaches for the treatment of aneurysms on the P2 segment of the posterior cerebral artery

OBJECTIVE: The P2 segment of the posterior cerebral artery has remained a challenging region to expose surgically. We establish a surgical strategy for P2-segment aneurysms. METHODS: Each segment of the posterior cerebral artery was classified according to Zeal and Rhoton's classification. Fourteen of 18 P2-segment aneurysms were surgically treated. The patient's outcome, the aneurysm location, and the surgical procedures were evaluated. A cadaveric study was performed to clarify the surgical view obtained via three different surgical approaches. RESULTS: Nine aneurysms were clipped, two were trapped, one was coated, and one was excised with parent artery reconstruction. Cerebral revascularization techniques were used for three patients. The pterional approach exposed the anterior half of the P2a segment. The subtemporal approach revealed the P2a segment, but its exposure was restricted by its localization in the ambient cistern. Via the occipital interhemispheric transtentorial approach, the P2p segment was visible and could be manipulated. When the posterior half of P2a segment was high on a coronal view of magnetic resonance imaging, it was extremely hard to access via any approach. CONCLUSION: A surgical strategy for the P2 aneurysm can be planned with accurate prediction of the aneurysm location. When the localization of an aneurysm on the posterior half of P2a segment is high, a resection of brain tissue may be required.     

Aneurysms arising from the cortical segment of the superior cerebellar artery--two case reports

Two unusual cases of partially thrombosed or fusiform type aneurysm on the cortical segment of the superior cerebellar artery (SCA) with subarachnoid hemorrhage are described. A 71-year-old female had a partially thrombosed, multi-lobular aneurysm located at the marginal branch of the SCA. This aneurysm was successfully clipped and wrapped via a subtemporal transtentorial approach in the acute stage. A 52-year-old female had an atherosclerotic fusiform aneurysm located at the distal portion of the hemispheric branch of the SCA. This aneurysm was successfully trapped using an infratentorial supracerebellar approach in the acute stage. Both patients were discharged without neurological deficits. The subtemporal transtentorial or lateral suboccipital approach for the proximal cortical segment, and the infratentorial supracerebellar approach for the distal cortical segment of the SCA are recommended for surgical treatment of these aneurysms.     

Selection of surgical approach for quadrigeminal cistern arachnoid cyst

Preoperative magnetic resonance imaging of 4 cases of quadrigeminal cistern arachnoid cyst were retrospectively reviewed and patterns of extension to surrounding cisterns from the quadrigeminal cistern were examined. Relationship between patterns of extension to surrounding cisterns and selected surgical approach were evaluated. In 2 cases, the cyst extended anteriorly and compressed the quadrigeminal plate. These two cases had hydrocephalus due to aqueductal stenosis. The anteroirly extending cyst was treated with endoscopic ventriculocystocisternostomy via the lateral and third ventricles. In one case, the cyst extended superiorly to the velum interpositum cistern, and was treated with endoscopic ventriculocystocisternostomy via the lateral ventricle. In one case, the cyst extended laterally to the ambient cistern and compressed the posterior horn of the lateral ventricle. This case had loculated hydrocephalus of the inferior horn. The laterally extending cyst was treated with resection of the wall of the arachnoid cyst via an infratentorial supracerebellar approach assisted by endoscope. All cysts were successfully treated. Injury of the foramen of Monro occurred during a procedure using a flexible endoscope in a case with an anterior extending cyst. Exact analysis of the preoperative imaging and selection of appropriate surgical approach are key factors for successful treatment of a quadrigeminal cistern arachnoid cyst.     

