Should Redo Surgery be Offered to Patients with Relapsed Glioblastoma? - Outcome Analyses of a Single Institution Comparative Cohort Study.

BACKGROUND: Glioblastoma multiforme (GBM) is the predominant malignant brain tumor originating intracranially. The established first-line treatment postsurgery is concurrent chemoradiation as a definitive measure. However, recurrent GBM's pose a challenge for clinicians who rely on institutional experience to determine the most suitable course of action. Second-line chemotherapy may be administered with or without surgery depending on the institution's practice. This study aims to present our tertiary center institution's experience with recurrent GBM patients who underwent redo surgery. METHODS: In this retrospective study we analyzed the surgical and oncological data of patients with recurrent GBM who underwent redo surgery at the Royal Stoke University Hospitals between 2006 and 2015. The group 1 (G1) comprised the reviewed patients, while a control group (G2) was randomly selected, matching the reviewed group by age, primary treatment, and progression-free survival (PFS). The study collected data on various parameters, including overall survival, PFS, extent of surgical resection, and postoperative complications. RESULTS: This retrospective study included 30 patients in G1 and 32 patients in G2, matched based on age, primary treatment, and PFS. The study found that the overall survival for the G1 group from the time of first diagnosis was 109 weeks (45-180) compared to 57 weeks (28-127) in the G2 group. The incidence of postoperative complications after the second surgery was 57%, which included hemorrhage, infarction, worsening neurology due to edema, cerebrospinal fluid leak, and wound infection. Furthermore, 50% of the patients in the G1 group who underwent redo surgery received second-line chemotherapy. CONCLUSIONS: Our study found that redo surgery for recurrent GBM is a viable treatment option for a select group of patients with good performance status, longer PFS from primary treatment, and compressive symptoms. However, the use of redo surgery varies depending on the institution. A well-designed randomized controlled trial in this population would help establish the standard of surgical care.

On day admissions in neurosurgery: a comparative cohort study.

Day of admission neurosurgery is a viable method to reduce health care associated costs, complications and length of stay. Within the national health service in England the picture is very mixed with some neurosurgery centres universally admitting patients the day before and others admitting on the day of surgery.We altered our admissions policy during a 4 month time period from 'day-before' surgery to 'day-of' surgery for elective neurosurgery. A number of patients still continued to be admitted the day before surgery due to consultant choice. We conducted a comparative cohort study of these two patient groups to see if there were any differences in surgical cancellation rates, the reasons for these cancellations and the implied cost savings.In total 199 patients underwent neurosurgery during this time period, 87 patients were admitted on the 'day-of' and 112 patients on the 'day-before' surgery. The overall cancellation rate was 18%. The cancellation rate in patients admitted on the 'day-of' surgery was 12.6% (11/87). The rate of cancellation in patients admitted the 'day-before' surgery was 22.3% (25/112). This difference was not significant (p = 0.1). Day of surgery admission resulted in a cost saving of almost £30,000 in this group of patients over a 4 month period. If extrapolated for all patients over the course of a year it would result in cost savings in the region of £150,000.In summary, admitting elective neurosurgery patients on the day of surgery does not affect cancellation rates, prevents unnecessary overnight hospital admission and results in significant cost saving.

Neurosurgery activity levels in the United Kingdom and republic of Ireland during the first wave of the covid-19 pandemic - a retrospective cross-sectional cohort study.

The impact of Covid-19 on surgical patients worldwide has been substantial. In the United Kingdom (UK) and the Republic of Ireland (RoI), the first wave of the pandemic occurred in March 2020. The aims of this study were to: (1) evaluate the volume of neurosurgical operative activity levels, Covid-19 infection rate and mortality rate in April 2020 with a retrospective cross-sectional cohort study conducted across 16 UK and RoI neurosurgical centres, and (2) compare patient outcomes in a single institution in April-June 2020 with a comparative cohort in 2019. Across the UK and RoI, 818 patients were included. There were 594 emergency and 224 elective operations. The incidence rate of Covid-19 infection was 2.6% (21/818). The overall mortality rate in patients with a Covid-19 infection was 28.6% (6/21). In the single centre cohort analysis, an overall reduction in neurosurgical operative activity by 65% was observed between 2020 (n = 304) and 2019 (n = 868). The current and future impact on UK neurosurgical operative activity has implications for service delivery and neurosurgical training.

Seizure Outcome After Surgery for Insular High-Grade Glioma.

