Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona
OBJECTIVE: To demonstrate the usefulness of the contralateral transcallosal approach for resecting lesions located laterally in or adjacent to the lateral ventricle.
METHODS: Modifications to the standard ipsilateral transcallosal technique include positioning the head with the midline oriented horizontally, placing the side with the lesion up, and performing the craniotomy and interhemispheric dissection on the contralateral side. This approach avoids a transcortical incision, allows gravity to hold open the interhemispheric fissure, and increases the lateral exposure of the lesion. This approach was used in 32 patients with a variety of lesions, including 6 cavernous malformations, 7 arteriovenous malformations, and 19 tumors of various types. All but three lesions were located on the left side.
RESULTS: All six cavernous malformations, all four benign tumors, and four of the seven arteriovenous malformations were resected completely. Malignant tumors were resected subtotally, and three arteriovenous malformations required stereotactic radiosurgery to treat residual deep nidus. There was no surgical mortality. Two patients experienced neurological deterioration.
CONCLUSION: The contralateral transcallosal approach can be used to treat a variety of lesions safely and successfully.
(Neurosurgery 39:729735, 1996)
Key words: Arteriovenous malformations, Cavernous malformations, Contralateral, Surgical technique, Transcallosal approach, Tumor
Lesions located laterally in or adjacent to the lateral ventricle can be difficult to expose. Traditional approaches to such lesions are transcortical through the superior or middle temporal gyrus or the superior parietal lobule (13, 21, 28). Neurosurgeons choosing a transcallosal approach usually do so through an ipsilateral route with the patient supine, with the midline of the head oriented vertically, and dissecting through the ipsilateral interhemispheric fissure and ipsilateral ventricle to reach the lesion (1, 22, 23). The authors prefer a contralateral transcallosal approach, with the patient supine, with the midline of the head oriented horizontally with the lesion on the upside, and dissecting through the contralateral interhemispheric fissure and ipsilateral ventricle to reach the lesion (17). The contralateral transcallosal approach has many important advantages, compared to other routes (15). It avoids a transcortical incision, and gravity retracts the hemisphere to open the interhemispheric fissure. A more lateral angle of approach increases the surgical exposure and minimizes retraction on the medial hemisphere. Finally, dominant hemisphere lesions can be resected while sparing an interhemispheric dissection on that side. We performed our first contralateral transcallosal approach in 1983 (17). Since that initial case, we have used the approach in 32 patients, who are reported here. The technique is safe and effective and warrants consideration for appropriate lesions.
Three patients had choroidal AVMs, two had thalamic AVMs, and two had pericallosal AVMs that extended into the ventricle. The choroidal AVMs were all small lesions with deep venous drainage (Spetzler-Martin Grade II) (Fig. 2). The pericallosal AVMs were both medium-size lesions with deep venous drainage (Spetzler-Martin Grade III). The thalamic AVMs were Grades III (small) and IV (medium). All seven AVMs were on the left side.
The AVMs tended to hemorrhage into the ventricle, with intraventricular blood and hydrocephalus evident on computed tomographic scans. Overall, the hemorrhages did not cause significant neurological deficits unless the AVMs were in the thalamus. Only the patient with the Grade IV thalamic lesion presented with neurological findings.
Four tumors appeared to arise from the lateral ventricular wall near the atrium, three were in the atrium, and one was in the choroid plexus. Two tumors were in the anterior thalamus, and one was in the caudate head. The two sellar tumors grew eccentrically to indent the left hypothalamus. Five tumors had their epicenter lateral in the corpus callosum and one in the cingulate gyrus. All but two tumors were located on the left side. The average tumor diameter was 3.4 cm.