Microsurgical anatomy of the choroidal fissure

The microsurgical anatomy of the choroidal fissure was examined in 25 cadaveric heads. The choroidal fissure, the site of attachment of the choroid plexus in the lateral ventricle, is located between the fornix and thalamus in the medial part of the lateral ventricle. The choroidal fissure is divided into three parts: (a) a body portion situated in the body of the lateral ventricle between the body of the fornix and the thalamus, (b) an atrial part located in the atrium of the lateral ventricle between the crus of the fornix and the pulvinar, and (c) a temporal part situated in the temporal horn between the fimbria of the fornix and the lower surface of the thalamus. The three parts of the fissure are the thinnest sites in the wall of the lateral ventricle bordering the basal cisterns and the roof of the third ventricle. Opening through the body portion of the choroidal fissure from the lateral ventricle exposes the velum interpositum and third ventricle. Opening through the temporal portion of the choroidal fissure from the temporal horn exposes the structures in the ambient and crural cisterns. Opening through the atrial portion of the fissure from the atrium exposes the quadrigeminal cistern, the pineal region, and the posterior portion of the ambient cistern. The neural, arterial, and venous relationships of each part of the fissure are reviewed. The operative approaches directed through each part of the fissure are also reviewed.     

The thalamogeniculate perforators of the posterior cerebral artery: the microsurgical anatomy

The thalamogeniculate (TG) arteries of 30 forebrain hemispheres were examined. These vessels varied from 2 to 12 in number (mean, 5.7), and from 70 to 580 microns in caliber (mean, 345.8 microns). The average caliber of all the TG vessels per posterior cerebral artery ranged from 700 to 3400 microns (mean, 1972 microns). The TG arteries most often originated as individual vessels; however, in 26.67% of the hemispheres examined they shared a common site of origin, and 33.33% of the hemispheres they arose from common stems. The common stems ranged from 320 to 800 microns in diameter (mean, 583 microns). The TG branches arose from the crural or ambient (P2) segment of the posterior cerebral artery in 80% of the hemispheres, from the P2 and the quadrigeminal (P3) segment in 20%, from both the distal segment of the posterior cerebral artery and the common temporal artery (13.33%), or from the distal segment and either the calcarine (3.33%) or parieto-occipital artery (3.33%). The TG arteries usually penetrated the medial geniculate body (100%), pulvinar thalami (80%), brachium of the superior colliculus (53.33%), or lateral geniculate body (13.33%). The collateral branches of the TG arteries were noted to reach the medial geniculate body (76.67%), pulvinar (70%), brachium of the superior colliculus (40%), crus cerebri (40%), and lateral geniculate body (6.67%). The anastomoses were present in 66.67%, usually between the TG vessels and the medial posterior choroidal artery (33.33%), or the mesencephalothalamic artery (26.67%). They ranged in number from 1 to 3 (mean, 1.2), and in caliber from 90 to 400 microns (mean, 197 microns).(ABSTRACT TRUNCATED AT 250 WORDS)     

The transsylvian trans-limen insular approach to the crural,ambient and interpeduncular cisterns

Summary Background. The authors introduce the transsylvian trans-limen insular approach to the crural, ambient and interpeduncular cisterns.Method. The transsylvian trans-limen insular approach was performed in 7 patients; 3 for aneurysm, 2 for isolated temporal horn hydrocephalus, one for tumour and one for an arteriovenous malformation. This approach is summarized in 4 procedures; the exposure of the inferior limiting sulcus of the insular cortex, the exposure of the inferior horn of the lateral ventricle, the dissection of the inferior part of the choroidal fissure and the splitting of the inferior border of the limen insula.Findings. Four among 7 patients underwent surgery for the lesions in the crural or ambient cistern. The other 3 patients underwent surgery for the lesion in the interpeduncular cistern. Two patients of the latter group postoperatively had temporal lobe infarction.Conclusions. The transsylvian trans-limen insular approach may be indicated for lesions in the crural and the anterior ambient cisterns, and the lesions which need wider exposure of the interpeduncular cistern. For the former lesions, this approach can afford good results. For the latter lesions, careful brain retraction and some other techniques to avoid temporal lobe infarction are necessary. Further neuropsychological assessment should be also necessary to prove the validity of this approach.     

Surgical management of arteriovenous malformations that follow the tentorial ring

In a series of 200 intracranial arteriovenous malformations (AVMs) treated surgically, 33 malformations were situated very close to the tentorial incisura. All but one of these AVMs were totally removed. Four operative approaches were utilized in this group of patients: an interhemispheric approach for lesions of the medial hemispheres, splenium of the corpus callosum, and posterior 3rd ventricle; a subtemporal approach to the inferior and medial temporal lobe; a supracerebellar-infratentorial approach to anterodorsal cerebellum and quadrigeminal regions; and a subtemporal transtentorial exposure to the dorsolateral mesencephalon. There were no surgical deaths. Three patients had unsatisfactory outcomes. Our experience with this series indicates that deep cerebral AVMs in the region of the tentorial incisura may be safely removed if there is proper selection of operative approach and attention to surgical technique.     

