Topographical anatomy of the subthalamic region with special interest in the human medial forebrain bundle.

OBJECTIVE: The medial forebrain bundle (MFB) is a novel promising deep brain stimulation (DBS) target in severe affective disorders that courses through the subthalamic region according to tractography studies. Its potential therapeutic role arose in connection with the development of hypomania during stimulation of the subthalamic nucleus (STN) in Parkinson's disease, offering an alternative explanation for the occurrence of this side effect. However, until now its course exclusively described by tractography had not yet been confirmed by any anatomical method. The aim of this study was to fill this gap as well as to provide a detailed description of the fiber tracts surrounding the STN to facilitate a better understanding of the background of side effects occurring during STN DBS. METHODS: Ten human cadaveric brains (20 hemispheres) and 100 healthy subjects (200 hemispheres) from the S500 Release of the Human Connectome Project were involved in this study. Nineteen hemispheres were dissected according to Klingler's method. One additional hemisphere was prepared for histological examinations to validate the macroscopical results and stained with neurofibril silver impregnation according to Krutsay. The authors also aimed to reconstruct the MFB using tractography and correlated the results with their dissections and histological findings. RESULTS: The white matter connections coursing through the subthalamic region were successfully dissected. The ansa lenticularis, lenticular fasciculus, thalamic fasciculus, ipsi- and contralateral cerebellar fibers, and medial lemniscus were revealed as closely related fiber tracts to the STN. However, the existence of a distinct fiber bundle corresponding to the MFB described by tractography could not be identified. Using tractography, the authors showed that the depiction of the streamlines representing the MFB was also strongly dependent on the threshold parameters. CONCLUSIONS: According to this study's findings, the streamlines of the MFB described by tractography arise from the limitations of the diffusion-weighted MRI fiber tracking method and actually correspond to subthalamic fiber bundles, especially the ansa lenticularis and lenticular fasciculus, which erroneously continue in the anterior limb of the internal capsule, toward the prefrontal cortex.

Anatomy and microsurgical relevance of the outer arachnoid envelope around the olfactory bulb based on endoscopic cadaveric observations.

BACKGROUND: Surgical approaches to the anterior cranial fossa have great risk of damaging the olfactory tract and bulb. The goal of this study was to describe the outer arachnoid envelope around the olfactory bulb which plays significant role in the approach-related injury of the nerve. MATERIAL AND METHODS: A total of 20 fresh human cadaveric heads were examined as a following: 5 cadaveric heads were used to describe a gross overview of the topographic anatomy of the outer arachnoid cover of the olfactory bulb. In 15 cadaveric heads endoscopic surgical approaches were performed to examine the in situ undisrupted anatomy of the outer arachnoid around the olfactory bulb. Four cadaveric heads were used for lateral subfrontal approach, 5 heads for medial subfrontal, 3 heads for median subfrontal approach and 3 heads for anterior interhemispheric approach. RESULTS: The outer arachnoid membrane of the frontal lobe attaches the olfactory bulb strongly to the above lying olfactory sulcus. Only the most rostral portion of the olfactory bulb became slightly detached from the frontal lobe. The outer arachnoid forms a decent protrusion around the tip of the olfactory bulbs. The fila olfactoria have their own outer arachnoid cover as a continuation of the same layer of the olfactory bulb. The effect of brain retraction and manipulation forces on the olfactory bulb and the role of the here located arachnoid membranes were visually analysed and described in detail through the performed four different neurosurgical approaches. CONCLUSION: The results of our observations provide important anatomical details for the preservation of smelling during neurosurgical procedures.

Surgical management of syringomyelia associated with spinal arachnoid web: strategies and outcomes.

