Neur surgery - Mosby€¦ · Proof Contents Section 1 intra-axial tumors 1 Awake craniotomy and...

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Video Atlas ofNeur surgeryContemporary Tumor and skull Base surgery

Alfredo Quiñones-Hinojosa

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Contents

Section 1 intra-axial tumors

1 Awake craniotomy and speech mapping for gliomas 000 Jordina Rincon-Torroella M.D., Ignacio Jusue-Torres M.D., Eibar Ernesto Cabrera-Aldana M.D. and Alfredo Quinones-Hinojosa M.D.

2 Cortical/subcortical motor mapping for gliomas 000 Norma Arechiga, MD; Karim Refaey, MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quiñones-Hinojosa, MD

3 Trans-sulcal versus transcortical resection of subcortical metastases 000 Kaisorn Chaichana, M.D., Jordina Rincon-Torroella, M.D., Shami Yesha Acharya, M.B.B.S. and Alfredo Quinones-Hinojosa, M.D.

4 Deep intra-axial lesions 000 Jordina Rincon-Torroella, M.D., Kaisorn L. Chaichana, M.D., Salvador Manrique-Guzman S. M.D., Alfredo Quinones-Hinojosa, M.D.

5 Brainstem tumors 000 Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quinones-Hinojosa, MD

6 Cerebellar tumors 000 Kaisorn L. Chaichana MD, Jordina Rincon-Torroella MD, Salvador Manrique-Guzman MD, Quinones-Hinojosa A MD.

7 Cervicomedullary tumors 000 Jordina Rincon-Torroella, MD; Karim Refaey, MD ; Kaisorn L. Chaichana, MD; Alfredo Quiñones-Hinojosa, MD

8 Supracerebellar-infratentorial approach 000 Jordina Rincon-Torroella, Arnau Benet, Alfredo Quiñones-Hinojosa

9 Intra-operative extent of resection 000 Jordina Rincon-Torroella; Eibar Ernesto Cabrera-Aldana; Alfredo Quiñones-Hinojosa

Section 2 extra-axial tumors

10 Convexity and parasagittal meningiomas 000 João Paulo Almeida,MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quiñones Hinojosa, MD

11 Falcine and falcotentorial meningiomas 000 João Paulo Almeida,MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quiñones-Hinojosa, MD

12 Posterior fossa meningiomas 000 João Paulo Almeida,MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Ignacio Jusue-Torres, MD; Alfredo Quiñones-Hinojosa, MD

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SSSection 3 intraventricular tumors

13 Transcortical approach to the lateral ventricles 000 Alejandro Ruiz-Valls, MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quinones-Hinojosa, MD.

14 Transcallosal approach to the third and lateral ventricles 000 Jordina Rincon-Torroella, MD; and Alfredo Quinones-Hinojosa M.D.

15 Telovelar approach 000 Jordina Rincon MD, Alfredo Quinones-Hinojosa MD

16 Endoscopic approach to the ventricles 000 Jordina Rincon-Torroella, MD; Kaisorn Chaichana, MD; Alfredo Quiñones-Hinojosa, MD

Section 4 Skull Base Approaches

17 Pterional craniotomy 000 Jordina Rincon-Torroella, MD; Alfredo Quiñones-Hinojosa, MD

18 Orbitozygomatic craniotomy 000 Jordina Rincon-Torroella, MD; Alfredo Quiñones-Hinojosa, MD

19 Supraorbital osteotomy 000 Jordina Rincon-Torroella, MD; Elizabeth Ogando, MD; and Alfredo Quinones-Hinojosa M.D.

20 Subfrontal and extended bifrontal craniotomy/transbasal approach 000 Jordina Rincon-Torroella and Alfredo Quinones-Hinojosa M.D.

21 Retrosigmoid/extended retrosigmoid approach 000 Jordina Rincon-Torroella, MD; Karim Refaey, MD; and Alfredo Quinones-Hinojosa M.D.

22 The far lateral approach 000 Arnau Benet, MD; Jordina Rincon-Torroella, MD; Tito Vivas-Buitrago, MD; Alfredo Quiñones-Hinojosa, MD

Section 5 endoscopic Approaches to Skull Base tumors

23 Principles and anatomy in endoscopic endonasal surgery 000 Arnau Benet, MD; Jordina Rincon-Torroella, MD, Alfredo Quiñones-Hinojosa, MD

24 Pituitary adenomas 000 Joao Paulo Almeida, MD; Alexandra Larsen, BS; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quinones-Hinojosa, MD

25 Surgical treatment of craniopharyngiomas 000 João Paulo Almeida, MD; Roberto Andrés Medina, MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quiñones

Hinojosa, MD

26 Clival chordomas 000 Jordina Rincon-Torroella, MD; Omar Antonio Perez morales, MD; Joao Paulo Almeida, MD; Alfredo Quinones-Hinojosa M.D.

