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.     

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.     

Anatomy of the periventricular white matter

The lateral ventricle (LV) has a deep position within the cerebral hemisphere. The LV is covered by white matter with important functional role in the dominant hemisphere. Lateral wall of the frontal horn is covered by the inferior occipitofrontal fasciculus (IOFF) and its roof by the corpus callosum (CC). The body of the LV has the same cranial relationship and is covered laterally by fibers of internal capsula and arcuate fasciculus; its lower part is in relationship with the body of the fornix. The atrium of the LV is covered by the arcuate fasciculus and its lower part is covered by the IOFF and optic radiations. The inferior horn or temporal horn is covered by optic radiations in depth of middle temporal gyrus (T2). The auditive radiations crossed the optic radiations at the level of the roof of the inferior horn.     

Ventricular diverticula in obstructive hydrocephalus secondary to tumor growth

OBJECTIVE: The association of ventricular diverticula with intra- and paraventricular tumors causing obstructive hydrocephalus has rarely been reported. METHODS: Records and imaging findings for 57 patients with obstructive hydrocephalus caused by tumors who were treated at our institution were reviewed for the presence of ventricular diverticula. For the anatomic study of ventricular diverticula, data were collected from five cadaveric heads. RESULTS: Ventricular diverticula were identified on magnetic resonance imaging scans in five cases. Diverticula were similarly located in the quadrigeminal cistern but originated from the medial wall of the atrium of the lateral ventricle in three cases and from the superior portion of the fourth ventricle in two cases. Regression of diverticula occurred in all cases after either insertion of a shunt or removal of the obstructing tumor. The cadaveric study suggested that the choroidal fissure and the rostral portion of the superior medullary velum might be the origins of diverticula from the atrium and from the superior portion of the fourth ventricle, respectively. CONCLUSION: Ventricular diverticula should be distinguished from other cystic lesions in the quadrigeminal region. Detection of an ostium of a diverticulum or communication between the cyst and the ventricular system is important for diagnosis.     

Arteries and veins of the lateral ventricle

Tumors of the frontal horn of the lateral ventricle (LV) are only supplied by the posteromedial choroidal artery. Tumors of the body of the LV are supplied by the same artery. Tumors of the atrium of the LV with anterior extension are supplied by both posteromedial choroidal and posterolateral arteries. Tumors of the atrium with inferior extension are supplied by both anterior choroidal artery and posterolateral choroidal arteries. Tumors of the inferior horn are only supplied by anterior choroidal artery. The tumoral venous drainage is organized with three main groups of veins: a medial group, a lateral group and a choroidal group.     

A combined subtemporal and transventricular/transchoroidal fissure approach to medial temporal lesions

OBJECTIVE: To minimize therapeutic morbidity such as cognitive function disturbance and vascular injury to perforating arteries, preoperative functional mapping of the basal temporal lobe functions was performed and the medial temporal lesions were resected via a combined subtemporal and transventricular/transchoroidal fissure approach. METHODS: Twenty-one patients with medial temporal lesions including tumors, arteriovenous malformations, and medial temporal lobe epilepsy underwent operation. The neurovascular structures in the ambient cistern were first dissected free from the medial temporal lobe with a conventional subtemporal approach. Then, the temporal horn was opened through the basal surface of the temporal lobe. Finally, the ambient cistern was accessed from the temporal horn through the choroidal fissure. In five patients whose lesions were revealed to be located on the dominant side by preoperative intracarotid amytal administration test (Wada test), functional mapping of the basal temporal lobe language cortex was monitored for 1 week by use of a subdural electrocorticogram grid before the extirpation surgery. The entrance point from the temporal base to the temporal horn was determined by the result of the functional mapping. RESULTS: The lesions were resected safely and completely in all cases. Language and cognitive functions were preserved even in patients with the basal language area on the dominant side. CONCLUSION: Surgeons can confirm the important neurovascular structures from the subtemporal route and from the transtemporal horn route by a combined subtemporal and transventricular/transchoroidal fissure approach. This approach is especially effective for avoiding ischemic complications by allowing direct confirmation of the anterior choroidal and thalamoperforating arteries.     