Spinal arachnoid web (SAW) is a rare disease entity characterized as band-like arachnoid tissue that can cause spinal cord compression and syringomyelia. This study aimed to analyze the surgical management of the spinal arachnoid web in patients with syringomyelia, focusing on surgical strategies and outcomes. A total of 135 patients with syringomyelia underwent surgery at our department between November 2003 and December 2022. All patients underwent magnetic resonance imaging (MRI), with a special syringomyelia protocol (including TrueFISP and CINE), and electrophysiology. Among these patients, we searched for patients with SAW with syringomyelia following careful analysis of neuroradiological data and surgical reports. The criteria for SAW were as follows: displacement of the spinal cord, disturbed but preserved CSF flow, and intraoperative arachnoid web. Patients were evaluated for initial symptoms, surgical strategies, and complications by reviewing surgical reports, patient documents, neuroradiological data, and follow-up data. Of the 135 patients, 3 (2.22%) fulfilled the SAW criteria. The mean patient age was 51.67 ± 8.33 years. Two patients were male, and one was female. The affected levels were T2/3, T6, and T8. Excision of the arachnoid web was performed in all cases. No significant change in intraoperative monitoring was noted. Postoperatively, none of the patients presented new neurological symptoms. The MRI 3 months after surgery revealed that the syringomyelia improved in all cases, and caliber variation of the spinal cord could not be detected anymore. All clinical symptoms improved. In summary, SAW can be safely treated by surgery. Even though syringomyelia usually improves on MRI and symptoms also improve, residual symptoms might be observed. We advocate for clear criteria for the diagnosis of SAW and a standardized diagnostic (MRI including TrueFISP and CINE).

Microsurgical anatomy and pathoanatomy of the outer arachnoid membranes in the cerebellopontine angle: cadaveric and intraoperative observations.

PURPOSE: The cerebellopontine angle (CPA) is a frequent region of skull base pathologies and therefore a target for neurosurgical operations. The outer arachnoid is the key structure to approach the here located lesions. The goal of our study was to describe the microsurgical anatomy of the outer arachnoid of the CPA and its pathoanatomy in case of space-occupying lesions. METHODS: Our examinations were performed on 35 fresh human cadaveric specimens. Macroscopic dissections and microsurgical and endoscopic examinations were performed. Retrospective analysis of the video documentations of 35 CPA operations was performed to describe the pathoanatomical behavior of the outer arachnoid. RESULTS: The outer arachnoid cover is loosely attached to the inner surface of the dura of the CPA. At the petrosal surface of the cerebellum the pia mater is strongly adhered to the outer arachnoid. At the level of the dural penetration of the cranial nerves, the outer arachnoid forms sheath-like structures around the nerves. In the midline, the outer arachnoid became detached from the pial surface and forms the base of the posterior fossa cisterns. In pathological cases, the outer arachnoid became displaced. The way of displacement depends on the origin of the lesion. The most characteristic patterns of changes of the outer arachnoid were described in case of meningiomas, vestibular schwannomas, and epidermoid cysts of the CPA. CONCLUSION: The knowledge of the anatomy of the outer arachnoid of the cerebellopontine region is essential to safely perform microsurgical approaches as well as of dissections during resection of pathological lesions.

Low incidence of hemorrhagic complications both during and after surgical procedures in patients maintained on prasugrel single antiplatelet therapy.

BACKGROUND AND PURPOSE: Prasugrel (Pra) is a third-generation thienopyridine that inhibits platelet aggregation via irreversible blockade of P2Y12 receptors. While several published studies have examined the use of Pra and acetylsalicylic acid (ASA) in coronary and neurovascular stenting procedures, there is only anecdotal evidence regarding the use of Pra as single antiplatelet therapy (SAPT) in open surgical procedures. This topic has become important because previous studies have revealed that neurovascular devices with antithrombotic coatings can be implanted using non-invasive procedures in patients maintained on Pra SAPT. MATERIAL AND METHODS: Patients who underwent open surgery under Pra SAPT between March 2020 and February 2022 were evaluated retrospectively. Adequate platelet inhibition both before and after the procedures was verified in all patients using Multiplate (Roche Diagnostics) and VerifyNow (Accriva) tests. Intraoperative and postoperative hemorrhagic events were recorded based on reviews of the procedure reports and interviews with the surgeons. RESULTS: The study enrolled 21 patients who underwent 23 open surgical procedures while maintained on Pra SAPT. The procedures included one extirpation of a brain arteriovenous malformation, seven extra-intracranial bypass surgeries, four ventriculoperitoneal shunts, one eye enucleation for an intractable orbital infection, two gastrostomies, one bone flap reinsertion after craniectomy, one decompressive craniectomy, one case requiring cranial surgical wound care, one colporrhaphy, one transurethral resection of urinary bladder cancer, two tumor oophorectomy/hysterectomy procedures, and one aneurysm clipping. None of the 23 procedures resulted in excessive intraoperative or postoperative hemorrhage. CONCLUSION: In a small retrospective series of patients who required antiplatelet therapy for neurovascular indications, Pra SAPT resulted in no significant increase in the incidence of perioperative and postoperative hemorrhagic complications.

