Departments of Neurosurgery (DLB) and Radiology (Neuroradiology) (RD), Emory University School of Medicine, Atlanta, Georgia Neurosurgery 35; 1046-1054, 1994 ABSTRACT: THE RESULTS IN the surgical management of 26 patients with arteriovenous malformations intimately related to the trigone of the lateral ventricle are presented. Three operative approaches were used in the series, including a transtemporal route through the inferior or middle temporal gyrus (15 patients), an interhemispheric approach (8 patients), and a transcortical parietooccipital approach (3 patients). The surgical approach was chosen on the basis of the relationship of the arteriovenous malformation to the trigone, the presence and location of associated hematoma, and preoperative neurological deficits. This report emphasizes the use of surgical adjuncts that are instrumental in the management of these challenging lesions, including magnetic resonance imaging for precise localization and operative planning, preoperative embolization to obliterate deep arterial supply, and intraoperative ultrasound and angiography to aid in localization and to document complete excision of the arteriovenous malformation before closure. The results of the management of these 26 patients are as follows: 21 had no or minor neurological deficits and were able to resume premorbid activities; 2 had a fair result, being independent but unable to resume their premorbid occupation; 2 had a poor result and were dependent as the result of an incapacitating neurological deficit; and 1 died. KEY WORDS: Arteriovenous malformation; Embolization; Surgery; Ventricles Arteriovenous malformations (AVMs) of the trigone or atrium of the lateral ventricle represent a distinct subset of vascular malformations. These lesions are associated with unique challenges for the neurosurgeon. Factors that contribute to the surgical difficulties of these lesions include: 1) the invariable location of the AVM within eloquent or functionally important brain tissue; 2) the lack of cortical representation of the AVM that requires retraction or traversing of important brain tissue (2); 3) a deep and often obscure arterial supply (12); 4) deep venous drainage; 5) the juxtaposition to the choroid plexus with which arterial supply and venous drainage are shared, adding to the bulk of the lesion (2,12); and 6) the necessity for tangential surgical approaches to the PATIENTS AND METHODS Epidemiology This series of 26 patients with AVMs in the region of the ventricular trigone includes 14 female and 12 male patients, ranging in age from 13 to 66 years (average, 31 yr). Twenty patients experienced at least one hemorrhage from their AVM before treatment, 6 of whom had multiple hemorrhages. The other six patients presented with a seizure disorder. Twelve patients had a homonymous hemianopia preoperatively as a result of hemorrhage, and 5 others had a preoperative quadrantanopsia. Eight patients had a significant hemiparesis, and five had some degree of speech disturbance at the time of treatment. Three patients had undergone previous attempts at surgical resection of their AVMs at other institutions, two having had two operations each (Fig. 1). The patient who underwent one unsuccessful attempt at surgical removal also had undergone proton beam radiosurgery. All three of these patients experienced rebleeding after their most recent surgical or radiosurgical procedures. Preoperative management Seven patients required a ventriculostomy with external ventricular drainage for emergency management of hydrocephalus, and two patients required permanent ventricular shunting. All patients underwent preoperative CT scanning and cerebral angiography. Twenty-five patients had an MRI scan before surgery, and one patient was unable to undergo MRI because of the presence of a surgical Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 AUTHOR(S): Barrow, Daniel L., M.D.; Dawson, Robert, M.D. malformation rather than safer and more standard perpendicular approaches (12). Although AVMs of the trigone represent a small subgroup of all intracranial AVMs, the aforementioned difficulties have spawned a variety of operative approaches in their surgical management. Various authors have described operative approaches based upon the following: arteriographic factors, the findings on computed tomography (CT), the presence or absence of preoperative neurological deficits, the precise relationship of the AVM to the trigone, and the experience with neoplasms in a similar location (2-5, 10,12-18) . We report our experience during the last 6 years with the surgical and endovascular management of 26 AVMs of the ventricular trigone. Although many large cortical AVMs extend to the ventricular system, this series includes only those AVMs immediately adjacent to the trigone, without any cortical exposure. All these patients underwent complete surgical removal of their lesions. This report emphasizes adjunctive modalities that were instrumental in the management of these difficult cases, including magnetic resonance imaging (MRI) for precise localization and operative planning, preoperative embolization to assist in obliterating a portion of the deep arterial supply, and intraoperative ultrasound and angiography to aid in intraoperative localization and to document complete excision before closure. Caveats gleaned from our management complications are also detailed. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Neurosurgery 1992-98 December 1994, Volume 35, Number 6 1046 Surgical Management of Arteriovenous Malformations in the Region of the Ventricular Trigone Clinical Study Characteristics of the arteriovenous malformations Sixteen AVMs were in the dominant hemisphere, and 10 were in the nondominant hemisphere. The size of the AVM nidus ranged from less than 1 to 6 cm. One AVM was angiographically occult. With the grading system of Spetzler and Martin (11), there were 13 grade III and 13 grade IV lesions. The primary arterial supply to the AVMs was through the cortical branches of the posterior cerebral artery. Eighteen malformations received contributions from the posterior choroidal arteries. Seven had significant contributions from the anterior choroidal arteries, and the middle cerebral artery was involved in six. Other arteries contributing to some of the AVMs included the pericallosal, the lenticulostriates, and the thalamoperforators. Four patients had aneurysms located on feeding arteries to the AVM. All but two AVMs had deep venous drainage into the galenic system, six of which also had a small component of superficial drainage. Based upon MRI (CT in one patient without an MRI scan), the relationship of the AVM to the trigone was lateral in 13 patients, medial in 8 patients, and both medial and lateral in 5 patients. Temporal approaches Fifteen of the 26 patients underwent resection of the AVM through a transtemporal approach. Eight of these lesions were in the dominant hemisphere, and seven were in the nondominant hemisphere. One patient (Patient 13) was found to have an unexpected right dominant brain, which was discovered after he developed a transient postoperative speech deficit. After induction of anesthesia, the patients were placed in the supine position with the ipsilateral shoulder elevated and the head parallel to the floor with the vertex angled slightly downward. The head was held in place with a radiolucent head holder. A horseshoe-shaped incision was based on the auricle of the ear. Four burr holes were placed to form a posterior temporal craniotomy carried down to the floor of the middle fossa. After placing tack-up dural sutures and opening the dura, the trigone of the ventricle, the AVM, and associated hematoma were identified with intraoperative ultrasound. A horizontal cortical incision, measuring 1 to 2 cm, was made in the inferior temporal gyrus on the dominant hemisphere and in the middle or inferior temporal gyrus in the nondominant hemisphere. The precise location of the cortical incision was planned to provide the most direct access to the trigone and any hematoma cavity associated with the AVM and to protect the vein of Labbé. Under relatively low microscopic magnification, the cortical dissection was continued with a small suction and bipolar coagulation to the trigone. A self-retaining retractor was used to maintain just enough retraction to allow a portal for the suction and bipolar coagulation. The approach was directed slightly superiorly and posteriorly. Once the trigone was exposed, the egress of cerebrospinal fluid created further brain relaxation and minimized retraction. The arterial supply within the choroidal fissure was visualized and secured first with bipolar coagulation or small clips. The temporal approach to trigonal AVMs was used for those lesions that involved the lateral wall of the ventricular trigone. The primary advantage of this approach is the short distance through the inferior temporal lobe to the trigone. A small horizontal cortical incision parallel to the optic radiations minimizes the risk of visual field deficits, although a superior quadrantanopsia is a common complication of this approach and is difficult to avoid. Preoperative embolization Theoretically, embolization is useful in decreasing the size of an AVM and curtailing blood flow to the lesion, obliterating deep feeding arteries that are difficult to access surgically, and gradually redistributing blood flow to the surrounding normal brain. Thirteen patients in this series underwent embolization before definitive surgical resection (Fig. 2). All embolizations were