27 Techniques for skull base reconstruction 000 Jordina Rincon-Torroella, MD; João Paulo Almeida, MD; Arnau Benet MD; and Alfredo Quinones-Hinojosa M.D.

Section 6 combined Approaches to the Skull Base

28 Combined subfrontal and endonasal approach 000 Karim Refaey, MD; Jordina Rincon-Torroella, MD and Alfredo Quinones-Hinojosa M.D.

29 Combined transconjunctival and endoscopic endonasal approach 000 Brian Hwang, Danilo Tueme, Jordina Rincon-Torroella, Alfredo Quiñones-Hinojosa M.D.

30 Combined transmaxillary and subfrontal approach 000 Eva F. Pamias-Portalatín, MD; Tito Vivas-Buitrago, MD; Jordina Rincon-Torroella, MD; Arnau Benet Cabero, MD; Alfredo Quiñones-Hinojosa, MD

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Section 7 Skull Base tumors

31 Anterior midline meningiomas 000 Jordina Rincon-Torroella, João Paulo Almeida,MD and Alfredo Quinones-Hinojosa M.D.

32 Medial sphenoid wing meningiomas 000 Jordina Rincon-Torroella, MD; Kaisorn Chaichana, MD; Alfredo Quiñones-Hinojosa, MD

33 Parasellar tumors 000 Christina Jackson, MD; Jordina Rincon-Torroella, MD; and Alfredo Quinones-Hinojosa M.D.

34 Invasive pituitary adenomas 000 João Paulo Almeida,MD; Martín A. Chacón Portillo, MD; Jordina Rincon-Torroella, MD; Kaisorn L. Chaichana, MD; Alfredo Quiñones

Hinojosa, MD

35 Approaches to the temporal bone: basic principles 000 Eva Pamias-Portalatín, MD; Arnau Benet, MD; Tito Vivas-Buitrago, MD; Jordina Rincon-Torroella, MD and Alfredo Quinones-Hinojosa M.D.

36 Approaches to the orbit 000 Elizabeth Ogando-Rivas, MD; Jordina Rincon-Torroella, MD; Alfredo Quiñones-Hinojosa, MD

37 Vestibular schwannomas 000 Eva F. Pamias-Portalatín, MD; Tito Vivas-Buitrago, MD; Jordina Rincon-Torroella, MD; Alfredo Quiñones-Hinojosa, MD

38 Foramen magnum meningiomas 000 Eva F. Pamias-Portalatín, MD; Tito Vivas-Buitrago, MD; Jordina Rincon-Torroella, MD; Alfredo Quiñones-Hinojosa, MD.

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Awake Craniotomy and Speech Mapping for Gliomas

Jordina Rincon-Torroella M.D., Ignacio Jusue-Torres MD, Eibar Ernesto Cabrera-Aldana MD and Alfredo Quinones-Hinojosa MD

Indications

• Intra-axial lesions invading, or located in elo-quent areas related to language cortex, especial-ly in the dominant hemisphere. The infiltrative rather displacing nature of gliomas makes this approach very suitable for low-grade gliomas (astrocytoma, oligoastrocytoma or oligodendro-gliomas) and high-grade gliomas.

• The goal of intraoperative speech mapping are:• To determine the limits of the resection and the

best surgical corridor to approach the lesion• To allow maximal resection while limiting func-

tional impairment of eloquent areas.• Increasing body of evidence supports longer

survival and better quality of life in low-grade gliomas (LGG) after gross total resection or smaller residual tumor volumes.

• Intra-operative mapping and functional imag-ing have transformed into resectable some brain tumors previously considered inoperable and has considerably decreased the post-operative functional deficits.

Contraindications• Non-cooperative patient because of disease or

psychosocial issues. • Inability to follow commands or to reproduce

the speech tests in the pre-operative training.• Anticipation of airway compromise during the

awake portion (e.g. morbid obesity, medically intractable seizures, or sleep apnea).

• Comorbidities that could promote brain hernia-

tion through the craniotomy window (e.g. antic-ipated intracranial hypertension)

Pre-operative Considerations

• Neuropsychological and language evaluation may be helpful to detect complex neurolog-ic symptoms and to determine the behavioral tasks (paradigms) that will be used for the func-tional MRI (fMRI) and intra-operative mapping.

• Neuro-imaging considerations (Figure 1a-f): Positron emission tomography (PET) and fMRI can be used for surgical planning and to localize the eloquent areas pre-operatively. If those tests indicate that the lesion is involving functional language cortex or is adjacent to it, an awake craniotomy with intra-operative speech map-ping is usually required.

• fMRI is preferred because it allows a non-in-vasive cortical mapping avoiding the use of radioisotopes. fMRI measures relative changes in oxygenated and deoxygenated hemoglobin. Especially in language mapping, fMRI or PET cannot distinguish in between essential and complementary but nonessential areas. fMRI can guide the surgical planning but cannot be the solely object to locate the eloquent areas and to establish the resection margins.