The "Valva Cerebri": Morphometry, Topographic Anatomy and Histology of the Rhomboid Membrane at the Craniocervical Junction.

The arachnoid membranes' anatomy is a controversial topic in the literature, and the rhomboid membrane at the craniovertebral junction is an element of this system that has been described poorly. Hence, the objective of our study was to examine this membrane's anatomy and histology. A total of 45 fresh formalin-fixed human cadaveric heads were examined, and anatomic dissections and histologic examinations using standard staining methods were performed. The membrane was found to be a constant structure. It has a rhomboid shape and is located on the medulla oblongata and upper cervical spine's ventral surface within the subarachnoid space. Its average craniocaudal length is 49 mm and the short axis is 26 mm. The cranial apex is attached to the vertebral arteries' junction, and the caudal apex reaches the level of C4. The lateral apices are attached to the dura mater at the level of the denticulate ligament's second insertion. The C1 spinal nerves perforate the membrane, while the C2 roots are located dorsal to it. The membrane is attached strongly to the underlying pia mater. Histologically, it has a typical arachnoid structure, in which its adhesions to the vertebral arteries as well as to the pia mater could be verified histologically. This is the first detailed examination of the rhomboid membrane. Our results suggest that the membrane serves a valve-like function between the spinal and cranial subarachnoid spaces. Based on our findings, further hydrodynamic studies should clarify the membrane's physiological role. Clin. Anat. 32:56-65, 2019. © 2019 Wiley Periodicals, Inc.

Neural and vascular architecture of the septum pellucidum: an anatomical study and considerations for safe endoscopic septum pellucidotomy.

OBJECTIVE: The septum pellucidum is a bilateral thin membranous structure representing the border between the frontal horns of the lateral ventricles. Its most examined components are the septal veins due to their surgical importance during endoscopic septum pellucidotomy (ESP), which is a well-accepted method for surgical treatment of unilateral hydrocephalus. It is widely accepted that the septum pellucidum contains nerve fibers as well, but interestingly, no anatomical study has been addressed to its neural components before. The aim of the present study was to identify these elements as well as their relations to the septal veins and to define major landmarks within the ventricular system for neurosurgical use. METHODS: Nine formalin-fixed human cadaveric brains (18 septa pellucida) were involved in this study. A central block containing both septa pellucida was removed and frozen at -30°C for 2 weeks in 7 cases. The fibers of the septum pellucidum and the adjacent areas including the venous elements were dissected under magnification by using homemade wooden spatulas and microsurgical instruments. In 2 cases a histological technique was used to validate the findings of the dissections. The blocks were sliced, embedded in paraffin, cut in 7-µm-thick slices, and then stained as follows: 1) with H & E, 2) with Luxol fast blue combined with cresyl violet, and 3) with Luxol fast blue combined with Sirius red. RESULTS: The septum pellucidum and the subjacent septum verum form the medial wall of the frontal horn of the lateral ventricle. Both structures contain nerve fibers that were organized in 3 groups: 1) the precommissural fibers of the fornix; 2) the inferior fascicle; and 3) the superior fascicle of the septum pellucidum. The area directly rostral to the postcommissural column of the fornix consisted of macroscopically identifiable gray matter corresponding to the septal nuclei. The histological examinations validated the findings of the authors' fiber dissections. CONCLUSIONS: The nerve elements of the septum pellucidum as well as the subjacent septum verum were identified with fiber dissection and verified with histology for the first time. The septal nuclei located just anterior to the fornix and the precommissural fibers of the fornix should be preserved during ESP. Considering the venous anatomy as well as the neural architecture of the septum pellucidum, the fenestration should ideally be placed above the superior edge of the fornix and preferably dorsal to the interventricular foramen.

Endoscope-Assisted Minimally Invasive Microsurgical Removal of a Medium-Sized Acoustic Neuroma (T3a) through a Retrosigmoid Mini-Craniotomy with Preservation of Hearing.

