Therapeutic functions of astrocytes to treat α-synuclein pathology in Parkinson's disease.

Intraneuronal inclusions of misfolded α-synuclein (α-syn) and prion-like spread of the pathologic α-syn contribute to progressive neuronal death in Parkinson's disease (PD). Despite the pathologic significance, no efficient therapeutic intervention targeting α-synucleinopathy has been developed. In this study, we provide evidence that astrocytes, especially those cultured from the ventral midbrain (VM), show therapeutic potential to alleviate α-syn pathology in multiple in vitro and in vivo α-synucleinopathic models. Regulation of neuronal α-syn proteostasis underlies the therapeutic function of astrocytes. Specifically, VM-derived astrocytes inhibited neuronal α-syn aggregation and transmission in a paracrine manner by correcting not only intraneuronal oxidative and mitochondrial stresses but also extracellular inflammatory environments, in which α-syn proteins are prone to pathologic misfolding. The astrocyte-derived paracrine factors also promoted disassembly of extracellular α-syn aggregates. In addition to the aggregated form of α-syn, VM astrocytes reduced total α-syn protein loads both by actively scavenging extracellular α-syn fibrils and by a paracrine stimulation of neuronal autophagic clearance of α-syn. Transplantation of VM astrocytes into the midbrain of PD model mice alleviated α-syn pathology and protected the midbrain dopamine neurons from neurodegeneration. We further showed that cografting of VM astrocytes could be exploited in stem cell-based therapy for PD, in which host-to-graft transmission of α-syn pathology remains a critical concern for long-term cell therapeutic effects.

Endoscopically assisted presigmoid retrolabyrinthine approach to the lateral mesencephalic sulcus: a cadaveric study with comparison to the variant supracerebellar infratentorial approaches.

The supracerebellar infratentorial (SCIT) approach is commonly used to gain access to the lateral mesencephalic sulcus (LMS), which has been established as a safe entry point into the posterolateral midbrain. This study describes a lateral variant of the SCIT approach, the supreme-lateral SCIT approach, for accessing the LMS through the presigmoid retrolabyrinthine craniectomy and quantitatively compares this approach with the paramedian and extreme-lateral SCIT approaches. Anatomical dissections were performed in four cadaveric heads. In each head, the supreme-lateral SCIT approach was established on one side, following a detailed description of each step, whereas the paramedian and supreme-lateral SCIT approaches were established on the other side. Quantitative measurements of the exposed posterolateral midbrain, the angles of LMS entry, and the depth of surgical corridors were recorded and compared between the three SCIT approach variants. The supreme-lateral (67.70 ± 23.14 mm2) and extreme-lateral (70.83 ± 24.99 mm2) SCIT approaches resulted in larger areas of exposure anterior to the LMS than the paramedian SCIT approach (38.61 ± 9.84 mm2); the supreme-lateral SCIT approach resulted in a significantly smaller area of exposure posterior to the LMS (65.24 ± 6.81 mm2) than the other two variants (paramedian = 162.75 ± 31.98 mm2; extreme-lateral = 143.10 ± 23.26 mm2; both P < .001). Moreover, the supreme-lateral SCIT approach resulted in a surgical corridor with a shallower depth and a smaller angle relative to the horizontal plane than the other two variants. The supreme-lateral SCIT approach is a more lateral approach than the extreme-lateral SCIT approach, providing a subtemporal approach with direct LMS visualization. The supreme-lateral SCIT offers the benefits of both subtemporal and SCIT approaches and represents a suitable option for the management of selected midbrain pathologies.

Microsurgical management of midbrain cavernous malformations: does lesion depth influence the outcome?