Microsurgical approaches to the perimesencephalic cisterns and related segments of the posterior cerebral artery: comparison using a novel application of image guidance

OBJECTIVE: To describe the exposure obtained through six approaches to the perimesencephalic cisterns with an emphasis on exposure of the posterior cerebral artery and its branches. METHODS: Dissections in 12 hemispheres exposed the crural, ambient, and quadrigeminal cisterns and related segments of the posterior cerebral artery. A Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO) was used to compare the approaches. RESULTS: The transsylvian approach exposed the interpeduncular and crural cisterns. The subtemporal approach exposed the interpeduncular and crural cisterns as well as the lower half of the ambient cistern. Temporal lobe retraction and the position of the vein of Labbé limited exposure of the quadrigeminal cistern. Occipital transtentorial and infratentorial supracerebellar approaches exposed the quadrigeminal and lower two-thirds of the ambient cistern. Transchoroidal approaches exposed the posterior third of the crural cistern, the upper two-thirds of the ambient cistern, and the proximal quadrigeminal cistern. Transchoroidal approaches exposed the posterior portion of the P2 segment (P2p) in 9 of 10 hemispheres and were the only approaches that exposed the lateral posterior choroidal arteries and the plexal segment of the anterior choroidal artery. Occipital transtentorial and infratentorial supracerebellar approaches provided access to the P3 segment in all cases and exposed the P2p segment in 4 of 10 hemispheres. The subtemporal approach provided access to the cisternal and crural segments of the anterior choroidal and medial posterior choroidal arteries and exposed the P2p segment in 3 of 10 hemispheres. CONCLUSION: Surgical approaches to lesions of the perimesencephalic cisterns must be tailored to the site of the pathological findings. The most challenging area to expose is the upper half of the ambient cistern, particularly the P2p segment of the posterior cerebral artery.     

Access to the posterior medial temporal lobe structures in the surgical treatment of temporal lobe epilepsy

The authors describe a surgical technique that allows access to the posterior temporal horn of the lateral ventricle with preservation of the most functional lateral temporal cortex. Development of the technique was stimulated by the need to resect posteromedial temporal lobe structures in patients with intractable complex partial epilepsy and well-identified unilateral posterior hippocampal foci. This technique has also been of value in the resection of some lateral ventricular and posteromedial temporal lobe masses. The operation consists of three steps. No more than 4.5 cm of the anterolateral temporal lobe is removed en bloc such that the most anterior aspect of the temporal horn is entered. An incision is carried from the floor of the temporal horn through the inferior longitudinal fasciculus to the middle fossa dura mater and posteriorally into the lateral ventricular atrium. The lateral temporal cortex and white matter are then elevated with a self-retaining retractor. This exposes the posteromedial temporal horn or intraaxial mass for excision or allows en bloc resection of the entire hippocampus and medial temporal lobe structures while preserving the functional association areas of the lateral temporal cortex, including speech and visual spatial function.     

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.     

Clipping of an aneurysm of the posterior cerebral artery via the transcortical transchoroidal-fissure approach: a case report

A 65-year-old woman suddenly developed severe headache with nausea. Computed tomographic scans revealed a diffuse subarachnoid hemorrhage with thick hematoma of the left ambient cistern. Cerebral angiogram did not show any aneurysm. On the 7th day after admission, 3D-CT angiogram showed an aneurysm of the left posterior cerebral artery. On the 14th day, axial and coronal magnetic resonance images showed the aneurysm, surrounding structures and the choroidal fissure. On the 26th day after admission, successful neck clipping was performed through the temporal horn via the inferior temporal gyrus. The postoperative course was uneventful except for transient aphasia. This approach may be preferable in such cases, because it protects the brain from the detrimental effects of strong temporal retraction and provides a wider working space. In our case, thin slice MRI and MRA showing the aneurysm in the ambient cistern and the choroidal fissure were useful for deciding the appropriate approach.     

