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The successful resection of a supratentorial glioma without further increase in the pre-existing neurological deficit of the patient is among the most difficult of all neurosurgical exercises. Significant palliation with good functional recovery cannot be achieved on a routine basis unless the surgeon undertakes such procedures with the same seriousness of purpose and attention to detail more commonly lavished upon less frequent disorders. It is my belief that optimal results are achieved when maximal resection of the tumor has been combined with minimal disturbance of the surrounding brain. Careful preoperative planning, scrupulous surgical technique, and the selective use of such aids as the operating microscope and the carbon dioxide laser all play a role in the gentle removal of the tumor and the fastidious preservation of adjacent nervous tissue. It is now possible to safely remove large glial tumors from virtually any hemispheric location without significant impairment of the patient. Radical removal accomplishes several goals for the oncologist-surgeon: (1) adequate sampling of the tissue for histopathologic study and diagnosis; (2) maximal mechanical cytoreduction of the tumor mass prior to the institution of other forms of therapy; (3) immediate relief from elevated ICP, permitting adequate exposure of the patient to other treatments; and (4) the removal of cells known to be insensitive to other treatment modalities. Because the length of survival of patients with gliomas can be correlated with the extent of the surgical resection, it is common policy to offer radical removal to all patients in whom an acceptable level of function can be predicted. As with other operations, the number of such patients tends to increase as the skill, experience, and judgment of the surgeon grow. Nevertheless, there remain some patients for whom a radical resection is an inappropriate procedure, and reasonable alternatives are considered.

Preoperative planning begins with a careful review of the neurological findings, the functional status of the patient, and the relevant features of the enhanced CT or magnetic resonance imaging (MRI) scans. The general condition of the patient, the presence or absence of specific neurological deficits, the prospects for useful recovery, and the precise location of the lesion all have considerable bearing upon the selection of a specific operative approach. For example, a tumor located close to a cortical surface is generally attacked through that surface if the associated cortical function is already lost and the prospect for its recovery is small, or if the potential loss of function (e.g., quadrantanopsia or weakness restricted to the distal leg) is considered justified by both patient and physician in view of the potential gains of the procedure.

Once the general approach has been chosen, rational design of an appropriate scalp incision and bone flap may proceed; it is highly preferable for these matters to be decided prior to the day of surgery, The surgeon should measure the maximum extent of the lesion in the vertical, transverse, and rostrocaudal directions as it appears on the enhanced CT or MRI scans, remembering to use the appropriate conversion factor to obtain the true physical dimensions in centimetres; the resection cavity obtained at the end of the operation must also be measured and should not exceed in any direction the preoperative radiographic estimates.

It is important for the surgeon to develop the capacity of forming a mental image of the three-dimensional extent of the lesion in such a way as to be capable of visualizing the spatial relationships of the lesion to the anatomic structures that surround it. It is especially critical for the surgeon, in both planning and conducting the resection of a supratentorial glioma, to be able to perceive the location of the tumor vis-a-vis the motor strip, the thalamus, the basal ganglia, the lateral ventricle, the angular gyrus, the superior temporal lobe, the tentorial incisura, the falx, the pterion, the coronal suture, and the external ear. In forming this three-dimensional concept of the tumor and its surrounding structures, the surgeon relies most on the preoperative enhanced CT and MRI scans, and a knowledge of normal anatomy. An arteriogram is usually not necessary in the preoperative evaluation of a patient with a supratentorial glioma, but if it is available, the relationship of the tumor to the superficial cortical veins is useful information. The cortical veins are sometimes visible by magnetic resonance angiography (MRV), and the relationship of the tumor to the motor strip can be judged on the preoperative MRI views. The surgeon should have all such information in mind when the operation begins, to facilitate an extensive but safe tumor resection. It is all too easy for the unprepared surgeon to become lost within the substance of the brain and to wander inadvertently into areas that preclude the successful recovery of the patient.

