Tumors of the third ventricle in children: review of 46 cases

In the national series, 46 patients out of 262 (17.5%) were children under 15 years of age. Most of them presented with gliomas (50 %), choroid plexus tumors were recorded in 8 cases (17%). Intracranial hypertension revealed the tumor in 80% of children, endocrine disorders were recorded in 8 patients. A stereotactic procedure was performed in 7 patients, 1 had ventriculoscopy, and a direct surgical approach to the third ventricle was performed in 37 patients, in one case after the failure of the endoscopic procedure. Two patients with a radiological appearance of hamartoma received no treatment. Most of patients were operated on via a transcortical approach (27 cases). The overall mortality in this series is 9%. The death was directly correlated to the surgical procedure (1 case), or to recurrence of the tumor (3 cases). The final outcome analysis recorded neurological impairment in 50% of cases, neuropsychological deficit in 58 % of patients, and residual endocrine disorders in 41%. Social independence was recovered by 82% of the children, and 68% returned to normal school attendance.     

Transcortical or transcallosal approach to ventricle-associated lesions: a clinical study on the prognostic role of surgical approach

Most entities in and around the anterior two-thirds of the supratentorial ventricles can be reached via transcortical or transcallosal approach. This study examined the effect of surgical approach on the postoperative neurological outcome. Thirty-eight patients with intra- and periventricular supratentorial lesions were operated on by either frontal transcortical or anterior transcallosal approach. Postoperative diencephalic damage occurred in 22% of patients in the transcortical group and in 36% in the transcallosal group; transient mutism was virtually equivalent in the two groups. Postoperative epilepsy (26%) and subdural fluid collections (30%) occurred only in the transcortical group. The incidence of postoperative hemiparesis was higher in the transcallosal group. There was a high correlation between postoperative Glasgow Outcome Score of 5 and preoperative severity of neurological disease but no correlation between postoperative Glasgow Outcome Score of 5 and location of the lesion or between postoperative clinical course and surgical approach. Surgical outcome of ventricle-associated lesions depends mainly on the severity of preoperative symptoms and not on surgical approach. Additionally, the incidence of postoperative seizures and subdural fluid collections after transcortical surgery is high.     

Transcortical or transcallosal approach to ventricle-associated lesions: a clinical study on the prognostic role of surgical approach

Most entities in and around the anterior two-thirds of the supratentorial ventricles can be reached via transcortical or transcallosal approach. This study examined the effect of surgical approach on the postoperative neurological outcome. Thirty-eight patients with intra- and periventricular supratentorial lesions were operated on by either frontal transcortical or anterior transcallosal approach. Postoperative diencephalic damage occurred in 22% of patients in the transcortical group and in 36% in the transcallosal group; transient mutism was virtually equivalent in the two groups. Postoperative epilepsy (26%) and subdural fluid collections (30%) occurred only in the transcortical group. The incidence of postoperative hemiparesis was higher in the transcallosal group. There was a high correlation between postoperative Glasgow Outcome Score of 5 and preoperative severity of neurological disease but no correlation between postoperative Glasgow Outcome Score of 5 and location of the lesion or between postoperative clinical course and surgical approach. Surgical outcome of ventricle-associated lesions depends mainly on the severity of preoperative symptoms and not on surgical approach. Additionally, the incidence of postoperative seizures and subdural fluid collections after transcortical surgery is high.     

Neuropsychological effects of third ventricle tumor surgery

OBJECTIVE: This study assessed the neuropsychological outcome of patients after surgical treatment for third ventricle brain tumors. Neuropsychological consequences of surgical intervention can have a major impact on patients' quality of life and therefore have important implications for treatment planning. METHODS: A retrospective analysis of 33 patients' neuropsychological data was performed. All patients received a comprehensive neuropsychological evaluation after treatment for a primary brain tumor in the third ventricular region. Twenty-six patients underwent surgery, 14 via the transcallosal approach and 12 via a subfrontal, left transcortical, right pterional, or infratentorial supracerebellar approach. Seven patients were not treated by surgical intervention. RESULTS: There was a significantly elevated frequency of cognitive impairment relative to normative values in memory, executive functioning, and fine manual speed and dexterity. There were no differences in mean neuropsychological scores between patients who underwent surgery and those who did not. There were no differences in mean performance on the basis of surgical approach, tumor infiltration, or history of cranial irradiation. Repeated measures data available for two patients revealed memory impairment before and after surgery, and one patient experienced major improvement after surgery on a measure of mental flexibility and problem solving. CONCLUSION: Patients with third ventricle tumors are at risk for developing impairments in memory, executive function, and fine manual speed and dexterity, which are domains associated with frontal subcortical functions. In the current study, different types of treatment were not associated with differential cognitive sequelae, and surgical intervention did not account for cognitive deficits.     