performed with microcatheters and real-time digital subtraction fluoroscopy. Superselective Wada tests were obtained in most feeding pedicles before embolization by injecting 35 mg of sodium amobarbital. A positive Wada test precluded embolization of that pedicle. All patients began receiving nimodipine, 60 mg every 4 hours, and 6 mg of dexamethasone every 6 hours before the procedure; the patients continued to receive these drugs until the time of surgery. Polyvinyl alcohol particles were employed as an embolic agent in these patients. In addition, small platinum microcoils were used to close a fistulous portion of one AVM. Postembolization, all patients were monitored in the neurosurgical intensive care unit for 12 hours. Surgical treatment Three different operative approaches were used to resect the AVMs in this series, including lateral Parasagittal interhemispheric approach Seven of the 26 patients underwent an interhemispheric approach to their AVMs. Six were in the dominant hemisphere, and two were in the nondominant hemisphere. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. temporal approaches through the middle or inferior temporal gyrus, an interhemispheric approach, and a direct transcortical approach through a parietooccipital incision (5). The selection of the operative approach was based upon the presence of preoperative neurological deficits, particularly visual field deficits, the presence of an intracerebral hematoma, and the relationship of the AVM to the trigone on the basis of angiography and MRI. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 clip placed at a previous operation. Thirteen patients underwent preoperative embolization to diminish blood flow in the AVM and to occlude deep feeders. All but one patient who presented with a hemorrhage underwent surgery after stabilization of their neurological condition, usually 3 to 4 weeks after the bleeding. One patient required emergency surgery for evacuation of a hematoma, with removal of his AVM 10 days later. Intraoperative angiography Twenty-one patients underwent intraoperative angiography to verify complete resection of the AVM (Fig. 3). Four of the five patients who did not undergo intraoperative angiography were managed before the availability of this technology at our institution. The fourth patient had an RESULTS The outcome for patients outlined in Table 1 was graded at the most recent follow-up, which ranged from 2 months to 5 years. "Excellent" was reserved for patients with no neurological deficit. "Good" was for patients with a mild neurological deficit (usually a visual field deficit) who were capable of engaging in their preoperative occupation and activities. "Fair" was a category of patients who were independent but unable to return to their premorbid activities because of a neurological deficit. A "poor" result was for patients who were incapacitated by a severe neurological deficit. There were 7 excellent, 14 good, 2 fair, 2 poor results, and 1 death. The fair and poor results and the one death occurred in patients with significant preoperative deficits from their initial hemorrhages. Of the 15 patients with a good result, 8 had a preoperative visual field deficit that remained postoperatively as the only neurological abnormality and 1 had a preoperative visual field deficit and mild hemiparesis that were unchanged by surgery. Three patients developed new or worsened visual field deficits after surgery, and one preoperative hemiparesis was mildly worsened after surgery. One patient with a good result developed a hemianopia after embolization, and another had a hemorrhage after embolization that resulted in a hemiparesis, which improved. Three patients experienced a complication of embolization. In two patients, the procedure was complicated by an intraventricular and parenchymal hemorrhage. Both of these patients initially presented with hemorrhages, one with three previous bleedings. The postembolization hemorrhage resulted in a hemiparesis in one patient and hemiparesis and dysphasia in the other. These deficits spontaneously improved. A third embolized patient developed a permanent hemianopia after occlusion of the calcarine branch of the posterior cerebral artery. Fortunately, each of these patients eventually was able to resume all premorbid activities. Nine patients developed new temporary or permanent neurological deficits related to surgery. In one patient, there was a mild superior quadrantanopsia that the patient was unaware of; there was one postoperative hemianopia that is improving at a 2-month follow-up; and in three Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Transcortical parieto-occipital approach Four patients underwent a direct transcortical approach to the malformation. This approach was used for lesions on