• With the combination of different speech para-digms fMRI can give an estimate of the localiza-tion of eloquent areas related to language cor-tex and hemispheric language lateralization or co-dominance.

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Figure 1a-f. Pre-operative imaging for a left frontal lesion consisting with a low-grade glioma. A. Axial T1-weigthed MRI with contrast showing the characteristic non-enhancement of low grade gliomas; B. Sagittal T1-weigthed MRI without contrast. A “M-shaped” gyrus has been highlight-ed with a yellow dotted line. It is a MRI landmark to locate the pars orbitalis, triangularis, and opercularis of the inferior frontal gyrus. This region is related to Broca’s area; C. Axial T2-weighted FLAIR showing hyperintense signal at the frontal lobe, anterior to the insula. FLAIR signal is used for the volumetric analysis in low-grade gliomas (pre-operative, post-operative, residual and recurrence volumes); D. Coronal T2-weighted FLAIR showing a hyperintense signal at the medial and inferior frontal gyrus; E. Axial DTI showed displacement of white matter tracts medially and the anatomic relation between the tumor and the superior longitudinal fascicle (SLF); F. PET image showing decreased uptake at the left frontal region, correlating with the lesion site.

• Despite its limitations, DTI can be also useful to assess the white matter tracks. The most import-ant tracks related to speech are the superior lon-gitudinalis fasciculus (SLF), the arcuate fasciculus and the inferior fronto-occipital fasciculus (IFOF). Those fascicles conform a dorsal pathway (phono-logical processing) and a ventral pathway (seman-tic processing).

• Regions of interest: Broca’s area (pars triangu-laris and opercularis of the inferior frontal gy-rus), Wernicke’s area (posterior temporal and inferior parietal areas in the angularis and su-pramarginal gyrus), supplementary motor area (superior frontal gyrus), dorsolateral prefrontal area and anterior insular cortex.

• Behavioral tasks (Paradigms): spontaneous speech, fluency, counting, object naming, spell-ing, reading, writing, comprehension, silent word generation, rhyme detection, semantic-de-cision, repetition, word stem completion, and switching from one language to another in bi-lingual patients. (Figure 2a-f)

• The functional maps can be fused with the mor-phologic regions depicted by standard MRI. (Figure 3a-d)

• Pre-operative redistribution and plasticity of the language function: In some cases, function is within the tumor, limiting the chances to perform a gross total resection. The eloquent areas can also be redis-tributed around the lesion, favoring wider resec-

Chapter 1 • Awake Craniotomy and Speech Mapping for Gliomas8

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ftions. In optimal cases, functional compensation by remote regions already exists pre-operatively favor-ing a complete macroscopic removal of the tumor.

Anesthetic Considerations• This surgery is performed under sedation with

propofol plus fentanyl or dexmedetomidine with-out intubation or with laryngeal airway. The patient will be sedated from the positioning time to the du-ral exposure monitoring with BIS (bispectral index) or entropy to control the moment of awakening. Then the patient is woken up to perform several tasks during brain mapping and tumor resection.

• When mannitol is needed, administrate a dose of 0.5g/Kg. Higher doses of mannitol may cause nausea. Alternative options to decrease brain edema are steroids and hypertonic solutions.

• The body temperature is aimed about 36-37ºC.• Possible adverse effects caused by electrical

stimulation are induced seizures and edema.• The major complaints during the awake portion

are: neck pain and stiffness, restlessness and dry mouth. Those can be comforted with good positioning, water-soaked sponges and slight changes in arms and legs position

Surgical Procedure Patient Positioning

• Before the head is fixed with a head holder, the occipital, temporal, and supraorbital nerves can be blocked. The local anesthetics that can be used are 1% lidocaine and 0.25% bupivacaine with 1:200,000 epinephrine.

• It is very important to provide local anesthe-sia in the points where the Mayfield pins will be clamped as well as the regions of the planed skin incision.

• After induction and local anesthesia, the head is fixed in a head clamp.

• The surgical approach and patient positioning varies depending on the location of the tumor.

• Typically, patient is positioned in right lateral po-sition. The draping is placed such as the patient can see the computer screen to answer the par-adigms and the team have easy access to assess possible complications.

• The head is turned towards the contralateral side and the neck is extended to facilitate the airflow during the awake portion.

Skin Incision

• C-shape or horse-shoe skin incision is performed• The temporalis and occipitalis muscles can be

infiltrated with local anesthetic before its inci-sion.

Craniotomy

• A standard craniotomy, tailored to the target re-gion is performed. Is preferable to not only ex-pose the tumor but at least 1-2 cm of surround-ing healthy parenchyma.

Dural Opening

• Before the durotomy, the dura mater is inject-ed with local anesthesia at the planed incision site and at the middle meningeal artery region.

