Telovelar Approach Research Articles

Telovelar Approach for Midline Posterior Fossa Tumors in Paediatrics: 25 Cases Experience

Background: The classic transvermian route for excision of fourth ventricular tumors could be associated with postoperative cerebellar mutism. The Telovelar approach leads to the fourth ventricle via the cerebellomedullary fissure, avoiding retraction on the dentate nuclei and vermian incisions, hence lowering the incidence of cerebellar mutism. Objective: The aim of this study is to evaluate the Telovelar approach for excision of fourth ventricular tumors. Patients and methods: This retrospective study was conducted on 25 cases with midline posterior fossa tumors collected between 2012 and 2014. All cases were operated upon via the telovelar approach succeeded by microscopic tumor excision. Follow up data were collected regarding the degree of excision (total, near total, and subtotal), and postoperative complications. Mean follow up period was 5 months. Results: Age ranged from 2 to 8 years (mean 5.6 years). The most common was medulloblastoma (13 cases), followed by ependymoma (10 cases), and then choroid plexus papilloma (2 cases). Gross total excision was achieved in 8 cases (32%), near total excision (Eƒ80% of tumor volume) in 14 cases (56%), and subtotal excision (E‚80% of tumor volume) in 3 cases (12%). We experienced cerebellar mutism in 2 cases (8%) which improved in one case in the long term postoperative follow up. None of the cases had truncal ataxia. Two cases (8%) had postoperative facial palsy, while 3 cases (12%) had postoperative bulbar affection. There were two mortalities in this study, which were related to bulbar palsy and chest infection. Conclusion: Telovelar approach to the fourth ventricle is becoming a widespread technique for removing midline posterior fossa tumors. It gives excellent access and visualization to the fourth ventricle, with a low incidence of postoperative cerebellar mutism.

Telo-velar approach to fourth-ventricle tumours: how I do it.

The "telo-velar" approach is an alternative to cerebellar splitting to gain access to the fourth ventricle through the so-called cerebello-medullary fissure (CMF). In this approach, the CMF is exposed and access to the ventricle is obtained by incising the tela chorioidea and inferior medullary velum. This approach enables the exploration of the entire ventricle cavity from the obex to the aqueduct. The exposure of the fourth ventricle is satisfactory and the floor of the fourth ventricle can be visualised early and protected. The extent of resection and outcome are satisfactory in most patients, including those with large tumours or lesions attached to the lateral or superolateral recesses of the ventricle. The deep rostral tumour attachment is the main limitation of the telo-velar approach. • Early exposure of the interface lesion-floor of the fourth ventricle favours a safer tumour dissection. • We feel that resection of tonsils is not necessary in the surgical setting. • The posterior arch of C1 should be removed only if the tonsils are below the level of the foramen magnum. • The improved access to the lateral recess of the ventricle makes the telo-velar approach particularly effective in lesions attached to cerebellar peduncles. • The wide dissection of the cerebello-medullary fissure and gentle tonsils retraction may prevent from the occurrence of cerebellar mutism or other major cerebellar dysfunctions. • Even the bilateral opening of the CMF does not result in cerebellar mutism if wide and cautious dissection, avoiding retraction and vascular injuries, is obtained. • The exposure of the fourth ventricle was satisfactory also in patients harbouring lesions attached to the lateral or even the superolateral recesses of the ventricle. • A deep rostral tumour attachment seems to be, at least in our experience, the main specific limitation of the telo-velar approach. • The risk of hydrocephalus can be reduced by opening of the fissure bilaterally, exposing the aqueduct, and by cisterna magna-fourth ventricle communication augmentation. • The EVD is taken in place for 48-72 h to prevent possible abrupt increase of the intracranial pressure and to favour wound closure.

Management of hydrocephalus in children with posterior fossa tumors.