the superior surface of the trigone of the ventricle or when the hematoma extended superiorly toward the parieto-occipital junction. This operation was performed in the manner described by Heros (5). The external landmark for the cortical incision was a point approximately 9 cm up from the inion and 1.5 to 2 cm lateral to the midline. The patients were placed in the semisitting position with the head slightly flexed and held in place with a radiolucent head-holder. Four burr holes were placed to create a parieto-occipital craniotomy centered on the external landmark outlined above and extending to the superior sagittal sinus. The dural opening was based on the sagittal sinus. Once the dura was opened, the point of cortical entry was located by measuring 7 cm up from the occipital tip along the convexity of the occipital lobe and 1.5 to 2 cm from the midline. A laterally oriented cortical incision approximately 2 cm in length was created, and the approach through the brain to the trigone was aimed at the ipsilateral pupil. This small transverse cortical incision is located between the parietal sensory association fibers and the occipital visual association fibers, which minimizes the risk of neurological injury (4,5,7,8). Intraoperative ultrasound was also used in locating the trigone, malformation, and associated hematoma to guide the approach. angiographically invisible AVM, and, therefore, intraoperative angiography was thought to be of no benefit. In 2 of the 21 patients who underwent intraoperative angiography, the study demonstrated residual AVM at a time when the malformation was thought to have been completely resected. This information allowed for the complete removal of the lesion before wound closure. In both instances when the intraoperative study demonstrated residual AVM, the patient had undergone two previous surgical procedures at other institutions in an attempt to remove the AVM. In all cases except the angiographically invisible AVM, postoperative angiography confirmed that all AVMs in this series were completely removed. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 The patients were placed in the lateral position or positioned with the ipsilateral shoulder elevated on a roll and the head turned parallel to the floor, with the side with the AVM down. A horseshoe-shaped incision was carried across the midline, and four burr holes were made to create a parasagittal craniotomy, based medially on the superior sagittal sinus. The small dural opening was based on the sagittal sinus. There are usually no draining veins from the occipital lobe to the sagittal sinus, which allowed for easy retraction of the occipital lobe from the falx. With the ipsilateral occipital lobe dependent, gravity permitted the brain to fall away, which minimized retraction. Depending upon the precise location of the malformation, either a superficial transcortical resection on the medial occipital lobe or opening of the parieto-occipital fissure provided access to the malformation and medial wall of the trigone. Feeding vessels were coagulated and divided, while larger feeding arteries were occluded with small aneurysm clips. The malformation was resected, and the venous drainage coagulated or clip ligated and divided. This approach was used primarily for AVMs that involved the medial wall of the trigone and/or the splenium of the corpus callosum. Commentary Patient 12 An 18-year-old woman presented with a seizure disorder. During her workup, she was discovered on MRI to have an AVM in the region of the ventricular trigone (Fig. 5A and B). Cerebral angiography revealed a 4.5-cm AVM with arterial supply from both the posterior and middle cerebral arteries (Fig. 5C-E). After careful review of our knowledge of the natural history of AVMs and the treatment options, preoperative embolization and surgery were advised. After embolization, the malformation was resected through a transcortical parieto-occipital approach. The AVM was completely removed (Fig. 5F-H); the patient has no neurological deficits and has remained seizure free for 3 years since surgery. DISCUSSION AVMs involving the region of the ventricular trigone are uncommon. They usually come to clinical attention after an intraventricular or parenchymal hemorrhage. A number of authors have emphasized the propensity of AVMs located in deep locations or near the ventricular system to bleed (2,3,10,13-17). This current series confirms the high incidence of hemorrhage from these lesions, occurring in 20 of the 26 patients, with multiple hemorrhages occurring in 6 patients. Despite the poor natural history of these AVMs, their surgical treatment is confounded by the lack of cortical representation, involvement of the choroid plexus, deep and obscure arterial feeders, deep venous drainage, intimate