AANS2000 Outline of

Neurosurgery

E. R. Flotte MD, 2009

Please send comments and corrections to admin@flotte2.com

www.outlineofneurosurgery.com

Miscellany

Critical Care/Neuromedicine

Neuroradiology

Stereotaxy

Stereotactic Radiosurgery

Awake Craniotomy & Cortical Mapping

Neuromonitoring

Neuroendovascular Procedures

Critical Care/Neuromedicine

Neuroanesthesia

· Sedatives: Versed, Thiopental

· Narcotics

· Nitrous oxide: Avoid with pneumocephalus. Stop before dural closure to prevent tension pneumocephalus.

· Ketamine increases CBF

· Sodium thiopental most rapidly lowers ICP (faster than other agents or hyperventilation)

· Dexmedetomidine (Precedex): α2-agonist, anxiolytic, analgesia, “cooperative sedation”. Used in awake craniotomy, NICU. (ON7/05)

· Paralytics

o Succinylcholine: 1mg/kg – 3.5 to 5cc, lasts 5-10min. do not use with spinal cord injury, hyperkalemia

o Pavulon reversal: Neostigmine (2.5-5mg IV) + atropine (0.5mg/mg neostigmine) or Robinul (0.2mg/mg neo). Takes 20 min

· Propofol:

o Propfofol Infusion Syndrome (PIS): pediatric and adults patients. Causes rhabdomyolysis, myoglobinuria. Increased CK, serum triglycerides, LFTs, renal failure. Doses > 4 mg/kg/hr

o Not approved for < 16yo.

· ASA Class estimates patient physical status (American Society of Anesthesiologists)

· Awake and/or fiber-optic intubation: used in patients with severe cervical spinal cord compression or instability to avoid injury during intubation

· Double-lumen endotracheal tube: used for thoracotomy (above T8), thoracoscopy

· Neuro-monitoring: Avoid inhalation agents, BZDs, barbs; use nitrous or narcotics, short-acting muscle relaxants (not for MEPs)

· Awake craniotomy

· Malignant hyperthermia:

o 50% have had previous normal anesthesia. Can test preoperatively with muscle biopsy.

o Check family history

o ↑ ETCO2.

o Occurs w/ inhalational + Sux.

o Treatment: Dantrolene (2.5mg/kg, up to 10mg/kg), 100% O2, D/C anesthesia & change tubing.

Air Embolism

· Occurs when venous pressure is lower than atmospheric pressure and the venous system is open to the atmosphere.

· Most likely to occur in the sitting position

· Preparation: CVL, precordial doppler

· Detection: precordial doppler (most sensitive), ¯ EtCO2 (earliest), FEN2,

· Cardiac: hypotension, ¯ CO, PAP, pulmonary vascular resistance, ventilation-perfusion mismatch.

· Treatment: Lower the head-of-bed, cover wound with wet laps, aspirate air through central line, 100% O2.

Ventilation

· Intubation/Extubation: 100mg lidocaine IVP, 100% O2 x 5min.

· Tube: 20-22cm at gum line, tip 5cm above carina

· PCWP <12, PA 15-30/4-12, CI 2.8-4.2

Arrythmias

· Afib/Aflutter: Verapamil (5mgx2), Diltiazem (0.25mg/kg 10-20mg). (adenosine, procainimide; digoxin for flutter) If unstable cardiovert 100J.

· Other SVT: Vagal maneuver, Adenosine (6mg-12mg-12mg), verapamil, diltiazem

· Vtach, Vfib: Pulseless: Epi (1-3-5mg); Other: Lidocaine (1mg/kg q5m x 3), procainamide (20-30mg/min to 12mg/kg), bretylium (10mg/kg q5m x 3)

· Asystole: Epi, atropine (0.5mg x 4)

· Bradycardia: atropine

Myocardial infarction

· Clopidogrel with aspirin is recommended for unstable angina or minor myocardial infarction; ticlopidine is not recommended

Antihypertensives

· Nipride: onset seconds, Follow thiocyanate levels if used >24hrs. 0.3-10mg/kg/min. Avoid in pregnancy

· Nitroglycerin: 10-20 mg/min, 0.4mg SL q5m x 3

· Both raise ICP.

· Nicardipine (Cardene)

· Hydralazine: onset 3-5min, duration 2-4hrs. OK in pregnancy. SE: tachycardia. IM 10mg, IV 20-40mg prn.

· Labetalol: onset 5m, duration 3-3hrs; 20-40-60-80mg IV, 200mg po bid

· Esmolol.

· Vasotec: 1.25-5mg q6hrs prn

Shock

· Types: hypovolemic, cardiogenic, septic, neurogenic, anaphylactic

· Dopamine: 2-20 mg/kg/min, b>ab.