Infratentorial supracerebellar approach to the colloid cysts of the third ventricle

OBJECTIVE: The transcallosal and the frontal transcortical approaches are the most widely used methods in surgery of third ventricle colloid cysts. However, these approaches require traction of the frontal lobe and dissection of the corpus callosum or corticotomy and involve some postoperative consequences. The rationale of the proposed method is to remove the colloid cyst by the infratentorial supracerebellar approach and the posterior wall of the third ventricle without dissection of any neural structures. METHODS: Five patients with a colloid cyst of the third ventricle were operated on by the proposed method. The first patient presented with several months' history of symptoms that included increased intracranial pressure and right-sided cerebellar signs, caused by a metastatic tumor of the right cerebellar hemisphere. The other four patients had symptoms including intracranial hypertension for an extended period of time without any other neurological deficits. In all patients, magnetic resonance imaging revealed a colloid cyst of the third ventricle without hydrocephalus. TECHNIQUE: With the infratentorial supracerebellar approach, the arachnoid of the quadrigeminal cistern is dissected. The pineal body is separated and displaced from the internal vein medially, and the posterior velum interpositum is opened. Perforation of the inferior layer of the tela choroidea just above the suprapineal recess allows opening of the third ventricle cavity. A foraminal region is exposed after a slight lateral displacement of medial surfaces of the thalamus along the third ventricle roof. CONCLUSION: The proposed approach through the infratentorial supracerebellar space and the posterior wall of the third ventricle may be used for removal of colloid cysts, especially in patients in whom the lateral ventricles are not enlarged.     

Early CT features of ruptured cerebral aneurysms of the posterior cranial fossa

This report describes our retrospective evaluation of CT features of the acute phase in 34 cases of ruptured cerebral aneurysms of the posterior cranial fossa. The results are as follows. 1. Examination of cisternal haematoma distribution revealed that SAH had extended to the supra- and infratentorial cisterns in 28 cases (82%). There were only 6 cases (18%) in which SAH was confined to the posterior cranial fossa only but even when there was subarachnoid haematoma in both the supra- and infratentorial cisterns, thick haematomas were seen at the periphery of the brain stem. In cases of vertebral artery-posterior inferior cerebellar artery aneurysms (VA-PICA AN), haematomas in the ambient cistern were thicker on the aneurysm side. In addition, in cases of basilar artery-bifurcation (BA-Bifurcation AN) and basilar artery-superior cerebelli artery aneurysms (BA-SCA AN), there were many thick, high-density haematomas in the interpeduncular cistern. 2. The rate of intracerebral haemorrhage was extremely low (1 patient). 3. The rate of intraventricular haemorrhage was high, and these haemorrhages demonstrated a reflux pattern. 4. The rate of hydrocephalus was high (76.5%) in comparison with that noted in association with SAH due to the rupture of anterior circulation aneurysms.     

Supracerebellar transtentorial approach.

The supracerebellar transtentorial (SCTT) approach, a modification of the infratentorial supracerebellar approach, facilitates simple and minimally invasive access to posterior temporomedial structures without requiring retraction of the temporal or occipital lobe. The SCTT approach was used in 16 patients over a 3-year period. Eleven patients harbored tumors confined to, or located mainly within, the posterior hippocampal formation, three patients harbored aneurysms (one ruptured posterior cerebral artery [PCA] aneurysm at the P2-P3 junction, one ruptured giant PCA [P2] aneurysm, and one giant basilar artery-superior cerebellar artery aneurysm), one patient had juvenile-type moyamoya disease, and one patient suffered from medically intractable epilepsy. In these patients, the SC approach enabled tumor removal, aneurysm clipping, and vascular bypass procedures. The authors' experience suggests that this approach can be used routinely in treating lesions in the posterior temporomedial region.     