relationship to functionally important brain, and tangential operative approaches often required to expose these lesions. These difficulties may account for the relatively small number of trigonal AVMs reported to have been successfully managed by surgery (2-4,12-14). Several patients in the current series had AVMs considered previously to be inoperable, were referred for consideration for stereotactic radiosurgery, or had undergone previous unsuccessful attempts at treatment. The technical challenges presented by these AVMs and their variable relationship to the trigone have resulted in the development of various operative approaches, each with specific advantages and disadvantages. By utilizing a variety of modern adjuncts, these lesions can be surgically cured with a risk that is significantly less than the risks of the natural history. Preoperative embolization is useful in obliterating some of the deep feeding vessels and in gradually throttling the blood flow to the malformation in preparation for surgery. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. ILLUSTRATIVE CASES Patient 8 A 52-year-old man presented with an intraventricular hemorrhage associated with a right hemiparesis, right homonymous hemianopia, and dysphasia (Fig. 4A and B). Cerebral angiography demonstrated a 4.5-cm AVM in the region of the trigone of the left lateral ventricle that was fed predominantly by the anterior and posterior choroidal arteries and laterally directed branches of the posterior cerebral artery (Fig. 4C and D). Two weeks after his hemorrhage, the patient's hemiparesis and dysphasia had improved but the hemianopia persisted. He underwent a left temporal craniotomy and approach to the AVM through the inferior temporal gyrus. During the final stages of the procedure, an aneurysm clip was placed on a large, laterally directed feeding artery arising from the P2 segment of the posterior cerebral artery. Postoperatively, the patient developed a worsened hemiparesis and dysphasia that slowly improved but remained significantly worse than his preoperative status. Postoperative angiography demonstrated complete obliteration of the AVM but also showed occlusion of the posterior cerebral artery well proximal to the clip that had been applied to a posterior cerebral branch (Fig. 4E). A postoperative CT showed the area of infarction (Fig. 4F). We believe this patient's postoperative neurological deficit was the result of retrograde thrombosis of the posterior cerebral artery that involved perforators from the P1 segment. This was likely a result of acute interruption of the high-flow lesion with sludging of flow within the feeding artery. It is possible that this complication could have been avoided by preoperative embolization to more slowly throttle the blood flow to the AVM. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 patients, there was a transient hemiparesis and dysphasia that improved to the point the patient could resume all premorbid activities. One patient experienced dysosmia after surgery, and she ultimately recovered. One patient with a large, highflow AVM developed retrograde thrombosis of the posterior cerebral artery after surgery that resulted in a thalamic infarction and worsened hemiparesis and dysphasia. Although the dysphasia improved considerably, the patient remained disabled. A fair result occurred in a patient with an AVM anterior to the trigone, extending into the thalamus, who experienced worsening of her preoperative hemiparesis. The single death in this series occurred in a patient who presented with a large left temporal hematoma from a small AVM. Postoperatively, she developed transient worsening of her preoperative dysphasia but improved before discharge. Approximately 1 month after her surgery, the patient's husband brought her back to the hospital after 4 days of progressive lethargy, worsening hemiparesis, and aphasia. She was discovered to have a large abscess at the operative site. Despite operative removal and antibiotic treatment, she developed progressive mass effect, probably due to a venous infarction, and died. After follow-up ranging from 6 months to 6 years, four patients have neurological deficits that prevent them from engaging in their premorbid activities (fair or poor) and one patient is dead. Disabilities in two of the four patients and the one death are the result of treatment complications. Disabilities in the other two patients are sequelae from the hemorrhage alone. Received, March 23, 1994. Accepted, July 5, 1994. REFERENCES: (1-18) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Barrow DL, Boyer KL, Joseph GJ: Intraoperative angiography in the management of neurovascular disorders. Neurosurgery 30:153-159, 1992. Batjer HH, Samson D: Surgical approaches to trigonal arteriovenous