BACKGROUND: The purpose of this study was to clarify whether the intrinsic depth of midbrain cavernous malformations (MCMs) influenced the surgical outcome. METHODS: The authors conducted a retrospective study of 76 consecutive patients who underwent microsurgical resection of a MCM. The vascular lesions were categorized into 4 distinct groups based on how these lesions had altered the brainstem surface. Additionally, it was verified whether the actual aspect of the brainstem surface could be predicted only by evaluating the pertinent preoperative MRI slices. Clinical outcome was assessed by determining the modified Rankin Scale Score (mRS) before and after surgery. RESULTS: Twenty-three MCMs (30.3%) were located deeply within the midbrain. The overlying midbrain surface appeared to be normal (group nl). In 33 patients (43.4%), the midbrain surface showed only a yellowish discoloration (group yw). In another 14 individuals (18.4%), the midbrain surface was distorted by the underlying MCM and bulging out while the vascular lesion still remained covered by a thin parenchymal layer (group bg). In the smallest group comprising 6 patients (7.9%), the exophytic MCM had disrupted the midbrain surface and was clearly visible at microsurgical exposure (group ex). The mean mRS decreased in the group nl from 1.43 preoperatively to 0.61 at follow-up. CONCLUSION: This study demonstrates in a large patient population that a deep intrinsic MCM location is not necessarily associated with an unfavorable clinical outcome after microsurgical lesionectomy. Predicting the aspect of the midbrain surface by evaluating preoperative MR images alone was not sufficiently reliable.

Endoscopic Endonasal Transclival Approach to Spontaneous Hypertensive Brainstem Hemorrhage.

Surgical management of spontaneous hypertensive brainstem hemorrhage remains a challenge for neurosurgeons, especially when the hemorrhage is located the ventral brainstem. Recently endoscopic endonasal approach has been applied for resection of ventral brainstem lesions, though no published literature has explored its utility in treating brainstem hemorrhage. Here we reported a successful evacuation of severe hypertensive brainstem hemorrhage through endoscopic endonasal transclival approach. A 37 years-old male with a 5-year history of uncontrolled hypertension was brought to the Emergency Department with sudden vomiting, limb convulsions, and loss of consciousness for 2 hours. Computed tomography demonstrated a hemorrhage measuring 2.5 × 2.2 cm in the ventral midbrain and pontine. He presented with a Glasgow coma scale (GCS) score of 3 and disrupted vitals, and was intubated in the Emergency Department. Considering the ventral location of the hemorrhage and the need for emergent surgical decompression, an endoscopic endonasal approach was applied. Evacuation of the brainstem hemorrhage was achieved and his spontaneous respiration improved immediately after surgery. He was weaned off the ventilator and extubated on postoperative day 1, along with an improved GCS score of 5 (E2V1M2). At 1 month postoperatively his GCS score improved to 11 (E4V2M5) and he is currently under rehabilitation. Endoscopic endonasal approach is a feasible alternative for emergent surgery of ventrally located brainstem hemorrhage in carefully selected cases by providing direct visualization of the area and a good working angle, which facilitate evacuation of the hemorrhage with minimal damage to the brainstem.

The transcallosal transchoroidal approach to the diencephalic-mesencephalic junction: how I do it.

BACKGROUND: Different approaches have to be considered for lesions of the diencephalic-mesencephalic junction based on the localization, extension of the lesion, and relationship to the ventricular system. METHOD: We present the case of a young lady who presented with a cavernoma of the junction of midbrain and diencephalon after an episode of hemorrhage. The microsurgical anatomy of the trans-callosal trans-choroidal approach for this lesion is described along with its advantages and limitations. CONCLUSION: The trans-choroidal approach allows adequate access to lesions of the diencephalic-mesencephalic junction that project into the third ventricle.

Endoscopic endonasal resection of a medullary cavernoma: a novel case.

Brainstem cavernomas can present very challenging operative problems. Endoscopic endonasal approaches to these lesions in the mesencephalon and pons have been described. In this article the authors present the first case of a medullary cavernoma resected by an endoscopic transclival approach. A 26 year-old woman with a 1.5 cm medullary cavernoma presented with imbalance, swallowing difficulty, and right hemibody weakness. She was taken to the operating room for endoscopic endonasal transclival resection. Her pre-existing neurologic deficits worsened initially after surgery, but at three-month follow-up she had made a full neurologic recovery.

The Subtemporal Approach to the Lateral Midbrain with and without Zygomatic Osteotomy: An Anatomical Study.