· Dobutamine: 2.5-10mg/kg/min, b only (inotrope, BP unchanged). Use for cardiac failure if normotensive.

· Palpable pulses: radial 80, femoral 70, carotid 60

Corticosteroids

· Cause pancreatitis, immunosuppression, osteoporosis, gastrointenstinal ulcers, Cushing’s syndrome

· Must be weaned after chonic use

· Stress dose given for surgery or other stressors

· Addisonian crisis: hydrocortisone (Solucortef) 100mg IVP then 50mg q6h (not Solumedrol)

Anaphylaxis

· Treatment: Epinephrine 1:1000 5ml SQ, Benadryl 50mg IM, Decadron 10mg IV

· Urticaria: Benadryl 50mg PO/IM + Cimetadine 300mg PO/IV

· Vasovagal reaction: hypotension, bradycardia. Tx: Atropine 0.75mg IV, q 15min to 3mg

Hyperthermia / Fever

· Ice down patient, cold gastric lavage, cold IF fluids

· Neuroleptic malignant syndrome: On Parkinsons meds or neuroleptics, given Haldol, Phenergan

DVT

· Incidence in neurosurgical patients: 15-20%

· May be increased in craniotomies due to release of brain thromboplastin

· Calf vein thrombosis has <1% risk of PE, however they may progress to DVT

· Prophylaxis: Heparin 5000 U SQ BID, Lovenox 30mg SQ BID. TEDs/SCDs (do not use if DVT is present)

o ACCP guidelines: fondaparinux is a alternative to low-molecular-weight heparin (LMWH), because it is equally safe and effective but has a longer half-life, a more predictable response, and fewer adverse effects

o Moderate-risk surgical patients: Heparin 5000mg SQ BID or LMWH (less than 3,400 U once daily)

o High-risk surgery patients: Heparin 5,000 U SQ TID or LMWH more than 3,400 U daily

o Aspirin is not recommended

· Diagnosis:

o Doppler ultrasound: Standard

o Clinical diagnosis (calf tenderness, warmth) is unreliable.

o The fibrinogen uptake test and impedance plethysmography have low accuracy and are not recommended

o Contrast venography has high sensitivity but limited availability and questionable use for small distal thrombi and high patient discomfort. Use is limited to research

· Treatment: Bedrest x 10days, then careful ambulation. 3-6 months full anticoagulation then low-dose coumadin (INR 1.5-2).

o Three randomized trials of anticoagulants vs no anticoagulants in DVT showed no benefit with heparin and coumadin (combined all-cause mortality: anticoagulants = 6/66, un-anticoagulated controls = 1/60, P = .07).

o No RCT of LMWH or thrombolytics have been done; they have not been proven safer or more efficacious than unfractionated heparin. Thrombolysis causes more major and fatal bleeds than heparin and is no more effective in preventing PE (CundiffDK 9/04).

o IVC (Greenfield) filter

Pulmonary Embolism

· Diagnosis:

o V/Q scan:

§ Normal scan rules out PE.

§ High probability (88% true positive) then treat.

§ Low or moderate probability then obtain leg dopplers and if positive then angiogram to confirm.

o Spiral CT

o Angiogram

· Treatment: anticoagulation or IVC (Greenfield) filter. Massive PE causing hemodynamic compromise should be treated with anticoagulation regardless of intracranial risk.

Fat embolism

· Occurs 12-48hrs post-injury

· Symptoms: dyspnea, petechiae over thorax, tachycardia, tachypnea.

· Labs: serum lipase in 50%. Look for fat in blood, urine. No specific test.

· Cerebral embolism (causing confusion, somnolence, seizures) does not occur without lung symtoms unless a PFO or ASD exists.

· Treatment: O2, PEEP. Steroids controversial.

Antibiotics

· Aminoglycosides/Gentamycin: Poor CSF penetration. SE: nephrotoxic (ATN), ototoxic, vestibulitis, worsens myasthenic crises,. Coverage: Gram (-) (no strep).