Case 1: A 2-year-old male with no prior medical history presented to the emergency room with a 3-week history of constant headache and daily vomiting. Computed tomography (CT) and subsequent magnetic resonance imaging (MRI) of the brain [Figure 1] showed a minimally enhancing mass in the fourth ventricle, which extended out through the foramen of Luschka on the left. There was associated supratentorial hydrocephalus. He had no evidence of spinal metastasis on MRI of the spine. There was no papilledema on the fundoscopic exam. He underwent placement of a right frontal external ventricular drain (EVD) and gross total resection of the tumor through a modified telovelar approach at the same time. The pathology was consistent with a grade II ependymoma. Postoperatively, the ventricular drain was unable to be weaned, and he underwent ventriculoperitoneal shunt placement without complication 1.5 weeks after initial surgery. He was eating and ambulatory after recovery. He went on to radiation therapy. Figure 1 Magnetic resonance images of patient described in case 1. (a) Sagittal precontrast. (b) Axial fluid-attenuated inversion recovery. (c) Axial postcontrast Case 2: A 9-year-old male with no prior medical history presented to an outside hospital emergency room with 2 weeks of progressive headaches and 1-day of vomiting. A CT of the head showed a posterior fossa mass. MRI of the brain [Figure 2] showed an enhancing fourth ventricular tumor with associated metastatic lesions throughout both cerebellar hemispheres and supratentorial hydrocephalus. There was no evidence of spinal metastasis. Fundoscopic exam was positive for papilledema. He underwent placement of a right frontal EVD and resection of the fourth ventricular mass through a modified telo-velar approach at the same time. The infiltrative lesions in the cerebellum were not resected. The pathology was consistent with medulloblastoma. Postoperatively, his EVD was weaned over the course of 2 weeks and removed. He did not require permanent cerebrospinal fluid diversion. He was discharged home after recovery and went on for adjuvant radiation therapy. Figure 2 Magnetic resonance images of patient described in case 2. (a) Sagittal precontrast. (b) Axial fluid-attenuated inversion recovery. (c) Axial postcontrast

Adult brainstem ganglioglioma bulging into the fourth ventricle

Summary The authors present a case report of a 43-year-old female patient with ganglioglioma of the brainstem, which is an unusual location for the adult type of ganglioglioma. The sitting position and telovelar approach were used, and the tumor was totally removed with comprehensive intraoperative neuromonitoring. The ganglioglioma was an intra-axial tumor infiltrating the brainstem; however, adjuvant radiotherapy was not used. The preoperative characteristics, surgical techniques, outcome, and distinct treatment strategy are discussed.

The Dentate Nucleus and Its Projection System in the Human Cerebellum

Neurosurgical management of cerebellar lesions remains challenging. Thus, it is important to have sound knowledge of the microsurgical anatomy of the cerebellum and dentate nucleus (DN) and to define different types of exposure in a variety of surgical interventions. To examine the anatomy of the DN from a neurosurgical viewpoint using fiber tracking techniques. Ten formalin-fixed human hemispheres were dissected with the Ludwig and Klingler fiber dissection technique under × 6 to × 40 magnification. Anatomic images were created with 3-dimensional diffusion tensor imaging. The relationships of the DN to tentorium and suboccipital and lateral surfaces of the cerebellum and its spatial positioning relative to different surgical approaches in the cerebellum and fourth ventricle were examined. The fiber tracts terminating at and surrounding the DN were defined. The DN is at greater risk of being injured in the transvermian and supratonsillar approaches to the cerebellum and fourth ventricle, with lesser risk in the telovelar and subtonsillar approaches. Superior approaches are safer compared with other approaches. The DN represents an important anatomic structure in surgical interventions involving the posterior fossa, particularly in the elderly because of the common occurrence of atrophy-related problems in this age group. Functionally and anatomically, the DN is closely related to the superior and middle cerebellar peduncles. The inferior cerebellar peduncle poses positional risks because it follows an anterior and superior course relative to the DN. The telovelar approach is a safer procedure for interventions involving the pathological lesions of the fourth ventricle floor.