Supracerebellar transtentorial approach to posterior temporomedial structures

The supracerebellar transtentorial (SCTT) approach, a modification of the infratentorial supracerebellar approach, facilitates simple and minimally invasive access to posterior temporomedial structures without requiring retraction of the temporal or occipital lobe. The SCTT approach was used in 16 patients over a 3-year period. Eleven patients harbored tumors confined to, or located mainly within, the posterior hippocampal formation, three patients harbored aneurysms (one ruptured posterior cerebral artery [PCA] aneurysm at the P2-P3 junction, one ruptured giant PCA [P2] aneurysm, and one giant basilar artery-superior cerebellar artery aneurysm), one patient had juvenile-type moyamoya disease, and one patient suffered from medically intractable epilepsy. In these patients, the SCTT approach enabled tumor removal, aneurysm clipping, and vascular bypass procedures. The authors' experience suggests that this approach can be used routinely in treating lesions in the posterior temporomedial region.     

Microsurgical anatomy of the posterior fossa cisterns

The microsurgical anatomy of the posterior fossa cisterns was examined in 15 cadavers using 3X to 40X magnification. Liliequist's membrane was found to split into two arachnoidal sheets as it spreads upward from the dorsum sellae: an upper sheet, called the diencephalic membrane, which attaches to the diencephalon at the posterior edge of the mamillary bodies, and a lower sheet, called the mesencephalic membrane, which attaches along the junction of the midbrain and pons. Several other arachnoidal membranes that separate the cisterns were identified. These include the anterior pontine membrane, which separates the prepontine and cerebellopontine cisterns; the lateral pontomesencephalic membrane, which separates the ambient and cerebellopontine cisterns; the medial pontomedullary membrane, which separates the premedullary and prepontine cisterns; and the lateral pontomedullary membrane, which separates the cerebellopontine and cerebellomedullary cisterns. The three cisterns in which the arachnoid trabeculae and membranes are the most dense and present the greatest obstacle at operation are the interpeduncular and quadrigeminal cisterns and the cisterna magna. Numerous arachnoid membranes were found to intersect the oculomotor nerves. The neural and vascular structures in each cistern are reviewed.     

Hematoma of the pineal region: a case report

A 44-year-old man came to our clinic, complaining of slowly progressive disturbance of visual acuity and of ocular movement. This patient suffered from headache, narrowing of visual field and polyuria about 20 years ago, and received surgical and radiation therapy under the diagnosis of pituitary adenoma. Clinical symptoms and signs of this patient, except for bitemporal hemianopsia, almost completely disappeared after these treatment. The detailed information about the histology and radiation dose are not available at the present time. CT scan in our clinic revealed a round low-density area at the suprasellar region and a high density area at the left quadrigeminal cistern. Pineal calcification was compressed to the right about 2-3 mm from midline. This high density mass were not enhanced with contrast medium. Vertebral angiography showed a slight lateral displacement of the left medial posterior choroidal artery. Specimen of tissue removed 20 years ago was reexamined but definitive diagnosis could not be established. Presumptive diagnosis of an ectopic pinealoma in the suprasellar region treated successfully 20 years ago, and its recurrence in the pineal region was made. On May 24, the patient underwent a posterior fossa craniectomy and the pineal region was explored via the infratentorial supracerebellar approach. On sectioning the precentral cerebellar vein, yellowish mass was seen in the quadrigeminal cistern. Aspiration of this mass yielded dark red liquid hematoma. Incising into the capsule, a dark brownish mass of about 4g was removed en bloc.(ABSTRACT TRUNCATED AT 250 WORDS)     

Management strategies for posterior cerebral artery aneurysms: A proposed new surgical classification