· Sinus entry: Gentamycin, Clindamycin

· A meta-analysis of eight randomized clinical trials (RCTs) showed that prophylactic antibiotics reduce rates of postoperative infection by approximately 75% after craniotomy (Barker FG N1994)

Electrolytes

· AG = Na – (Cl + HCO3)

· Osm = 2(Na+K) + BUN/2.8 + Glu/18

· Hyponatremia: 1.0-1.5 meq/L/hr, 25meq/L/d, 3% Na 25-50cc/hr + Lasix

· SIADH

o Diagnosis: Na<134, Osm<280, UNa >50.

o Treatment: Fluid restriction <1L/d. 3% NaCl. Chronic: demeclocycline (300mg po q8°) or lithium

o Versus cerebral salt wasting: SIADH has ↓↓ serum Na, ↓ or wnl BUN/CR, ↑ plasma volume, ↑ CVP/PCWP, no dehydration signs

· Diabetes Insipidus (DI)

o Treatment: 1/2NS, DDAVP/desmopressin (0.5-4 μg IV°). Chronic: Intranasal DDAVP (10-40μg BID)

· Hyperkalemia: 10% CaGluconate 5-10cc over 2m; 1 amp HCO3; 5-10U regular insulin + 1 amp D50; Kayexalate

Hematology

· Estimate of pediatric blood volume: 90-100ml/kg for premature infant, 80mg/kg for term infant, 75ml/kg for 1-12mos, 70ml/kg for >1 year

· Platelets: 1 units raises platelet counts by 5-10K. Do not use with autoimmune destruction (eg ITP).

· Fresh Frozen Plasma

· Vitamin K: 10mg IM. PT reversal requires 6-12 hrs. (Do not give IV)

· Prothrombin complex concentrate reverses coumadin 5x more quickly than FFP

· Transfusion Reactions

Hemolytic: Due to ABO incompatibility. Symptoms: chest pain, shock. Stop transfusion, mannitol, IV fluids.
Allergic: Due to plasma proteins. Causes hives. Treatment: Benadryl.
Febrile: Treatment: Tylenol. Send blood for analysis to rule out hemolysis

· Recombinant activated Factor VII (rFVIIa): used for quick coagulopathy reversal

FDA Approved for patients with hemophilia but used in many coagulopathic patients
Dosing controversial. 40-120μg/kg. 20-80μg/kg used for ICH trials. Minimum effective dose 5μg/kg.
Half-life 2.3 hours. Manufacturer recommends repeat dosing every 3-6 hrs for severe hemorrhage but data is limited
Ideally should be given concomitantly with FFP.
Effective in 10-20mins. Repeat dosing may be used.
Platelet count >50K necessary to be effective.
RCT suggests it may improve outcome in ICH
Single dose is approximately $12,600
See Hawryluk GWJ JN12/06

DIC

· Labs: Increased PT, PTT & Bleeding Time. Platelets <100K. d-dimer, fibrin degradation products (FDPs >40g/ml). ¯ fibrogen (<100mg/mm³) = best correlation ().

· Treatment: FFP ± Heparin (thrombotic) (cryoprecipitate if fibrinogen is low, platelets if low)

Hypercoaguability

· Workup: antithrombin III, protein C, protein S, APC resistance, factor V Leiden, plasminogen, fibrinogen, aPL antibodies, ANA panel, anti-DNA antibodies, cryoglobulins, homocysteine, SPEP/UPEP, hemolysis screen, rheumatoid factor. Pregnancy test.

Anticoagulation/Antiplatelets:

· Perioperative Management

o Mechanical valves: stop coumadin 2-3d preop, admit and heparinize.

o A-fib: stop 4-5d preop. Can restart 5d postop

o Bleeding time not predictive of intraoperative bleeding

o Brain tumors reportedly carry no higher risk of hemorrhage with anticoagulation

o Stop coumadin, heparinize, and stop heparin 6hrs prior to angiography, myelograpy, or surgery

· Postop

o Craniotomy: wait at least 3-5d before restarting anticoagulation.

o Starting LMWH <24hr postop clinically significant hemorrhage: 1.5% for major procedures, 0.07% for minor procedures (vs 4.3% with SQ heparin) (N11/03)

· Coumadin

o Always preheparinize before starting coumadin (decreases proteins C&S initially causing hypercoaguability).

o INR: Mechanical Heart valve: 3-4. All other (DVT, TIA, afib, PE): 2-3.

· Heparin

o Increases Antithrombin III.

o IV: 5000U bolus then 1000U/hr. SQ: 5000U Q8h.

o Causes thrombocytopenia (use lepirudin/Refludan).

o Protamine: 1mg reverses 100U heparin.