A 45-year-old male patient with reduced hearing in the right ear was diagnosed with a medium-sized (T3a) acoustic neuroma. The operation was performed through an individually tailored retrosigmoid mini-craniotomy. Endoscope-assisted microsurgical technique was applied to early detect the location of the facial and cochlear nerves as well as to look around the hidden corners during the surgery. The entire operation was performed without using brain retractors. The moderate intrameatal extension of the tumor and the use of angled endoscopes allowed to avoid the drilling of the internal auditory meatus. The lesion could be completely removed and the patient showed a satisfactory hearing recovery in the follow-up examinations 3 months after the surgery. The link to the video can be found at: https://youtu.be/dAYLakih924 .

Arachnoid Membranes Around the Cisternal Segment of the Trigeminal Nerve: A Cadaveric Anatomic Study and Intraoperative Observations During Minimally Invasive Microvascular Decompression Surgery.

OBJECTIVE: The minimally invasive microvascular decompression (MVD) for trigeminal neuralgia is technically a more challenging operation compared with the standard retrosigmoidal approach. Endoscopic assistance could help to widen the field of view of the microscope during MVD. An extended view around the cisternal segment of the trigeminal nerve can be achieved only with the targeted dissection of the arachnoid membranes. The goal of our study was to analyze the three-dimensional organization of these membranes around the trigeminal nerve. METHODS: Microsurgical, endoscopic, and macroscopic anatomic examinations were performed on 50 fresh human cadaveric specimens. Retrospective analysis of the video documentations of 50 MVDs was performed to describe the surgical relevance of the examined membranes. RESULTS: The trigeminal nerve is surrounded circumferentially by 4 inner arachnoid membranes: laterally and caudally by the trigeminal membrane (TM), cranially by the superior cerebellar membrane (SCM), and medially by the junction between the cranial edge of the anterior pontine membrane and the lateral edge mesencephalic leaf of the Liliequist membrane complex. The superior cerebellar artery was located in every case cranial from the SCM. This membrane served as a safety plane to dissect the vessel from the nerve. The SCM was laterally adherent to the TM, which made the arachnoid dissection challenging. The superior petrosal vein was located cranially and laterally from the described inner arachnoid membranes, but the transverse pontine vein was embedded into the membrane complex. CONCLUSIONS: Knowledge of the described anatomy of the arachnoid membranes around the trigeminal nerve is essential to safely perform an MVD.

The Clival Line as an Important Arachnoid Landmark During Endoscopic Third Ventriculostomy: An Anatomic Study.

OBJECTIVE: Endoscopic third ventriculostomy (ETV) is a well-accepted treatment option instead of ventriculoperitoneal shunt placement in cases of obstructive hydrocephalus. A sufficient flow from the ventricles to the basal cisterns requires perforation of the arachnoid membranes in the retroclival region. This point is critical to achieve an optimal outcome. The complex arachnoid relations were investigated in the retroclival region from the viewpoint of ETV, and anatomic landmarks were defined for subarachnoid dissections. METHODS: Sixty fresh human cadaveric specimens were dissected under macroscopic, microscopic, and endoscopic control. The recordings of 100 operated cases of ETVs were analyzed to ascertain the clinical-anatomic relevance. RESULTS: The Liliequist membrane complex and the anterior pontine membranes are located just above and parallel to both sides of the basilar artery. The basal attachment of these membranes forms an inverted U-shaped, white-grey thickening on the outer arachnoid. We refer to this structure as the clival line. During ETV, if arachnoid dissections were performed ventrally to the clival line, the outer arachnoid was opened; this resulted in a limited flow to the subarachnoid spaces (ventriculo-subdural). If the perforation on the arachnoid membranes was dorsal to the clival line, the prepontine cistern could be directly reached through the Liliequist membrane complex. CONCLUSIONS: Sufficient arachnoid dissection is essential for a successful ETV. The clival line is an important landmark that helps to perform the subarachnoid dissections correctly and achieve an undisrupted cerebral spinal fluid flow between the ventricles and the basal cisterns.

Endoscope-Assisted Microsurgical Removal of an Optic Foramen Meningioma through a Frontolateral Minicraniotomy.