A few words are in order concerning the premedication of the patient. All glioma patients are put on glucocorticosteroids and prophylactic anticonvulsants. Because transcortical approaches are required in virtually all glial tumors, it is vitally important to minimize the amount of postoperative somnolence, brain swelling, and seizure activity. A minimum of 2 to 3 days of dexamethasone (4 to 10 mg every 4 to 6 h) or an equivalent dose of methylprednisolone is required to adequately prepare the brain for surgery. Aggressive use of corticosteroids and good neuroanesthesia can avoid unnecessary intraoperative administration of mannitol or ethacrinic acid. Several days should also be allowed for preoperative loading of anticonvulsants; sodium phenytoin is the preferred drug because it does not cause central nervous system (CNS) depression at therapeutic levels and because it can be given intravenously during the operation. Patients who have not received adequate amounts of anticonvulsants may suffer a seizure during emergence from anaesthesia, and the associated motor activity and systemic hypertension pose serious threats to haemostasis and relaxation at the operative site. Many postoperative problems can be avoided by careful preoperative planning and close communication between the surgeon and the neuroanesthesiologist.

All patients are operated on under general anaesthesia. Airway management and intubation must be smooth so as not to produce elevations in the ICP or sudden bleeding within the tumor. Proper positioning of the patient is essential in producing a relaxed brain and a relaxed surgeon. The major axis of the tumor should lie in a plane parallel to the floor of the operating theatre. The head of the patient is slightly elevated above the level of the chest to promote venous drainage; for similar reasons, extreme rotation of the neck is avoided, as is extreme forward flexion. The majority of glial tumors can be operated on in the supine position and in an ordinary headrest; this is especially the case for many frontal and temporal and some parietal lesions. When the major axis of the tumor requires that the patient be placed in a full lateral, three-quarter prone, or semi sitting position, secure fixation in head pins is always employed; this situation is frequently encountered with high parietal, posterior temporal, true occipital, parapineal, and para­midline tumors. The line of incision is always marked, even for reoperations, because the combination of an iodine preparation and a plastic drape will usually obscure the old incision scar as well as all superficial landmarks. A prophylactic antibiotic should be administered just prior to making the incision.

In general, operations for tumor require much larger cranioto­mies than procedures carried out in similar locations for cerebrovascular, infective, or traumatic diseases. Retraction can be quite difficult during tumor surgery, and some provision must be made for swollen brain. In addition, the exposure must be large enough and versatile enough to permit a change in either the angle of attack or the general nature of the procedure (e.g., intratumoral resection as opposed to lobectomy). In other words, although radical intratumoral resection is sufficient in most cases, the incision is planned as if a major lobectomy might have to be carried out. For frontal lobe tumors, the incision must give access to the frontal pole, the pterion, the orbital plate, the sphenoid wing, and the mid­line. Anterior temporal lobe tumors are best approached through a question mark-shaped incision that begins on the zygoma, just anterior to the ear, and curves forward above the superior temporal line until it meets the external orbital angle. Incisions close to the ear spare the main trunk of the superficial temporal artery and the superior branch of the facial nerve. Posterior temporal lobe and inferior parietal lobe lesions require a formal temporal craniotomy, either through a reverse question mark- or through a horseshoe-shaped incision. The posterior limb of the incision comes down at or just behind the interaural line and should not reach the asterion. The latter is however, the most anterior and inferior point of large occipital horse­shoe flaps, the mesial limb of which may reach the posterior mid­line. Parietal flaps are almost always made as horseshoe incisions, the apex just touching or crossing the sagittal suture; the base of the flap is at the level of the superior temporal line. All the standard incisions are planned in such a way as to provide access to important anatomic landmarks with preservation of the superficial blood supply as it enters the flap from the inferior margin. Fresh incisions are infiltrated with a mixture of lidocaine and epinephrine to prevent blood loss and undue traumatization of the scalp from clips and cauterization. Because glioma patients are likely to be subjected to radiation, reoperation, and chemotherapy, every attempt must be made to handle all tissue layers with the utmost gentleness. The plastic barrier drape will usually serve to keep the skin towels in place; if it does not, the towels should be sewn and not clipped to the skin. If the incision is made in short segments with firm finger pressure on either side, the use of clips and epinephrine should keep blood loss at a minimum. It is a common error for the surgeon to progressively reduce the exposure by placing the burr holes well within the margins of the scalp incision and making the dural opening much smaller than the bone flap; this tendency must be avoided at all costs, because it defeats the purpose of designing a generous scalp flap in the first place. Prior to placement of the burr holes, the scalp margins should be retracted to take maximum advantage of the skin opening. Saw cuts are made at the outer margin of each burr hole to include the entire burr hole within the boundaries of the bone flap. During these manoeuvres, tears in the dura must be avoided, because they may lead to strangulation of the brain as it herniates through the laceration. When mannitol is to be used, it should be given as a continuous drip of the 20 percent solution and not as a bolus; the infusion is usually begun with the first burr hole and continued until a total dose of 0.5 to 1.0 mg/kg body weight has been achieved. Osteoplastic bone flaps are preferable in patients likely to be exposed to devitalizing adjuvant treatments, because the bone is hinged on its own blood supply; but free flaps are quicker and are the sole option for parietal lesions. When control of the midline is required and the sagittal sinus must be crossed, burr holes should be placed on either side of the sinus; unilateral parietal flaps require only four holes and are rectangular in shape. Temporal and frontal flaps must sit low enough to expose the skull base, and extra burr holes may be required to cross the coronal and squamosal sutures. It is always useful to place burr holes directly over the pterion and on the external orbital process (the "key­hole"), to achieve control of the sphenoid wing and orbital plate, respectively. The first point of danger is reached with the dural opening. If the dura feels tight, the head should be elevated and the neck checked for undue rotation. If these manoeuvres are unsuccessful, hyperventilation may have to be increased and mannitol administered. The dura is opened rapidly to prevent strangulation of the brain in a small incision, and a decision is made as to whether the herniating tissue must be resected. If the dura is slack, it is recommended that it be opened in the following manner. The dural incision is planned to take maximal advantage of the bony opening, and the base of the dural flap is placed in the direction of the structures to be protected. In a frontoparietal exposure, for example, the apex of the incision points forward and the limbs are drawn backward toward the unexposed motor cortex; in a parietal exposure, the base is toward the sagittal sinus; and so forth. A dural stitch is first placed in the longest side of the intended incision, and a no.11 blade is used to just nick the dura; the knife is employed with its cutting edge up, so that inadvertent laceration of the cortex is nearly impossible, and narrow cottonoid strips (4-in. width) are immediately inserted to depress the brain from the dura. Advancement of the strip under the dura is much easier if it is floated by intermittent irrigation from a miniature irrigating bulb. The rest of the dura is then opened with small Metzenbaum scissors reserved only for this purpose. Once adequate control of the midline, the temporal fossa, the orbital plate, and other anatomic landmarks has been obtained, the further and unnecessary exposure of cortex not pertinent to the procedure should be avoided.

