Susumu Miyamoto, M.D., Ph.D. SURGICAL APPROACH Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Hiroharu Kataoka, M.D., Ph.D. Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Akio Ikeda, M.D., Ph.D. Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan A COMBINED SUBTEMPORAL AND TRANSVENTRICULAR/ TRANSCHOROIDAL FISSURE APPROACH TO MEDIAL TEMPORAL LESIONS Jun Takahashi, M.D., Ph.D. Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Nobuhiro Mikuni, M.D., Ph.D. Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Keiko Usui, M.D. Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan Motohiro Takayama, M.D. Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Takeshi Satow, M.D. Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Nobuo Hashimoto, M.D., Ph.D. Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan Reprint requests: Susumu Miyamoto, M.D., Ph.D., Department of Neurosurgery, The National Cardiovascular Center, 5-7-1 Fujishiro-dai, Suita, Osaka, 565-8565, Japan. Email: miy@hsp.ncvc.go.jp OBJECTIVE: To minimize therapeutic morbidity such as cognitive function disturbance and vascular injury to perforating arteries, preoperative functional mapping of the basal temporal lobe functions was performed and the medial temporal lesions were resected via a combined subtemporal and transventricular/transchoroidal fissure approach. METHODS: Twenty-one patients with medial temporal lesions including tumors, arteriovenous malformations, and medial temporal lobe epilepsy underwent operation. The neurovascular structures in the ambient cistern were first dissected free from the medial temporal lobe with a conventional subtemporal approach. Then, the temporal horn was opened through the basal surface of the temporal lobe. Finally, the ambient cistern was accessed from the temporal horn through the choroidal fissure. In five patients whose lesions were revealed to be located on the dominant side by preoperative intracarotid amytal administration test (Wada test), functional mapping of the basal temporal lobe language cortex was monitored for 1 week by use of a subdural electrocorticogram grid before the extirpation surgery. The entrance point from the temporal base to the temporal horn was determined by the result of the functional mapping. RESULTS: The lesions were resected safely and completely in all cases. Language and cognitive functions were preserved even in patients with the basal language area on the dominant side. CONCLUSION: Surgeons can confirm the important neurovascular structures from the subtemporal route and from the transtemporal horn route by a combined subtemporal and transventricular/transchoroidal fissure approach. This approach is especially effective for avoiding ischemic complications by allowing direct confirmation of the anterior choroidal and thalamoperforating arteries. KEY WORDS: Functional mapping, Language area, Medial temporal lobe epilepsy, Subtemporal approach, Temporal horn, Temporal lobe Neurosurgery 54:1162-1169, 2004 DOI: 10.1227/01.NEU.0000119234.61432.E8 www.neurosurgery-online.com Received, June 6, 2003. Accepted, December 17, 2003. I schemic complication caused by vascular injuries is the most formidable cause of morbidity in surgery for medial temporal lobe epilepsy (5, 18, 19). To avoid this, some authors have advocated subpial resection of the hippocampus without confirming the important neurovascular structures in the ambient cistern under the operating microscopic view, leaving these structures under the coverage of pia and residual thin cortex (8). In contrast, a combined subtemporal and transventricular/transchoroidal fissure approach offers a thorough exposure of these critical neurovascular structures. We present the technical considerations of this approach. 1162 | VOLUME 54 | NUMBER 5 | MAY 2004 The disturbance of higher cognitive functions is another serious complication of the subtemporal or transbasal approach (4, 15). To avoid this, we discuss the benefit of functional mapping with subdural grids. PATIENTS AND METHODS Clinical Data Table 1 summarizes the clinical data of patients who underwent operations with the combined subtemporal/transchoroidal fissure approach. Eight patients had tumors (pilocytic www.neurosurgery-online.com APPROACH TO MEDIAL TEMPORAL LESIONS TABLE 1. Patient data Patient Age (yr)/sex no. Side Diagnosis Epilepsy Dominant side by Wada test BLA by mapping Surgical complication Seizure frequency after operation 1 58/M Left Trigonal AVM ⫺ 2 31/M Left Trigonal AVM ⫺ 3 19/M Right Trigonal AVM ⫺ 4 22/F Right Trigonal AVM ⫺ 5 6/M Right Pilocytic astrocytoma ⫺ Contralateral 6 11/M Left Pilocytic astrocytoma ⫹ Contralateral None 7 11/M Right Pilocytic astrocytoma ⫹ Contralateral None 8 25/F Left Trigonal meningioma ⫺ 9 6/F Left DNT ⫹ 10 31/F Right DNT ⫹ 11 60/F Left Epidermoid ⫺ 12 25/F Left Oligodendroglioma ⫹ Ipsilateral ⫹ None 13 29/F Left MTLE ⫹ Ipsilateral ⫺ Reduced 14 31/M