Bilateral telovelar approach: A safe route revisited for resections of various large fourth ventricle tumors

Background:Tumors located in the posterior fossa and especially in the middle and upper fourth ventricle are comparatively rare and technically very challenging. For some lesions, the telovelar approach has been shown to be a suitable approach. The unilateral approach is sufficient in most cases of small lesions. However, large fourth ventricle tumors are more problematic since they distort the normal anatomy with both vermis and cerebellar peduncles thinned and stretched out. This puts the patient at increased risk for a neurological deficit, which is minimized with a bilateral telovelar approach. By illustrating the adequacy of this technique, we emphasize the suitability of a rather unusual bilateral approach, which will provide excellent panoramic visualization of entire fourth ventricle and thus avoids complications usually associated with resections of large fourth ventricle tumors.Case Description:Here we present three cases of benign intraventricular tumors (meningioma, solitary fibrous tumor and ependymoma) in patients with site specific symptoms from local mass effect. Typical symptoms of posterior fossa lesions were present preoperatively and resolved after surgery. The bilateral telovelar approach was used to remove these tumors completely and the pertinent intraoperative steps are described for each case. All three patients had excellent postoperative outcome and could be discharged after short hospital stays.Conclusion:The different pathological entities could be completely resected without added neurological deficit employing a bilateral approach. In cases of large or giant fourth ventricle tumors, the bilateral telovelar approach provides excellent intraoperative visibility allowing complete excision of extensive tumors with minimal morbidity.

Telovelar approach for choroid plexus papilloma in the foramen of Luschka: A safe way using a neuromonitor

BackgroundTumors located in the 4th ventricle are always challenging to neurosurgeons, especially tumors that extend to the cerebellopontine (CP) angle by the foramen of Luschka. Recent advances in microsurgical technique, including the neuromonitor and brainstem mapping, facilitate the surgical resection of tumors located in the foramen of Luschka. Herein, we present the use of the telovelar approach to access a choroid plexus papilloma within the right foramen of Luschka. Case presentationA 28-year-old female presented with a history of sudden onset pulsatile headache and syncope twice without prodrome. The brain MRI revealed a 4th ventricular tumor deviated to the right foramen of Luschka and extending to the CP angle, 2.2cm in diameter. There was no secondary hydrocephalus due to the patent foramen of Magendie and left foramen of Luschka. The patient underwent suboccipital craniotomy and C1 laminectomy with a telovelar approach. The right tonsil was elevated and teal chloride was incised from the foramen of Magendie to the telovelar junction. The tumor was centrally decompressed, and the margin was gently dissected from the brainstem and cerebellum peduncles. Functions of the facial, cochlear, glossopharyngeal, vagus, and hypoglossal nerves and nuclei were monitored. Mapping of the facial nucleus, ambiguous nucleus, and hypoglossal nucleus was also done. Total tumor removal was achieved and the histology showed choroid plexus papilloma. No functional neurological disorientation was observed after surgery. ConclusionThe report demonstrated a safe and effective surgical approach to the foramen of Luschka. The approach yielded a better view of the foramen of Luschka laterally, and up to the middle cerebellar peduncle superiorly. Also, it minimized neural damage, and preserved the function of the cranial nerves and nucleus.

Endoscopic telovelar approach to the fourth ventricle: anatomic study

The telovelar approach allows reliable access to the fourth ventricle and avoids the splitting of the vermis and its associated "posterior vermal split syndrome." Our objective was to describe the endoscopic topographical anatomy of the telovelum approach to the fourth ventricle as accessed by the cerebellomedullary corridor. A series of 20 fresh and fixed injected anatomical specimens were used. The endoscopic equipment consisted of rigid endoscopes with different lens angles, while the extradural step required the use of the microscope and/or the exoscope. All the anatomical landmarks and relationships within the fourth ventricle and the cerebellomedullary fissure were identified by means of the endoscopic microscope/exoscope-assisted telovelar approach. In conclusion, we showed that the endoscope is a valid tool to gain an anatomic understanding of the fourth ventricle reached by means of the telovelar approach.