BACKGROUND: The insular cortex is an eloquent island of mesocortex surrounded by vital structures making this region relatively challenging to neurosurgeons. Historically, lesions in this region were considered too high risk to approach given the strong chance of poor surgical outcome. Advances in recent decades have meant that surgeons can more safely access this eloquent region. Seizure outcome after excision of insular low-grade gliomas is well reported, but little is known about seizure outcomes after excision of insular high-grade gliomas. METHODS: A retrospective analysis was performed of all patients presenting with new-onset seizures during 2015-2019 who underwent excision of an insular high-grade glioma at 3 regional neurosurgical centers in the United Kingdom. RESULTS: We identified 38 patients with a mean (SD) age of 45.7 (15.3) years with median follow-up of 21 months. At long-term follow-up, of 38 patients, 23 were seizure-free (Engel class I), 2 had improved seizures (Engel class II), 6 had poor seizure control (Engel class III/IV), and 7 died. CONCLUSIONS: Excision of insular high-grade gliomas is safe and results in excellent postoperative seizure control.

Glioblastoma Multiforme: A Rare Case of Spinal Drop Metastasis.

BACKGROUND: The occurrence of spinal drop metastasis in patients diagnosed with glioblastoma multiforme (GBM) is rare. In previous reports, this diagnosis occurred after surgical resection of GBM, which was believed to increase the likelihood of tumor seeding. Diagnosis of spinal drop metastasis prior to surgery remains rare. CASE DESCRIPTION: We report a 57-year-old woman with a brief history of confusion, altered behavior, and agitation without any other significant past medical history. Computed tomography and magnetic resonance imaging (MRI) of the head demonstrated an intra-axial lesion of the right temporal lobe as well as evidence of leptomeningeal disease around the medulla. A spine MRI scan revealed spinal drop metastases at the level of C1 and T6/T7. Subsequent biopsy confirmed WHO-2016 grade IV GBM. CONCLUSIONS: The awareness of the possibility of spinal drop metastasis prior to surgical resection of GBM is important. The use of routine MRI of the whole neuroaxis in patients diagnosed with GBM can aid in prognosis and management options.

Impact of COVID-19 pandemic on surgical neuro-oncology multi-disciplinary team decision making: a national survey (COVID-CNSMDT Study).

OBJECTIVES: Pressures on healthcare systems due to COVID-19 has impacted patients without COVID-19 with surgery disproportionally affected. This study aims to understand the impact on the initial management of patients with brain tumours by measuring changes to normal multidisciplinary team (MDT) decision making. DESIGN: A prospective survey performed in UK neurosurgical units performed from 23 March 2020 until 24 April 2020. SETTING: Regional neurosurgical units outside London (as the pandemic was more advanced at time of study). PARTICIPANTS: Representatives from all units were invited to collect data on new patients discussed at their MDT meetings during the study period. Each unit decided if management decision for each patient had changed due to COVID-19. PRIMARY AND SECONDARY OUTCOME MEASURES: Primary outcome measures included number of patients where the decision to undergo surgery changed compared with standard management usually offered by that MDT. Secondary outcome measures included changes in surgical extent, numbers referred to MDT, number of patients denied surgery not receiving any treatment and reasons for any variation across the UK. RESULTS: 18 units (75%) provided information from 80 MDT meetings that discussed 1221 patients. 10.7% of patients had their management changed-the majority (68%) did not undergo surgery and more than half of this group not undergoing surgery had no active treatment. There was marked variation across the UK (0%-28% change in management). Units that did not change management could maintain capacity with dedicated oncology lists. Low volume units were less affected. CONCLUSION: COVID-19 has had an impact on patients requiring surgery for malignant brain tumours, with patients receiving different treatments-most commonly not receiving surgery or any treatment at all. The variations show dedicated cancer operating lists may mitigate these pressures. STUDY REGISTRATION: This study was registered with the Royal College of Surgeons of England's COVID-19 Research Group (https://www.rcseng.ac.uk/coronavirus/rcs-covid-research-group/).

Multifocal Infratentorial Pilocytic Astrocytoma in an Adult Patient.