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Figure 2a-f. Example of lan-guage paradigms for the fMRI and intraoperative mapping. A. Reading-comprehension. In this case incongruent; B. Silent word generation; C. Intra-operative reading paradigm. Notice that the letters are rotated to allow the patient to read them while lying in right lateral position during the procedure; D., E. Rhyme detec-tion; F. Object naming. Notice that the figure is rotated to allow the patient to recognize it while lying in right lateral position.

Chapter 1 • Awake Craniotomy and Speech Mapping for Gliomas 9

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This is done at each side of the vessels since the nerves causing pain follow similar courses. For easier maneuverability during the injection, a bended hypodermic needle can be used.

• The propofol sedation is stopped and the pa-tient is waked up. Some patients can be initially confused or agitated. The dural incision is not placed until the patient is fully awake, calmed and taking deep breaths.

Neurophysiological monitoring

• Electrocorticography (ECoG) monitors brain basal electrical activity, after-discharges, and

electrical seizures. It is recorded by subdural monopolar strip electrodes placed at the cortical surface adjacent to the stimulated cortex. Alter-natively, crown arrays can be used. A semicir-cular sterile crown attached to the outer table of the cranium can be used to arrange the cables of several cortical electrodes.

• Electroencephalogram (EEG) is used to monitor the cortical electrical activity when ECoG is not available and it is recorded by subdermal needle electrodes inserted in the scalp.

• Continuous EEG or ECoG are running during all the surgery to monitor for seizures or after-dis-

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Figure 3a-d. Pre-operative fMRI. A. Axial T1-weigthed MRI showing bilateral codominant activation of Wernicke’s areas; B. Axial T2-weighted FLAIR showed Broca’s area involved in within the lesion and left dominance was evident; C. Sagittal T1-weigthed MRI showing the relation in be-tween the lesion and Broca’s area (double arrow) and dorsolateral prefrontal area (single arrow); D. Coronal T1-weigthed MRI. The left Broca’s area is displaced inferiorly probably due to redistribution of the language function suggesting evidence of plasticity. The close contact with the tumor and invasion of eloquent areas favored the use of an awake craniotomy with speech mapping.


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charge. After-discharges (AD) indicate subclini-cal seizures due to the electric stimulation.

• Somatosensory evoked potentials (SSEPs) and mo-tor evoked-potentials (MEPs) allow detection and monitoring of the motor activity. MEPs provide real time information about the integrity of the motor pathways during the tumor resection and changes in its status can indicate injury to the motor path-ways or brain ischemia. Intraoperative-evoked po-tentials cannot be used for language monitoring.

Intra-operative mapping

• A continuous EEG or ECoG are running during all the surgery (Figure 4). The neurophysiologist monitors them for seizures or after-discharge. After-discharges indicate subclinical seizures due to the electric stimulation.

• Behavioral tasks (Paradigms): The most com-mon tests used for intra-operative mapping are counting, reading and object naming.

• Direct electrical stimulation is used for the speech mapping. 60-Hz biphasic current is applied to the cortical surface using a bipolar electrode tip spaced 5 mm and connected to an Ojemann stimulator.

• The optimal current intensity for mapping and the AD threshold are determined before starting the mapping. The upper limit of current intensi-ty with local anesthesia is 6mA. The stimulation trial starts from a baseline of 2mA. After several areas are tested without evoking after-discharges,

the intensity is increased by 1mA. This sequence is repeated until after discharges are seen or un-til reaching the upper limit. This intensity is set as the AD threshold. The mapping will be performed with an intensity 1-2 mA under the AD threshold.

• An optional technique to identify the optimal intensity for the mapping is stimulating the ventral premotor cortex at increasing intensities until inducing speech arrest.

• Each stimulation is applied before the item is presented, maintained for 1-2 seconds and fol-lowed by one task without stimulation. The cor-tex is stimulated at 1.5 cm intervals. To avoid induced seizures, the same site should not be stimulated two times in succession.

• A transient disruption of the task performed by the patient is noticed when an essential area is stimu-lated (speech arrest, speech apraxia, phonological disturbances, semantic paraphrases, persevera-tion, anomia, acalculia,). The function normalizes when the stimulation is stopped. Three noncon-secutive positive trials (stimulation that produc-es language disturbances) are enough to ensure whether an area is critical for language or not.

• A transient disruption with concomitant evi-dence of AD is considered a potential subclinical seizure activity and not a positive mapping.

• Finding one or two eloquent areas is not enough to consider a complete mapping. The entire area at risk may be mapped during the surgery, even

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Figure 4. A. Intra-operative view. The neurosurgeon applies the bipolar tip of the Ojemann stimulator to the cortical surface. ECoG: Monopolar strip electrodes for Electrocorticography ; B. Intra-operative view under the surgical microscope. Eloquent region was recognized and marked with a numbered sterile tag (*). The resection of the lesion is performed keeping 1 cm margin from the eloquent areas.


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when specific language regions have been al-ready recognized. This is one reason most of the neurosurgeons are in favor of wide craniotomies.