Current approach techniques to fourth ventricle

To approach the pathologies of base of fourth ventricle, cerebellar peduncle and lateral recess, it is possible to use three different surgical approach techniques. These are transvermian approach to fourth ventricle via incision of inferior vermis, telovelar approach that reaches the base, lateral recess and foramina of Luschka via incising the roof of the fourth ventricle between the uvula and tonsil and supra tonsillar approach that reaches the inferior and partially the middle cerebellar peduncle by following the cerebellar tonsil peduncle. In this article, actual techniques for approaching to fourth ventricule was reviewed.

Cavernous Malformations: A Paradigm for Progress

Cavernous Malformations: A Paradigm for Progress

Cerebellar mutism: definitions, classification and grading of symptoms

Dear editor, We would like to thank Dr. Frassanito and Dr. Massimi for their interesting and valuable comments on our review article on cerebellar mutism, particularly in sharing their own operative experience [1]. However, their interpretation of the incidence of cerebellar mutism syndrome, following surgery for cerebellar ependymoma in von Hoff's article, seems to be based on a misunderstanding regarding definitions of two different problems related to the cerebellum in this article—“postoperative cerebellar mutism” versus “postoperative cerebellar syndrome”. von Hoff et al. define the “cerebellar syndrome” as a motoric triad of ataxia, nystagmus, and dysmetria, grade it as mild, moderate, or severe as proposed by Riva et al. in 1991 [2] and refer to it as a general measure of cerebellar damage. They do not relate it to the wellrecognized posterior fossa/cerebellar mutism syndrome as such. Thus, a closer look at Table 1 reveals that the incidence of postoperative cerebellar mutism was in fact 0 [3]. The same motoric cerebellar syndrome is described in a group of patients as a measure of pre-operative clinical status in another article by Callu et al from 2009. The incidence of ataxia, nystagmus and dysmetria before surgery was 31%, while the incidence of post-operative mutism was 8% [4]. In both series, the telovelar approach was used from year 2004 and onwards, but only in patients whose tumor was located in the inferior part of the vermis. This was recommended after recognizing the role that splitting of the vermis plays in post-operative intellectual impairment [5]. This discussion highlights the confusion that exists in the literature regarding classification and definitions. We have defined “cerebellar mutism” as muteness following lesion of the cerebellum as opposed to the cerebrum or the lower cranial nerves. It is further characterized by delayed onset, limited duration, and (usually) long-term linguistic sequelae [6]. A common synonym is “transient cerebellar mutism” [7]. The “posterior fossa syndrome” is a broad term that usually includes cerebellar mutism as its main feature, but also encompasses motoric problems such as ataxia, hypotonia, cranial nerve palsies together with neurobehavioral abnormalities such as emotional lability, poor oral intake, decreased spontaneous initiation of movements, and impaired eye opening [8]. The “cerebellar mutism syndrome” was initially used as a synonym for isolated cerebellar mutism [9, 10], but has more recently in T. Gudrunardottir :A. Sehested :K. Schmiegelow (*) Department of Pediatrics, University Hospital Rigshospitalet, Copenhagen, Denmark e-mail: kschmiegelow@rh.dk

Abscess of the Medulla Oblongata in a Toddler: Case Report and Technical Considerations Based on Magnetic Resonance Imaging Tractography