A 72-year-old male patient with visual disturbance of the right eye was diagnosed with a small meningioma of the right optic foramen extending to the carotid cistern. The operation was performed through an individually tailored frontolateral minicraniotomy via a curvilinear skin incision behind the hairline. Endoscope-assisted microsurgical technique was used to resect the lesion. The roof of the optic canal was partly removed to get access to the intraforaminal tumor parts. The lesion could be completely removed and the patient showed a satisfactory visual recovery in the follow-up examinations. The link to the video can be found at: https://youtu.be/p8EZx7aryeQ .

Primary Obstruction of the Foramen of Luschka: Anatomy, Histology, and Clinical Significance.

BACKGROUND: The foramen of Luschka is a natural aperture between the fourth ventricle and the subarachnoid space at the cerebellopontine angle. Membranous closure of this foramen is referred to as primary obstruction. Available information about this variant and its role in the development of the cysts of the posterior fossa is contradictory. METHODS: The macroscopic and histologic features of the obstructed foramina were examined in 61 formalin-fixed human brains (122 foramina). Three rhomboid lips of various sizes with lateral recess were used for comparison. Five postoperative cases of diverticulum of the foramen of Luschka were included in this study, with 1 case presented in detail to illustrate anatomic and histologic findings. RESULTS: Primary obstruction was present in 11 of 122 cases. In 1 case, an enlarged rigid pouch with a thick wall was found. The wall of the membrane in primary obstruction and the rhomboid lip were composed of an inner ependymal, a middle glial, and an outer leptomeningeal layer. CONCLUSIONS: The rhomboid lip is a remnant of the roof of the fourth ventricle. Imperforation of the foramen of Luschka results in a pouch in the cerebellopontine angle that contains choroid plexus (Bochdalek's flower basket) and communicates with the fourth ventricle. This pouch has the potential to grow to a diverticulum and cause clinical symptoms. Based on our clinical observations, detailed radiologic and surgical-anatomic criteria were proposed to support the differential diagnosis of a diverticulum of the foramen of Luschka. Treatment strategies were also suggested.

Morphometry and microsurgical anatomy of Bochdalek's flower basket and the related structures of the cerebellopontine angle.

BACKGROUND: Bochdalek's flower basket (Bfb) is the distal part of the horizontal segment of the fourth ventricle's choroid plexus protruding through the lateral aperture (foramen of Luschka). The microsurgical anatomy of the cerebellopontine angle, fourth ventricle and its inner choroid plexus is well described in the literature, but only one radiological study has investigated the Bfb so far. The goal of the present study was to give an extensive morphometric analysis of the Bfb for the first time and discuss the surgically relevant anatomical aspects. METHOD: Forty-two formalin-fixed human brains (84 cerebellopontine angles) were involved in this study. Photomicrographs with scale bars were taken in every step of dissection to perform further measurements with Fiji software. The lengths and widths of the Bfb, rhomboid lip and lateral aperture of the fourth ventricle as well as the related neurovascular and arachnoid structures were measured. The areas of two sides were compared with paired t-tests using R software. Significance level was set at p < 0.05. RESULTS: Protruding choroid plexus was present in 77 cases (91.66%). In 6 cases (7.14%), the Bfb was totally covered by the rhomboid lip, and in one case (1.19%), it was absent. The mean width of the Bfb was 6.618 mm (2-14 mm), the mean height 5.658 mm (1.5-14 mm) and mean area 25.80 mm2 (3.07-109.83 mm2). There was no statistically significant difference between the two sides (p = 0.1744). The Bfb was in contact with 20 AICAs (23.80%), 6 PICAs (7.14%) and 39 vestibulocochlear nerves (46.42%). Arachnoid trabecules, connecting the lower cranial nerves to the Bfb or rhomboid lip, were found in 57 cases (67.85%). CONCLUSIONS: The Bfb is an important landmark during various surgical procedures. Detailed morphology, dimensions and relations to the surrounding neurovascular structures are described in this study. These data are essential for surgeons operating in this region.

Endoscopic approach-routes in the posterior fossa cisterns through the retrosigmoid keyhole craniotomy: an anatomical study.