The general location of the cortical incision is chosen prior to the design of the scalp incision and the bone flap. Tumors located superficially in the hemisphere are usually approached directly through the overlying cortex, and those deep in the hemisphere are often reached through a paramedian approach. At all times, the approximate location of the motor strip and all language areas must be known. A useful rule is to draw a line from the pterion to a point 2 in. behind the coronal suture in the midline and at a 45-degree angle to the orbital plate; the motor strip can be expected to lie along this line, and Broca's area just posterior to it in the inferior frontal gyrus. The dominant angular gyrus is usually located just above the ear. When the cortical incision must be made in the vicinity of the motor strip, it should be drawn at an acute angle to the 45-degree line, cutting across the motor homunculus at a single point; the incision should always be drawn toward the motor strip and never along its long axis. The approximate location of the motor strip can also be determined through use of the Taylor-Haughton lines and by noticing that the initial segment of the middle meningeal artery at the pterion usually points in the direction of the 45-degree line. It is useful to keep eloquent cortex covered by a large cottonoid throughout the operation and to run the free edge of the cottonoid along the long axis of the motor strip.

The average length of the cortical incision is 2 to 3 cm, and it is made with the aid of a two-point suction cautery; such as the Scarff modification of the original Greenwood bipolar forceps. The instrument combines the advantages of restricted bipolar coagulation with suction at the tips of a bayonet forceps that also can be used for grasping; as a consequence, the other hand is free to hold another bayonet forceps or a microdissector or microscissors. Although the initial subpial incision for lobectomies is made with the unaided eye, it is preferable to use the operating microscope in making the small cortical incisions required for deep hemispheric work in critical areas. The suction of the two-point cautery is pinched off and the cautery used to paint the incision on the pial surface; the incision is opened with the no.11 blade and large microscissors. The incision is deepened by spreading with the two-point forceps; no cortical plug is resected. Tapered Sugita blades are attached to a Leyla self-retaining retractor, and the lips of the cortical incision are gently spread apart; the blades are always oriented parallel to the long axis of the incision, because a transverse orientation tends to cut into the brain and produce subpial hemorrhage. At this point, use of the operating microscope is absolutely essential, because a 5- to 8-cm tumor cannot be gently and safely removed through a 2-cm incision without it. The length of the cortical tunnel can be shortened by using the microscope to make an approach through a sulcus, a fissure, or the crown of a gyrus.