Pre-coronal, paramedian minicraniotomy: a minimal access approach for microsurgical, transcallosal, transforaminal removal of colloid cysts of the third ventricle

OBJECTIVE: Microsurgical excision of colloid cysts of the third ventricle is accomplished along the transcallosal or the transfrontal routes. In the transcallosal approach, venous tributaries of the superior sagittal sinus can often act as an impediment to entry into the interhemispheric fissure for accessing the corpus callosum. We propose a paramedian minicraniotomy anterior to the coronal suture for removing colloid cysts via the transcallosal approach as veins are relatively rare in this area. METHODS: A triangular minicraniotomy was designed with each side measuring 3 cm based on the midline in the pre-coronal area of the frontal bone on the right side. Nineteen cases of symptomatic colloid cysts of the third ventricle whose diagnoses were proven by CT and/or MRI were subjected to microsurgery in the period from June 2004 to May 2007. Following the minicraniotomy the cysts were removed utilizing the transcallosal transforaminal route. RESULTS: Venous tributaries crossing the interhemispheric fissure were seen in 2 patients and these could be avoided to access the corpus callosum. Complete excision could be achieved in all cases. All patients had a good outcome although one patient had transient left lower limb weakness. The mean operating time was 163 minutes, while the mean duration of stay in the intensive care unit and hospitalization were 1.35 days and 3.73 days, respectively. CONCLUSION: The pre-coronal, paramedian minicraniotomy is safe and effective for the total excision of colloid cysts of the third ventricle. As a minimal access approach, it needs only a short duration of postoperative hospitalized care.     

Intraventricular meningiomas: a review of 16 cases with reference to the literature

BACKGROUND: Primary intraventricular meningiomas are notably rare with an incidence of 0.5 to 3% among all intracranial meningiomas. We present a series of 16 patients with histologically verified intraventricular meningiomas, the clinical and neuroradiological findings, and surgical results. METHODS: The charts of the patients including surgical records, discharge letters, histologic records, follow up records and imaging studies were analyzed retrospectively from 1978 to 2001. RESULTS: Collectively, 110 primary intraventricular tumors were surgically resected in our neurosurgical department from 1983 through 2001. There were 16 patients with primary intraventricular meningiomas. Thirteen (81.3%) of these tumors were located in the lateral ventricles, one (6.2%) in the third and two (12.5%) in the forth ventricle. Mean age was 47.1 years and there was no difference in incidence between the sexes. The most common presenting symptoms and signs were headache, mental change, and hemianopia. Other symptoms included gait ataxia, vertigo, hemiparesis, double vision, aphasia, and alexia/agraphia. On CT and MR studies most of the lateral ventricular meningiomas were located in the trigone (11 cases), two tumors originated at the level of foramen of Monro or in the frontal horn. The tumors were approached via a transcortical parieto-occipital (11 cases), transcallosal (3 cases), or median suboccipital (2 cases) route. Total removal was achieved in 15 out of 16 cases. There was no operative mortality. Clinical improvement was seen in symptoms like headaches, paresis, cerebellar signs and visual disturbances, whereas mental change showed less improvement. CONCLUSIONS: Although intraventricular meningiomas are quite rare, they represent an important differential diagnosis of intraventricular neoplasms. They can reach a substantial size by the time of diagnosis, yet total removal can be achieved in most cases.     