malformations. J Neurosurg 67:511-517, 1987. Drake CG: Cerebral arteriovenous malformations: Considerations for an experience with surgical treatment in 166 cases. Clin Neurosurg 26:145-208, 1979. Fornari M, Savaiardo M, Morello G, Solero CL: Meningiomas of the lateral ventricles: Neuroradiological and surgical considerations in 18 cases. J Neurosurg 54:64-74, 1981. Heros RC: Brain resection for exposure of deep extracerebral and paraventricular lesions. Surg Neurol 34:188-195, 1990. Nagata SL, Matsushima T, Fujii K, Takeshita I, Fukui M, Yasumori K: Lateral ventricular arteriovenous malformations: Natural history and surgical indications. Acta Neurochir (Wien) 112:37-46, 1991. Ojemann RG, Heros RC, Crowell RM: Arteriovenous malformations of the brain, in Ojemann RG: Surgical Management of Cerebrovascular Disease, Baltimore, Williams & Wilkins, 1988, ed 2, pp 347-413. Rhoton AL Jr, Tamamoto I, Peace DA: Microsurgery of the third ventricle: Part 2. Operative approaches. Neurosurgery 8:357372, 1981. Seeger W: Supratentorial structures near the ventricles, in Seeger W: Atlas of Topographical Anatomy of the Brain and Surrounding Structures. New York, Springer, 1978, pp 368-427. Solomon RB, Stein BM: Surgical management of arteriovenous malformations that follow the tentorial ring. Neurosurgery 18:708-714, 1986. Spetzler RF, Martin NA: A proposed grading system for arteriovenous malformations. J Neurosurg 65:476-483, 1986. Stein BM: Arteriovenous malformations of the medial cerebral hemisphere and the limbic system. J Neurosurg 60:23-31, 1984. U HS: Microsurgical excision of paraventricular arteriovenous malformations. Neurosurgery 16:293-303, 1985. Waga S, Shimosaka S, Kojima T: Arteriovenous malformations of the lateral ventricle. J Neurosurg 63:185-192, 1985. Wilson CB, Martin NA: Deep supratentorial arteriovenous malformations, in Wilson CB, Stein BM (eds): Intracranial Arteriovenous Malformations. Baltimore, Williams & Wilkins, 1984, pp 184-208. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. CONCLUSION Our experience with 26 AVMs of the ventricular trigone has reinforced our preference for direct surgical management of these lesions. The combined use of selective preoperative embolization, MRI, and angiography to select the optimal operative approach and the use of intraoperative ultrasound and angiography to enhance exposure and ensure the completeness of resection allow for highly acceptable results in this group of patients who have a predilection for recurrent hemorrhage. Reprint requests: Daniel L. Barrow, M.D., Department of Neurosurgery, Emory Clinic, 1327 Clifton Road, NE, Atlanta, GA 30322. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Nevertheless, embolization carries its own inherent risks and should be used judiciously only in those cases where there appears to be clear benefit. Two of our patients experienced hemorrhages after embolization, and a third patient developed a permanent hemianopia; however, all three of these patients ultimately had a good outcome. MRI is another preoperative adjunct that we have found to be invaluable in planning operative approaches to these and other AVMs. The multiple imaging planes provided by MRI clearly demonstrate not only the extent and precise location of the malformation, but also its relationship to adjacent critical structures. Associated hematomas are well delineated and occasionally will alter decisions regarding the operative approach. In their series of trigonal AVMs, Batjer and Samson (2) chose the operative approach based upon the relationship of the AVM to the P2-P3 junction of the posterior cerebral artery, as determined by angiography. Their series was published before the widespread use of MRI. For those lesions lying medial to the P2-P3 junction, an interhemispheric approach was used, whereas an approach through the inferior or middle temporal gyrus was utilized for lesions lying lateral to the P2-P3 junction (2). Although this is an extremely useful landmark, we have found MRI to be more helpful in selecting the operative approach. Four of our patients had malformations that straddled the P2P3 junction with equal volume of AVM on either side. In two of these patients, an interhemispheric approach was selected and, in one each, an inferior temporal gyrus approach and transcortical parietooccipital approach were used. We have found intraoperative ultrasound and angiography to be quite helpful. Ultrasound is an expedient adjunctive modality to plan the cortical incision and trajectory to the trigone and AVM for both temporal and posterior parietal transcortical approaches. Associated hematoma cavities are readily imaged and occasionally can be entered to improve exposure. Intraoperative angiography was used in 21 of our patients and demonstrated residual AVM in 2 patients (twice in one patient), at a time when the AVM was thought to be completely resected. This not only avoided a repeat procedure, but may have prevented a postoperative hemorrhage from residual AVM before postoperative angiography and another craniotomy. 