• The eloquent areas are recognized and marked with a numbered tag.

• If clinical seizures (incidence 4% of the cases) or after-discharges occur, the parenchyma is irri-gated vigorously with cold saline and anti-sei-zure medication is started. If seizure persist a doses of midazolam is administrated. If seizures persists, then the patient is intubated and an-ti-seizure medication is continued.

• Once the relationship between the language cor-tex and the tumor has been elucidated by map-ping, the surgical trajectory and resection mar-gins are established.

• Continuous speech test and motor evoked poten-tial for motor areas can be sustained throughout the resection to monitor any change in the func-tion. Direct electrostimulation can also identify eloquent subcortical structures when applied over white matter tracts or deep nuclei. The patient can perform counting or object-naming task within the resection. Semantic paraphasias, phonetic paraphasias or speech arrest may oc-cur with the stimulation of the subcortical tracts.

Intradural dissection

• Intra-operative frameless stereotactic neuronav-igation can help verifying the gyri and sulci lo-cation. The extent of resection can be assed but not based on it. After dural opening significant brain shift can happen, making the correlation with the neuronavigation unreliable.

• A transcortical subpial approach is often used for en-bloc resection of low-grade gliomas. Piece-meal resection is also a feasible technique. After finding the boundaries with the eloquent areas the non-eloquent tumoral tissue is removed. The eloquent areas limit the borders of the resection.

• To decrease the risk of post-operative deficits, it is recommended to keep 0.5-1 cm margin between the resection margins and the eloquent regions.

• Is important to preserve the vessels running in within the sulci, to avoid potential damage of functional areas.

• During the resection, the patient can be awake or sedated with propofol. Keeping the patient awake during the complete resection is highly recommended in the following cases:• If the lesion is very close to the speech areas or

is invading them.• If the speech areas were not be found during

the mapping (negative mapping).• When subcortical connections and vascular

structures related to the speech are in risk. Direct electrostimulation can also identify eloquent subcortical structures when applied over white matter tracts or deep nuclei. The patient can perform counting or object-naming task within the resection. Semantic paraphasias, phonetic paraphasias or speech arrest may occur with the stimulation of the subcortical tracts.

• Complementary techniques as intra-operative MRI, ultrasound and fluorescence-guided tu-mor identification (e.g. 5-aminolevulinic acid: 5-ALA, indocyanine green) have been imple-mented to monitor the extent of resection.


• A laryngeal airway and general anesthesia induction should be available anytime.

• The distribution of language function in well delineated Broca´s and Wernicke’s areas is quite uncommon. The majority of patients have several areas involved in speech processing. Distortion of the topography from mass effect or functional reorganization from plasticity is a common feature. Pre-operative fMRI is very useful in determining the distribution of speech in several regions but is not completely reliable for surgical decision-making.

• There is no battery of paradigms standardized for lan-guage mapping. A lack of specificity of the available testing paradigms can potentially miss eloquent areas.

• Mapping multiple languages: If the patient is multilin-gual, all the languages are tested. Different areas can be in charge of different languages. If the native tongue is injured, all the language function can be disrupted.

On the other hand, if a secondary language is impaired, the native language can still be preserved.

• The awake patient can be tired at the end of the re-section producing false negative results because of ex-haustion

• Backward spreading of the electric signal can cause false positives.

• Negative mapping vs. positive mapping. Small and tai-lored craniotomies sometimes do not expose essential functional regions. In those cases, tumor resection is di-rected by the localization of cortex that does not contain stimulation-induced language or motor function (negative mapping). Negative language mapping not necessarily guarantees the absence of eloquent areas. To ensure pro-tection of the eloquent cortex, some authors advocate ob-taining a positive mapping systematically when the tumor is close to an eloquent area.

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Closure

• After the tumor resection is completed the patient can be either awake or sedated for the closure.

• Standard dura mater, bone and skin closure are performed.

• Transitory worsening of the function is common in the immediate postoperative. Peritumoral edema or regional ischemia are possible explana-tions for this event. However, in LGG, functional recovery has been reported in 93-98% of the cas-es, with a functional improvement compared to the preoperative status in 15-20% of cases.

• After surgery, anticonvulsant levels are main-tained for several months.

Suggested ReadingDuffau, H., Quinones-Hinojosa, A. Schmideck & Sweet Operative Neurosurgical

Techniques. Chapter 9- Surgical management of low grade gliomas. (6th edition 2012). Volume 1; Pg. 80-93. Philadelphia, PA: Elsevier.

Zacà D., Jarso S., Pillai J.J.: Role of Semantic Paradigms for Optimization of Language Mapping in Clinical fMRI Studies. AJNR Am J Neuroradiol. 2013 Jun 20. [Epub ahead of print] PMID: 23788599

McGirt M.J., Chaichana K.L., Attenello F.J., et al. Extent of surgical resection is independently associated with survival in patients with hemispheric infiltrating low-grade gliomas. Neurosurgery. 2008 Oct;63(4):700-7.