Tumors of the lateral ventricle. Review of 284 cases

The data from 284 cases of lateral ventricle (VL) tumors treated in 18 departments of Neurosurgery in France between 1995 and 2010 were collected in this series. The mean age was 33 years with a large proportion of children (79/284). CLINICAL PRESENTATION: The mean duration of symptoms was short in time (2 months). The revelation was incidental in 10% of the cases; for symptomatic lesions, raised intracranial pressure (ICP, due to hydrocephalus) and neuropsychological signs were the most frequent. Only one third of the patients had no CSF disorder. HISTOPATHOLOGY: The two most frequent tumors were meningiomas (40 cases, 15%) and neurocytomas (35 cases, 13%). The sub-ependymal giant cells astrocytomas, the ependymomas and sub-ependymomas were also common (11, 10 and 9% respectively). THERAPEUTIC MANAGEMENT: A surgical procedure was performed in 258 patients, with the help of neuronavigation in one third of cases. The patients were most frequently operated with a transfrontal approach (40%). The resection was complete in 73%, which was a statistical factor of global survival. The postoperative mortality rate was 4.9%. OUTCOME: Neuropsychological deficits were the most frequent sequelae (22.8%) due to raised ICP. Campimetric deficits (19%), seizures (19%), hemiparesis (15%) and language disorders (12%) were then found. The mean follow-up was 52 months with good evolution for 58% of patients. Fifteen percent of patients had a handicap and, finally, 12.9% will die. At last, two third of living patients had no tumoral residue or re-evolution.     

Microsurgical management of lateral ventricular meningiomas: a report of 51 cases

BACKGROUND: Lateral ventricular meningiomas are notably rare and the optimal surgical management for them remains a challenge. We made a retrospective study of patients with these lesions and analyzed the clinical findings, radiological features and especially the surgical treatment on the basis of surgical approaches and techniques. MATERIALS AND METHODS:A total of 51 patients with lateral ventricular meningiomas were operated on between 1996 and 2006 in our institution. The mean patient age was 44 years (range: 14-75 years). The most common presenting symptoms were related to the gradually increasing high cranial pressure (82.4%) rather than the location of the tumor. The transcortical parieto-occipital approach was used in 38 patients, the temporal approach was used in 9 patients and the transcallosal approach was used in 4 patients. RESULTS: The total surgical excision was complete in 48 patients (94.1%), and 3 patients with subtotal excision received radiotherapy after the operation. The previous visual fields deficits in two patients worsened and a new visual disturbance or sensory aphasia appeared in two patients. One patient died of postoperative hypothalamus complications. Thirty-eight patients underwent follow-up (range: 6 months-10 years). The conditions of 35 of these were excellent or good. No recurrence has been seen in any patient. CONCLUSIONS: Understanding the features of lateral ventricular meningiomas will help one to select an appropriate surgical approach. An individualized approach is needed, and the transcortical parieto-occipital approach or transtemporal approach is advantageous for most cases in our opinion. Also, it is possible to achieve a good surgical outcome with little neurological morbidity if we take wise strategies and techniques during excision.     

Twenty colloid cysts--comparison of endoscopic and microsurgical management.

The management of colloid cyst remains controversial, evaluation of the competing methods seems to be necessary. We report on our experience with colloid cysts in the last decade: ten were managed solely endoscopically, 10 were resected microsurgically (9 via a transcortical/transventricular, 1 via a transcallosal approach). The outcome in the endoscopic group was excellent in 9 cases and unsatisfying in 1 case (recurrence). In the microsurgical group we achieved a good outcome in 5 of 10 cases, a fair outcome in 4 cases and 1 lethal outcome (caused by pulmonary embolism). Complications in the endoscopic group: one intraoperative bleeding, 1 stitch granuloma, 1 mispuncture of the ventricle, and 1 meningitis. Complications in the microsurgical group: 1 subdural effusion, 1 flap infection, 1 mild hemiparesis, 1 transient impairment of consciousness and 1 pulmonary embolism.Mean operative time and length of hospitalization of the endoscopic group were clearly shorter than in the microsurgical group: 91 min versus 267 min time of surgery, 5.1 days versus 18.9 days of hospitalization. Complete resection was achieved in 8 of 10 cases of microsurgery, and in 3 of 10 cases in endoscopy. Endoscopic management results in lower costs and superior patients' comfort. The reduced number of total resections in the endoscopic group may lead to a higher recurrence rate in long-term follow-up, which might be a serious disadvantage of endoscopy. However, more experience in the endoscopic techniques may result in a higher rate of total resection of colloid cysts.     