17. COMMENTS Barrow and Dawson have thoughtfully reviewed the surgical decisions encountered in treating a large group of trigonal AVMs. We agree entirely with the criteria that they used to describe why these lesions are unique and with the specialized surgery that is required in the treatment of these cases. The authors mentioned two aspects of the surgery, which we have used only on rare occasions. The first is the positioning of the patients for a parafalx exposure with the lesion dependent. We have used this to good advantage on one occasion, but in most of our operations, we use a semisitting slouch position to approach these lesions. We have also used an oblique approach for the medial lying trigone lesions described previously (1). It requires cutting of the falx, which results in a more perpendicular view from the side opposite the AVM. This is particularly useful when the AVM extends out to the lateral wall of the trigonum which is difficult to reach from a parafalx, same-side approach. We find that the transcortical superior parietal lobule approach to the trigone violates a great deal of white matter, whereas, with some difficulty, the lesion can be exposed from a medial, interhemispheric, parafalx exposure in most cases, unless it extends significantly lateral to the lateral edge of the trigone of the ventricle. We are also intrigued by their transcortical (transtemporal) approach to those lesions lying lateral in the trigone (even those in the dominant side), of which they had eight cases. This demonstrates that even on the dominant side, the cortex can be violated to reach these lesions. These, of course, are the most difficult AVMs, those that we have termed as being in "no mans land." We would be curious as to how many of these were approached through fairly large hematomas that extended laterally from the AVM toward the cortical surface. Also, there are some difficulties in approaching these lesions from a lateral approach, because their arterial supply and venous drainage are almost exclusively from a medial direction and the surgeon encounters these important vessels on the far side of the AVM. As these authors point out, magnetic resonance imaging has been the single most valuable tool in determining the approach to these difficult lesions. It is the only technique that truly shows the associated brain anatomy and the exact position, size, and configuration of the AVM; coronal views are most helpful. We were surprised that the authors did not encounter short-term memory problems, usually transient postoperatively, especially with lesions on the dominant side. These usually occur with the lesions involving not only the dominant fornix, but also the caudate, lateral pulvinar, and posterior parahippocampal gyri. The left side or the dominant hemisphere is associated with a greater incidence of recent memory difficulties in our experience. Finally, we have not espoused intraoperative angiography to the extent that these authors have. The reasons that we do not perform it frequently are technical, related to the long duration of these operations and then the necessity for 1 to 2 hours more of general anesthesia in which to perform the intraoperative angiography, Moreover, there are technical difficulties associated with getting excellent and appropriate views, while discounting hyperemic venous shunting that is often seen immediately after removal of an AVM that then disappears within 24 hours. Accordingly, most of our postoperative angiograms are done a few days after surgery. Bennett M. Stein Abraham Kader New York, New York REFERENCES: (1) 1. Almeida GM, Shibata MK, Nakagawa EJ: Contralateral parafalcine approach for parasagittal and callosal arteriovenous malformations. Neurosurgery 14:744-746, 1984. Barrow and Dawson have presented an excellent series of AVMs of the region of the ventricular trigone. It should be noted that some authors would reserve the title "trigone AVMs" for those lesions located within the ventricular trigone and fed predominately by the choroidal arteries, with drainage into the deep venous system. This series includes a number of true trigonal ventricular AVMs. In addition, it includes a number of AVMs located in the deep cortical areas on the medial surface of the hemisphere behind the trigone or in the area around but not within the ventricular trigone. The operative approach to such lesions should be individualized, as described by the authors. AVMs located in the region of the part of the trigone adjoining the temporal horn