We report a unique case of a toddler (the only one reported) successfully operated on for a medulla oblongata abscess and comment on the influence of neuroimaging modalities in the preoperative planning of the surgical approach. We report a case of a 20-month-old child with a solitary medulla oblongata abscess. The abscess appeared to be in close proximity to the anterior medulla oblongata, but preoperative planning based on diffusion tensor imaging (DTI) tractography motivated us to try to remove this lesion through a midline suboccipital approach. The ventral medulla oblongata abscess was surgically removed via a telovelar approach. At the anterior wall of the 4th ventricle, a fenestration was made with pus release and evacuation of the cavity. The child was discharged 1 week later with an uneventful and full recovery. Modern imaging modalities of the nervous system can be very helpful in preoperative planning. Functional visualization of the nervous system provided by modern imaging techniques, such as the DTI tractography, can alter the classic topographic concept of surgical approach. In the case presented, approaching an anterior medulla oblongata abscess based on DTI tractography data, through a suboccipital midline transventricular approach, proved to be an effective and safe technique.

Microsurgery for brainstem vascular malformation:report of 19 cases

Objective To investigate the microsurgical treatment of brainstem vascular malformation and evaluate the surgical outcome. Method Brain stem vascular malformations in 19 cases were resected by microsurgical techniques. Six cases of cavernous malformations ( CM ) in the dorsal of pons and medulla underwent operations via through the base of the forth ventrical approach. Another nine cases of CM in lateral and ventral lateral pons were treated via suboccipito - retrosigmoid approach. Three cases of arteriovenous malformation(AVM) in cerebellomedullary fissure were treated via telovelar approach. One case of AVM in the dosal medulla were resected via transvermian approach. Results All the lesions were totally resected. Pathologic diagnosis were CM( 15 cases) and AVM(4 cases). The diameter of all the CM were less than 1 centimeter. One AVM was 1.5 centimeter in diameter, the other two lesions was 2. 0 centimeter, the last one was 2. 5 centimeter. The functional disorders were improved after operation in 13 cases. Complications appeared in five patients, which improved between one week and three months. One patient died of sever pneumonia. During two months to six years after operation, the brainstem vascular malformation didn't recrudesce and re - bleed. No one patient appeared new syndromes. Conclusions The microsurgical management of brainstem vascular malformation can effectively prevent re - bleeding. Selecting different surgical approach basing on the locations can reduce the neurofunction damage. In order to accelerate the recovery of damaged brainstem, early surgery should be choosen for the patients with surgical indications. Basing on the correct choice of surgical indications, using the extensive knowledge of microanatomy,new concept of minimal invasive surgery and skillful microsurgical techniques, the surgical results of brainstem vascular malformation are satisfactory. Key words: Brain Stem; Central nervous system vascular malformations; Hemangioma,cavernous,central nervous system; Intracranial arteriovenousmalformations; Microsurgery

Experiences with the Telovelar Approach to Fourth Ventricular Tumors in Children

Background: Fourth ventricular tumors are amongst the most common tumors in the pediatric population. Traditionally, these tumors are approached through the cerebellar vermis, but the telovelar approach is now becoming widespread. Posterior fossa syndrome/cerebellar mutism is a complication of surgery for fourth ventricular tumors whose precise cause remains elusive, but may be related to the surgical approach or injury to adjacent cerebellar structures. We present a small series of fourth ventricular tumors and our initial experience in using the telovelar approach for this surgery. Methods: Twenty patients with fourth ventricular tumors were operated on using the microsurgical telovelar approach, sparing the cerebellar vermis. Data were collected prospectively for all patients with respect to the degree of resection achieved, complications and the incidence of posterior fossa syndrome. Results: A complete resection was achieved on postoperative MRI in 70% of the patients. Residual disease <1.5 cm³ remained in 15% and a further 15% had subtotal resection with >1.5 cm³ of residual disease. Thirty percent had evidence of posterior fossa syndrome in the postoperative period, of which 84% had resolved at the last follow-up. Thirty percent of the patients developed symptomatic hydrocephalus requiring shunting. There were no new neurological deficits and no procedure-related deaths. Conclusion: The telovelar approach provides excellent access to tumors of the fourth ventricle with sparing of the vermis in children. The high incidence of cerebellar mutism in our patients confirms that this phenomenon is unlikely to be related to vermian injury and further study is recommended.