The most common presentation was weakness in one leg, typically causing a clumsy gait, imbalance, and occasional collapse. Seven patients with these symptoms had tumors in the corpus callosum, parafalcine region, or lateral ventricular wall, and six of them had motor deficits and gait abnormalities as revealed by neurological examination. Three of these patients also described difficulties with memory. Six other patients presented with headaches; three were progressive, and three that were sudden and severe were caused by intraventricular hemorrhage. Hydrocephalus produced symptoms in three patients; one patient with a choroid plexus papilloma had symptoms of progressive hydrocephalus, and two patients with atrial tumors had episodes of trapping the temporal horn. Two patients presented with seizures, and the patient with the craniopharyngioma presented with symptoms from optic nerve compression.
The dura is opened contralateral to the lesion with a C-shaped flap based along the superior sagittal sinus, taking care to protect important bridging veins. The dural flap is tented superiorly to open the interhemispheric fissure, which is opened further under the operating microscope, working between the bridging veins. Every effort is made to preserve the bridging veins. The arachnoid membrane deep to the free edge of the falx is opened to expose the pericallosal arteries and corpus callosum.
Gravity allows the contralateral hemisphere to separate from the falx, eliminating the need for retraction (Fig. 4C). A retractor is placed along the inferior free edge of the falx to expose the pericallosal arteries and corpus callosum. Care must be taken not to retract aggressively on the superior falx, which may stenose or occlude the superior sagittal sinus, thereby promoting sinus thrombosis and venous infarction (6, 27). The pericallosal arteries are separated, and the corpus callosum is incised 2 cm to permit entry to the lateral ventricle ipsilateral to the lesion (Fig. 4D). The incision site can be identified with an intraoperative navigational system, such as the ISG Viewing Wand (ISG Technologies, Inc., Mississauga, Ontario) or by retracting the ipsilateral pericallosal artery laterally and entering the ventricle beneath the artery's normal location. Once inside the ventricle, normal ventricular anatomy is identified (including choroid plexus, thalamostriate vein, and septal vein), and the proper ventricle is confirmed. The lesion is then identified and treated. Further exposure can be obtained by deepening the retractor so that its tip is in the ventricle retracting the corpus callosum.
At the end of the procedure, the ventricles are irrigated extensively and filled with saline. If a ventriculostomy catheter has not already been inserted preoperatively, one is left in the ventricle at the end of the operation to clear residual blood that could obstruct the flow of cerebrospinal fluid.
This approach is also used for lesions located laterally in the corpus callosum and cingulate gyrus. The corpus callosum may not be traversed, but the same advantages of the contralateral approach apply to these lesions. With these more superficial lesions, the falx often is cut inferiorly after the inferior sagittal sinus has been coagulated to enable a sharper angle across to the opposite side.
All six of the cavernous malformations were resected completely in a single surgical stage. Five AVMs were resected in a single stage, and two required a second stage. The three choroidal AVMs were resected completely and required no adjunctive therapy. The two thalamic AVMs were resected incompletely and required stereotactic radiosurgery to the deep residual nidus. One patient with pericallosal AVMs refused his second surgical stage and instead was treated with stereotactic radiosurgery. Two years later, angiography demonstrated that the AVMs were completely obliterated.
The four benign tumors (i.e., meningioma, choroid plexus papilloma, and prolactinoma) were resected completely through the contralateral transcallosal approach. The prolactinoma was first approached transphenoidally to remove the sellar component, and the remaining tumor was resected completely during the second transcallosal stage. Gross total resection was attempted with the low-grade astrocytomas and oligodendrogliomas. The anaplastic astrocytomas, glioblastomas multiforme, and central neurocytomas were resected subtotally. Ten patients received adjunctive treatment, which consisted of external beam radiation in 10, chemotherapy in 4, and implanted iodine125 seeds in 1 patient.
Ventriculostomy catheters often were indicated preoperatively for hydrocephalus from intraventricular hemorrhage, trapped ventricular horns, or obstruction of the foramen of Monro. When not already present, ventricular catheters were inserted during the operation and left in place for several days. Only four patients required ventriculoperitoneal shunting.