The subtemporal approach provides a narrow operative corridor to the crus cerebrum and adjacent structures of the crural, interpeduncular, and ambient cistern. Addition of a zygomatic osteotomy widens this narrow corridor and spares retraction of the temporal lobe. We investigate and compare the morphometric parameters of the subtemporal approach with versus without zygomatic osteotomy. On each side of four cadaveric heads, a temporal craniotomy was performed to gain access to the crus cerebrum and adjacent subarachnoid cisterns using a subtemporal approach. Operative corridor width and corridor working angle were measured with and without brain retraction on each specimen side. Next, a zygomatic osteotomy was performed followed by full downward reflection of the temporalis muscle and further drilling of the squamous part of the temporal bone. Lastly, operative corridor width and corridor working angle were measured again for comparison. The subtemporal operating corridor was (mean/SD): 5.8/2.6 mm without retraction, 11.4/4.3 mm with retraction, and 13.5/6.5° working angle. After addition of a zygomatic osteotomy, the operative corridor was 8/9.2/4.3 mm without retraction, 14.7/4.5 mm with retraction, 31.8/3.1° working angle. Zygomatic osteotomy significantly increased the operative corridor working angle of the subtemporal approach. Furthermore, we demonstrate a direct approach into the interpeduncular fossa. Clin. Anat. 32:710-714, 2019. © 2019 Wiley Periodicals, Inc.

The paramedian supracerebellar infratentorial approach.

BACKGROUND: Lesions of the superior cerebellar surface, pineal region, lateral and dorsal midbrain and mesial temporal lobe are challenging to treat and often require neurosurgical intervention. METHODS: The paramedian variation of the supracerebellar infratentorial approach utilizes the downward slope of the cerebellum to facilitate exposure and the lower density of cerebellar bridging veins away from the midline decreases the need to sacrifice larger venous channels. We also discuss our experiences with the approach, and some of the drawbacks and nuances that we have encountered as it has evolved over the years. CONCLUSIONS: This approach is versatile and effective and the authors' surgical approach of choice for resecting these challenging lesions.

[An aneurysm of the medial posterior choroidal artery: a case report and a literature review]. / Anevrizma medial'noi zadnei vorsinchatoi arterii: opisanie klinicheskogo nabliudeniia i obzor literatury.

INTRODUCTION: Aneurysms of the medial posterior choroidal artery are very rare. To date, only 5 cases have been reported. The article presents a case of successful surgical treatment of an aneurysm of the medial posterior choroidal artery and a literature review. CLINICAL CASE: A 57-year-old male was admitted to the Center 1 month after a massive subarachnoid hemorrhage. CT angiography revealed an aneurysm of the right posterior medial choroidal artery in the perimesencephalic cistern and resolved hemorrhage. TREATMENT: The paramedian supracerebellar transtentorial approach to the lateral surface of the midbrain was used. The posterior cerebral artery was identified in the perimesencephalic cistern, and the medial posterior choroidal artery aneurysm was isolated and successfully clipped, with the parent artery being preserved. Postoperative CT and MRI scans revealed a small asymptomatic ischemic lesion in the tectal region on the right. The patient was discharged without any neurological symptoms 10 days after surgery. CONCLUSION: Medial posterior choroidal artery aneurysms can be clipped using the paramedian supracerebellar transtentorial approach.

The supracerebellar infratentorial approach to the dorsal midbrain.

The supracerebellar infratentorial approach provides access to the dorsal midbrain, pineal region, and tentorial incisura. This approach can be used with the patient in a sitting, prone, park-bench, or supine position. For a patient with a supple neck and favorable anatomy, we prefer the supine position. The ipsilateral shoulder is elevated, the head turned to the contralateral side, the chin is tucked, and the neck extended toward the floor to open the craniocervical angle for added working room. Care must be taken to place the craniotomy laterally to make use of the ascending angle of the tentorium for ease of access to deep-seated lesions. The video can be found here: https://youtu.be/BZh6ljmE23k .

Giant cavernous malformation in the ventrolateral midbrain with extension into the thalamus: a case report of a paramedian supracerebellar transtentorial approach.