BACKGROUND: Pilocytic astrocytoma is a benign glial tumor typically presenting in children. It is rare for adults to present with pilocytic astrocytoma and even less likely to manifest with multiple foci of lesions especially in nonoptic or hypothalamic locations. CASE DESCRIPTION: Our patient was a 37-year old man presenting with varied cranial neuropathies, cerebellar dysfunction, and long tract signs, with imaging demonstrating 3 discrete ill-defined contrast-enhancing lesions affecting the cerebellar peduncles, brainstem, and cervicomedullary junction. Neuronavigation-guided biopsy confirmed World Health Organization grade 1 pilocytic astrocytoma; the patient was treated with radiotherapy. CONCLUSIONS: To our knowledge, we believe this is the first reported case with multifocal infratentorial pilocytic astrocytoma on presentation in an adult patient in the absence of a prior history of associated risk factors such as neurofibromatosis 1 or chemoradiotherapeutic intervention.

Rare case of radiation-induced trigeminal schwannoma occurring in a long-term glioblastoma multiforme survivor.

Glioblastoma multiforme (GBM) is a high-grade primary brain tumour with a notably poor prognosis. Research demonstrates a median survival of just over 1 year following aggressive treatment. Long-term survival is notably rare. Cranial radiotherapy and postexcisional prophylactic treatment is associated with the development of second, histologically distinct tumours in rare cases. Radiation-induced intracranial schwannomas are uncommon, with only a small number of cranial nerve schwannoma cases reported in recent decades. To our knowledge, this is the first reported case of a radiation-induced benign trigeminal schwannoma occurring following long-term survival from glioblastoma. Here we present (1) a rare case of 14-year survival following treatment of a right parietal glioblastoma and the development of a radiation-induced benign trigeminal schwannoma in a 35-year-old man, and (2) a review of radiation-induced schwannoma cases reported in the existing literature.

A novel impermeable adhesive membrane to reinforce dural closure: a preliminary retrospective study on 119 consecutive high-risk patients.

OBJECTIVE: Postoperative cerebrospinal fluid (CSF) leak in neurosurgery remains a significant source of morbidity. TissuePatchDural (TPD), a novel impermeable adhesive membrane, can be used to reinforce dural closure in cases considered at high risk to develop postoperative CSF leak. METHODS: A retrospective, single-center, clinical investigation was conducted on 119 patients who underwent elective neurosurgical procedures between January and June 2010. Inclusion criteria included adult patients undergoing clean elective surgeries where a primary watertight closure was not possible. Three groups of patients were considered: 1) infratentorial, 67 cases; 2) supratentorial, 34 cases; and 3) spinal, 18 cases. All these patients received TPD to reinforce dural closure. Preoperative (long-term corticosteroid therapy, previous surgery and radiotherapy), intraoperative (site of procedures and size of dural gap), and postoperative (early and late hydrocephalus) conditions were analyzed as possible risk factors associated with CSF leakage. RESULTS: The mean follow-up was 7.14 months (range 6-12 months). CSF leak was detected in 11 of 119 cases (9.2%). The presence of pre- and postoperative risk factors was associated with a higher percentage of CSF leakage: 8 of 22 cases (36.3%) vs. 3 of 97 cases (3.1%) (P < 0.0001). All leaks could be conservatively treated and no patient required readmission or second surgery. No TPD-related adverse or allergic effects were observed. CONCLUSIONS: TPD seems to be a safe tool to be used to reinforce dural closure in patients with a high risk of developing CSF leaks.

Minimally invasive supracondylar transtubercular (MIST) approach to the lower clivus.

OBJECTIVE: Drawbacks of the far-lateral approach to the lower clivus and pontomedullary region include the morbidity of a large incision extending into the cervical musculature and tedious exposure of the vertebral artery (VA), particularly when performing the transcondylar and transtubercular extensions. The authors describe a minimally invasive alternative to the far-lateral approach that has the potential to minimize operative morbidity and decrease the need for VA manipulation. METHODS: The minimally invasive supracondylar transtubercular (MIST) and far-lateral supracondylar transtubercular (FLST) approaches were performed in 10 adult cadaveric specimens (20 sides). The microsurgical anatomy of each step and the surgical views were analyzed and compared. In addition, the endoscopic view through the MIST was examined in five fresh cadaveric specimens (10 sides). RESULTS: The MIST approach provided exposure of the inferior-middle clivus, the anterolateral brainstem, and the premedullary cisterns, including the PICA-VA and vertebrobasilar junctions. The endoscope provided a clear view of cranial nerves III through XII, as well as the vertebrobasilar system. The FLST approach increased visualization of the anterolateral margin of the foramen magnum; otherwise, the surgical view is similar between the MIST and FLST approaches. CONCLUSIONS: The MIST approach could be considered as a potential alternative to the FLST approach in the treatment of lesions involving the inferior and middle clivus, and anterolateral lower brainstem; it does not require a C1 laminectomy, significant disruption of the atlanto-occipital joint, nor extensive exposure of the extracranial VA. Moreover, the MIST approach is an ideal companion to endoscope-assisted neurosurgery.