Assessment of memory and new learning ability following stereotaxy-guided transcortical resection of anterior third ventricular colloid cysts

In a prospective study, memory and new learning ability functions were assessed pre-operatively (17 patients) and in the early post-operative period (22 patients) at 7-26 days following surgery in patients undergoing stereotactic transcortical excision of their colloid cysts. Pre-operative assessment detected impaired memory in 5 patients, 2 of whom had no memory-related complaints. Impaired new learning ability was detected pre-operatively in 7 patients. There was a statistically non-significant trend towards improvement in the dysfunction scores post-operatively in most patients. No correlation was detected between the cyst size, presence of raised intracranial pressure at presentation, hydrocephalus and the pre-operative dysfunction scores. Stereotactic transcortical resection of colloid cysts does not impair these functions in the majority of patients and might improve these functions in some. In the absence of clinical or radiological predictors of dysfunction of memory and new learning ability, pre-operative neuropsychological assessment has a role in detecting impaired memory and new learning ability in patients with anterior third ventricular colloid cysts who may not even complain of them.     

Neuronavigation in third ventricle tumors

The authors present the results of neuronavigation as a help to open neurosurgery for the tumors of the third ventricle. From January, 1995 to August, 1999, six image-guided surgical procedures were performed to remove third ventricle lesions : 4 collo?d cysts, 1 ependymoma, and 1 craniopharyngioma. The operative approach was transcortical in 5 cases, and transcallosal in 1 case. The use of neuronavigation allows a decrease of the surgical trauma during the surgical approach. The procedure secures the neurosurgeon in the choice and execution of his pathway to the target. It becomes however less accurate after opening the ventricle, because of the brainshift induced by the loss of cerebrospinal fluid becomes important. Nevertheless, neuronavigation is useful in the surgery of the third ventricle, especially if it is used with neuroendoscopy.     

Surgical anatomy and surgical approaches of the third ventricle

Careful analysis of MRI images is mandatory before any surgical procedure in the third ventricle. This analysis should take in account the relationship of the tumor itself, but also the grade of hydrocephalus and the main anatomical landmarks along the surgical approach. The first step is the access to the lateral ventricle, which may be achieved via transcortical or anterior transcallosal routes : these two operative procedures are detailed. The transforaminal entry to the third ventricle may be easy if hydrocephalus has widened the foramen of Monro. In other cases, a subchoroidal (or interthalamo-trigonal) approach is necessary, and the division of the thalamostriate vein is sometimes required. In this series, the transcortical route has been favoured by neurosurgeons. The advantages and drawbacks of both transcortical and anterior transcallosal routes are discussed. The anterior interhemispheric and pterional approaches are briefly evoked, as they were used in very few cases of this series. The management of hydrocephalus is discussed.     

Ductulo-insular pancreatic endocrine neoplasms: clinicopathologic analysis of a unique subtype of pancreatic endocrine neoplasms

Pancreatic neoplasms with mixed ductal and endocrine components are a heterogeneous group of tumors. The least recognized of these are pancreatic endocrine tumors (PETs) displaying benign-appearing tumor-associated ductules. To characterize these ductulo-insular pancreatic endocrine tumors (DI-PETs), we reviewed a series of 92 resected PETs. To be considered as a DI-PET we required the presence and tight intermingling of ductules with the dominant endocrine component (including the presence of ductulo-insular units). A total of 15 PETs fulfilled our criteria (16.3%). The average age of the DI-PET patients was similar to typical PETs (54 years vs 56 years). These tumors were smaller and more often insulin positive than typical PETs (p <0.05). Diffuse stromal fibrosis was more frequent in DI-PETs (11 of 15; 73.3.7%) compared with PETs (8 of 72; 11.1%) (p <0.05). The tumor-associated ductules were composed of cuboidal cells with dense eosinophilic cytoplasm and round nuclei without atypia or mitoses. They were positive for cytokeratin 7 and cytokeratin 19 and lacked any neuroendocrine markers. Reversibly, the endocrine component was negative for cytokeratin 7 and cytokeratin 19 and positive for neuroendocrine markers. Ultrastructural examination of ductulo-insular units confirmed a dual ductal and endocrine differentiation with amphicrine differentiation in one case. Follow-up was available in 12 cases with an average follow-up of 70.1 months (range 25-203 months). Ten patients are currently alive, and two patients died 81 and 158 months after surgery. We conclude that DI-PETs are not uncommon and that they are biologically similar to other PETs. We also hypothesize that the ductal cells develop by transdifferentiation of the endocrine cells.     