Surgical approaches to brainstem cavernous malformations

Brainstem cavernous malformations (CMs) are low-flow vascular lesions in eloquent locations. Their presentation is often marked with symptomatic hemorrhages that appear to occur more frequently than hemorrhage from supratentorial cavernomas. Brainstem CMs can be removed using 1 of the 5 standard skull-base approaches: retrosigmoid, suboccipital (with or without telovelar approach), supracerebellar infratentorial, orbitozygomatic, and far lateral. Patients being referred to a tertiary institution often have lesions that are aggressive with respect to bleeding rates. Nonetheless, the indications for surgery, in the authors' opinion, are the same for all lesions: those that are symptomatic, those that cause mass effect, or those that abut a pial surface. Patients often have relapsing and remitting courses of symptoms, with each hemorrhage causing a progressive and stepwise decline. Many patients experience new postoperative deficits, most of which are transient and resolve fully. Despite the risks associated with operating in this highly eloquent tissue, most patients have had favorable outcomes in the authors' experience. Surgical treatment of brainstem CMs protects patients from the potentially devastating effects of rehemorrhage, and the authors believe that the benefits of intervention outweigh the risks in patients with the appropriate indications.

Accessing the Recesses of the Fourth Ventricle

To compare the effectiveness of the telovelar approach with tonsillar manipulation for approaching the recesses of the fourth ventricle. A telovelar approach was performed in 8 injected cadaveric heads. Areas of exposure were measured for the superolateral and lateral recesses. Horizontal angles were evaluated by targeting the cerebral aqueduct and medial margin of the lateral recess. Quantitative comparisons were made between the telovelar dissections and various tonsillar manipulations. Tonsillar retraction provided a comparable exposure of the superolateral recess with tonsillar resection (26.4 +/- 17.6 vs 25.2 +/- 12.5 mm2, respectively; P = .825). Tonsillar resection significantly increased exposure of the lateral recess compared with tonsillar retraction (31.1 +/- 13.3 vs 20.2 +/- 11.5 mm2, respectively; P = .002). Compared with tonsillar retraction, the horizontal angle to the lateral recess increased after either contralateral tonsillar retraction (22.7 +/- 4.8 vs 36.7 +/- 6.5 degrees) or tonsillar resection (22.7 +/- 4.8 vs 31.5 +/- 7.6 degrees; all adjusted P < .01). The horizontal angle to the cerebral aqueduct increased significantly with tonsillar resection compared with tonsillar retraction (17.6 +/- 2.3 vs 13.2 +/- 2.8 degrees; P < .001) Compared with tonsillar retraction, tonsillar resection provides a wider corridor to, and a larger area of exposure of, the cerebral aqueduct and lateral recess. Contralateral tonsillar retraction improves access to the lateral recess by widening the surgical view from the contralateral side.

Surgical treatment for choroid plexus tumors in the fourth ventricle: brain stem infiltration hinders total extirpation

The significance of surgery for choroid plexus tumors is well established, but surgical resection of those in the fourth ventricle has not been evaluated. This study reviewed five consecutive patients with choroid plexus tumors in the fourth ventricle treated in our institute between 1996 and 2005, focusing on the factors that hindered total extirpation. Two cases were choroid plexus papillomas, and three cases were choroid plexus carcinomas. Preoperative T2-weighted magnetic resonance imaging showed a diffuse high-intensity lesion in the brain stem in four patients. Infiltration into the fourth ventricle floor was apparent in all five patients during surgery, which hindered total resection of the tumors without neurological deterioration. Intraoperative bleeding was well controlled in all five patients by cauterizing the feeding arteries at the early stage of surgery through the telovelar approach. Performance status was improved in all patients postoperatively. All patients with choroid plexus carcinomas underwent radiation therapy after the surgical removal. No patient suffered tumor progression within the follow-up of 24-129 months (mean 64 months). Total resection of choroid plexus tumors in the fourth ventricle is difficult because of invasion into the fourth ventricle floor. Adjuvant therapy for choroid plexus tumors with brain stem infiltration must be established.