There was no surgical mortality in this series. Two patients experienced transient neurological deficits. After resection of thalamic AVMs, the first patient developed a small thalamic infarction with right arm weakness, which resolved completely. After resection of a left atrial meningioma, the second patient developed left moderate hemiparesis, which resolved completely. A patient with an anaplastic astrocytoma developed a bone flap infection after treatment with stereotactic catheter implantation and iodine125 seeds and required a craniectomy, antibiotics, and replacement of the bone flap. Permanent neurological morbidity was encountered in two patients. One patient with central neurocytoma experienced postoperative intraventricular hemorrhage that required multiple ventriculostomies. He subsequently developed a Serratia ventriculitis. The other patient developed a venous infarction after resection of a left glioblastoma multiforme, with resultant right hemiparesis and expressive aphasia.
At last examination, patient outcome in terms of Glasgow Outcome Score (GOS) (10) was determined over a mean follow-up of 1.6 years. Twenty-six patients had good recoveries (GOS 1), four patients had moderate disabilities (GOS 2), and two had severe disabilities (GOS 3).
Two approaches available for exposing ventricular lesions are the transcortical-transventricular approach (4) and the transcallosal-transventricular approach (3, 12, 16). Although the transcortical approach is more direct, with a shorter working distance to the lesion, it has distinct disadvantages. First, transcortical approaches traverse normal brain, increasing the risk of neurological deficits. Various trajectories through cortex have been described (i.e., through the superior and middle temporal gyri and through the inferior [Van Wagenen] and superior parietal lobules), each associated with neurological sequelae (21). Second, transcortical approaches are more difficult than the transcallosal approach, because fewer anatomic landmarks are present to guide the surgeon transcortically to the ventricle. The approach is particularly difficult when the ventricles are not dilated. The exposure tends to be limited because of the surgeon's inclination to minimize the cortical incision. Last, the transcortical approach can produce postoperative seizures (11, 22).
The limitations of the transcortical approach led to the development of the transcallosal approach by Dandy (3), Milhoratand Baldwin (16), Shucart and Stein (22), and Stein (23). The transcallosal approach does not traverse cortex, going through the interhemispheric fissure and corpus callosum instead. This route has identifiable anatomic landmarks to guide the surgeon to the ventricle (30), and enlarged ventricles are not a necessity. The third ventricle can be exposed simply by enlarging the foramen of Monro, a maneuver not easily accomplished through a more oblique transcortical approach. Most importantly, many studies have demonstrated that the transcallosal approach is well tolerated and produces no functional neurological deficits or postoperative seizures (2, 7, 9, 1820, 29).
Most neurosurgeons position their patients supine or sitting with the head and neck in neutral position and the sagittal midline oriented vertically (1, 22, 23). We prefer to rotate the neck laterally to orient the midline horizontally. This horizontal position is easier on the surgeon's hands, allowing them to work in the same plane rather than one above the other. The surgeon can use an instrument in each hand without obscuring the operative field. This position also permits gravity to retract the downside hemisphere and open the interhemispheric fissure while the falx retracts the upside hemisphere. The advantages of this position are becoming increasingly recognized (8, 25, 26).
The horizontal position necessitates a decision regarding laterality. In most cases, the head is positioned with the lesion side down (i.e., right-sided lesions are approached with the right side down and left-sided lesions with the left side down). This position works well for lesions located close to the midline. However, exposure of laterally placed lesions in or adjacent to the lateral ventricle requires significant retraction of the hemisphere and risks injury to the parafalcine and cingulate gyri. The contralateral transcallosal approach offers a better angle of approach that increases lateral exposure of the lesion and minimizes the retraction required on the medial hemisphere. In addition to opening the interhemispheric fissure to facilitate the approach, gravity pulls the upside lesion medially into the surgeon's view. Without this angle of approach, the lateral margin of the lesion can be reached only with excessive retraction. The contralateral transcallosal approach is ideal for left-sided lesions. Although added lateral exposure is gained regardless of the side of approach, the approach to a left-sided lesion from the right spares the dominant hemisphere from retraction injury and potential sacrifice of bridging veins and is, therefore, safer than the approach to a right-sided lesion from the left. Thus, the contralateral transcallosal approach from the left is used judiciously when the need for more lateral exposure offsets these added risks of a left interhemispheric dissection.