· Low molecular weight heparin (LMWH)

o AKA fractionated heparin

o enoxaparin (Lovenox): 30mg SQ BID. nadroparin (Fraxiparin) 0.3ml SQ. dalteparin.

o Protamine can reverse 60% of effect

o Versus SQ heparin: greater bioavailability, more predictable anticoagulation, lower risk

· Antiplatelets: Clopidogrel, ticlopidine, aspirin

o antithrombotic therapy for coronary artery disease, stroke, etc: because of many adverse effects which are sometimes fatal, ticlopidine is no longer recommended for coronary interventions when other treatments are available. Clopidogrel plus aspirin is now recommended for most patients with unstable angina or minor myocardial infarction

o Reversal: Platelets, repeat after 6-8 hours

o Assays exist to determine platelet inhibition

· GP IIb-IIIa inhibitors: Integrellin (eptifibatide), amaxicab (Reopro), tirofiban (Aggrastat)

Fluids

· Hetastarch: Cheaper than albumin. Possible anticoagulant effect at high dosage (>500 cm³/d)

Nutrition

· Postoperative ileus treated with dietary restriction, NG suction for symptomatic relief

· Ogilvie’s syndrome: acute massive dilation of the cecum and distal colon. Normal small bowel sounds. Increased with PCA. Diagnosis: KUB. Requires rectal tube, colonoscopy.

Alcohol

· Wernicke’s syndrome

o Symptoms: Triad: gait ataxia, nystagmus/opthalmoplegia, confusion. (also hypothermia). Due to thiamine deficiency. Ocular problems recover 1^st. Usually reversible. IV glucose worsens – always give thiamine (banana bag) before IV glucose.

· Kosakoff’s syndrome: memory deficits, usually permanent

Brain Death

· Review: Wang MY N9/02

Neuroradiology

Neuroradiology References

· Osborn A., Diagnostic Neuroradiology,1994.

· Osborn A. et al, Diagnostic Imaging: Brain, 2004.

· Loevner LA, Case Review: Brain Imaging.

· Iodinated Contrast Allergy: If minor, can prep with prednisone 32mg PO 12hrs and 2hrs before; Benadryl 50mg either IM 1hr before, or IV 5min before. Use non-ionic contast (Iohexol) if possible. With a history of anaphylaxis do not give even with prep.

o IV Iodinated contrast and Glucophage (metformin) can cause renal failure.

Angiography

· Risk of permanent major morbidity from surveillance angiography is 0.04% (other series 0.3-2.3%) (Ringer AJ N11/08) – Table 1 Literature Summary

Myelography

· Only intrathecal contrast (nonionic water-soluble) agents: Iohexol (Omnipaque).

o Metrizamide and Pantopaque (iodinated non-water soluble) have been supplanted by Iohexol - caused seizures, etc.

o Pantopaque caused arachoiditis with diffuse nodules (dense on CT)

· Lumbar puncture performed, dye injected. For cervical myelogram head of table lowered.

· Plain films usually combined with CT (CT-myelogram)

· Spinal block patterns: “Feathering” = extradural; meniscus = intradural, extramedullary

MRI

· MRI contraindications: www.MRIsafety.com, www.IMRSER.org. Partial list:

o Pacemakers, neurostimulators, cochlear implants, recent vascular stent, coil, or filter, some aneurysm clips, some metallic implants or fragments

o Pregnancy in 1^st trimester. Gadolinium at any time.

· Diffusion-weighted: ischemia shows up as high signal within minutes

· Dynamic MRI designed to detect dynamic stenosis or listhesis - Fonar Upright MRI

· AANS Course: BASICS OF MR & MR ANGIOGRAPHY

MR Angiography (MRA)

· Phase-contrast

· Time-of-flight

MR Spectroscopy

· Measures metabolites in a 1cm² voxel

o Choline: indicative of cell membrane turnover (eg tumors)

o Lactate: indicative of necrosis

o NAA: N-acetyl aspartate, found in neurons (normal brain)

· Tumors (generally nonspecific): ↑ Choline (& choline:creatinine ratio), ¯ NAA, ↑ lactate.

o Cho:Cr ratio can predict survival & guide biopsy in gliomas.

o Radiation necrosis: low Cho & Cho/Cr

o Abscess: medium Cho/Cr

MR tractography (Diffusion Tensor Imaging)

· Maps subcortical fiber tracts (ie corticospinal pathways) using diffusion tensor imaging.

· Limited in areas of tumor or edema.

MR Neuroanatomy

· MR landmarks for precentral gyrus: on most rostral axial cuts, look for L-shape. On midsagittal cuts it is just anterior to the termination of the cingulated sulcus. On lateral sagittal cuts it is bisected by a perpendicular line emanating from the posterior corner of the insular triangle.

Functional imaging

Functional MRI (fMRI)

· Detects changes in deoxyhemoglobin.

· Useful for motor mapping, not sensitive enough for speech.

· Motor paradigms: 1) thumb-index opposition, 2) toe flexion, 3) tongue movement.

· Speech paradigms: 1) visualizing presented verbs, 2) decipher complex noun.