Endoscopy in cerebellopontine angle surgery is an increasingly used technique. Despite of its advantages, the shortcomings arising from the complex anatomy of the posterior fossa are still preventing its widespread use. To overcome these drawbacks, the goal of this study was to define the anatomy of different endoscopic approaches through the retrosigmoid craniotomy and their limitations by surgical windows. Anatomical dissections were performed on 25 fresh human cadavers to describe the main approach-routes. Surgical windows are spaces surrounded by neurovascular structures acting as a natural frame and providing access to deeper structures. The approach-routes are trajectories starting at the craniotomy and pointing to the lesion, passing through certain windows. Twelve different windows could be identified along four endoscopic approach-routes. The superior route provides access to the structures of the upper pons, lower mesencephalon, and the upper neurovascular complex through the suprameatal, superior cerebellar, and infratrigeminal windows. The supratentorial route leads to the basilar tip and some of the suprasellar structures via the ipsi- and contralateral oculomotor and dorsum sellae windows. The central endoscopic route provides access to the middle pons and the middle neurovascular complex through the inframeatal, AICA, and basilar windows. The inferior endoscopic route is the pathway to the medulla oblongata and the lower neurovascular complex through the accessory, hypoglossal, and foramen magnum windows. The anatomy and limitations of each surgical windows were described in detail. These informations are essential for safe application of endoscopy in posterior fossa surgery through the retrosigmoid approach.

Supraorbital Keyhole Approach to the Skull Base: Evaluation of Complications Related to CSF Fistulas and Opened Frontal Sinus.

AIM: Cerebrospinal fluid (CSF) rhinorrhea due to a breach in the frontal sinus (FS) presents one of the main postoperative complications of the supraorbital keyhole approach. The goal of this study was to further analyze the actual surgical morbidity and potential risk for patients due to an opened FS after a surgery via a supraorbital craniotomy and compare the results with data published in the current literature. METHODS AND PATIENTS: A total of 350 consecutive patients who underwent surgeries via the supraorbital keyhole approach for various lesions were included in this retrospective study. Information on clinical history, neurologic symptoms, surgical approach, and postoperative complications was obtained retrospectively by a review of the patients' charts, the radiologic reports, and a thorough review of pre- and postoperative cranial computed tomography (CCT) imaging. RESULTS: The frequency of CSF rhinorrhea after this type of craniotomy in the literature is reported to range between 0% and 9.1%. In this study, analysis of postoperative CCT scans revealed that 88 patients (25.1%) showed a radiographic breach of the FS. Only 8 of these patients (2.3%) developed a CSF leak with rhinorrhea postoperatively. In all cases conservative treatment with lumbar drainage failed, and therefore a surgical revision for permanent closure was required. Only one patient (0.3%) with a CSF leak also developed meningitis. CONCLUSION: Inadvertent opening of the FS during the supraorbital craniotomy is a common surgery-related morbidity; however, the risk for the patient to develop a potentially dangerous meningitis was found to be minimal.

Endoscopic surgery for tumors of the pineal region via a paramedian infratentorial supracerebellar keyhole approach (PISKA).

The tumors of the pineal region represent a significant challenge in terms of patient selection and surgical approach. Traditional surgical options were commonly used to approach this area causing considerable surgical morbidity and mortality. We report for the first time on a series of endoscopic procedures for lesions of the pineal region performed via an infratentorial supracerebellar keyhole approach (PISKA) in the prone position using endoscope-assisted and endoscope-controlled technique. A single-institution series of 11 consecutive patients (five male and six female patients [11 total cases]; mean age 21 years, range 1-75 years) treated via the endoscope-assisted and endoscope-controlled PISKA for a pathological entity in the pineal region was retrospectively reviewed. The mean follow-up time was 24 months. The endoscopic PISKA was successfully used to approach a variety of pineal lesions, including pineocytoma (three patients), pineal cysts (four patients), germinoma, lipoma, medulloblastoma, and glioblastoma (one patient each). Gross total resection was achieved in ten cases and subtotal resection in one case. The mean preoperative tumor volumes were approximately 2 × 2 cm. Five patients developed postoperatively transient Parinaud's syndrome. One patient underwent surgical revision for cerebrospinal fluid leak. There was no mortality. Ten patients had an uneventful postoperative course with restitutio ad integrum after a mean follow-up duration of 13.5 months. The endoscopically PISKA is a safe and effective minimally invasive approach that enables endoscopic treatment of different lesions of the pineal region with comparable results to standard microsurgical technique but less morbidity.