Microanatomy of the subependymal arteries of the lateral ventricle

BACKGROUND: Scarce information about the anatomy of the subependymal arteries (SEAs) is present in the scientific literature. METHODS: Twenty cerebral hemispheres with injected arteries were microdissected, and the magnetic resonance imaging scans of 100 patients with lacunar infarcts were examined. RESULTS: The SEAs were found to range in diameter from 40 to 490 microm (mean, 149 microm) and in number between 3 and 12 (average, 5.2). Of these, numbers from 1 to 3 originated from the anterior choroidal artery (AChA), between 1 and 10 from the lateral posterior choroidal artery (LPChA), 1 from the medial posterior choroidal artery (MPChA), and 1 from the internal carotid artery. The SEAs most often arose from the choroidal branches (90%) and less frequently from the thalamic (30%), caudate (35%), or thalamocaudate twigs (20%). The SEAs of the AChA supplied the walls of the temporal horn (100%), the occipital horn (85%), and the atrium (35%). Those of the LPChA perfused the walls of the occipital horn (15%), the atrium (65%), the body of the ventricle (100%), and partially the frontal horn. The SEAs of the MPChA partially nourished the body and the frontal horn (10%). The SEAs may also occasionally supply the caudate nucleus (20%) and the stria terminalis. The anastomoses involving the SEAs were absent. In spite of this, ischemia in the territory of a single SEA was noticed in only 1% of our patients. CONCLUSIONS: The SEAs are tiny vessels that supply the walls of the lateral ventricle, as well as the caudate nucleus and the stria terminalis occasionally. The obtained anatomic data can have important neurosurgical implications in intraventricular operations.     

Saccular aneurysm of the distal anterior choroidal artery--case report.

The authors report a case of a distal anterior choroidal artery aneurysm in a 75-year-old female who presented with nausea, vomiting, and severe headache. Computed tomographic (CT) scans revealed a hematoma in the right lateral ventricle and a subarachnoid hemorrhage in the right parasellar-Sylvian cistern. Cerebral angiography showed a saccular aneurysm at the right distal anterior choroidal artery. The authors intended to operate at the chronic stage, and carried out conservative management. After 1 month her condition suddenly worsened and she died, although a CT scan showed no remarkable changes. At autopsy, a pulmonary artery thrombosis was considered the cause of death. The aneurysm was identified in the temporal horn of the right lateral ventricle, and was a true aneurysm.     

显微镜与内镜下不同纵裂入路的结构显露特点及其解剖结构标志定位

目的探讨显微镜与内镜下不同纵裂入路的结构显露特点及解剖结构标志定位。方法成人尸头10具,分为A组和B组,每组5具,分别采用经前额纵裂入路和经纵裂胼胝体脉络膜裂入路联合室内孔入路,在显微镜和内镜下观察内部结构。结果显微镜与内镜下经前额纵裂入路微创并可充分显露和定位鞍区和第三脑室,有利于切除第三脑室前部和鞍区肿瘤,而经纵裂胼胝体脉络膜裂入路联合室内孔入路微创并可充分显露和定位第三脑室及侧脑室解剖结构,有利于第三脑室、房部、体部及侧脑室额角的手术操作。结论两种纵裂入路均可在显微镜、内镜下充分显露第三脑室等部分结构,组织创伤小,临床上可根据病变特点和手术需求选择合理的入路方式。     

A large arachnoid cyst of the lateral ventricle extending from the supracerebellar cistern--case report

BACKGROUND: The pathogenetic mechanism of intraventricular arachnoid cyst development is still controversial, but is believed to originate from the vascular mesenchyme or as an extension of the arachnoid cyst in the subarachnoid space into the ventricle through the choroidal fissure. We report a case supporting the extension hypothesis and suggest differential points between an intraventricular arachnoid cyst that extended from the supracerebellar space and a lateral ventricular diverticulum that extended into the supracerebellar cistern. CASE DESCRIPTION: A 12-month-old girl presented with macrocephaly and developmental delay. Her magnetic resonance imaging showed an arachnoid cyst that had developed from the supracerebellar space in the posterior fossa, and which extended into the left lateral ventricle resulting in expansion of the left lateral ventricle and displacing the choroids plexus anteriorly and laterally and the midline to the right. We treated an intraventricular arachnoid cyst by endoscopic fenestration resulting in dramatic reduction of the intraventricular arachnoid cyst with large bilateral subdural fluid collection. We performed a subduroperitoneal shunt for subdural fluid collection and subsequent cystoperitoneal shunt for the remnant cyst. CONCLUSION: We suggest that this case supports the extension hypothesis from the subarachnoid space through the choroidal fissure into the lateral ventricle. We also suggest that one of the radiological differential points between an intraventricular arachnoid cyst and a ventricular diverticulum is displacement and compression of the choroid plexus of the lateral ventricle.     