Left MTLE ⫹ Ipsilateral ⫺ 15 21/F Left MTLE ⫹ Contralateral None 16 29/F Left MTLE ⫹ Contralateral None 17 24/F Left MTLE ⫹ Ipsilateral 18 40/F Left MTLE ⫹ Contralateral 19 25/M Right MTLE ⫹ Ipsilateral 20 33/F Right MTLE ⫹ Contralateral 21 28/F Left MTLE ⫹ Ipsilateral Transient hemiparesis Transient hemiparesis Reduced Contralateral Oculomotor nerve palsy Trochlear nerve palsy ⫹ None None None Trochlear nerve palsy ⫹ None None None ⫹ None AVM, arteriovenous malformation; ⫺, absent; ⫹, present; DNT, dysembryoplastic neuroepithelial tumor; BLA, basal language area; MTLE, medial temporal lobe epilepsy. a astrocytoma, three; dysembryoplastic neuroepithelial tumor, two; meningioma, one; oligodendroglioma, one; epidermoid, one). Four patients had arteriovenous malformations (AVMs) in the trigone, and nine patients had hippocampal sclerosis as the focus of intractable medial temporal lobe epilepsy. Five patients with tumor also had intractable epilepsy. In 14 recent patients among this series, an intracarotid amytal administration test (Wada test) was performed to determine the dominant side of the cerebral hemisphere concerning language and memory functions. In six of these patients, functional mapping of the basal surface of the temporal lobe was performed with subdural electrocorticographic grids. The language functions were detected in the lateral part of the temporal base (basal surface of the inferior temporal gyrus and fusiform gyrus) in four patients. NEUROSURGERY Technique (see video at web site) After induction of general anesthesia, a lumbar spinal drainage tube is inserted and left clamped. The patient is placed in the lateral position with the head flexed toward the floor as much as possible. The upper half of the body is elevated slightly to position the head above the level of the heart and reduce venous pressure. A temporal craniotomy is performed to fully expose the temporal base of the middle fossa (Fig. 1A). In most patients, the zygomatic arch is removed for this purpose. The size of the craniotomy should be sufficiently large to confirm the venous bridging point within the craniotomy (Fig. 1A). If the venous bridging point is outside the craniotomy, the surgeon will have difficulty managing unexpected venous bleeding from it. After the dura is VOLUME 54 | NUMBER 5 | MAY 2004 | 1163 MIYAMOTO ET AL. FIGURE 1. Schematic illustration of craniotomy and operative view of the combined subtemporal and transventricular/transchoroidal fissure approach. A, skin incision (thick lines) and extent of craniotomy (shading). In most patients, the zygomatic arch is removed. B, the bridging point of the vein of Labbé is covered and reinforced with pieces of oxidized cellulose. The temporal lobe is retracted as if it were rotated around the bridging point of the vein. Cottonoid roll is inserted beneath the anterior temporal lobe as a soft retractor. The ambient cistern is opened medial to the trochlear nerve, and the neurovascular structures in the ambient, crural, and carotid cisterns are dissected and confirmed. These neurovascular structures include the oculomotor nerve, the superior cerebellar artery, the posterior cerebral artery, the posterior communicating artery, the internal carotid artery, and the anterior choroidal artery (from, Wen HT, Rhoton AL Jr, de Oliveira EP, Cardoso AC, Tedeschi H, Baccanelli M, Marino R Jr: Microsurgical anatomy of the temporal lobe: Part 1—Mesial temporal lobe anatomy and its vascular relationships as applied to amygdalohippocampectomy. Neurosurgery 45:549–592, 1999 [27]). opened, the bridging point of the vein of Labbé into the transverse sinus is dissected and reinforced with a piece of oxidized cellulose cotton. The spinal drainage tube should be left clamped until this maneuver is completed and dural tenting sutures have been placed. Otherwise, the vein of Labbé may be damaged at the bridging point during the evacuation of cerebrospinal fluid (CSF), resulting in venous bleeding or disturbance of venous drainage of the temporal lobe. A total of 50 to 80 ml of CSF is evacuated gradually to gain access to the ambient cistern. The CSF drainage is crucial to avoid retraction injury of the temporal lobe. To reduce the volume of temporal lobe that must be retracted, proper use of anesthesia also is essential. PaCO2 should be maintained at approximately 30 mm Hg. Intravenous anesthesia such as propofol or barbiturate is more effective in reducing brain volume than inhalation gas anesthesia, which increases cerebral blood volume. However, we use 2 to 2.5% sevoflurane for the intraoperative electrocorticographic monitoring during epilepsy surgery, as intravenous anesthesia suppresses the metabolic activity of the neurons, making it difficult to detect the electrical activity of the epileptic focus. 