Subtemporal Approach Research Articles

Surgical anatomy and landmarks for the basal vein of Rosenthal

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. 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. The authors hope that these data will help the neurosurgeon operating near the BV to avoid injury to this important structure.

Tentorial dural arteriovenous fistulas

Background Tentorial dural arteriovenous fistula is uncommon but is a life-threatening lesion. We present our experience with 5 patients with TDAVFs, review the relevant literature, and present the rationale of our current management strategy. Method The data of 5 patients with TDAVFs treated in Huashan Hospital, Shanghai, China, between June 2002 and May 2003 were reviewed retrospectively, including their illness history, neuroimaging, operation records, and follow-up data. Results There were 3 females and 2 males with ages from 25 to 52 years (average, 38 years). Clinical manifestations were acute SAH in 2 patients and progressive neurologic deficits in 3 patients. Magnetic resonance imaging and DSA were major diagnostic and follow-up modalities. All cases belonged to Borden classification type 3. A tentorial marginal type was present in 3 cases, a tentorial lateral type in 1 case, and a tentorial medial type in 1 case. Preoperative transarterial embolization was done in 3 patients. All patients underwent craniotomy with the coagulation of the fistulas and surrounding tentorial dura mater, and the disconnection of leptomeningeal venous drainage. The surgical approaches were via transanterior petrous approach in 3 cases, subtemporal intradural approach in 1 case, and unilateral occipital and transtentorial approach in 1 case. All patients had clinical improvement. There was no surgical mortality and morbidity. Postoperative DSA confirmed obliteration of TDAVFs in 3 cases; MRI demonstrated the thrombosis of venous aneurysm and disappearance of previous brainstem edema in 1 case, and partial thrombosis of venous aneurysm in another case. Follow-up study ranging from 2 to 3 years (average, 2.5 years) showed no recurrence, and all patients have resumed their normal activities. Conclusions Tentorial dural arteriovenous fistulas are aggressive vascular lesions causing SAH and progressive neurologic deficits. Prompt diagnosis and definite treatment are mandatory. Obliteration of the fistulas and/or leptomeningeal venous drainage should be the goal of treatment. Microsurgical procedures with/without endovascular intervention are the best choice of treatment.

Microsurgical treatment of complex intracranial aneurysms via keyhole approaches

To explore the feasibility and effect of microsurgical treatment of complex intracranial aneurysms via keyhole approaches. Operation via keyhole approach was performed on thirty-one patients with 42 complex intracranial aneurysms were operated on, including 2 internal carotid artery bifurcation aneurysms, 1 anterior cerebral artery aneurysm, 12 posterior communicating artery aneurysms, 2 anterior choroids artery aneurysms, 7 middle cerebral artery aneurysms, 6 anterior communicating artery aneurysms, 2 basilar artery aneurysms, 2 vertebral artery aneurysms, 4 posterior cerebral artery aneurysms and 4 ophthalmic artery aneurysms, among which were 10 cases with multiple intracranial aneurysms, 14 with giant aneurysms, and 7 with posterior circulation aneurysms, and 4 aneurysms clipped by drilling off anterior clinoid process. Six of the 31 patients who had giant aneurysms came to hospital because of the symptoms, such as dizziness, headache, oculomotor paralysis, loss of vision, etc, and the other 25 patients were grouped according to the subarachnoid hemorrhage (SAH) Grade: 5 in grade I, 12 in grade II, 7 in grade III and 1 in grade IV. Eight patients were operated on after SAH in the early-phase, while 8 in the middle-phase and 9 in the late-phase. The supraorbital subfrontal keyhole approach was used 25 times, the pterional approach 5 times, the subtemporal approach 3 times, and both the suboccipital lateral approach and the retromastoid approach once. 31 of the 42 aneurysms were clipped, 2 mini-aneurysms wrapped, 5 giant aneurysms clipped and resected, 2 aneurysms trapped with thrombotic aneurysm partially resected, 1 aneurysm trapped, while 1 ruptured before operation and untreated. Short-term Glasgow outcome scoring showed good recovery in 27 patients, moderate disability in 2, and death in 2. Operation via keyhole approaches effectively controls the immature rupture of intracranial aneurysm, removes anterior clinoid process, respects giant aneurysm, and reconstructs the parent artery of wide-neck aneurysm. Based on individualized surgical approaches and excellent microsurgical skills, the complex intracranial aneurysms can be treated safely, directly and effectively via minimally invasive keyhole approaches.