De Benedictis A., Moritz-Gasser S., Duffau H. Awake Mapping Optimizes the Extent of Resection for Low-Grade Gliomas in Eloquent Areas. Neurosurgery 2010;66(6):1074–84.

Berger M.S., Hadjipanayis C.G. Surgery of Intrinsic Cerebral Tumors. Neurosurgery 2007;61(1): 279–305.

Stummer W., Pichlmeier U., Meinel T., et al. Fluorescence-guided surgery with 5-aminolevulinic acid for resection of malignant glioma: a randomised controlled multicentre phase III trial. Lancet Oncol. 2006 May;7(5):392-401.

Duffau H. Lessons from brain mapping in surgery for low-grade glioma: insights into associations between tumour and brain plasticity. The Lancet Neurology 2005;4(8):476–86.

Walker J.A., Quiñones-Hinojosa A., Berger M.S. Intraoperative speech mapping in 17 bilingual patients undergoing resection of a mass lesion. Neurosurgery. 2004 Jan;54(1):113-7; discussion 118.

Quiñones-Hinojosa A., Ojemann S.G., Sanai N., Dillon W.P., Berger M.S. Preoperative correlation of intraoperative cortical mapping with magnetic resonance imaging landmarks to predict localization of the Broca area. J Neurosurg. 2003 Aug;99(2):311-8.


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Telovelar ApproachJordina Rincon-Torroella MD, Alfredo Quinones-Hinojosa MD

Indications

• Indicated for lesions located within the fourth ventricle or brainstem lesions that extend higher than the pontomedullary junction. The alterna-tive approach has traditionally been the trans-vermian approach where the vermis is split. This approach takes advantage of natural corri-dors without the consequences of neural deficits at risk from other techniques.

Contraindications• Cervical pathology that opposes neck flexion.

To access the foramen magnum region the neck needs to be markedly flexed.

• Diffuse lesions (e.g. diffuse pontine glioma). How-ever, the telovelar approach may be used if a biopsy is required to establish adjuvant treatment regime.

• Lesions located laterally at the pons and me-dulla may be better approached trough a lateral approach (e.g. retrosigmoid, far lateral, extreme lateral, transpetrosal approaches) since the telovelar approach is ideal for midline lesions.

Preoperative Considerations• Anatomically the approach provides visualization

from the obex up to the cerebral aqueduct and to the lateral recesses of the fourth ventricle bilaterally.

• In patients acutely presenting with symptomat-ic hydrocephalus, an intraventricular catheter is placed for judicious CSF drainage until the time of surgery.

• Anesthetic considerations: • For resection of intrinsic brainstem lesions, the

anesthesiologist should be advised to watch for signs of cardiovascular instability (i.e. HR, BP changes).

• In situations where brainstem motor mapping will be performed, it is imperative that the patient’s body temperature is approximately 36.0 – 36.5oC, the anesthetic MAC is no higher than 0.5 and that muscle paralysis is not employed.

• The anesthesiologist should also be advised to employ a NIM (nerve integrity monitoring) endotracheal tube for lower cranial nerve monitoring.

• Neuromonitoring considerations: • Neuromonitoring is performed for cranial

nerves V, VII-XII in addition to somatosensory evoked potentials.

• For intrinsic brainstem lesions, motor evoked potentials are performed in addition to continuous EMGs throughout the tumor resection.

Patient Positioning

• Patient is positioned straight prone. Once fixed in a Mayfield clamp and positioned, the head is flexed and translated posteriorly (‘Military Tuck’). This facilitates access to the foramen magnum and also flattens the plane of surgery to be parallel to the floor.

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• The head of the bed is elevated above the heart in order to prevent venous congestion.

Surgical ProcedureSkin Incision, Soft Tissue Dissection and Craniotomy:

• A skin incision extending from the inion down to the level of C3/C4 is performed. The suboc-cipital musculature is dissected such that the suboccipital bone, foramen magnum, C1 lamina and the superior most aspect of the C2 lamina is exposed.

• Prior to the craniotomy, neuronavigation is em-ployed to mark the level of the transverse sinus-es and torcula.

• Two burr holes on each side of midline below the transverse sinus and a craniotomy is performed after the underlying dura has been dissected. In patients with tonsillar herniation through foramen magnum, the craniotome footplate is not used to cross foramen magnum – the foramen is removed separately after the bone flap has been elevated.

• In addition to the suboccipital craniotomy, a C1 laminectomy is also performed.



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978-0-323-26149-4

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PiCA BranchesPiCA Branches

Cerebellartonsilelevated

Telachoroidea

Right cerebellarhemisphereRight cerebellarhemisphere

(access tothe floor ofthe IVth

ventricle)

Cerebellartonsilelevated

Telachoroidea

(access tothe floor ofthe IVth

ventricle)

Figure 1. Illustration depicting the relationship of the tela choroidea and inferior medullary velum with each other, the fourth ventricle and surrounding cerebellar peduncles.