Received, February 14, 1996.
Accepted, April 26, 1996.
Correspondence: Robert F. Spetzler, M.D., Neuroscience Publications, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, AZ 85013-4496.
Bennett M. Stein
New York, New York
The authors demonstrate the value of the contralateral transcallosal approach. As described, the approach is best performed with the midline oriented horizontally with the side of the lesion uppermost and the craniotomy and intrahemispheric dissection on the contralateral or downside. A major advantage of the approach is in dealing with lesions in the ventricle of the dominant hemisphere. In this situation, the intrahemispheric dissection is directed along the right side of the falx rather than along the medial surface of the dominant left hemisphere. The authors have extended the exposure from the lateral to the third ventricle by opening the choroidal fissure, the cleft between the fornix and thalamus, along which the choroid plexus is attached. The choroid plexus is attached by two arachnoid-like extensions of ependyma on the thalamic and forniceal site of the choroidal fissure. We have found that it is better to open the choroidal fissure by dividing the tenia fornix, which is the filmy attachment of the choroid plexus, to the edge of the fornix. Opening the fissure on the thalamic side, between the choroid plexus and thalamus, risks damaging the large veins, such as the thalamostriate vein, which drain the part of the hemisphere lateral to the ventricle. Dividing the tenia fornix avoids the risk of damaging the large veins that drain the internal capsule and other deep areas lateral to the wall of the lateral ventricle. After opening the choroidal fissure, which is similar to opening thin arachnoidal adhesions, the approach can be directed through the velum interpositum between the internal cerebral veins into the upper part of the third ventricle. The opening along the choroidal fissure can be extended into the foramen of Monro, thus avoiding the need to incise part of the fornix to gain adequate exposure. The authors have demonstrated that this approach provides satisfactory exposure of lesions as far posteriorly as the atrium. We agree that this approach deserves wider usage and has significant advantages over the ipsilateral transcallosal approach for selected lesions.
Albert L. Rhoton, Jr.
Although approaching the lateral ventricle through the contralateral interhemispheric fissure may not be a novel operative approach, the authors succeed in describing an operative technique with great clarity and persuasion. However, there may be some limitations. For example, if the lesion is not situated in the direct line of vision, more retraction against the falx and against the upside lip of the incised corpus callosum, and therefore against the contralateral anterior cerebral artery, may become necessary. I suspect further that any lesion with a medial extension toward the foramen of Monro, choroid fissure, and thalamus may not be readily accessible or removable. One should also not forget that what might seem to be an easy and simple technique for a master may prove cumbersome for those who are less experienced. With this in mind, I suggest the stereotactic transcortical approach. This approach has been associated with very gratifying results in our practice, as well as in the hands of other surgeons (1). With the transsulcal approach, the depth of the traversed frontal lobe substance is minimal and the danger of causing seizures or producing a neurological deficit is especially minimal.
The authors describe their extensive experience with the contralateral interhemispheric transcallosal approach to lesions located in and around the lateral ventricle. In these predominantly left brain lesions, they point out that it is better to retract the right hemisphere than the left, although, clearly, this approach puts both sides of the brain at risk. One wonders if extensive retraction on the contralateral side with the risk of interrupting venous drainage is advisable when there has already been injury to one side of the brain by a lesion such as an invasive tumor or hemorrhage from a vascular malformation. Although the authors point out potential advantages in terms of providing a direct approach to various specific lesions, readers should be cautioned about the inherent risks to this approach.
William F. Chandler
Ann Arbor, Michigan
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