Summary In a period of 10 years fifteen patients bearing sixteen aneurysms arising at the posterior cerebral artery were operated at our institution. Based on the approaches selected for each location a division of the posterior cerebral artery into three surgical segments is proposed. The first segment (S1), or anterior extends from the basilar artery bifurcation to the point where the artery reaches the level of the most lateral edge of the cerebral peduncle, the second segment (S2), or middle extends from the posterior limit of S1 to a point located just before the most medial extent of the artery in the quadrigeminal cistern (collicular point), and the third segment (S3), or posterior corresponds to the collicular point and to the portions of the posterior cerebral artery distal to it.Utilizing the concept of surgical segments all aneurysms in our series were satisfactorily exposed. Those arising at the S1 segment (8 cases) were operated either through a pterional or a pretemporal approaches; those from the S2 segment (6 cases) were operated either via the subtemporal or the subtemporal transventricular routes; and that arising from the S3 segment (1 case) was managed through the occipital interhemispheric approach. Among the aneurysms eleven were small, one was large, and four were large or giant. Ten of these aneurysms were surgically clipped, two coagulated, three treated by trapping and in one case the aneurysm was resected and the posterior cerebral artery was reconstructed by a termino-terminal anastomosis. The surgical results were considered good in all cases but one, where the patient died due to clinical complications three months after surgery.It is our belief that the use of this classification can provide the means to best select the most appropriate surgical approach to treat aneurysms arising at the posterior cerebral artery.     

Transtentorial approach to the posterior temporomedial structures

The supracerebellar transtentorial (SCTT) approach, a modification of the infratentorial supracerebellar approach, facilitates simple and minimally invasive access to posterior temporomedial structures without requiring retraction of the temporal or occipital lobe. The SCTT approach was used in 16 patients over a 3-year period. Eleven patients harbored tumors confined to, or located mainly within, the posterior hippocampal formation, three patients harbored aneurysms (one ruptured posterior cerebral artery [PCA] aneurysm at the P2-P3 junction, one ruptured giant PCA [P2] aneurysm, and one giant basilar artery-superior cerebellar artery aneurysm), one patient had juvenile-type moyamoya disease, and one patient suffered from medically intractable epilepsy. In these patients, the SC     

Surgical anatomy and landmarks for the basal vein of rosenthal

OBJECT: The basal vein of Rosenthal (BV) courses from the premesencephalic cistern, through the ambient cistern, and terminates in the quadrigeminal cistern. The aim of this study was to describe and quantitate the surgical anatomy of this structure and specifically to provide landmarks for identifying this vessel along its course. These data may be of use, for example, to surgeons using subtemporal operative approaches through regions where this vessel is concealed. METHODS: The authors examined 15 latex-injected adult cadaveric brains (30 sides) to delineate the morphological characteristics of the BV. Dissections of the BV were then performed and measurements were made between this structure and the tentorial incisura at the anterior, middle, and posterior borders of the lateral midbrain. All specimens were found to have a left and right BV with varying morphological characteristics. The mean distance between the BV and posterior cerebral artery at the midpoint of the lateral midbrain was 16 mm. The BV was always found superomedial to the posterior cerebral artery along the lateral aspect of the midbrain, and the BV ranged in diameter from 1 to 5 mm. The BV drained into the vein of Galen in all but two specimens. The mean distances from the tentorial edge to the BV at the anterior, middle, and posterior borders of the lateral midbrain were 11, 1 3, and 4 mm, respectively. No statistically significant differences were found when comparing left and right sides or male and female specimens. CONCLUSIONS: The authors hope that these data will help the neurosurgeon operating near the BV to avoid injury to this important structure.     

Subarachnoid hemorrhage due to ruptured posterior cerebral artery aneurysm simultaneously associated with multiple remote intracerebral hemorrhages--case report

A 61-year-old woman presented with aneurysmal subarachnoid hemorrhage (SAH) associated with multiple remote intracerebral hemorrhages (ICHs). She had undergone microsurgical neck clipping for ruptured right middle cerebral artery aneurysm and ventriculo-peritoneal shunting 16 years previously. Computed tomography revealed SAH predominantly in the basal cistern and ambient cistern, in association with multiple ICHs in the bilateral tegmentum of the brain stem and right caudate nucleus. Digital subtraction angiography revealed an aneurysm at the P(1) segment of the left posterior cerebral artery. The ruptured aneurysm was microsurgically clipped via a left subtemporal approach without complications. Simultaneous occurrence of aneurysmal SAH and multiple remote ICHs is rare. The spatial pattern of the ICHs in the present case is apparently unique.     