Surgical treatment of arteriovenous angiomas localised in the corpus callosum,basal ganglia and near the brain stem

Seven cases of deep angiomas, in regions near the midline, were operated on in the National Institute of Neurosurgery, Budapest. In four cases the malformation was not so circumscribed that it could be localized in one structure alone. On two occasions it involved the corpus callosum and the neighbouring hemispheral substance; in one instance it involved the head of the caudate nucleus and the lateral ventricle also. Two intraventricular angiomas, supplied by the choroidal arteries, involved the corpus striatum and the thalamus. Three cases of juxtapeduncular angiomas are described in this series. They were situated in the deep medial part of the temporal lobe, closely adhering to the peduncle, and supplied by branches of the posterior cerebral and the lateral choroidal arteries. In one case the malformation, which involved the thalamus, could be only partly removed. In six cases total extirpation was carried out. All patients ar alive and six are working. No symptoms which were not present before operation have appeared. The importance of adequate radiological studies prior to surgery is emphasized. Attention is drawn to the possibility of eventual obstruction in the CSF circulation in the postoperative period following intraventricular manipulation.     

Intraventricular occurrence of a melanocytoma

Melanocytomas are rare tumors of the central nervous system that are believed to arise from leptomeningeal melanocytes. A young girl presented with a contrast-enhancing cystic mass in the temporal horn of the left lateral ventricle. Microsurgical resection of a black-colored vascular tumor supplied by the anterior choroidal artery was performed. Appropriate immunohistochemical staining and electron microscope evaluations were used to confirm the pathological diagnosis. The patient made an excellent recovery; follow-up imaging revealed no recurrent or residual tumor. This is the first documented primary occurrence of a melanocytoma in an intraventricular location. The intraventricular occurrence of this tumor suggests that melanocytes may migrate into the choroidal fissure and may infrequently undergo neoplastic proliferation in that location. This case contains implications for the differential diagnosis of intraventricular tumors.     

Microanatomy and surgical relevance of the olfactory cistern

All surgical approaches to the anterior skull base involve the olfactory cistern and have the risk of damaging the olfactory nerve. The purpose of this study was to describe the microanatomical features of the olfactory cistern and discuss its surgical relevance. In this study, the olfactory cisterns of 15 formalin-fixed adult cadaveric heads were dissected using a surgical microscope. The results showed that the olfactory cistern was situated in the superficial part of the olfactory sulcus, which separated the gyrus retus from the orbital gyrus. In coronal section, the cistern was triangular in shape; its anterior part enveloped the olfactory bulbs and was high and broad; its posterior part was medial-superior to internal carotid artery and was also much broader. There were one or several openings in the inferior wall of the posterior part in 53.4% of the cisterns. The olfactory cistern communicated with the surrounding subarachnoind cisterns through these openings. The middle part of the olfactory cistern gradually narrowed down posteriorly. Most cisterns were spacious with a few fibrous trabeculas and bands between the olfactory nerves and cistern walls. However 23% of the cisterns were narrow with the cistern walls tightly encasing the olfactory nerve. There were two or three of arterial loops in each olfactory sulcus, from which long, fine olfactory arteries originated. The olfactory arteries coursed along the olfactory nerve and gave off many terminal branches to provide the main blood supply to the olfactory nerve in most cisterns, but the blood supply was in segmental style in a few cisterns. Moreover, the veins of the cistern appeared to be more segmental than the olfactory arteries in most cisterns. These results suggested that most olfactory cisterns are spacious with relatively independent blood supply, and it is reasonable to separate the olfactory tract with its independent blood supply from the frontal lobe by 1-2 cm in the subfrontal approach, the pterional approach, or anterior interhemispheric approach. However, in the minority of cases, separation of the olfactory tract is not safe because of the anterior origin of the olfactory arteries or segmental blood supply. It is difficult to separate the olfactory nerve without any damage to the olfactory nerve, even with very skilled hands.     