Venous sacrifice in neurosurgery: new insights from venous indocyanine green videoangiography.

OBJECT: The purpose of this paper is to evaluate whether venous indocyanine green (ICG) videoangiography has any potential for predicting the presence of a safe collateral circulation for veins that are at risk for intentional or unintentional damage during surgery. METHODS: The authors performed venous ICG videoangiography during 153 consecutive neurosurgical procedures. On those occasions in which a venous sacrifice occurred during surgery, whether that sacrifice was preplanned (intended) or unintended, venous ICG videoangiography was repeated so as to allow us to study the effect of venous sacrifice. A specific test to predict the presence of venous collateral circulation was also applied in 8 of these cases. RESULTS: Venous ICG videoangiography allowed for an intraoperative real-time flow assessment of the exposed veins with excellent image quality and resolution in all cases. The veins observed in this study were found to be extremely different with respect to flow dynamics and could be divided in 3 groups: 1) arterialized veins; 2) fast-draining veins with uniform filling and clear flow direction; and 3) slow-draining veins with nonuniform filling. Temporary clipping was found to be a simple and reversible way to test for the presence of potential anastomotic circulation. CONCLUSIONS: Venous ICG videoangiography is able to reveal substantial variability in the venous flow dynamics. "Slow veins," when they are tributaries of bridging veins, might hide a potential for anastomotic circulation that deserve further investigation.

Indocyanine green (ICG) temporary clipping test to assess collateral circulation before venous sacrifice.

BACKGROUND: As a general principle, sacrifice of cerebral veins at surgery is avoided. However, at times sacrifice of a vein may be desirable to increase surgical exposure. At present, no method exists to predict whether such sacrifice will be accommodated by the presence of collateral venous drainage. We show a simple technique to examine cerebral venous blood flow using indocyanine green videoangiography. METHODS: In two patients, parasagittal meningiomas were found to be associated with paramedian veins that impeded complete removal of the tumors. The suitability of veins removal was assessed by applying a temporary aneurysm clip and performing an indocyanine green videoangiogram. RESULTS: In one patient, stasis was observed in the vein. In the second patient, a collateral flow allowed the venous blood to drain. The former test was considered a counterindication for venous sacrifice, whereas the latter supported its feasibility. The vein was preserved in the former case and coagulated in the latter. In both cases, the patients did well. CONCLUSIONS: Although our limited study cannot prove that venous congestion or infarction can be avoided with this technique, it does provide direct evidence of the presence or absence of collaterals that can help guide intraoperative surgical decision-making.

High anterior cervical approach to the clivus and foramen magnum: a microsurgical anatomy study.

BACKGROUND: Surgical exposure of lesions located along the ventral foramen magnum (FM) and clivus poses a unique set of challenges to neurosurgeons. Several approaches have been developed to access these regions with varying degrees of exposure and approach-related morbidity. OBJECTIVE: To describe the microsurgical anatomy of the high anterior cervical approach to the clivus and foramen magnum, and describe novel skull base extensions of the approach. METHODS: Eight adult cadaveric specimens were included in this study. The high anterior cervical approach includes a minimal anterior clivectomy and its lateral skull base extensions: the extended anterior far-lateral clivectomy and the inferior petrosectomy. The microsurgical anatomy and exposure of the various extensions of the approach were analyzed. In addition, the capability of complementary endoscopy was evaluated. RESULTS: With proper positioning, the minimal anterior clivectomy exposed the vertebrobasilar junction, proximal basilar artery, anteroinferior cerebellar arteries, and 6th cranial nerve. The lateral skull base extensions provided access to the anterior FM, mid-lower clivus, and petroclival region, up to the Meckel cave, contralateral to the side of the surgical approach. CONCLUSION: The high anterior cervical approach with skull base extensions is an alternative to the classic approaches to the ventral FM and mid-lower clivus. A minimal anterior clivectomy provides access to the midline mid-lower clivus. The addition of an extended anterior far-lateral clivectomy and an inferior petrosectomy extends the exposure to the anterior FM and cerebellopontine angle lying anterior to the cranial nerves. The approach is also ideally suited for endoscopic-assisted techniques.

Normal anatomical variations of the V3 segment of the vertebral artery: surgical implications.