Surgical treatment of anterior third ventricle tumours

Summary A review is given on the operative management of anterior third ventricle tumours, with special emphasis on the selection of the approach, the postoperative results and complications. The review is based on our own experiences with 337 cases and 340 operations, among them 198 craniopharyngiomas, 80 gliomas, 23 colloid cysts, 11 ependymomas, and 25 others.The tumours can be approached through the lamina terminals or transcallosally or using a combination of both of these approaches.The approach through the lamina terminalis is useful only in rather small tumours, because it does not allow a sufficient revision of the upper and posterior third ventricle compartments.For larger tumours the transcallosal approach is preferable. We have abandoned the approach through the anterior horn of the lateral ventricle, because it does not allow an equally good vision of both sides of the third ventricle.In some of the craniopharyngioma cases it was necessary to combine the transcallosal and subfrontal approaches in order to achieve total or subtotal tumour resection.In craniopharyngiomas total or subtotal tumour removal was possible in 66% of the children and 59% of the adult patients, with a mortality higher in adults (30%) than in children (18.5%).The main causes of complications in craniopharyngiomas were acute disturbances of hypothalamic circulation and function, with water-electrolyte imbalance and other signs of diencephalic insufficiency. In glioma cases an additional important cause of complications has been haemorrhage into the remaining tumour parts.Colloid cysts could be exstirpated without mortality, using the transcallosal approach.Preconditions for improvement of results are: stricter selection of patients, proper choice of approach, excellent microsurgical technique and optimal intensive care. Also earlier diagnosis of the tumours would contribute much to better results.Presented of the EANS Wintermeeting on High Risk Neurosurgery, Budapest, February 20–23, 1991.     

Arteriovenous malformations of the lateral ventricle

Nine cases with arteriovenous malformations (AVM's) predominantly involving the lateral ventricle are presented. All the AVM's were small, but caused intraventricular hemorrhage in eight cases. Only two patients had an intracerebral hemorrhage large enough to warrant evacuation. Eight patients were under the age of 40 years at the onset of their disease. Computerized tomography demonstrated intraventricular hemorrhage in eight patients, and after intravenous administration of contrast medium a small area of enhancement with dilated subependymal draining veins was seen in seven. The lateral ventricles were of normal size in seven cases, and only two patients required a shunting procedure. Angiography demonstrated that the lesion was an AVM in eight patients, and did not visualize the lesion in the ninth. One patient suffered a recurrent intraventricular hemorrhage when the AVM was demonstrated, although repeated angiography had failed to disclose a vascular lesion at his first intraventricular hemorrhage 14 months before. All nine lesions were resected by microsurgical techniques, and the results were excellent in eight patients. Of four caudate lesions, three were resected through a frontal transcortical approach and the other was operated on through an anterior transcallosal approach; the results were excellent in three of these patients. Only one (Case 4) was left with neurological deficits; he had confusion and disorientation following a right frontal transcortical approach. Even in the dominant hemisphere, lesions in the head of the caudate nucleus could be safely resected by an anterior transcallosal approach. Two choroidal lesions located in the temporal horn and trigone on the dominant side were resected through a middle temporal gyrus approach, and three thalamic lesions through a posterior transcallosal approach, all with excellent results. In all cases the brain opening required was about the width of the retractor (maximum 2.0 cm, average 1.5 cm).     

Subependymal giant cell astrocytoma: a report of five cases

Five cases of intraventricular subependymal giant cell astrocytomas (SEGCA) were retrospectively reviewed. Records and detailed work-up of all five cases were well maintained in view of rare occurrence of these tumors. The five patients were males aged 10, 12 (2 cases), 14 and 18 years. The 18-year-old aged male had no stigmata of tuberous sclerosis (TSC) on examination, while the rest presented with features of TSC, intraventricular tumors and hydrocephalus. None of the five cases had renal tumors and did not reveal cardiac tumors. Skin manifestations like shagreen patches were present in two, facial angiofibromas in three, periungal fibromas in two, hypopigmented macules in two and ash-leaf spot in two patients. Fundoscopic examination revealed retinal astrocytomas in two cases only. Two of the five children did not have mental compromise. A child who started throwing seizures early (at 5 months of age) had severe mental retardation. Although SEGCA is a less vascular tumor, one tumor bled profusely intraoperatively; it was excised rapidly via the transcortical route to salvage the life of the child, though he was planned for the transcallosal route like the other cases. The tumor of another child was also very vascular. Four children survived surgery and required no shunt CSF diversion, while one died of severe ventriculitis and septicemia 3 weeks after surgery.     