Telovelar approach: technical issues for large fourth ventricle tumors

Fourth ventricle is conventionally accessed via resection of the part of the vermis for total excision of the tumors at the expense of significant morbidity. Numerous avenues have been identified to minimize the morbidity; some of which include transforaminal, subtonsillar, telovelar approaches, etc. These approaches are devised on the basis that accurate dissection along the natural avascular planes will avoid injury to the important structures in this area minimizing morbidity. We attempt to emphasize the technique of telovelar approach and the problems encountered while employing this technique for excision of large fourth ventricle tumors. Fifteen patients with fourth ventricle tumors were operated during January to September 2005 at Sree Chitra Tirunal Institute for Medical Sciences and Technology, Thiruvananthapuram, Kerala, India. Fourteen of these cases were medulloblastomas, and one was ependymoma. All the patients were operated in prone oblique position via telovelar approach. Clear understanding of the normal anatomy will help in meticulous dissection and will result in reduced morbidity. Significant incidence of postoperative ataxia and mutism is seen with this approach in large tumors, and this can be avoided by staged dissection of the uvulotonsillar cleft.

The Supratonsillar Approach to the Inferior Cerebellar Peduncle: Anatomy, Surgical Technique, and Clinical Application to Cavernous Malformations

To introduce the supratonsillar approach, an approach that traverses the tonsillobiventral fissure in a trajectory over the cerebellar tonsil to the inferior cerebellar peduncle, and to demonstrate the utility of this approach for resecting peduncular cavernous malformations. Anatomy of the cerebellar tonsil and surrounding fissures, arteries, and veins are reviewed using cadaveric brain specimens. The surgical approach uses the three-quarter prone position, a suboccipital craniotomy, and wide splitting of the tonsillobiventral fissure. Of our experience with 171 patients with cavernous malformations, six patients had lesions in the inferior cerebellar peduncle that were resected using the supratonsillar approach. All cavernous malformations were removed completely and no patients experienced surgical complications or new deficits. The supratonsillar approach differs from the transvermian and telovelar approaches to the fourth ventricle, with a more superolateral trajectory that leads instead to the inferior cerebellar peduncle. By splitting the tonsillobiventral fissure and mobilizing the tonsil inferomedially, the point of access to the lesion is deepened and transgression of normal cerebellar tissue is minimized. This elegant approach is ideally suited to the removal of cavernous malformations.

Quantification And Comparison Of Telovelar And Transvermian Approaches To The Fourth Ventricle

To quantify the exposure to the fourth ventricle obtained with the telovelar and transvermian approaches. The telovelar, with and without C1 posterior arch removal, and transvermian approaches were performed on six cadaveric heads. The area of surgical exposure was calculated from triangles formed by defined anatomic points. A robotic microscope was used to determine the "angle of approach" for the same points. The maximal allowable vertical angle of attack to the obex of the fourth ventricle was significantly greater with the telovelar approach than with the transvermian approach (P < 0.002), but there was no difference at the rostral fourth ventricle. The maximal allowable horizontal angle of attack at the level of the obex, Luschka, and rostral fourth ventricle was significantly greater with the telovelar than with the transvermian approach (P < 0.001). Removal of the C1 posterior arch with the telovelar approach significantly increased the vertical angle of approach to the obex (P < 0.001) and rostral aspect of the fourth ventricle (P = 0.005) compared with the telovelar alone. The telovelar approach with C1 arch removal offered a larger working area than the transvermian approach (P < 0.001). Except for the vertical angle to the rostral aspect of the fourth ventricle, the telovelar approach provides greater angle of exposure in all planes than the transvermian approach. Removal of the C1 posterior arch obviates this sole advantage of the transvermian approach. The telovelar approach offers a corridor through noneloquent arachnoid planes and a safe and capacious working environment.