Distal Superficial Temporal Artery to Proximal Posterior Cerebral Artery Bypass by Posterior Oblique Transzygomatic Subtemporal Approach

This article investigates the possibility for the distal superficial temporal artery (STA) to proximal posterior cerebral artery (PCA) direct bypass by subtemporal oblique posterior transzygomatic approach. Five adult cadaveric specimens were dissected. Cadeveric dissection protocol was approved by the Research Ethics Committee. A preauricular vertical skin incision was made, the trunk of STA was identified, and bifurcation, frontal, and parietal branches of the STA were followed distally. Posterior zygomatic arch osteotomy and microcraniotomy were then performed, and the dura was opened. The temporal lobe was retracted, interpeduncular and ambient cisterns were opened, and the P2 segment of the PCA was exposed. Parietal branch of STA and P2 segment of the PCA was anastomosed. The average length of the transected STA from the bifurcation and the zygomatic arch were 47.3 ± 2.1 mm and 71.4 ± 2.3 mm, respectively. The mean calibers of the parietal and frontal branch of the STA at this distance were 1.6 ± 0.1 and 1.4 ± 0.2, respectively. The mean diameter of the P2 was 2.1 ± 0.2 mm. Because of the calibers of the parietal branch of the STA and proximal PCA are over 1.5 mm and 2.0 mm, respectively, this direct end-to-side bypass technique may be a reasonable alternative in suitable cases.     

Paramedian supracerebellar transtentorial approach for a medial tentorial meningioma with supratentorial extension: technical case report

OBJECTIVE AND IMPORTANCE: The choice of surgical approach to treat medial tentorial meningiomas is crucial and sometimes difficult to make. Although the subtemporal approach is most commonly used for lesions that extend mostly supratentorially, it risks injury to the vein of Labbé or the veins coursing along the subtemporal surface. To avoid venous injury, a medial tentorial meningioma was removed transtentorially through the infratentorial space via the paramedian supracerebellar transtentorial (PSCTT) approach. CLINICAL PRESENTATION: A 35-year-old right-handed woman presented with a generalized convulsion. Magnetic resonance imaging scans revealed a left medial tentorial meningioma with supratentorial extension at the dominant hemisphere. The main venous drainage route from the ipsilateral temporal lobe was a sphenopetrosal vein. INTERVENTION: An operation was performed with the patient in a sitting position, and the tumor was resected totally via the paramedian supracerebellar transtentorial approach without perioperative complications. CONCLUSION: The paramedian supracerebellar transtentorial approach is useful for supratentorially located medial tentorial meningiomas without retraction of the temporal lobe and without damage to the vein of Labbé or the sphenopetrosal vein.     

Surgical indications and microsurgical anatomy of the transchoroidal fissure approach for lesions in and around the ambient cistern

OBJECTIVE: Opening the temporal part of the choroidal fissure (CF) makes it possible to expose the crural cistern, the ambient cistern, and the medial temporal lobe. We examined the microsurgical anatomy and the surgical indications for use of the trans-CF approach. METHODS: The microsurgical anatomy encountered in the trans-CF approach for lesions in and around the ambient cistern was studied in three cadavers. On the basis of these cadaveric studies, the trans-CF approach was used during surgery in three live patients with such lesions. RESULTS: The angiographic "plexal point," which indicates the entrance of the anterior choroidal artery as it enters the temporal horn of the lateral ventricle, was thought to be a key anatomic landmark of the trans-CF approach. A cortical incision for entry into the temporal horn should be made in the inferior temporal gyrus to minimize the potential damage to the optic radiations and to the speech centers. After the CF is opened posteriorly to the plexal point between the tenia fimbria and the choroid plexus, the posterior cerebral artery (PCA) in the ambient cistern can be observed with minimal caudal retraction of the hippocampus. In this study, surgical procedures using the trans-CF approach were successfully performed on patients with high-positioned P2 aneurysms whose PCA ran close to the plexal point or higher, whose medial temporal arteriovenous malformations were fed mainly by the PCA, and whose tentorial hiatus meningiomas protruded into the temporal horn through the CF, with no resulting postoperative visual or memory disturbances. CONCLUSION: The trans-CF approach is especially useful in surgery for lesions in and around the ambient cistern.