The trapped temporal horn: a trap in neuroradiological diagnosis.

Although the advent of computerized cranial tomography (CT) has decreased the number of pneumoencephalograms performed for the diagnosis of hydrocephalus and lesions of the posterior fossa, brain stem, and ventricles, there are some patients in whom pneumoencephalography should still be done because it adds valuable information to that obtained with CT. When the temporal horn becomes obstructed, the choroid plexus and ependymal surface "upstream" from the obstructing mass continue to produce cerebrospinal fluid (CSF). The temporal horn can thus enlarge enough to appear as a mass on CT because of its reduced x-ray attenuation coefficient. Pneumoencephalography is effective in this situation because air will flow past a mass that obstructs CSF and because the ventricular system dilates during pneumoencephalography. When pneumoencephalography is used in a patient with a trapped temporal horn, the partially trapped horn may enlarge approximately 24 hours later. With that precaution in mind, the neurosurgeon should find pneumoencephalography to be a useful adjunct to CT in delineating the cause of a trapped temporal horn. In the three patients reported here CT had indicated a unilateral trapped temporal horn; pneumoencephalography confirmed that finding and demonstrated both the location and the nature of the lesion. One patient had a Grade II astrocytoma fungating into the atrium of the right lateral ventricle, one had a mass extending into the right ventricle from the medial and superior ventricular wall with nodular encroachment on the ventricle, and one had a meningioma in the atrium of the right lateral ventricle.     

Anatomical landmarks for hemispherotomy and their clinical application

OBJECT: The authors introduce the surgical concept of the central core of a hemisphere, from which anatomical structures are disconnected during most current hemispherotomy techniques. They also propose key anatomical landmarks for hemispherotomies that can be used to disconnect the hemisphere from its lateral surface around the insula, through the lateral ventricle toward the midline. METHODS: This anatomical study was performed in five adult cadaveric heads following perfusion of the cerebral arteries and veins with colored latex. Anatomical landmarks were used in five hemispheric deafferentations. The central core of a hemisphere consists of extreme, external, and internal capsules; claustrum; lentiform and caudate nuclei; and thalamus. Externally, this core is covered by the insula and surrounded by the fornix, choroid plexus, and lateral ventricle. During most hemispherotomies, the surgeon reaches the lateral ventricle through the frontoparietal opercula or temporal lobe; removes the mesial temporal structures; and disconnects the frontal lobe ahead, the parietal and occipital lobes behind, and the intraventricular fibers of the corpus callosum above the central core. After a temporal lobectomy, the landmarks include the choroid plexus and posterior/ascending portion of the tentorium to disconnect the parietal and occipital lobes, the callosal sulcus or distal anterior cerebral artery (ACA) to sever the intraventricular fibers of the corpus callosum, and the head of the caudate nucleus and ACA to detach the frontal lobe. CONCLUSIONS. These landmarks can be used in any hemispherotomy during which a cerebral hemisphere is disconnected from its lateral surface. Furthermore, they can be used to perform any resection around the central core of the hemisphere and the tentorial incisura.     

Telovelar approach to the fourth ventricle: microsurgical anatomy

OBJECT: In the past, access to the fourth ventricle was obtained by splitting the vermis or removing part of the cerebellum. The purpose of this study was to examine the access to the fourth ventricle achieved by opening the tela choroidea and inferior medullary velum, the two thin sheets of tissue that form the lower half of the roof of the fourth ventricle, without incising or removing part of the cerebellum. METHODS: Fifty formalin-fixed specimens, in which the arteries were perfused with red silicone and the veins with blue silicone, provided the material for this study. The dissections were performed in a stepwise manner to simulate the exposure that can be obtained by retracting the cerebellar tonsils and opening the tela choroidea and inferior medullary velum. CONCLUSIONS: Gently displacing the tonsils laterally exposes both the tela choroidea and the inferior medullary velum. Opening the tela provides access to the floor and body of the ventricle from the aqueduct to the obex. The additional opening of the velum provides access to the superior half of the roof of the ventricle, the fastigium, and the superolateral recess. Elevating the tonsillar surface away from the posterolateral medulla exposes the tela, which covers the lateral recess, and opening this tela exposes the structure forming the walls of the lateral recess.