· Protocols: Hirsch J N9/00

· May be used after previous surgery (Peck KK N4/09)

Positron Emission Tomography (PET)

· Measures metabolism. Radioisotopes (emit positrons, eg ¹⁸F) conjugated to metabolically active substance (eg glucose).

o Requires cyclotron (for radioisotopes). Positron = same mass of electron but + charge.

· Radiotracers used:

o ¹⁸F flouro-deoxyglucose (FDG): measures glucose metabolism.

o ¹¹C-methionine (Met): Amino acid, measures protein synthesis. Hot in low-grade tumors (unlike FDG). May be better for stereotactic targeting (see JN9/04)

· Resolution 8mm.

· Findings:

o Hot: GBM/ high grade tumor, ictal seizure foci

o Cold: Low grade tumor, radiation necrosis, cortical dysplasia, interictal seizure foci, mesial temporal sclerosis.

Single Proton Emission Tomography (SPECT)

· Measures blood flow.

· ²⁰¹Tl (thallium), ⁹⁹Tc (technetium, HMPAO), or ¹³³Xe used.

· Resolution 10mm.

· Findings similar to PET.

· Thallium-SPECT can distinguish tumor recurrence from radiation necrosis in metastases (JN1/05S)

High-Intensity Focused Ultrasound (HIFU)

· Review: see Jagannathan J N2/09 (History)

· HIFU Societies:

o International Society of Therapeutic Ultrasound (ISTUS)

o Foundation for Focused Ultrasound

o Focused Ultrasound Surgery Foundation

Stereotaxy

· Approaches Uses preoperative imaging (CT/MRI) registered to 3-D space

· Since imaging is pre-operative, it does not account for intraoperative brain-shift, which can be up to 1cm for tumor resections

· Uses:

· Preop/Intraoperative planning: incision, craniotomy, approach

· Extent of resection for tumors

· Stereotactic Needle Biopsy

· Lesioning or placement of electrodes for functional neurosurgery

Frame-Based Stereotaxy

· Talraich or Schaltenbrand atlases used

· AC-PC line: may be used to scale other measurements

· Stereotactic Frames:

· Cosman-Roberts-Wells (CRW) Radionics

· Leksell Elekta

· Historical: Brown-Roberts-Wells (BRW)

Frameless Stereotaxy

· Use LEDs or passive reflectors on instruments, tracked by mounted camera

· Registration:

o Skin fiducials placed prior to imaging

o “face mask” with LEDs

o Surface matching

· Frameless Stereotactic Systems

o BrainLab: VectorVision, Kolibri

o GE: InstaTrak

o Medtronic: StealthStation

o Radionics/Integra: Omnisight

o Stryker: System II, Elite

Stereotactic Needle Biopsy

· 4% morbidity, 1% mortality

· Stereotactic electrode placement: 0.5-2% risk of hemorrhage – higher with sulcal (10%) or ventricular (5%) penetration, hypertension (Elias WJ JN2/09)

Intraoperative MRI (IMRI)

· Allows for real time imaging

o Real-time biopsy

o Confirmation of extent of resection

o Accounts for brain-shift

· Generally require non-ferromagnetic instrumentation

· Other systems move into standard operative field

· IMRI Systems

o General Electric Signa SP: 0.5T “double-donut”. Operative performed in MRI – no patient movement. Original IMRI design. Obsolete.

o GE MR Surgical Suite

o Medtronic PoleStar (formerly Odin): Portable MRI

o Brainlab BrainSuite: Rotating or movable table moves patient into adjacent MRI

Stereotactic Radiosurgery

· Given as a single dose, conformal, stereotactic targeting, as opposed to conventional radiotherapy

o Standard XRT kills rapidly dividing cells, spares normal tissue and hypoxic tissue resistant. SRS kills tissue regardless of mitotic activity, oxygenation, or inherent radiosensitivity.

o Stereotactic Radiotherapy: Fractionated radiosurgery.

o “Staged-radiosurgery”: treating portions of large lesions 3-12 mos apart

o Definition: See Pollock BE N12/04 and Adler JR N12/04 for controversy

o See “Chained Lightning”: Hoh Dj N7/07, 9/07

· Systems:

o LINAC: Linear accelerator accelerates electrons into heavy metal (tungsten) which emits photons.

o Advantages: Frameless treatment, multiple-fractionation possible, can treat extracranial lesions.

o Systems:

§ Varian Trilogy

§ Brainlab/Varian Novalis Tx

§ CyberKnife (Accuray): uses computer controlled robotics to move LINAC

· See Neurosurgery 2/09S – abstracts from 2008 Cyberknife Users’ Meeting

§ Radionics X-knife

o Gamma Knife (Elekta): 201 Cobalt⁶⁰ sources, emit photons.

o Frame-based treatment only. Multiple fractions difficult due to repeated frame placement.