1164 | VOLUME 54 | NUMBER 5 | MAY 2004 A temporal basal vein attached to the middle fossa base is dissected as completely as possible so that it can be freely mobilized, and its bridging point is reinforced with a piece of oxidized cellulose. The vein coursing within the basal dura of the middle fossa should be dissected with the strip of dura around the vein because dissection just beside the vein may injure the dural venous collateral channels, resulting in unintentional injury to the temporal basal vein. Important neurovascular structures are dissected via the subtemporal approach. The brain spatula is inserted anterior to the temporal basal vein, and the temporal lobe is gently retracted as if rotating the temporal lobe in a clockwise direction (in the left temporal craniotomy) or in a counterclockwise direction (in the right temporal craniotomy) around the vein bridging point as the center of the circle, rather than retracting the temporal base (Fig. 1B). Insertion of a cottonoid roll beneath the anterior temporal lobe as a soft retractor is effective in the rotatory retraction of the temporal lobe (Fig. 1B). The ambient cistern is opened medial to the trochlear nerve, and sharp dissection forward confirms neurovascular structures including the oculomotor nerve; the superior cerebellar, basilar, posterior cerebral, and posterior communicating arteries; the internal carotid, anterior and posterior thalamoperforating arteries; and finally the anterior choroidal arteries (27) (Fig. 1B). These neurovascular structures then are covered with a cottonoid sheet. After neurovascular structures in the ambient cistern are dissected, the temporal part of the transchoroidal fissure is opened via the temporal horn. The temporal horn is accessed from the basal surface of the temporal lobe via the collateral sulcus, occipitotemporal sulcus, or fusiform gyrus to avoid the complication of visual field defect (Fig. 2). The entrance point is determined according to the results of functional mapping with electrocorticography and the distribution of the epileptic focus on the basal surface. We use the transsulcal approach as much as possible. It may be difficult to find the location of the temporal horn, especially in a patient in whom the ventricle is distorted by mass effect. The distance from the bottom of the collateral occipitotemporal sulcus to the temporal horn is usually less than 10 mm, and it can be measured with preoperative magnetic resonance imaging (MRI). A surgeon easily can understand the anatomic orientation toward the temporal horn, as the parahippocampal gyrus already has been dissected within the ambient cistern (Fig. 2). Therefore, after the sulcus is dissected toward its bottom, white matter is deliberately aspirated in the anticipated direction of the temporal horn. Just before the temporal horn is entered, CSF springs out through the bottom of the aspirated white matter, suggesting that the temporal horn is located directly beneath. Within the temporal horn, the hippocampus and the choroid plexus are observed. The choroidal fissure is dissected between the hippocampal fimbria and the choroid plexus, because vessels entering through the choroidal fissure usually pass between the choroid plexus and the thalamus. Dissection proceeds forward through the plexal point, where the anterior choroidal artery enters the temporal horn to its anterior pole, www.neurosurgery-online.com APPROACH TO MEDIAL TEMPORAL LESIONS FIGURE 3. Patient 7. A, preoperative T1-weighted MRI scan showing a huge tumor (pilocytic astrocytoma) extending from the medial temporal region to the midbrain in the right side. B, postoperative MRI scan showing total removal of the tumor. FIGURE 2. Schematic illustration of the combined subtemporal and transventricular/transchoroidal fissure approach. First, the neurovascular structures in the ambient cistern are dissected free from the medial temporal lobe via a conventional subtemporal approach (1). Next, the temporal horn is opened through the collateral sulcus or the occipitotemporal sulcus (2). Finally, the ambient cistern is accessed from the temporal horn through the choroidal fissure (3). F, fusiform gyrus; H, hippocampus; ITG, inferior temporal gyrus; MTG, middle temporal gyrus; PH, parahippocampal gyrus; STG, superior temporal gyrus. which is located 1 cm anterior to the plexal point. In a patient with medial temporal lobe epilepsy, the parahippocampal gyrus is transected out from the anterior pole to communicate the temporal horn and the ambient cistern, which already has been dissected. Use of cottonoid to cover important neurovascular structures in the ambient cistern provides a landmark for the ambient cistern and avoids unintentional injury to these structures. Dissection proceeds posteriorly along the choroidal fissure. The parahippocampal gyrus then is transected again to communicate the posterior portion of the temporal horn and the posterior ambient cistern. The hippocampus and parahippocampal gyrus are removed en bloc to confirm the important