Combined Subtemporal and Retrosigmoid Keyhole Approach for Extensive Petroclival Meningioma Surgery: Report of Experience with 7 Cases

Resection of petroclival meningiomas offers great challenges to the neurosurgeons. Our experience of 7 cases using a combined subtemporal and retrosigmoid keyhole approach surgery was evaluated for the treatment of extensive petroclival meningiomas. From July 2002 to July 2005, resections of 7 petroclival meningiomas, which involved both supra- and infratentorial regions, were performed via a combined subtemporal and retrosigmoid keyhole approach. The extent of tumor resection was evaluated by MRI 3 months after surgery, and postoperative complications were investigated. The maximum diameter of the tumors ranged from 3.4 to 6.0 cm (mean: 4.4 cm). Gross total resection (GTR) was achieved in 3 cases, giving a GTR rate of 43%. Subtotal resection (STR) was carried out in 4 cases. Neurological status remained intact in one case, while others presented with cranial nerve deficits (VII, VI, V, III and lower CN). No death was reported in the cases during the postoperative period. The combined keyhole approach is suitable for the treatment of extensive petroclival meningiomas. It provides easy and quick access to the supra- and infratentorial juxtaclival region without any petrous bone drilling. Complications related to the approach can be minimized.

Extradural Dermoid Tumor of the Petrous Apex

Purpose: Dermoid cysts are rare, benign, congenital tumors. Most case series report the tumors as intradural. We present a case of an extradural dermoid tumor of the middle cranial fossa with bony invasion that we removed successfully using a left subtemporal extradural approach. We report the clinical presentation, histology, radiological findings, and our management of this unique case. No other cases of completely extradural supratentorial dermoid cysts have been reported.

Subtemporal approach for a P2–P3 junction aneurysm of the posterior cerebral artery

Aneurysms are seen rarely at the P2–P3 junction of the posterior cerebral artery (PCA). P2–P3 junction aneurysm surgery is challenging. Here, a successful clipping of a large P2–P3 junction aneurysm via a subtemporal approach is reported. A 26-year-old woman presented with a 6-month history of left occipito-parietal headache. Computed tomography (CT) scan, magnetic resonance imaging (MRI) and cerebral angiography revealed a 2-cm aneurysm at the P2–P3 junction of the left PCA. Successful neck clipping of the aneurysm was performed via a subtemporal approach without additional neurological deficits or surgical complications. Coil embolization has been suggested as the treatment of choice but PCA aneurysms are also good candidates for microsurgical clipping. The subtemporal approach is simple and safe in experienced hands. P2–P3 junction PCA aneurysms can be successfully clipped via the subtemporal approach without excessive brain retraction, resection of brain tissue or disruption of surface veins.

Quantification of Increased Basilar Artery Proximal Control Obtained by Transecting the Tentorium in a Subtemporal Approach

Introduction: Basilar apex aneurysms remain one of the most difficult aneurysms to control proximally. The subtemporal approach to basilar apex aneurysms is often advocated when the aneurysm is below the posterior clinoids. We used a stereotactic method to quantify increased proximal control of the basilar artery obtained by transecting the tentorium during a subtemporal approach. Methods: A subtemporal approach to the basilar apex was performed on three latex-injected cadaveric heads (three sides). Using a stereotactic method, the point of maximum proximal control of the basilar artery was measured from the basilar apex. Proximal control was compared before and after transecting the tentorium both anterior and posterior to the trochlear nerve. Results: Our preliminary results show that working inferior to the oculomotor nerve the proximal control measured before transecting the tentorium was 7.7 ± 2.8 mm. After transecting the tentorium just behind the trochlear nerve this was essentially unchanged at 8.6 ± 2.4 mm, but increased significantly to 12.7 ± 2.0 mm after cutting in front of the trochlear nerve (P = 0.022, repeated measures ANOVA, BonFeronni adjusted). Conclusion: We conclude that transecting the tentorium in a subtemporal approach to the basilar apex improves proximal control. In the future we intend to investigate the effect of cutting the tentorium on other measurements such as working area and surgical freedom.