The improved illumination provided by the microscope readily permits exploration of a large space through a narrow aperture and facilitates the delineation of edematous white matter from either a low-grade glioma or the peripheral fringe of a glioblastoma. Resection of the tumor must be restricted to those areas of tissue that are clearly abnormal by virtue of their altered consistency, texture, or colour. Most soft tumors can be resected with just the large two­point suction cautery, a large microscissors for cutting coagulated blood vessels, and a large microFreer dissector for establishing planes. Firm areas in fresh oligodendrogliomas, calcified astrocytomas, or previously irradiated glioblastomas are best handled with the carbon dioxide laser. With the two-point suction cautery in one hand and the micromanipulator of the laser in the other, it is possible to gently and efficiently remove large tumors with a minimum loss of blood. Small vessels are coagulated by the laser and large ones by the two-point suction cautery; the laser can be used to transect coagulated vessels as well as to vaporize the tumor on the edges of the resection field. When the low-power laser is used at 30 watts, the suction of the two-point cautery is sufficiently strong to keep the microsurgical field clear of smoke. As soon as edematous white matter is reached, fluid can be seen to glisten under the illumination of the microscope, and in some areas, actual weeping of the tissue will be observed. Throughout the resection, the size of the cavity should be measured along its major axes and these measurements compared with radiographic determinations made by CT or MRI; it goes without saying that both the actual scans and the measurements should be immediately available on the viewer of the operating theatre.

At the conclusion of the resection, scrupulous haemostasis must be obtained through patient irrigation of the field and liberal use of the two-point suction cautery. The return from the irrigating fluid should be crystal clear prior to the use of oxidized cellulose or microfibrillary collagen to line the walls of the cavity. The oxidized cellulose should be laid down in thin wisps so as not to decrease the size of the resection cavity; because gelatine sponge swells and because it does not provide as satisfactory a surface for platelet adhesion, it is better to avoid leaving it in tumor resection beds. When the self-retaining retractor blades are removed, the two edges of the cortical incision should just come to rest against each other without any obvious holes or bruises in the cortical surface. The dura is always closed in a watertight fashion, and the bone flap is secured with heavy silk sutures. The scalp is closed in layers, with a closed drainage system inserted into the subgaleal space. Perioperative antibiotic coverage, as well as soaking the bone flap in an iodine solution during the operation and using iodine irrigation liberally after the dura is closed are routine measures.

When radical intratumoral resection is not feasible, normal brain may have to be sacrificed in order to achieve decompression; under these unfortunate circumstances, frontal lobectomy becomes the procedure of choice. Lobectomies are always carried out as subpial resections in which the pial envelope is circumferentially incised at the point of amputation and every attempt is made to avoid repeated violation of the pial surface at other points. The frontal lobe is removed along a 45-degree plane with its base at the edge of the sphenoid wing and its superior edge more posteriorly placed along the upper surface of the lobe. In this fashion it is possible to avoid entering the frontal horn and endangering either the thalamus or the basal ganglia. Since the main trunk of the anterior cerebral artery winds tightly around the rostrum of the corpus callosum, this structure is usually not visualized and all major frontal arteries may be sacrificed with impunity. Concerning the temporal lobe, it is always safer to carry out lobectomies in the anterior and inferior portions of the lobe. The inferior and middle temporal gyri, as well as those areas medially located along the edge of the tentorium, are always safe to remove. The dominant superior temporal gyrus should not be removed any farther posteriorly than 5 cm back from the temporal tip; remember that the temporal pole is hidden under the edge of the sphenoid wing and that the measurement must be made from there. It is sometimes easier to free the tentorial edge under the operating microscope, and every temporal lobectomy should conclude with removal of the most medial aspects of the temporal lobe, a manoeuvre that is sure to prevent most midnight surprises.

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Facts of life

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Introduction |Imaging | Astrocytomas | Glioblastoma Multiforme | Oligodendrogliomas | Ependymomas | Pilocytic Astrocytomas | Gangliogliomas | Mixed Gliomas | Other Astrocytomas | Surgical treatment | Stereotactic Biopsy | Gliadel Wafers |Results and complications | When to Reoperate? | Colloid cyst

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