Cavernous malformations (CMs) of the midbrain and thalamus are relatively rare and particularly difficult to be resected given their location in eloquent tissues. Here, we report a case of a 14-year-old boy who experienced repeated and progressive right hemiparesis. Image examinations showed a gradually enlarged CM originated in the left ventrolateral midbrain extending to the left thalamus with repeated hemorrhage. By performing a paramedian supracerebellar transtentorial approach, the CM was totally removed, and the patient recovered without any new neurological deficit. The authors' experience suggests that this approach is eminent in treating giant lesions involving the ventrolateral midbrain and thalamus.

Stereotactic mesencephalotomy for palliative care pain control: A case report, literature review and plea to rediscover this operation.

Introduction Stereotactic mesencephalotomy is an ablative procedure which lesions the pain pathways (spinothalamic and trigeminothalamic tracts) at the midbrain level to treat medically refractory, nociceptive, contralateral pain. Sparsely reported in contemporary English language literature, this operation is at risk of being lost from the modern-day neurosurgical practice. Methods We present a case report and brief review of the literature on stereotactic mesencephalotomy. A 17-year-old girl with cervical cord glioblastoma and medically refractory unilateral head and neck pain was treated with contralateral stereotactic mesencephalotomy. The lesion was placed at the level of the inferior colliculus, half way between the lateral edge of the aqueduct and lateral border of the midbrain. Results The patient had no head and neck pain immediately after the procedure and remained pain-free for the remainder of her life (five months). She was weaned off her pre-operative narcotics and was able to leave hospital, meeting her palliative care goals. Conclusions Cancer-related unilateral head and neck nociceptive pain in the palliative care setting can be successfully treated with stereotactic mesencephalotomy. We believe that stereotactic mesencephalotomy is the treatment of choice for a small number of patients typified by our case. The authors make a plea to the palliative care and neurosurgical communities to rediscover this operation.

[Brainstem cavernous malformation and its surgical treatment].

OBJECTIVE: To analyze the clinical characteristics and surgery approach for patients with brainstem cavernous malformation (BSCM). METHODS: The clinical data of 23 BSCM patients (5 cases at midbrain, 16 cases at pons, and 2 cases at medulla) treated in the Second Affiliated Hospital Zhejiang University School of Medicine from July 2003 to June 2014 were retrospectively reviewed. The medical history, radiological findings, operation records, postoperative course and follow-up results were analyzed. RESULTS: Suboccipital approach, retrosigmoid approach, subtentorial supracerebella approach, Poppen approach, pterional approach, Kawase approach, interhemispheric transcallosal third ventrical approach were applied for the surgery of BSCM patients. Among them, Kawase approach and interhemispheric transcallosal third ventrical approach were firstly reported in treatment of BSCM. Total resection was achieved in 22 cases. Neurological function was improved in 15 cases, unchanged in 7 cases and deteriorated in 1 case. Fifteen cases were followed up for a mean period of 3.5 years and signs of recurrence was found. CONCLUSION: Proper selection of surgical approach is important to assure total resection of the lesions, to protect surrounding normal vital structures and to avoid post-surgical complications.

Infragalenic triangle as a gateway to dorsal midbrain and posteromedial thalamic lesions: descriptive and quantitative analysis of microsurgical anatomy.