Pneumocephalus as a delayed mastoidectomy complication

We report the case of a 43-year-old woman who presented with a spontaneous pneumocephalus, 37 years after a mastoidectomy. Clinical examination showed a cerebrospinal fluid leak, meningeal herniation in the superior part of the middle ear, and an audible noise from her ear when she stood up due to the entrance of air into the cranium. A computed tomography scan and magnetic resonance imaging showed the complete destruction of the tegmen tympani and the pneumocephalus in the temporal lobe. The patient underwent an emergency operation via a double middle-ear and subtemporal approach. The meningoencephalocoele and pneumocephalus were probably due to long term pressure upon too thin a tegmen tympani. Pneumocephalus should be considered as a potential delayed post-operative complication of middle-ear surgery. Computed tomography and magnetic resonance imaging scanning supply accurate information and enable a planned surgical approach; they also allow a pathophysiological understanding and a correlation between the clinical signs and the radiological and peri-operative findings.

Microsurgical anatomy and surgical approach of the ambient cistern

to describe detailed anatomy and compare four surgical approach of the ambient cistern, to assist in the process of conceptualizing a reliable surgical approach to allow for a successful course of surgery. The microsurgical anatomy of the ambient cistern and four surgical approach was studied in 12 formalin-fixed brain specimens (24 hemispheres). Four simply formalin-fixed, the cerebral arteries of eight brain specimens were perfused with colored silicone, and they were dissected with the aid of an operating microscope. Special attention was paid to the anatomic structures limiting visualization in each approach. The ambient cistern extends from the posterior margin of the crural cistern to the lateral edge of the midbrain colliculi, and round the lateral surface of the upper portion of the brainstem; The ambient cistern mainly contained P(2) segment of the posterior cerebral artery, superior cerebellar artery, anterior choroidal artery, basal vein and trochlear nerve. The subtemporal approach allow for excellent exposure of the lower half of the ambient cistern, the vein of Labbé and the parahippocampal gyrus obstacle to exposure through this approach; The transtemporal transchoroidal approaches exposed the upper half of the ambient cistern of non-dominance hemisphere, its major drawback is the need to perform a corticectomy in the temporal lobe. In addition, the vein of Labbé extended far enough anteriorly to limit the cortical incision in the temporal lobe. The transinsular transchoroidal exposed the anterior upper half of the ambient cistern. Its major disadvantage is damage the temporal stem, the longer the inferior limiting sulcus, the shorter the incision, the better for preservation the temporal stems; The occipital transtentorial approaches exposed the posterior lower half of the ambient cistern, the parahippocampal gyrus also blocked to exposure through this approach. Surgical approaches to lesions of the ambient cistern must be tailored to the site of the pathological findings. Position of the vein of Labbé, and the midpoint of the rounded medial edge of the parahippocampal gyrus, is key to determine Surgical Approach.

Extension of the One-Piece Orbitozygomatic Frontotemporal Approach to the Glenoid Fossa

Objective: Resection of the glenoid fossa has been described as one of the cranial approaches to the clivus and subtemporal approaches. However, radical resection carries a significant risk of postoperative temporomandibular joint (TMJ) dysfunction.We examine a variation of our previously described one-piece frontotemporal-orbitozygomatic (FTOZ) osteotomy that includes the en bloc resection of the root of the zygomatic arch and a portion of the glenoid fossa.

Unusual Intracranial Lesions Managed with Skull Base Neurosurgical Approaches—Why We Must Continually Emphasize Cerebrovascular/Skull Base Training in Neurological Surgery