o Cannot be used for extracranial lesions.

o Recent Models: 4, 4c, Perfexion: robotized

· Imaging: MR: spoiled-GRASS sequence, 1-2mm slices, 512x256 matrix, 2 excitations. Fat suppression for previous TSRP with fat graft. MR appears to be as accurate as CT (shift is minimal). Use short posts to avoid artifact.

o MRSpect data can be used for planning

· Dose toleration

o Max. dose to optic n.: Tishler 93: 8Gy. Leber 98: 10Gy had 0% optic neuropathy (had better dosing). Stafford 01: up to 12-16 Gy if < 9-12mm exposed (1% if <12Gy). 2mm margin from optic pathway is debateable.

o Brainstem 15Gy max.

o Spinal Cord: 800Gy

· Side-effects

o Radiation-associated neoplasms: 6 reported cases of, 6-19yr latency. Estimated risk 1:1000. Some studies show no increase from baseline (RoweJ N1/07)

o Deficits may appear over 2yrs postop. Complications or tumor progression rarely occur after 3yrs with benign lesions. (N03)

o Tumors may enlarge before contracting. Debateable whether SRS makes subsequent surgery more difficult.

o Cavernous sinus 2% risk of CN4 or CN6 injury. (37% of pre-treatment cranial nerve deficits improve).

· Specific Conditions

o Tumors

§ Brain Metastases

§ Gliomas

§ Pituitary Adenomas

§ Meningiomas

§ Acoustic neuromas

§ Cavernous sinus tumors: 98% local control. 37% improved cranial nerve deficits, 2% new deficits.

§ Benign tumors (acoustics, meningiomas) may take over 5 years to begin regressing after treatment

o Trigeminal neuralgia

o AVMs

§ Cavernous malformations

o Also used for thalamic pain (hypophysectomy), Graves disease ophthalmopathy, glaucoma

Proton Beam Therapy

· Requires cyclotron.

o Current PBT Centers: Loma Linda (CA), Indiana University, MD Anderson (TX), Hampton University (VA), University of Florida, Massachusetts General Hospital, Northern Illinois University

· Uses Bragg Peak Effect to maximize fall-off to surrounding tissues

· The National Association for Proton Therapy

Radiation Therapy

· “4 Rs” of radiobiology to semiselectively target dividing cells: reoxygenation, reassortment, repopulation, repair of normal tissue (favors fractionation)

· Intensity-modulated radiotherapy (IMRT) is as a way of delivering highly conformal radiation to tumors

· Miniature linear accelerators have mounted on a robotic arm (CyberKnife) or mounted in a ring gantry (TomoTherapy)

· Multileaf collimators (MLC) replaces the custom-fabricated collimators. It consists up to 60 pairs of opposing tungsten fingers, or leaves. The position of each leaf can be adjusted to shape the beam. Depending on the manufacturer, the width of each leaf varies from 1 cm to 3 mm. MLC has enabled intensity-modulated radiation therapy (IMRT).

· The MLC can be used to vary the integrated intensity of the photon beam as a function of position within the aperture. This can be achieved using either of two techniques: stop and shoot or dynamic mode.

o Using stop and shoot, the beam is divided into eight or more segments, each of which is delivered using a different MLC aperture. When the segments are delivered, the superposition of the beams results in a field that can have eight or more intensity levels, the highest intensity occurring at points where all segment apertures overlap.

o The dynamic technique involves moving the MLC leaves across the field while the beam is being delivered. In effect, a slit opens on one side of the field, moves across the field, and finally closes on the other side. As it crosses the field, its shape and width change. This modulates the beam intensity because at any point, the intensity is a function of what fraction of the time the point was under the gap.

· IMRT can be used in conjunction with a software tool known as inverse treatment planning in which you start with the final dose distribution and working backward toward the intensities for each beam.

· The patient must remain stationary in the correct position throughout dose delivery. The techniques used can be grouped into two approaches:

o In the first, the patient is immobilized in a stereotactic body frame or immobilization cradle. Such devices are noninvasive and, thus, do not guarantee that the patient will remain perfectly positioned.

o A second approach is used when localization images can be taken frequently during the treatment without greatly lengthening the procedure. It is especially suited to procedures in which dual in-room kilovolt units are available. The patient can be set up conventionally on the treatment machine couch without additional immobilization. The positions of the bony structures are checked many times during treatment

· Cognitive effects

o Memantine, a NMDA receptor antagonist used to treat Alzheimer’s disease, is being studied in the prevention of cognitive effects of WBRT – RTOG 0614