OBJECTIVE: Anatomical triangles provide neurosurgeons with the specificity required to access deep targets, supplementing more general instructions, such as craniotomy and approach. The infragalenic triangle (IGT), bordered by the basal vein of Rosenthal (BVR), precentral cerebellar vein (PCV), and the quadrangular lobule of the cerebellum, is one of a system of anatomical triangles recently introduced to guide dissection to brainstem cavernous malformations and has not been described in detail. This study aimed to quantitatively analyze the anatomical parameters of the IGT and present key nuances for its microsurgical use. METHODS: A midline supracerebellar infratentorial (SCIT) approach through a torcular craniotomy was performed on 5 cadaveric heads, and the IGT was identified in each specimen bilaterally. Anatomical measurements were obtained with point coordinates collected using neuronavigation. Three cadaveric brains were used to illustrate relevant brainstem anatomy, and 3D virtual modeling was used to simulate various perspectives of the IGT through different approach angles. In addition, 2 illustrative surgical cases are presented. RESULTS: The longest edge of the IGT was the lateral edge formed by the BVR (mean ± SD length 19.1 ± 2.3 mm), and the shortest edge was the medial edge formed by the PCV (13.9 ± 3.6 mm). The mean surface area of the IGT was 110 ± 34.2 mm2 in the standard exposure. Full expansion of all 3 edges (arachnoid dissection, mobilization, and retraction) resulted in a mean area of 226.0 ± 48.8 mm2 and a 2.5-times increase in surface area exposure of deep structures (e.g., brainstem and thalamus). Thus, almost the entire tectal plate and its relevant safe entry zones can be exposed through an expanded unilateral IGT except for the contralateral inferior colliculus, access to which is usually hindered by PCV tributaries. Exposure of bilateral IGTs may be required to resect larger midline lesions to increase surgical maneuverability or to access the contralateral pulvinar. CONCLUSIONS: The IGT provides a safe access route to the dorsal midbrain and reliable intraoperative guidance in the deep and complex anatomy of the posterior tentorial incisura. Its potential for expansion makes it a versatile anatomical corridor not only for intrinsic brainstem lesions but also for tumors and vascular malformations of the pineal region, dorsal midbrain, and posteromedial thalamus.

Microsurgical management of midbrain gliomas: surgical results and long-term outcome in a large, single-surgeon, consecutive series.

OBJECTIVE: The authors report on a large, consecutive, single-surgeon series of patients undergoing microsurgical removal of midbrain gliomas. Emphasis is put on surgical indications, technique, and results as well as long-term oncological follow-up. METHODS: A retrospective analysis was performed of prospectively collected data from a consecutive series of patients undergoing microneurosurgery for midbrain gliomas from March 2006 through June 2022 at the authors' institution. According to the growth pattern and location of the lesion in the midbrain (tegmentum, central mesencephalic structures, and tectum), one of the following approaches was chosen: transsylvian (TS), extreme anterior interhemispheric transcallosal (eAIT), posterior interhemispheric transtentorial subsplenial (PITS), paramedian supracerebellar transtentorial (PST), perimedian supracerebellar (PeS), perimedian contralateral supracerebellar (PeCS), and transuvulotonsillar fissure (TUTF). Clinical and radiological data were gathered according to a standard protocol and reported according to common descriptive statistics. The main outcomes were rate of gross-total resection; extent of resection; occurrence of any complications; variation in Karnofsky Performance Status score at discharge, 3 months, and last follow-up; progression-free survival (PFS); and overall survival (OS). RESULTS: Fifty-four patients (28 of them pediatric) met the inclusion criteria (6 with high-grade and 48 with low-grade gliomas [LGGs]). Twenty-two tumors were in the tegmentum, 7 in the central mesencephalic structures, and 25 in the tectum. In no instance did the glioma originate in the cerebral peduncle. TS was performed in 2 patients, eAIT in 6, PITS in 23, PST in 16, PeS in 4, PeCS in 1, and TUTF in 2 patients. Gross-total resection was achieved in 39 patients (72%). The average extent of resection was 98.0% (median 100%, range 82%-100%). There were no deaths due to surgery. Nine patients experienced transient and 2 patients experienced permanent new neurological deficits. At a mean follow-up of 72 months (median 62, range 3-193 months), 49 of the 54 patients were still alive. All patients with LGGs (48/54) were alive with no decrease in their KPS score, whereas 42 showed improvement compared with their preoperative status. CONCLUSIONS: Microneurosurgical removal of midbrain gliomas is feasible with good surgical results and long-term clinical outcomes, particularly in patients with LGGs. As such, microneurosurgery should be considered as the first therapeutic option. Adequate microsurgical technique and anesthesiological management, along with an accurate preoperative understanding of the tumor's exact topographic origin and growth pattern, is crucial for a good surgical outcome.

Transcallosal-Transchoroidal Fissure Approach for Midbrain and Thalamic Cavernous Malformations: 2-Dimensional Operative Video.