Introduction: Neurosurgery in the United States has evolved mainly into surgery for spinal fusion, primarily because of economic incentives. Contemporaneously, the introduction of “minimally invasive” treatments such as radiosurgery and endovascular therapy has resulted in a marked de-emphasis on the microsurgery of complex intracranial diagnoses. Statements rife in the current neurosurgical environment such as “the death of cerebrovascular neurosurgery” are unjustified and underscore a need to further emphasize cerebrovascular/skull base training. This resurgence of emphasis would facilitate the appropriate continuing treatment of complex intracranial diagnoses that present in everyday clinical scenarios in the neurosurgical care of the populations being served. Methods: The author presents the microneurosurgical management of 13 unusual intracranial diagnoses with skull base microsurgical approaches ranging the gamut from cerebellomedullary angle arachnoid cyst to bilateral distal anterior cerebral artery aneurysms. Results: Five major intracranial approaches and variations were used in this clinical series: pterional transylvian approach with skull base modifications, anterior and posterior interhemispheric approaches, subtemporal approach with modifications, and far lateral transcondylar approach which subsumes other posterior fossa approaches. Conclusions: Adequate exposure and control of hemorrhage are the major tenets of any intracranial operation. The author contends that technical mastery of the aforementioned five major intracranial approaches satisfactorily addresses most if not all conditions likely to be encountered by a neurosurgeon in intracranial neurosurgical practice. It is easy to abdicate responsibility of “difficult” intracranial cases to minimally invasive and “novel” therapeutic modalities. However, under such circumstances, a highly variable fraction of patients will receive suboptimal care, particularly based on current trends in neurosurgery in the United States. Future progress in intracranial neurosurgery requires a revival in enthusiasm and commitment to push the frontiers of surgical progress by further emphasizing the critical elements of cerebrovascular/skull base neurosurgery.

The Radiographic Prevalence of Geniculate Ganglion Dehiscence in Normal and Congenitally Thin Temporal Bones

To determine the prevalence of a dehiscent geniculate ganglion on routine temporal bone computed tomography (CT). Retrospective case review. Tertiary referral center. Two hundred seventy-eight consecutive temporal bone CT examinations for a total of 556 sides were reviewed. One hundred ninety-one sides were excluded. Reasons for exclusion included reconstructed coronal views, no coronal views, or a pathologic process, which involved the geniculate ganglion. Six examinations were from patients with clinical superior canal dehiscence confirmed by surgical repair or positive vestibular evoked myogenic potentials. Twenty-four scans were from patients with radiographic superior canal dehiscence confirmed by two independent readings. The incidence of geniculate ganglion dehiscence in patients with and without radiographic or clinical superior canal dehiscence. Dehiscent geniculate ganglion was defined as at least two consecutive cuts on a coronal CT showing no bone overlying the geniculate ganglion. The overall incidence of a dehiscent geniculate ganglion was 14.5% in the 365 sides reviewed. The incidence of a dehiscent geniculate ganglion is increased in patients with radiographic and clinical superior canal dehiscence as compared with normal patients and was significantly different by chi analysis (38.1 versus 11.4%). The presence of radiographic geniculate ganglion dehiscence is common. This finding has particular importance when the middle cranial fossa or subtemporal approach is used, as the facial nerve is more at risk especially when used to address superior canal dehiscence.

Extradural Dermoid Tumor of the Petrous Apex

✓ Dermoid cysts are rare, benign, congenital tumors. Most case series thus far have featured intradural tumors. The authors report on a case of an extradural dermoid tumor of the middle cranial fossa with osseous invasion, successfully removed using a left subtemporal extradural approach. The clinical presentation, histological features, radiological findings, and management of this unique case are described.

Chondroblastoma of the apex portion of petrousal bone

Skull chondroblastoma is extremely rare. We described in this study the first case of petrousal bone apex chondroblastoma. The tumor occurred in a 12-year-old girl and was revealed by left hypoacusis, vertigo, and walking instability. Computerized tomography scan depicted well-demarcated and osteolytic lesion of the left petrousal bone just before the internal acoustic meatus. The tumor was operated on by a subtemporal approach with a subtotal resection. Lesion recurred and was operated a second time by a combined approach subtemporal and translabyrinthine. This treatment was completed by radiotherapy. We used a combination of photon therapy and proton therapy. Outcome was good and free of recurrence 36 months after the second operation. Proton therapy can be particularly useful for skull base tumors frequently radioresistant and near very important structures. This case is the first one of a successful treatment by proton therapy for chondroblastoma recurrence.