Thalamus

Superior Colliculus

Inferior Colliculus

Facial Colliculus

Inferior Medullary Velum

Area Postrema

Vestibular AreaStriae Medullaris

Hypoglossal TrigoneVagal Trigone

Obex

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Figure 2. Posterior view of the brainstem. Anatomy of the IVth ventricle.

Chapter 15 • Telovelar Approach16

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Dural Opening and Intradural dissection

• The dura is subsequently opened in a Y-shaped fashion and tacked back with retention sutures.

• Under microscope visualization, the arachnoid over the cisterna magna is incised and tacked to the dura with small vascular clips.

• At this point, dissection is aimed at opening the telovelotonsillar fissures bilaterally in order to free the uvula from the tonsils; early identifica-tion of the PICA branches coursing through this fissure can aid this dissection (Figure 1).

• Once the tonsils have been dissected, the next com-ponent of the dissection is aimed at opening the cerebellomedullary fissures bilaterally. Tracing the telovelotonsillar segment of the PICA will aid in opening this fissure. In the process of this dissec-tion, the tela choroidea and inferior medullary ve-lum will be exposed. The tela choroidea forms the roof of the inferior half of the fourth ventricle and attaches to the inferior cerebellar peduncles lateral-ly. This structure also merges with the inferior med-ullary velum at the telovelar junction to form the roof of the remainder of the ventricle (Figure 2).

• Once the tela choroidea and inferior medullary velum are exposed, they are incised to open the roof of the fourth ventricle. In this process, small arterial tributaries of PICA may have to be bipolared and divided; if necessary, ensure that sacrifice occurs as close to the roof as pos-sible. Otherwise, no neural structures are sac-rificed in the process of opening the tela and medullary velum. However, as the incision extends superiorly and laterally, one must be careful not to injure the cerebellar peduncles (Figure 3).

• At this point, a retractor can be placed on the uvula to maintain this structure out of the field.

• Tumor resection then proceeds. • There are two types of tumors that can be re-

moved trough the telovelar approach. The focal intrinsic lesions will require an incision into the dorsal surface of the medulla or at the floor of the IVth ventricle. The dorsally exophytic le-sions may not require an incision into the brain-stem since the lesion itself is either occupying the space in the IVth ventricle or protruding to the brainstem surface.

Trochlear nucleus

Pontine nucleus of trigeminal n.

Mesencephalic nucleus of trigeminal n.

Spinal tract and spinal nucleus of trigeminal n.

Motor nucleus of trigeminal n.

Abducens nucleus

Rostral salivary nucleus

Caudal salivary nucleus

Facial nucleus

Vestibular nucleus

Cochlear nuclei

Hypoglossal nucleus

Dorsal vagal nucleusSolitary tract nucleus

Nucleus ambiguus

Spinal nucleus of accessory n.

Accessory oculomotor nucleus

Oculomotor nucleusRed nucleus

Trochlear n. IV

Trigeminal n. V

Abducens n. VI

Facial n. VIIVestibulocochlear n. VIII

Glossopharengeal n. IX

Hypoglossal n. XII

Vagus n. X

Accessory n. XI

Oculomotor n. III


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Figure 3. Posterior view of the brainstem. Anatomy of the cranial nerves nuclei. Motor nuclei in red and sensopy and special nuclei in green tones. This illustrates the complexity and high eloquence of the brainstem.

Chapter 15 • Telovelar Approach 17

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Lateral Sulcus

Supracollicular

Infracollicular

Suprafacial Triangle

Infrafacial Triangle

Posterior Median Fissure

Posterior Intermediate Sulcus


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Figure 4. Posterior view of the brainstem. Delineation of the safe entry zones. Although some “safe entry zones” have been described in the past, with the modern technology we highly recommend used brainstem mapping instead of relying on the safe entry zones.


Neuromonitoring and Brainstem Mapping

• For intrinsic brainstem lesions, the floor of the fourth ventricle is then mapped in order to iden-tify a safe entry zone. In exophytic tumors, the le-sion can be already present to the ependymal sur-face.

• Is pertinent to remember that the floor of the fourth ventricle (i.e. dorsal surface of the brain-stem) has a rhomboid shape with subtle surface clues that divide into different compartments. Running between the two lateral recesses, the stria medullaris (Figure 4) marks the pontomed-ullary junction (i.e. the facial colliculus will lie above this). Running in the cranial-caudal direc-tion on each side of midline, the sulcus limitans marks the division between the motor and sen-sory nuclei.