· Yamada Y N8/07

· See “Chained Lightning”: Hoh Dj N7-9/07

Neuroendoscopy

· Neuroendoscopic Systems

· Endoscope may be passed thru ventricular catheter to confirm placement

Awake craniotomy

· Anesthesia

o Some do not intubate, use IV propofol during opening and closing, with versed or fentanyl while awake. In this case do not open dura until the patient is fully awake, to prevent swelling

o Local anesthesia (lidocaine+marcaine) is used on incision. Additional local anesthetic is infused around the supraorbital rim, the zygoma, the posterior auricular region, and the temporalis insertion to produce a field block. Pin sites are injected if a headholder is used. The dura is also injected.

o Asleep-awake-asleep technique: Intubation/General anesthesia > opening with hyperventilation > extubation > mapping > intubation (fiberoptic laryngoscope or tube changer) > general anesthesia

o Inhalational (isofluane, nitrous oxide) and remifentanyl after verifying muscle relaxants are worn off by train of four.

o Berger feels propofol may adversely affect cortical depolarization.

· Some use head-pins, others use doughnut.

Cortical Mapping

· Slow-growing lesions may shift eloquent areas, even contralateral

· Stopping resection 1-2cm from eloquent cortex greatly reduces postop deficits

· See Tharin S N4/07

Cortical stimulation

· Done with bipolar stimulator (60Hz, 1msec, single-phase, 2-6mA awake, 4-16mA general anesthesia). Increase current by 2mA until response is obtained. Hold tips on cortex for 2-3 secs.

· Patient temperature >36º.

· EMG recording may improve sensitivity.

· May be done asleep or awake.

· Always have cold irrigation ready to irrigate cortex in the event of a stimulation-induced seizure. Seizures stopped by cold irrigation of cortex, bezodiazapines, and Dilantin

· Some vary current at different sites (while monitoring afterdischarges), others don’t (JN9/04)

· Afterdischarges monitored by electrocorticography – i.e. 5-grid strip laid next to stimulated area. This prevents seizures and ensures that stimulation effects are local only (ie specific)

· Negative results may not ensure safe resection; a positive result (ie speech arrest) is necessary to be sure of the location of essential language sites

· May be done at bedside with implanted electrode grids.

Language Mapping

· Hemispheric dominance: Left hemisphere for 99% of right-handers. Overall: 85% left, 9% bilateral, 6% right.

· In left-handers use WADA test to determine language dominance.

· Obtain baseline language function. Test the patient preoperatively and eliminate objects the patient can’t identify. Naming errors must be less than 25%. If patient is unable to participate preoperatively a trial of higher-dose steroids can be attempted to see if enough improvement occurs than language testing can be used.

· Awake craniotomy with cortical stimulation

· Object naming is the most reliable test. Reading may also be tested (posterior temporal)

· Each site is tested 3 times, never twice in succession

· Essential language sites exist primarily on the surface of the gyri and not in the depths. Primary language sites are vertically organized with respect to subcortical fibers, and surface stimulation can be used to predict the results subcortical resection. But subcortical mapping can be used to identify language fibers near the insula

· Subcortical language mapping has been performed (Duffau H JN9/08)

Motor Mapping

· Resection may be continued into the anterior bank of the precentral gyrus without causing an adverse event

· Resection may be performed in both the dominant and nondominant supplementary motor areas without causing permanent sequelae, as long as the primary motor cortex is not violated

· Primary somatosensory cortex resection will produce a temporary hypesthesia and proprioceptive deficit. When they affect the dominant hand, such deficits are problematic to the patient and the patient should be counseled preoperatively regarding this

· Cortical stimulation: Motor area identified in 94%.

o May be done under general anesthesia or awake. Motor stimulation is elicited in 50% under general anesthesia and 100% of conscious sedation cases in a small series, with electrographic seizures in 30% and 10% respectively (NF7/03)

§ General anesthesia: inhalation agents combined with Versed and fentanyl without paralytics.

o Children under age 5 often cannot be mapped with stimulation because of cortical inexcitability – use SSEPs instead

o After resection, motor pathways should be stimulated again to ensure their function. If motor pathways respond to stimulation after resection, any motor deficit observed after the operation will be temporary

· Subcortical stimulation: Identifies subcortical motor tracts in 50%. If motor cortex is identified then tracts are mapped from there. If not, then white matter is stimulated at 10-16mA. Stimulation of corpus callosum does not elicit clinical response. 8% of patients have subcortical pathways within gross tumor

Reversal of SSEP wave

· Reversal of SSEPs with cortical strip placed over central sulcus used to identify central sulcus and motor and sensory cortex

Neuromonitoring

· Used in spine surgery, or cranial surgery near motor pathways or vascular (aneurysms)

· Used during positioning (e.g. spinal stenosis) as well as during procedure

· Done by CNIM (certified neurophysiologic intraoperative monitoring tech – EEG tech with national certification), audiologist, neurophysiologist, or MD (e.g. neurologist)

· Avoid inhalation agents, BZDs, barbs; use nitrous or narcotics, short-acting muscle relaxants (not for MEPs)

· Evoked potentials: neural pathways’ integrity assessed by stimulating at one end and recording at another

· Amplitude and latency of transmission is recorded and compared to baseline

· Baseline data best obtained after exposure (normalizes anesthesia, temp, vitals, etc.)