neurovascular structures from both the subtemporal and the transventricular/transchoroidal fissure views. The basal vein of Rosenthal, which is usually located highest in the ambient cistern, is observed during the final stage of the procedure. Lesions other than medial temporal lobe epilepsy may be resected in a similar manner, but the hippocampus and parahippocampal gyrus should be left intact as much as possible (Fig. 3). When the anterior choroidal artery is one of the feeders to an AVM or a tumor, it should be coagulated and cut distally to its entrance point into the temporal lobe, leaving its cisternal branches intact. sometimes accompanied by nausea or chest discomfort, as an aura before an epileptic seizure. During a seizure, she lost consciousness for approximately 30 seconds, and afterward, she could not recall what happened during the seizure. These attacks occurred two to three times per week despite administration of anticonvulsants (50 mg of phenobarbital, 400 mg of phenytoin, and 800 mg of carbamazepine). She was admitted to our hospital to undergo surgical resection of the epileptic focus. MRI revealed a mass lesion in the basal surface of the left temporal lobe (Fig. 4A). A Wada test demonstrated that her language and memory center was located on the left side. Therefore, we performed functional mapping with subdural electrocorticographic grids, which revealed the existence of a basal language area in the basal surface of the temporal lobe (Fig. 5). Electric stimulation to this area provoked a disturbance in comprehension and reading of Japanese or Chinese characters. Surgical resection of the tumor was performed via the combined subtemporal and transventricular/ transchoroidal fissure approach. The posterior portion of the tumor, which extended into the basal language area, was not removed. The histopathological diagnosis was oligodendroglioma Grade 2. Therefore, local irradiation was given for the residual tumor. The patient experienced no epileptic seizures postoperatively. Her language and memory functions were not disturbed by the operation. No tumor regrowth was noted on MRI scans 11 months later (Fig. 4B). RESULTS Illustrative Case A 25-year-old woman had had intractable epilepsy since she was 14 years old. The patient experienced an unpleasant and sad feeling, NEUROSURGERY FIGURE 4. Patient 12. A, preoperative fluid-attenuated inversion recovery MRI scan showing a hyperintense lesion (oligodendroglioma) in the basal surface of the left temporal lobe. B, postoperative MRI scan 11 months later showing no tumor regrowth. VOLUME 54 | NUMBER 5 | MAY 2004 | 1165 MIYAMOTO ET AL. FIGURE 5. Patient 12. A, intraoperative photograph showing electrocorticographic monitoring. B, schematic drawing of the result. Functional mapping revealed the existence of basal language area in the basal surface of the temporal lobe (checked circles). Shaded circles represent areas of epileptic focus; thick line indicates resected area. Surgical Results Among 21 patients in this series, no permanent surgical complications occurred. There were five transient neurological complications, three in patients with tumors and two in patients with medial temporal lobe epilepsy. Transient motor paresis was observed in two patients, one in a patient with a huge pilocytic astrocytoma involving the midbrain, and the other in a patient with a massive trigonal meningioma. Temporary oculomotor palsy occurred in a patient with dysembryoplastic neuroepithelial tumor. Two patients with medial temporal lobe epilepsy reported double vision, which was caused by transient trochlear nerve palsy postoperatively. Visual field defects did not occur in any patients. All of these neurological deficits were resolved within 2 to 3 months. In all 14 patients who presented with intractable epilepsy, epilepsy frequency was reduced postoperatively and 12 patients became completely seizure-free. No language and cognitive dysfunction was detected after surgery, even in patients with a basal language area as detected by functional mapping. DISCUSSION Lesions located in the parahippocampal gyrus and the hippocampus can be a good indication for the combined subtemporal and transventricular/transchoroidal fissure approach. Lesions extending to the ambient cistern, the upper brainstem, or the temporal horn also can be accessed via this approach. Most of the anterior lesions involving only the interpeduncular cistern and anterior half of the ambient cistern can be accessed safely via a pterional approach (28). Lesions located mainly in the quadrigeminal cistern or the trigone should be accessed via an occipital interhemispheric or transcortical approach (2, 20, 22). The subtemporal approach has been the most common surgical approach to the ambient cistern, middle medial temporal lobe, and upper brainstem (3, 6, 14, 16). However, operative morbidities such as venous infarct or contusional