OBJECT: The authors undertook this cadaveric and angiographic study to examine the microsurgical anatomy of the V3 segment of the vertebral artery (VA) and its relationship to osseous landmarks. A detailed knowledge of these variations is important when performing common neurosurgical procedures such as the suboccipital craniotomy and the far-lateral approach and when placing atlantoaxial instrumentation. METHODS: A total of 30 adult cadaveric specimens (59 sides) were studied using magnification × 3 to × 40 after perfusion of the arteries and veins with colored silicone. Seventy-three vertebral angiograms were also analyzed. The morphological detail of the V3 segment was described and measured in both the cadavers and angiograms. Transarticular screws were placed into 2 cadavers and the relationship of the trajectory to the V3 segment was analyzed. RESULTS: The authors identified 4 sites along the V3 segment that are anatomically the most likely to be injured during surgical approaches to the craniovertebral junction. In 35% of the cadaveric specimens the vertical portion of V3 formed a posteriorly oriented loop that could be injured during surgical exposures of the dorsal surface of C-2. The mean distance from the midline to the most posteromedial edge of the loop was 25.6 ± 3.5 mm (range 20-35 mm) on the left side and 30.4 ± 3.8 mm (range 23-36 mm) on the right side. On lateral angiograms, this loop projected posteriorly, with a mean distance of 9.8 ± 3.5 mm (range 0-15.7 mm) on the right side and 11.7 ± 1.2 mm (range 10-13.6 mm) on the left side. The horizontal segment of V3 can be injured when exposing the lower lateral occipital bone and when the C-1 arch is exposed. The mean distance from the inferior border of the occipital bone to the superior surface of the horizontal segment of V3 was 6 ± 2.8 mm on the right side and 5.6 ± 2.3 mm on the left. In 12% of cases the authors found no space between the horizontal portion of V3 and the occipital bone. The medial edge of the horizontal segment of V3 was located 23 ± 5.5 mm (range 10-30 mm) from the midline on the right side and 24 ± 5.7 mm (range 15-32 mm) on the left side. The transition between the V2-V3 segments after exiting the C-2 vertebral foramen is the most likely site of injury when placing C1-2 transarticular screws or C-2 pars screws. CONCLUSIONS: The normal variation of the V3 segment of the VA has been described with quantitative measurements. An awareness of the anatomical variations and the relationships to the surrounding bony anatomy will aid in reducing VA injury during suboccipital approaches, exposure of the dorsal surfaces of C-1 and C-2, and when placing atlantoaxial spinal instrumentation.

Ultrahigh-dose intraarterial infusion of verapamil through an indwelling microcatheter for medically refractory severe vasospasm: initial experience. Clinical article.

OBJECT: Vasospasm is one of the leading causes of morbidity and death following aneurysmal subarachnoid hemorrhage (SAH). Many patients suffer devastating strokes despite the best medical therapy. Endovascular treatment is the last line of defense for cases of medically refractory vasospasm. The authors present a series of patients who were treated with a prolonged intraarterial infusion of verapamil through an in-dwelling microcatheter. METHODS: Over a 1-year period 12 patients with medically refractory vasospasm due to aneurysmal SAH were identified. Data were retrospectively collected, including age, sex, Hunt and Hess grade, Fisher grade, aneurysm location, aneurysm treatment, day of the onset of vasospasm, intracranial pressure, mean arterial pressures, intraarterial treatment of vasospasm, dosages and times of verapamil infusion, presence of a new ischemic area on CT scan, modified Rankin scale score at discharge and at the last clinical follow-up, and discharge status. RESULTS: Twenty-seven treatments were administered. Between 25 and 360 mg of verapamil was infused per vessel (average dose per vessel 164.6 mg, range of total dose per treatment 70-720 mg). Infusion times ranged from 1 to 20.5 hours (average 7.8 hours). The number of treated vessels ranged from 1 to 7 per patient. The number of treatments per patients ranged from 1 to 4. There was no treatment-related morbidity or death. Blood pressure and intracranial pressure changes were transient and rapidly reversible. Among the 36 treated vessels, prolonged verapamil infusion was completely effective in 32 cases and partially effective in 4. Only 4 vessels required angioplasty for refractory vasospasm after prolonged verapamil infusion. There was no CT scanning evidence of new ischemic events in 9 of the 12 patients treated. At last clinical follow-up 6-12 months after discharge, 8 of 11 patients had a modified Rankin Scale score ≤2. CONCLUSIONS: Prolonged intraarterial infusion of verapamil is a safe and effective treatment for medically refractory severe vasospasm and reduces the need for angioplasty in such cases.