The Subtemporal Interdural Approach to Dumbbell-Shaped Trigeminal Schwannomas: Cadaveric Prosection

Successful resection of dumbbell-shaped trigeminal schwannomas via a subtemporal interdural approach requires an understanding of both the anatomy related to the bone dissection of the petrous apex (Kawase's triangle or quadrilateral) and meningeal anatomy. We studied the meningeal anatomy related to this approach and describe the dural incisions and stepwise mobilization. Meningeal anatomy around Meckel's cave and porus trigeminus was examined during the subtemporal interdural anterior transpetrosal approach in both sides of 15 cadaveric heads. Histological study of the Meckel's cave region was performed in two cadaveric heads. The Gasserian ganglion and trigeminal roots have two layers of dura propria on their dorsolateral surface: an inner layer from the posterior fossa dura propria that constitutes the dorsolateral wall of Meckel's cave and an outer layer from the dura propria of the middle fossa. The cleavage plane between these two layers continues distally as the cleavage plane between the epineural sheaths of the trigeminal divisions and the dura propria of the middle fossa. This cleavage plane serves as the anatomic landmark for the interdural exposure of the contents of Meckel's cave. The superior petrosal sinus is sectioned at the medial aspect of Kawase's triangle and reflected along with the porus trigeminus roof. Understanding the critical meningeal architecture in and around Meckel's cave allows experienced cranial neurosurgeons to develop a subtemporal interdural approach to dumbbell-shaped trigeminal schwannomas that effectively converts a multiple-compartment tumor into a single-compartment tumor. Dural incisions and stepwise mobilization complements our previous description of the bony dissection for this approach.

Microsurgical experience with keyhole operations on intracranial aneurysms

Background We report our experience with keyhole approaches as favorable treatments for various intracranial aneurysms including multiple aneurysms and giant aneurysms. Methods According to the different locations of 105 aneurysms harbored in 100 patients, different keyhole approaches were designed elaborately, among which a supraorbital keyhole approach was used in 91 cases, a pterional keyhole approach in 5 cases, a subtemporal keyhole approach in 3 cases, a retromastoid keyhole approach in 2 cases, and a unifrontal interhemispheric keyhole approach in 1 case. Results Among those 105 aneurysms, 99 were clipped successfully, including 4 that were resected after clipping. One mini-aneurysm was wrapped. The other aneurysms were trapped, including 1 VA aneurysm, 1 giant ICA aneurysm, 1 giant PCoA aneurysm, and 2 giant aneurysms in the PCAs (P2-P3 segment). Multiple aneurysms in 5 cases were treated in 1 surgical session, including 3 cases via unilateral approaches and 2 cases via bilateral approaches. There were no severe keyhole approach–related complications in this present series. Conclusion The keyhole approaches, based on improvements in diagnostic imaging, advanced surgical instruments, and microsurgical skills, are effective and ideal craniotomy techniques in the hands of experienced neurosurgeons for the treatment of intracranial aneurysms, including multiple and giant aneurysms, in patients without diffuse SAH, severe cerebral vasospasm, and severe brain edema or brain swelling.

Keyhole approach surgery for petroclival meningioma

In China, the feasibility of keyhole approach in surgical treatment of petroclival meningioma has not been well evaluated. This report summarized our experience in 25 patients with petroclival meningioma who had been treated with keyhole approach surgery. From July 2000 to July 2005, 25 patients with petroclival meningioma were subjected to resection via subtemporal, retrosigmoid or combined keyhole approaches. The extent of tumor resection was evaluated by MRI 3 months after surgery, and postoperative complications were investigated. The maximum diameter of tumors ranged from 2 to 7 cm (mean, 4.5 cm). Gross total resection (GTR) was achieved in 14 patients, giving a GTR rate of 56%. Subtotal resection (STR) was carried out in 8 patients and partial resection in 3. Thirteen patients kept normal neurological status, whereas others suffered from cranial nerve deficits (VII, VII, III and lower CN). One patient died in the postoperative period. Keyhole approach surgery, especially the combined keyhole approach is suitable for the treatment of petroclival meningioma. It provides easy and quick access to the supra- and infratentorial juxta-clival region without drilling of the petrous bone. Complications related to the approach can be minimized.