and fed by branches of the anterior and posterior choroidal arteries should be approached through the inferior temporal gyrus. This series also includes a significant number of patients having lesions located along the medial surface of the hemisphere behind the trigone, which can best be dealt with by using a posterior interhemispheric approach. Those lesions located in the central part of the trigone adjoining the posterior part of the body of the lateral ventricle and fed by the posterior choroidal arteries should be approached by a transcortical parieto-occipital approach. The cortical incision would be located high enough to avoid the optic Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 18. Yasargil MG, Jain KK, Antic J, Laciga R, Kletter G: Arteriovenous malformations of the anterior and middle portions of the corpus callosum: Microsurgical treatment. Surg Neurol 5:67-80, 1976. Yasargil MG, Jain KK, Antic J, Laciga R: Arteriovenous malformations of the splenium of the corpus callosum: Microsurgical treatment. Surg Neurol 5:5-14, 1976. Yasargil MG: Microsurgery, IIIB: AVM of the Brain. Stuttgart, Thieme (Verlag), 1988. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. 16. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. radiations and far enough posterior to avoid the speech areas if the dominate hemisphere is opened. Albert L. Rhoton, Jr. Gainesville, Florida Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Figure 1. Patient 18. Axial T1-weighted MRI (A) in an 18-year-old patient who had undergone two previous operations at another institution for attempted resection of the AVM located medial and posterior to the trigone. Although complete resection was believed to have been accomplished, he experienced another hemorrhage that was demonstrated on an MRI scan. Anteroposterior (B) and lateral (C) vertebral angiograms show residual AVM fed by cortical branches of the posterior cerebral artery and the lateral posterior choroidal artery. There was also supply from the pericallosal artery on the carotid injection. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Figure 3. Patient 11. Anteroposterior (A) and lateral (B) vertebral angiogram illustrates the AVM fed by parieto-occipital branches of the posterior cerebral artery. There is both superficial and deep venous drainage. Anteroposterior (C) intraoperative angiogram documents complete obliteration of the AVM, with normal filling of the surrounding vasculature. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Figure 2. Patient 21. Lateral (A) left carotid angiogram demonstrates a fetal circulation to the posterior cerebral artery that subsequently supplies an AVM through multiple cortical feeders as well as branches of the middle cerebral artery. Superselective anteroposterior (B) injection of the posterior cerebral artery at the time of embolization shows a venous aneurysm within the nidus of the AVM (arrow). Lateral (C) left carotid angiogram performed immediately after embolization demonstrates marked reduction in the arterial supply to the AVM. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Figure 4. Patient 8. Axial (A) and coronal (B) MRI demonstrate the AVM within and lateral to the trigone associated with a hemorrhage extending laterally into the posterior temporal lobe. Anteroposterior (C) and lateral (D) preoperative vertebral angiogram shows the AVM fed by the lateral and medial posterior choroidal arteries and the parieto-occipital branch of the posterior cerebral artery. The malformation was also supplied by the anterior choroidal artery. Anteroposterior and vertebral angiogram (E) documents complete excision of the AVM and occlusion of the left posterior cerebral artery. The aneurysm clip was placed on a large feeding artery arising from the P2 segment of the posterior cerebral artery. The angiogram demonstrates the apparent retrograde thrombosis of the posterior cerebral artery. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Figure 5. Patient 12. Sagittal T1-weighted MRI (A) shows AVM is in the region of the ventricular trigone. Anteroposterior (B) and lateral (C) vertebral angiograms demonstrate arterial supply from the posterior cerebral artery, and anteroposterior (D) left carotid angiogram reveals middle cerebral arterial supply. Postoperative anteroposterior (E) and lateral (F) vertebral and anteroposterior (G) carotid angiograms document complete excision of the AVM. Redistribution of this article permitted only in accordance with the publisher’s copyright provisions. Downloaded from https://academic.oup.com/neurosurgery/article-abstract/35/6/1046/2757660 by Universitaetsbibliothek Muenchen user on 28 January 2019 Table 1. Management Results of 26 Patients with Arteriovenous Malformations in the Region of the Ventricular Trigonea