Transcallosal parafornicial approach for third ventricle tumors: neuropsychological consequences

Five adult patients with 3rd ventricle tumors underwent a transcallosal intraventricular parafornicial approach. Pre- and postoperative cognitive reviews were conducted on all patients. Each review consisted of: a standardized neuropsychological battery, mental status reviews, specific tests for disconnection, and a personality variable, where possible. Computed tomography and magnetic resonance imaging are also presented. The three patients with colloid cysts and the two with oligodendrogliomas showed no significant postoperative cognitive deficits compared to the preoperative review. These additional subtle neuropsychometric measures, along with the methodological advantage of preoperative review, support a parafornicial approach where indicated to preserve cognitive abilities.     

Cystic supratentorial gliomas: natural history and evaluation of modes of surgical therapy

The management of cystic supratentorial gliomas is hampered by lack of documentation of the natural history of these lesions and by a lack of evaluation of modes of surgical therapy. We analyzed these factors in 25 patients with solitary cysts operated upon over a 20-year period. Two distinctive patterns of symptoms were seen: short duration (increased pressure and hemiparesis), most often heralding a malignant lesion, and long duration (commonly seizure disorder), associated more often with a benign pathological condition. Large solitary cysts were found in tumors of all histological grades. Surgical procedures included extirpation, biopsy/partial resection, cyst communication to ventricle or marsupialization, burr hole aspiration, aspiration via an indwelling reservoir, and cyst-peritoneal shunting. Radiotherapy, given in all cases, did not prevent cyst recurrence. Of the 25 patients, 76% are alive and remain cyst free at follow-up intervals of 1 to 16 years (mean, 3.2). Five patients died from their tumors, with a mean survival of 33 months after decompression. In 7 of 8 patients with cysts largely or entirely within the basal ganglia or thalamus, successful operative cyst control was achieved. Patients with solitary cystic gliomas seem to have a favorable prognosis, and vigorous efforts to control cyst recurrence and limit disability are warranted. Analysis of our data suggests that craniotomy for tumor resection, cyst decompression, and tissue diagnosis is the initial procedure of choice. Cyst recurrence without major solid tumor should be controlled by computed tomography-guided tap or shunt drainage. Reexploration is indicated when cyst reaccumulation is accompanied by clear regrowth of a solid component.     

Dermoid cysts of the nose: review of 21 cases

Twenty-one cases of histologically confirmed dermoid cysts of the nose are reviewed. The sites involved were the dorsum (18), septum (5), glabella (2), nasal tip (2), and columella (1), with several patients having multiple sites of involvement. Bony or cartilaginous destruction occurred in 14 patients (67%). A sinus tract was evident in ten patients (48%). Complete excision of these lesions is necessary for prevention of recurrence. The differential diagnosis includes hemangiomas, gliomas, encephaloceles, epidermoid cysts, neurofibromas, and lipomas.     

Endoscopic approaches for third ventricular tumors

Endoscopic approaches for third ventricular tumors, both transcortical and transcallosal approaches, are described. A 4-mm diameter, 0-degree rod-lens endoscope is used in both procedures, and angled rod-lens endoscopes are used for angled views. The transcortical transventricular approach is made via a burr hole placed at the nondominant frontal area, 1-inch lateral to the midline along the coronal suture. A folded vinyl tube, which can be expandable to a 1-cm tube by unfolding, is placed into the lateral ventricle toward the tumor under an image-guidance system. The transcallosal approach is made via a burr hole placed along the lateral margin of the superior sagittal sinus at the nondominant frontal area. The surgical corridor is made along the interhemispheric fissure. A rolled, cigarette-shaped, cotton patty is placed anteriorly and posteriorly along the surgical trajectory to keep the corridor open. The corpus callosum is opened, and the tumor is removed with surgical instruments inserted through the supported corridor parallel with the endoscope, which is mounted to an endoscope holder. Endoscopic transcortical and transcallosal approaches for the removal of third ventricular tumors are described. Compared with endoscopy performed through fixed working-channels, these techniques increase flexibility for surgeons to maneuver surgical instruments for delicate microdissection and tumor removal.