• Motor mapping is performed with a Kar-tush side-by-side stimulator probe (Medtronic Xomed, Inc., Jacksonville, FL), which is narrow profile and has minimal electrical spread beyond the site of stimulation. Mapping then proceeds in a systematic anatomic fashion beginning at 0.2 mA and then increased in 0.1 increments un-

til a positive site is found. • The muscles employed for lower cranial nerve

motor mapping: • CN V – masseter • CN VII – orbicularis oculi and oris • CM IX/X – posterior pharyngeal wall (via

VIM tube) • CN XII – lateral wall of intrinsic tongue

muscles. • The facial and hypoglossal nerves can be stimu-

lated with a monopolar stimulator. EMG is used to record the changes in the stimulation. The cochlear nulei can be stimulated through ear phones with sound and direct recordings from the nuclei.

• Once motor mapping is completed, the appro-priate safe entry zone can be identified for ac-cess to the lesion. (Figure 5-9).

Closure

• Once lesion resection is completed and hemosta-sis is achieved, the ventricle and subarachnoid space is thoroughly inspected for any blood clots that could case CSF flow obstruction.

• The dura is closed in a watertight fashion with

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Figure 6. The incision is placed in a zone with negative mapping (no signal) avoiding major vessels. Small surface vessels can be carefully coagulated to avoid bleeding during the incision. However, coagulation of surface vessels has to be limited to the minimum. Incision can be dove with a microblade or a needle tip and widened with the use of for-ceps. The forceps are introduced closed into the incision and opened carefully to widen the opening.


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Figure 5. Illustration depicting intra-operative mapping of the floor of the IVth ventricle. The intrinsic pontine tumor can be seen ghosted. The incision will be placed over a non-functional area over the tumor.

Chapter 15 • Telovelar Approach 19


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Figure 7. A. Due to the tiny surgical corridor, instruments needs to be used wisely. One may limit the time that instruments go in and out to de-crease the contact and traction to the surrounding healthy brainstem. A small forceps-retractor is a special instrument used in those cases, it allows smooth separation of the walls from the inside out opening the surgical corridor to avoid collapse of the incision. B. Low rate suction is applied at the epicenter of the tumor. With this technique, suction is used at the same time as a way to pull the tumor gently while aspirating the blood and CSF that could obscure the surgical field. While the tumor is pulled with the suction, biopsy forceps, low bipolar cautery or dissectors can be used to separate the tumor from the walls formed by healthy brainstem parenchyma. The suction will be used to remove the small tumor pieces.

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Figure 8. After central debulking the tumor margins are resected. A cotton ball can be inserted at the center. This is used to apply aspiration without direct contact with the parenchyma and to avoid collapse of the surgical cavity.


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Figure 9. Slightly different strategy is used for hard tumors. An ultra-sonic aspirator can be used for central debulking and sharp dissection with forceps and scissors may be needed to dissect the tumor in a piecemeal fashion. Some exophytic lesions (e.g. choroid plexus pap-illoma) are placed within the IVth ventricle or protruding to the brain-stem surface and a brainstem incision is not required. In those cases a dissection plane may be found in between the tumor walls of the IVth ventricle. The tumor is gently peeled away from the ependymal surface and can be removed en bloc.

a dural patch and reinforced with a dural onlay graft and a dural sealant.

• The craniotomy is then reattached with titanium plates and screws and the suboccipital muscula-ture is re-approximated and skin closed with a running nylon.

• For intrinsic brainstem tumors, patients are left intubat-ed overnight. The following morning, vocal cord func-tion is inspected after which the decision to extubate the patient is made. After extubation, it is important to remember that the respiratory drive in these patients (particularly with medullary lesions) can be impaired; hence, requiring a higher CO2 than normal patients to initiate respiration. In such patients, narcotics are with-held and frequent arterial blood gas levels are drawn for several hours after extubation to ensure they are not CO2 retaining.

Pearls Summary

Suggested ReadingsMussi CM, Rhoton AL Jr. Telovelar approach to the fourth ventricle:

microsurgical anatomy. J Neurosurg 92: 812-823, 2000. Giliberto G, Lanzino DJ, Diehn FE, Factor D, Flemming KD, Lanzino G.

Brainstem cavernous malformations: anatomical, clinical and surgical considerations. Neurosurg Focus 29 (3): E9, 2010.

Morota N, Deletis V. The importance of brainstem mapping in brainstem surgical anatomy before the fourth ventricle and implication for intraoperative neurophysiological mapping. Acta Neurochir (Wien) 148: 499-509, 2006.

Quinones-Hinojosa A, Lyon R, Du R, Lawton MT. Intraoperative motor mapping of the cerebral peduncle during resection of a midbrain cavernous malformation: technical case report. Neurosurgery 54 [ONS Suppl 2]: ONS-439, 2005.

Adib A. Abla, Michael T. Lawton. Cerebellomedullary Fissure Dissection and Tonsillar Mobilization: A Gateway to Lesions Around the Medulla. World Neurosurgery 82: e591-e592.

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www.elsevierhealth.com

Video Atlas ofNeur surgeryContemporary Tumor and skull Base surgery

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