INDICATIONS CORRIDOR AND LIMITS OF EXPOSURE: Cavernous malformations of the third ventricle arise from the medial thalamus and/or periaqueductal midbrain. Microsurgical resection is indicated when the lifetime risk of hemorrhage outweighs the surgical risks. ANATOMIC ESSENTIALS NEED FOR PREOPERATIVE PLANNING AND ASSESSMENT: superior sagittal sinus, callosomarginal and pericallosal arteries, corpus callosum, foramen of Monro, choroidal fissure, fornix, thalamostriate veins, internal cerebral veins (ICVs), velum interpositum, and thalamus. ESSENTIAL STEPS OF THE PROCEDURE: The patient consents to the procedure. With the patient supine, the head is turned 90° and laterally flexed 45°. A bifrontal craniotomy positioned two-thirds anterior and one-third posterior to the coronal suture is performed. The interhemispheric fissure is opened, and a 2-cm corpus callosotomy is performed. Choroid plexus cauterization exposes the choroidal fissure. Sharp division of the taenia fornicea opens the velum interpositum, where the thalamostriate vein can be followed around the venous angle to the ICV. The anterior septal vein may be divided to communicate between the foramen of Monro and choroidal fissure. Dissection between the ICVs opens the velum interpositum into the third ventricle. PITFALLS/AVOIDANCE OF COMPLICATIONS: Frontal or deep vein occlusion causes venous infarction, and dissection on the nondominant hemisphere is preferred. Other complications include arterial infarction, fornix injury from choroidal fissure dissection or forniceal retraction, and thalamic or midbrain injury during lesion resection. VARIANTS AND INDICATIONS FOR THEIR USE: The contralateral choroidal fissure is used for low-lying medial thalamic and midbrain lesions. The ipsilateral choroidal fissure is used for high-lying or large lesions extending laterally. Transchoroidal approaches are not needed for superior (transcallosal only) or anterior (contralateral transcallosal-contralateral transforaminal) thalamic lesions. Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

A novel radiological classification of midbrain pilocytic astrocytomas and its implication for surgical management: a single-institution experience of 57 cases.

OBJECTIVE: Surgery for midbrain pilocytic astrocytoma (PA) remains a formidable challenge. To facilitate decision-making and achieve a better outcome in the management of patients with midbrain PA, the authors have proposed a novel radiological classification of midbrain PAs with long-term follow-up. METHODS: Fifty-seven midbrain PA patients who underwent surgery at Beijing Tiantan Hospital, Capital Medical University, from January 2008 to June 2021, were reviewed. Based on tumor location and the topological anatomical change identified on MRI, midbrain PAs were categorized into four types: crural (12/57, 21.1%), tegmental (25/57, 43.9%), aqueductal (5/57, 8.8%), and tectal (15/57, 26.3%) PAs. The relevant clinical, radiological, and pathological data; surgical procedures and results; and long-term outcomes were collected and analyzed. RESULTS: The 1-, 3-, and 5-year survival rates reached 98%, 96%, and 96%, respectively, with gross-total resection achieved in 66.7% of cases, followed by near-total resection in 17.5% cases. The clinical and radiological features, selection of surgical approaches, and long-term postoperative deficits were distinct among each type. Crural PAs were associated with younger age (median 9 years, IQR 5.0-12.8 years); the largest tumor volume (median 31.9 cm3, IQR 17.2-42.6 cm3); the lowest preoperative Karnofsky Performance Scale (KPS) score (median 65, IQR 50-70); the most frequent preoperative motor deficit (91.7%); a mixed solid-cystic component (75%); occupation of the crural cistern; elevation and rotation of the thalamus (medial and/or lateral); displacement of the anterior third ventricle, uncus, and anterior commissure; the most diverse surgical approaches; more frequent use of multimodality image-guided surgery (58.3%); and the most remarkable improvement in KPS score at long-term follow-up. Tegmental PAs were associated with adolescents and young adults (median age 21 years, IQR 8-33 years); tumor volume (median 13.9 cm3, IQR 9.5-20.5 cm3); a good preoperative KPS score (median 80, IQR 70-80); a mixed solid-cystic component (72%); occupation of the ambient cistern and cerebellomesencephalic fissure; a close relationship with the dorsal pons, superior cerebellar peduncle, and posterior inferior third ventricle; and a higher probability of permanent postoperative sensory deficits (40%). Aqueductal and tectal PAs were associated with small tumor volume (median 9.14 cm3, IQR 5.1-17.4 cm3 and median 11.84 cm3, IQR 5.7-18.3 cm3, respectively), a higher percentage of hydrocephalus (80% and 86.7%, respectively), and a straightforward selection of limited surgical approaches. CONCLUSIONS: A novel and comprehensive radiological classification of midbrain PAs was established, which will serve as a valuable tool in patient management and promote uniform communication and comparison across different studies and publications.