hematoma after excessive temporal lobe retraction have been cited as drawbacks of this approach (7). To avoid such morbidities, some authors have 1166 | VOLUME 54 | NUMBER 5 | MAY 2004 advocated the transchoroidal fissure approach to the ambient cistern without retraction of the basal surface of the temporal lobe (9, 17, 22). The transchoroidal fissure approach has been reported to be useful in surgery for intra-axial medial temporal lesions (17) and extra-axial vascular lesions in the ambient cistern (9, 22). We agree that the aforementioned lesions are suitable for the transchoroidal fissure approach. For extra-axial vascular lesions such as P2 segment aneurysms or medial temporal AVMs in the ambient cistern, however, a conventional subtemporal approach is more effective than the transventricular/ transchoroidal fissure approach for proximal artery control. It is not necessary to make a cortical incision in the temporal lobe to access the ambient cistern. For lesions within the temporal horn such as intraventricular AVMs, a laterobasal transventricular approach to the temporal horn is essential (7, 11). One of the advantages of the combined subtemporal and transventricular/transchoroidal fissure approach over the transchoroidal fissure approach alone is that vascular injury in the ambient cistern can be avoided with the combined approach. In the transchoroidal fissure approach, important neurovascular structures within the ambient cistern cannot be confirmed until the final stage of access, which may lead to the ischemic complications often associated with surgery for medial temporal lobe epilepsy (5, 18, 19). To avoid unintentional vascular injury, subpial dissection sometimes has been advocated in epileptic surgery (8). In our approach, however, the important neurovascular structures first have been confirmed and covered with cottonoid during the subtemporal approach. Thus, the risk of unintentional injury to these structures is minimized through the transchoroidal fissure dissection from the temporal horn. The other advantage is that anatomic orientation to the temporal horn is easier to gain in the combined approach. In large tumors with marked mass effect, this advantage is pronounced. With appropriate anesthesia and lumbar CSF drainage, we do not need to make a cortical incision to the temporal lobe merely to gain access to the ambient cistern. With proper direction and degree of temporal lobe retraction, neurovascular structures within the ambient cistern can be exposed through a subtemporal approach without difficulty by use of step-by-step microsurgical procedures. Some authors have advocated dissection of the vein of Labbé from the temporal lobe to enable wider retraction (8, 24). In contrast, we do not dissect the vein of Labbé to enhance its mobilization, as we do not need to retract the temporal lobe at the bridging point. The temporal lobe should be retracted gently as if rotating the temporal lobe around the vein bridging point as the center of a circle. Neuro-ophthalmological complications are an inherent risk of this type of approach. To avoid such complications, we access the temporal horn through the basal aspect of the temporal lobe. Some authors make the cortical incision in the middle temporal gyrus (26) or in the inferior temporal gyrus (9), which entails certain risks for upper quadrantanopsia caused by injury to Meyer’s loop. In our series, no visual field defect was detected postoperatively in any patient. www.neurosurgery-online.com APPROACH TO MEDIAL TEMPORAL LESIONS Another purpose of this article is to draw attention to language function in the basal surface of the temporal lobe (basal temporal language area), which generally has been considered outside of Wernicke’s language area. The basal temporal language area has been described mainly in reports of epilepsy surgery. Lüders et al. (13) used subdural electrode grid stimulation to demonstrate the existence of language areas in the laterobasal surface of the temporal lobe such as the fusiform gyrus and the basal surface of the inferior temporal gyrus. In our series, a basal language area was demonstrated in four patients among six who had lesions in the dominant side temporal lobe. In the surgical treatment of medial temporal lesions, determination of hemispheric dominance is essential. Dominance of speech and memory functions between both hemispheres can be evaluated by use of a Wada test and its modifications with intracarotid administration of amytal (10, 25) or propofol (23). To avoid cognitive function disturbances caused by cortical incisions to the basal temporal lobe, functional mapping with subdural electrocorticographic grids offers important information (1, 12). Surgery performed while the patient is awake is another option for resection of such lesions in the dominant temporal lobes (21). In contrast with awake surgery, subdural grid monitoring performed when the patient is fully alert enables more accurate functional mapping of repetitive or different paradigms of language testing. REFERENCES 1. Awad IA, Rosenfeld J, Ahl J, Hahn JF, Lüders H: Intractable epilepsy and structural lesions of the brain: Mapping, resection strategies, and seizure outcome. Epilepsia 32:179–186, 1991. 