Distal intracranial catheterization of patients with tortuous vascular anatomy using a new hybrid guide catheter.

BACKGROUND: A hybrid guide catheter mates the traditional strong guide catheter with a thin, soft distal tip, allowing placement further into the distal cervical or proximal cranial circulation. CASE DESCRIPTION: We present 5 cases in which traditional guide catheters were unable to successfully navigate tortuous anatomy or provide stable support for intervention. CONCLUSION: Hybrid guide catheters provided safe, stable support for successful treatment. Hybrid guide catheters allow for treatment for patients who previously were not candidates for neuroendovascular surgery.

Submandibular approach to the C2-3 disc level: microsurgical anatomy with clinical application.

OBJECT: Approaching the C2-3 disc level is challenging because of its location behind the mandible and the vital neurovascular structures overlying the area. The purpose of this study was to illustrate in a stepwise fashion the microsurgical anatomy of the submandibular approach to the C2-3 disc. METHODS: Ten adult formalin-fixed cadaveric specimens (20 sides) were studied. Particular attention was paid to the structures limiting the exposure. The authors measured the distance between the inferior border of the mandible and the marginal mandibular branch of the facial nerve running inferior to the mandible, the distance between the horizontal segment of the hypoglossal nerve and the hyoid bone, and the distance between the horizontal segment of the hypoglossal nerve and the mandible. They compared the location of the superior laryngeal nerve with regard to the submandibular and the standard Smith-Robinson approaches. A clinical case illustrating the usefulness of the surgical technique in this region is presented. RESULTS: The mean distance between the inferior border of the mandible and the lowest point of the marginal mandibular branch of the facial nerve was 6.7 +/- 1.69 mm. The hypoglossal nerve's mean distance above the hyoid bone was 8.4 +/- 1.78 mm and below the mandible was 19.6 +/- 6.39 mm. The internal branch of the superior laryngeal nerve, with respect to the cervical spine, always entered the thyrohyoid membrane just inferior to the C-3 vertebral body. The superior laryngeal nerve was found to be an impediment to approaching the C2-3 disc through the standard Smith-Robinson approach. CONCLUSIONS: The submandibular approach provides excellent exposure, with a perpendicular view of the C2-3 disc level. This approach is one of the options to be considered when dealing with high cervical pathologies.

Limitations of the transcallosal transchoroidal approach to the third ventricle.

OBJECT: The aim of this study was to determine the anatomical limitations of the transcallosal transchoroidal approach to the third ventricle. METHODS: Twenty-six formalin-fixed specimens were studied. Sagittal dissections were used to determine the anatomical relationships of the foramen of Monro, the angle of approach to landmarks, and placement of a callosotomy. Lateral ventricular dissections were performed to quantitate the forniceal anatomy. RESULTS: The foramen of Monro was found 1.07+/-0.11 cm superior and slightly anterior to the mammillary bodies, 1.48+/-0.16 cm posterosuperior to the optic recess, and 2.26+/-0.16 cm anterosuperior to the aqueduct. Relative to the genu, a callosal incision 2.64+/-0.53 cm long and angled 37+/-4.3 degrees anterior was needed to access the aqueduct, and an incision 4.92+/-0.71 cm long and angled 49+/-7.4 degrees posterior was needed to access the optic recess. The fornix progressively widened within the lateral ventricle, from 1.25+/-0.63 mm at the foramen of Monro to >7 mm at 2 cm behind the foramen. Three zones of exposure were identified, requiring unique craniotomies, callosotomies, and angles of approach. The major limiting factors in the approach included the columns of the fornix anteriorly, the width of the fornix posteriorly, and the draining veins of the parietal cortex. The choroidal fissure opening was limited to 1.5 cm posterior to the foramen of Monro; this limited opening created an aperture effect that required an anterior-to-posterior angle, an anterior craniotomy, and an anteriorly placed callosotomy to access the posterior landmarks. In contrast, a posterior-to-anterior angle, posteriorly placed craniotomy, and posteriorly placed callosotomy were required to access anterior landmarks. CONCLUSIONS: The transcallosal transchoroidal approach was ideally suited to access the foramen of Monro and the middle and posterior thirds of the third ventricle. Exposure of the anterior third ventricle was limited by the columns of the fornix and by the presence of parietal cortical draining veins.