Ependymal cyst of the midbrain.

We present the case of a 30-year-old man who developed an acute hydrocephalus secondary to an obstruction of the cerebral aqueduct by a midbrain cystic lesion. After a ventriculo-peritoneal shunt was placed to relief symptoms of intracranial hypertension, the patient underwent a neuronavigation-assisted endoscopic fenestration of the cyst. A careful immunohistochemical staining confirmed the diagnosis of an ependymal cyst. An extensive review of the literature has revealed that this is the first report of a periaqueductal ependymal cyst with definite histological diagnosis. This is a rare cause of acute non-communicating hydrocephalus but an important entity in the differential diagnosis.

[Temporal transchoroidal approach for tumors of the midbrain and thalamus].

Surgical approach to the tumors of deep localization depends on the predominant direction of tumor growth. The main task of the surgeon in such cases is to choose less traumatic approach with a sufficient angle of operational action to achieve greater surgical radicality. The article describes temporal transchoroidal approach to the tumors of the midbrain, thalamus, and optic tract. This approach in selected cases allows to remove deep-seated tumors with less damage compared with pterional and subtemporal approach.

A system of anatomical triangles defining dissection routes to brainstem cavernous malformations: definitions and application to a cohort of 183 patients.

OBJECTIVE: Anatomical triangles defined by intersecting neurovascular structures delineate surgical routes to pathological targets and guide neurosurgeons during dissection steps. Collections or systems of anatomical triangles have been integrated into skull base surgery to help surgeons navigate complex regions such as the cavernous sinus. The authors present a system of triangles specifically intended for resection of brainstem cavernous malformations (BSCMs). This system of triangles is complementary to the authors' BSCM taxonomy that defines dissection routes to these lesions. METHODS: The anatomical triangle through which a BSCM was resected microsurgically was determined for the patients treated during a 23-year period who had both brain MRI and intraoperative photographs or videos available for review. RESULTS: Of 183 patients who met the inclusion criteria, 50 had midbrain lesions (27%), 102 had pontine lesions (56%), and 31 had medullary lesions (17%). The craniotomies used to resect these BSCMs included the extended retrosigmoid (66 [36.1%]), midline suboccipital (46 [25.1%]), far lateral (30 [16.4%]), pterional/orbitozygomatic (17 [9.3%]), torcular (8 [4.4%]), and lateral suboccipital (8 [4.4%]) approaches. The anatomical triangles through which the BSCMs were most frequently resected were the interlobular (37 [20.2%]), vallecular (32 [17.5%]), vagoaccessory (30 [16.4%]), supracerebellar-infratrochlear (16 [8.7%]), subtonsillar (14 [7.7%]), oculomotor-tentorial (11 [6.0%]), infragalenic (8 [4.4%]), and supracerebellar-supratrochlear (8 [4.4%]) triangles. New but infrequently used triangles included the vertebrobasilar junctional (1 [0.5%]), supratrigeminal (3 [1.6%]), and infratrigeminal (5 [2.7%]) triangles. Overall, 15 BSCM subtypes were exposed through 6 craniotomies, and the approach was redirected to the BSCM by one of the 14 triangles paired with the BSCM subtype. CONCLUSIONS: A system of BSCM triangles, including 9 newly defined triangles, was introduced to guide dissection to these lesions. The use of an anatomical triangle better defines the pathway taken through the craniotomy to the lesion and refines the conceptualization of surgical approaches. The triangle concept and the BSCM triangle system increase the precision of dissection through subarachnoid corridors, enhance microsurgical execution, and potentially improve patient outcomes.