2. Barrow DL, Dawson R: Surgical management of arteriovenous malformations in the region of the ventricular trigone. Neurosurgery 35:1046–1054, 1994. 3. Batjer HH, Samson DS: Surgical approaches to trigonal arteriovenous malformations. J Neurosurg 67:511–517, 1987. 4. Baxendale S: Amnesia in temporal lobectomy patients: Historical perspective and review. Seizure 7:15–24, 1998. 5. Behrens E, Schramm J, Zentner J, Konig R: Surgical and neurological complications in a series of 708 epilepsy surgery procedures. Neurosurgery 41:1–9, 1997. 6. Drake CG: Cerebral arteriovenous malformations: Considerations for and experience with surgical treatment in 166 cases. Clin Neurosurg 26:145–208, 1979. 7. Heros RC: Arteriovenous malformations of the medial temporal lobe: Surgical approach and neuroradiological characterization. J Neurosurg 56:44– 52, 1982. 8. Hori T, Tabuchi S, Kurosaki M, Kondo S, Takenobu A, Watanabe T: Subtemporal amygdalohippocampectomy for treating medically intractable temporal lobe epilepsy. Neurosurgery 33:50–56, 1993. 9. Ikeda K, Shoin K, Mohri M, Kijima T, Someya S, Yamashita J: Surgical indications and microsurgical anatomy of the transchoroidal fissure approach for lesions in and around the ambient cistern. Neurosurgery 50: 1114–1119, 2002. 10. Kanemoto K, Kawasaki J, Takenouchi K, Hayashi K, Kubo H, Morimura T, Kakeuchi J: Lateralized memory deficits on the Wada test correlate with the side of lobectomy only for patients with unilateral medial temporal lobe epilepsy. Seizure 8:471–475, 1999. 11. Kikuchi H, Miyamoto S, Nagata I, Taki W, Nakahara I: Surgical extirpation of the posterior hippocampal arteriovenous malformation. Surg Neurol 47:251–256, 1997. NEUROSURGERY 12. Lüders H, Hahn J, Lesser RP, Dinner DS, Morris HH III, Wyllie E, Friedman L, Friedman D, Skipper G: Basal temporal subdural electrodes in the evaluation of patients with intractable epilepsy. Epilepsia 30:131–142, 1989. 13. Lüders H, Lesser RP, Hahn J, Dinner DS, Morris HH, Wyllie E, Godoy J: Basal temporal language area. Brain 114:743–754, 1991. 14. MacDonald JD, Antonelli P, Day AL: The anterior subtemporal, medial transpetrosal approach to the upper basilar artery and ponto-mesencephalic junction. Neurosurgery 43:84–89, 1998. 15. Ojemann GA, Dodrill CB: Verbal memory deficits after left temporal lobectomy for epilepsy: Mechanism and intraoperative prediction. J Neurosurg 62:101–107, 1985. 16. Oka N, Kamiyama K, Nakada J, Endo S, Takaku A: Surgical approach to arteriovenous malformation of the medial temporal lobe: Report of three cases. Neurol Med Chir (Tokyo) 30:940–944, 1990. 17. Park TS, Bourgeois BF, Silbergeld DL, Dodson WE: Subtemporal transparahippocampal amygdalohippocampectomy for surgical treatment of mesial temporal lobe epilepsy: Technical note. J Neurosurg 85:1172–1176, 1996. 18. Pilcher W, Roberts DW, Flanigin HF, Crandall PH, Wieser HG, Ojemann GA, Peacock WJ: Complications of epilepsy surgery, in Engel JJ (ed): Surgical Treatment of the Epilepsies. New York, Raven Press, 1993, pp 565–581. 19. Polkey CE: Complications of epilepsy surgery, in Shorvon S, Dreifuss F, Fish D, Thomas D (eds): The Treatment of Epilepsy. Oxford, Blackwell Science, Ltd., 1996, pp 780–793. 20. Poppen JL: The right occipital approach to a pinealoma. J Neurosurg 25: 706–710, 1966. 21. Sahjpaul RL: Awake craniotomy: Controversies, indications and techniques in the surgical treatment of temporal lobe epilepsy. Can J Neurol Sci 27[Suppl 1]:S55–SS63, 2000. 22. Seoane ER, Tedeschi H, de Oliveira EP, Siqueira MG, Calderon GA, Rhoton AL Jr: Management strategies for posterior cerebral artery aneurysms: A proposed new surgical classification. Acta Neurochir (Wien) 139:325–331, 1997. 23. Silva TM, Hernandez-Fustes OJ, Bueno ML, Varela AM, Machado S: The Wada test with propofol in a patient with epilepsy. Arq Neuropsiquiatr 58:348–350, 2000. 24. Sugita K, Kobayashi S, Yokoo A: Preservation of large bridging veins during brain retraction: Technical note. J Neurosurg 57:856–858, 1982. 25. Trenerry MR, Loring DW: Intracarotid amobarbital procedure: The Wada test. Neuroimaging Clin N Am 5:721–728, 1995. 26. Waga S, Shimosaka S, Kojima T: Arteriovenous malformations of the lateral ventricle. J Neurosurg 63:185–192, 1985. 27. Wen HT, Rhoton AL Jr, de Oliveira EP, Cardoso AC, Tedeschi H, Baccanelli M, Marino R Jr: Microsurgical anatomy of the temporal lobe: Part 1—Mesial temporal lobe anatomy and its vascular relationships as applied to amygdalohippocampectomy. Neurosurgery 45:549–592, 1999. 