Surgical approaches to the atrium of the lateral ventricle: microsurgical anatomy

Background Managing lesions situated in the atrium of the lateral ventricle remains a challenging neurosurgical problem. The purposes of this study were to examine the microsurgical anatomy of the atrium of the lateral ventricle and the optic radiation and to define the differences in the exposure obtained by various surgical approaches. Methods Fifteen adult cadaveric specimens were studied using magnification ×3 to ×40 after perfusion of the arteries and veins with colored silicone. The microsurgical anatomy of the atrium of the lateral ventricle was examined. The relationship between the optic radiation and the atrium was studied using the white matter fiber dissection technique. Surgical approaches to the atrium of the lateral ventricle were examined in stepwise dissection. Results The medial and inferior walls of the atrium were free from optic radiation fibers. Surgical approaches to the atrium of the lateral ventricle are divided into 3 routes: (1) anterior approach: transsylvian approach, (2) posterior approaches: posterior transcortical, posterior transcallosal, occipital, and supracerebellar transtentorial approaches, and (3) lateral approaches: transtemporal and subtemporal approaches. Conclusion Knowledge of the microsurgical anatomy of the atrium of the lateral ventricle and surrounding vital structures and the choice of an appropriate surgical approach will help surgeons perform safe and minimally invasive surgery.

Subtemporal Approach To The Tentorial Incisura: Normative Morphometric Data Based On Magnetic Resonance Imaging Scans

The tentorial notch can be contained within a transversal line made in front of the cerebral peduncles and another line through the posterior border of the quadrigeminal plate into the anterior, middle and posterior parts. Different approaches to the tentorial incisura have been established. The subtemporal approach represents one of those options. Since morphometrical analyses of this approach in this region have not yet been performed, the aim of the present study was to measure the surgical corridor along these borders. Fifty-three magnetization prepared rapid acquisition gradient echo-sequences of individual brains without pathological lesions were analyzed. For this study, an axial section along the pontomesencephalic sulcus and two coronal sections along the above-described borders were measured using a program specially written by one of the coauthors to obtain various parameters. A triangle circumscribing the surgical corridor was delimited by exactly defined anatomic landmarks for the coronal section, and the depths of the temporal lobe at the incisural borders were measured for the axial section. Various data are given concerning the surgical corridor of a subtemporal approach to the tentorial incisura. The different shapes of this corridor to the incisural region were recorded. According to our measurements, four different types of the temporal lobe could be differentiated. Knowledge of these distances and various contours of the path is crucial to avoid brain damage during retraction or manipulation. The curvature of the floor of the middle cranial fossa is highly variable and thus determines the surgical path chosen.

脳動脈瘤手術ｕｐｄａｔｅ 椎骨脳底動脈系脳動脈瘤手術における術中モニタリング

The efficacy of intraoperative neurophysiological monitoring in vertebro-basilar artery aneurysm (VB-AN) was clinically examined. Since June 2001, intraoperative monitoring was performed in 12 operations for VB-AN. Five operations were for vertebral artery aneurysms: 4 through the lateral suboccipital route and 1 endovascular surgery. Among 5 operations for basilar bifurcation aneurysms, 3 were through the subtemporal route and 2 were by the anterior temporal approach. The other 2 operations were for the posterior cerebral artery aneurysms by the subtemporal approach. Auditory brain stem responses (ABR) were recorded in 5 operations, somatosensory evoked potential in 1 operation, and motor evoked potential (MEP) in 9 operations by 7 of 300～600 (400 in general) V bipolar transcranial (TC) stimulations or 7 of 3～10 mA brain stem direct (BSD) stimulations. In 5 operations, both TCMEP and BSDMEP were used together. Glasgow outcome scales of 12 patients were divided into 6 good recoveries, 2 moderate disabilities, 3 severe disabilities and 1 persistent vegetative state. Among 3 patients with BA aneurysms who had a significant decrease or disappearance of the amplitude of MEP by the temporally occlusions of the BA or both VA, 2 patients have never suffered from the prolonged motor palsy. ABR monitoring seems to be essential in the operation by lateral suboccipital approach since it is very easy and sensitive. It is also applicable in endovascular surgery. TCMEP seems to be useful in VB-AN surgery in which the primary motor cortex connot always be exposed. BSDMEP was successfully recorded in 5 of 7 operations tried and it seems to be a more effective way to monitor motor functioning than TCMEP.