· Amplitude ↓50% or latency ↑ 10% is significant (others say 80% drop or “all-or-none” significance)

· Loss of EPs:

· Check wound – compression, retractors, etc. Irrigate with warm saline (r/o cold irrigation).

· Check with technician for system integrity

· Check with anesthesia (type used), vitals (temp, BP, O2, etc)

· Raise BP

· Can wake up patient and test function (Stagnara wake-up test) or ankle clonus test (clonus normally present in anesthetized patients – absence indicates damage)

· Reviews: Quinones-Hinojosa A NCNA04

· EMG used to monitor nerve root function

· During pedicle screw placement, screw electrically stimulated – EMG reaction suggests pecidle fracture/ violation by the screw

· Burst EMG: mechanical irritation. Train EMG: nerve root injury

· Spinal cord monitoring : MEPs and SSEPs

· Motor Evoked Potentials (MEPs)

Used for cervical-thoracic intramedullary spinal cord tumors, spinal AVMs, mapping motor cortex, aneurysm clipping.
Stimulation: motor cortex (transcranially or by direct cortical grids) – or spinal cord (transesophageal, percutaneous).
Recording: 2 types:

1. Muscles (CMAP): detected by EMG

· CMAPs: switch to muliphasic waveform or loss in multiple muscles worrisome (Matsuyama Y JN:S5/09)

2. Peripheral mixed nerve (NMEP or CNAP): measured by electrodes over nerves

· Epidural electrode recording distal to intramedullary resection site (“D waves”) may also be used

Significant changes: ↓ amplitude 80%, ↑ latency 10%
Twitch artifact of erector spinae muscles may limit. Leg MEPs may require too strong stimulation. (Supratentorial MEPs N5/04)
MEPs superior to SSEPs in detecting motor impairment during aneurysm clipping.
Direct spinal cord stimulation with monopolar stimulator

· Somatosensory Evoked Potentials (SSEPs)

Monitor posterior column sensory function (not motor)
Stimulate: peripheral nerve (median n., posterior tibial n.)

· Square wave, 300μsec, 25-30mA max, 5.3Hz.

Record EEG: Erbs (N9) > N11 cervical > N13/P13 medulla > N19/P22 thalamocortical (sensory cortex).
Variables for latency, duration: age, sex, limb length, temp, BP
Reversal of SSEPs with cortical strip used to identify central sulcus and motor and sensory cortex (see above)
Dorsal median sulcus can be mapped with elicited SSEPs
“The preservation of SEPs encourages us to proceed with aggressive intervention, but observation of SEP loss is of little value” Brotchi J N5/02

· Brainstem auditory evoked responses (BAERS):

Used for surgery near CN8 (eg acoustic neuromas)
I° cochlear n. > II° cochlear nuc > III° Superior olive > IV° lateral lemniscus > V° Inf. Colliculus > VI° MGB > VII° Cortex
Intraoperative: microphone placed in ear, electrodes on scalp

Magnetoencephalography (MEG)

· Used in preop evaluation of epilepsy

· Used for pre-surgical mapping of visual, auditory, somatosensory, and motor cortex functional areas.

· MEG Systems: Elekta Neuromag

Neuroendovascular Procedures and Devices

· Embolization: Coils, Liquid embolic agents

· Coils

o Guglielmi Detachable Coil (GDC): Platinum microcoils. Used since the early 1990s. For aneurysms, supplanted balloons, pushable coils, and liquid embolic agents. (Boston Scientific)

o Matrix Detachable Coils (Boston Scientific): coated with bioactive polymer (polyglycolic/polylactic acid)

o Micrus ACT Microcoil

o Hydrogel-coated coils: MicroVention HydroCoil Embolic System

o Ev3: AXIUM, Nexus, NXT

o TruFill (Cordis

)

· Liquid Embolic Agents

o Onyx: ethylene vinyl copolymer (ev3)

o NBCA: n-Butyl Cyanoacrylate, ex. TruFill (Cordis)

· Embolic/Ischemic complications

o Due to vessel wall injury and thrombosis on catheters, coils, etc.

o See Qureshi AI N6/00.