28. Yaşargil MG: Deep central AVMs in special surgical considerations, in Microneurosurgery: AVM of the Brain, Clinical Considerations, General and Special Operative Techniques, Surgical Results, Nonoperated Cases, Cavernous and Venous Angiomas, Neuroanesthesia. Stuttgart, Georg Thieme, 1988, vol IIIB, pp 204–367. COMMENTS T he authors describe the advantages gained by combined subtemporal and transventricular approaches to medial temporal lobe lesions. There is little question that having a full complement of surgical techniques available enables an optimal operative procedure for any individual patient. Miyamoto et al. illustrate this nicely. It is likely that larger, more complex, nonstereotypical pathological features, including many medial temporal arteriovenous malformations and tumors, especially benefit from the combined approach. I have not found medial resections for mesial temporal sclerosis to need a more extensive exposure, and removal of the zygomatic arch for this VOLUME 54 | NUMBER 5 | MAY 2004 | 1167 MIYAMOTO ET AL. operation seems unnecessary. That a fourth nerve palsy, albeit temporary, was encountered twice in this relatively small series renders the argument that the approach is safer and less morbid somewhat unconvincing. Nevertheless, the authors remind us of the need for flexibility in our surgical approach and of the variety of strategies that may be brought to bear in medial temporal lobe surgery. David W. Roberts Lebanon, New Hampshire M iyamoto et al. present a combined subtemporal and transventricular/transchoroidal fissure approach to medial temporal lesions. They analyzed a series of 21 patients harboring tumors, arteriovenous malformations, and mesial temporal lobe epilepsy. The microsurgical anatomy of this approach has been reviewed thoroughly in the literature (1–5), and we have commented on it previously. An important technical issue to consider before attempting to remove a mesial temporal lobe lesion, as is clearly discussed by the authors, is determining whether the lesion is located in the anterior, middle, or posterior portion of the mesial temporal lobe region. Most of the anterior lesions may be accessed safely via a pterional transsylvian or pretemporal approach, but the middle and posterior regions must be approached by a subtemporal occipitotemporal and/or interhemispheric parafalcial posterior route. In cases of tumors with some mass effect, the ventricular anatomy may be severely distorted and its location may make access very difficult. A relevant accessory tool to locate the ventricular system in those cases and to lessen brain damage is the intraoperative ultrasonogram. Another important issue is the risk of neuro-ophthalmological sequelae inherent in this kind of approach. The functional outcomes (ophthalmological and speech preservation) of patients are remarkable and are the result of a thorough understanding of microsurgical anatomy and the application of functional mapping of eloquent areas. This article reports a variation of a previously reviewed surgical approach applied to lesions of the mesial temporal region. David Rojas-Zalazar Jorge Mura Evandro de Oliveira São Paulo, Brazil 1. de Oliveira E, Tedeschi H: Arteriovenous malformations of specific regions of the brain, in Sekhar LN, de Oliveira E (eds): Cranial Microsurgery: Approaches and Techniques. New York, Thieme, 1999, pp 601–618. 2. de Oliveira E, Siqueira M, Ono M, Tedeschi H, Peace D: Arteriovenous malformations of the mediobasal temporal region. Neurosurgeons 11:349– 358, 1992. 3. Ikeda K, Shoin K, Mohri M, Kijima T, Someya S, Yamashita J: Surgical indications and microsurgical anatomy of the transchoroidal fissure approach for lesions in and around the ambient cistern. Neurosurgery 50:1114–1119, 2002. 4. Seoane ER, Tedeschi H, de Oliveira E, Siqueira MG, Calderón GA, Rhoton AL Jr: Management strategies for posterior cerebral artery aneurysms: A proposed new surgical classification. Acta Neurochir (Wien) 139:325–331, 1997. 1168 | VOLUME 54 | NUMBER 5 | MAY 2004 5. Wen HT, Rhoton AL Jr, de Oliveira E, Cardoso AC, Tedeschi H, Baccanelli M, Marino R Jr: Microsurgical anatomy of the temporal lobe: Part 1—Mesial temporal lobe anatomy and its vascular relationships as applied to amygdalohippocampectomy. Neurosurgery 45:549–592, 1999. T he authors have presented an interesting alternative to the standard temporal lobe surgery for removal of mesial temporal lobe lesions. The impetus in their search for a new approach to the hippocampal region was their perception, both from personal experience and the literature, that subpial resection of the hippocampus, without prior identification of the neurovascular structures in the ambient cistern, can be associated with a significant risk of injury to these structures, resulting in formidable morbidity. Consequently, the authors’ principal idea is that the neurovascular structures in the ambient cistern, such as the basilar, posterior cerebral, and superior cerebral arteries, the carotid artery and its branches, the third and fourth nerve, and so forth, should be identified first and protected before proceeding with the resection of the hippocampus or of lesions in that vicinity. They accomplish this by performing an extended temporal craniotomy, as illustrated by their skin incision in Figure 1B. In this regard, I should point out that to my eye, Figure 1, A and B, is anatomically incongruous, with the head pointing in opposite directions in these two images. Be that as it may, the authors then proceed to identify the point of entrance of the vein of Labbé into the lateral sinus. They further describe in every detail the importance of the direction of the retraction of the undersurface of the temporal lobe. Specifically, they point out that the retraction should not be in a cephalad direction but rather clockwise, with the point of entry of the vein of Labbé into the lateral sinus as the epicenter of the circular retracting motion (clockwise in right craniotomies). They keep the anterior temporal lobe elevated with moist cellulose cotton. They then proceed to open the arachnoid membrane of the ambient cistern medial to the trochlear nerve. After all the structures in the ambient cistern are identified, these are protected, again with moist cellulose cotton. With this accomplished, the authors then proceed to enter the temporal horn via a sulcal incision along the collateral sulcus or somewhere in this region. Thus, the temporal horn is entered from lateral to medial. Once in the temporal horn, the authors proceed to reach their above-described exposure site in the ambient cistern by working themselves through the choroid fissure. Eventually, the hippocampus is resected in patients with epilepsy, or other lesions in this vicinity are removed with excellent visual control of the area and without fear of proceeding too far medially. The authors recognize that the main downside and risk associated with this procedure is an injury to the subtemporal venous structures, with the possibility of a hemorrhagic infarct in the temporal lobe. Consequently, they offer advice regarding how to handle these veins during the subtemporal approach toward the ambient cistern. My own view on this www.neurosurgery-online.com APPROACH TO MEDIAL TEMPORAL LESIONS approach is that this technique requires a nearly virtuoso performance and a very experienced hand in terms of safeguarding the vein of Labbé and especially the basilar temporal veins. Not every neurosurgeon is really facile with microsurgical dissection of venous structures, and, therefore, perhaps some surgeons are not as adept in their preservation as are the authors. As far as I am concerned, intuitively, I would still prefer the standard techniques of reaching the hippocampus. I am comfortable with subpial resections from my experience with intra-axial brain tumor operations. So far, I have been fortunate not to penetrate through the mesial arachnoid, safeguarding the important neurovascular structures in the ambient cistern. I am not at all sure that I would always be successful in safeguarding the temporal veins. Ivan S. Ciric Evanston, Illinois M iyamoto et al. have provided a diligent and detailed account of a combined subtemporal/transchoroidal fissure approach to the mesial temporal lobe. Six of the 21 patients underwent subdural electrocorticogram mapping for functional mapping of the basal temporal lobes. The authors provide a meticulous description of this subtemporal transtemporal approach (1). The approach allows early entrance into the temporal horn and thus more brain relaxation and a wider angle of resection. In the experience of the senior commentator (MGY), lesions involving the mesial temporal lobe or the temporal horn are accessed via a pterional transsylvian approach, which aims to avoid the use of a self-retaining retractor (spatula) while providing a wider trajectory into the area of resection. The transsylvian approach additionally preserves the basal temporal cortical area, which, according to the authors, can encompass language function in some patients. We disagree with the authors regarding whether the anterior choroidal artery can be sacrificed. Although the authors indicate that they sacrifice this vessel after it enters the temporal lobe, thus preserving its cisternal branches, we advocate complete preservation of the anterior choroidal artery to avoid the risk of capsular infarction. The authors achieved good results using this extensive approach in these 21 patients. M. Gazi Yaşargil Little Rock, Arkansas Saleem I. Abdulrauf St. Louis, Missouri 1. Yaşargil MG: Cases 17.1–17.7, in Microneurosurgery: Microneurosurgery of CNS Tumors. Stuttgart, Georg Thieme, 1996, vol IVB, pp 277–280. The Artist and His Father Hunting Reed Birds (oil on canvas on panel, c.1874) by Eakins (courtesy of the Virginia Museum of Fine Arts, The Paul Mellon Collection, Richmond).