Presigmoid Approach for Cavernous Angioma in the Pons

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1 Neurol Med Chir (Tokyo) 42, 91 98, 2002 Presigmoid Approach for Cavernous Angioma in the Pons Technical Note Yoshitsugu OIWA, KunioNAKAI, YasutomoMASAKI, OsamuMASUO, Toshikazu KUWATA*, HiroshiMORIWAKI*, andtoruitakura Department of Neurological Surgery, Wakayama Medical University, Wakayama; *Department of Neurological Surgery, Hidaka General Hospital, Gobo, Wakayama Abstract Surgical treatment of brainstem lesions has been encouraged after the development of magnetic resonance imaging. However, direct approaches to intra-axial lesions in the brainstem still carry a high risk of morbidity because the neuronal structures can be injured along the entry routes. We present two patients whose pontine cavernous angiomas were removed via incision of the lateral aspect of the pons with presigmoid approach. The first case, a 41-year-old woman, presented with paresis of the cranial nerves VI, VII, and VIII, and left hemiparesis progressing over 2 weeks caused by a cavernous angioma ventrally located in the lower pons. The second case, a 50-year-old woman, developed dizziness over 2 months due to a large cavernous angioma in the center of the pons. These lesions were totally removed through the presigmoid approach and no additional neurological deficits were observed. An imageguided navigation system was used for the craniotomy and removal of the lesion in the second patient. The presigmoid approach provides a safe route to intra-axial lesions in the pons. A technique for presigmoid craniotomy with one-piece bone flap under the image-guided navigation is also described. Key words: brainstem, cerebellum, sigmoid sinus, image-guided navigation, craniotomy Introduction Magnetic resonance (MR) imaging can clearly show brainstem lesions, allowing treatment with direct surgery. 3,6,8,9,12,16,18,21,23) However, surgical approaches to intra-axial lesions of the brainstem are still considered hazardous because of the high risk of neuronal damage. MR imaging also identifies cavernous angiomas more frequently, so the natural history and the possibility of recurrent bleeding and growth are now known. 6,9,13,17) In addition to hemorrhagic events, enlargement of the cavernous angioma related to neovascularization and connective tissue proliferation will induce a slow and stepwise deterioration. Direct surgery is now encouraged when the brainstem cavernous angiomas are found with minor hemorrhage, because of the risk of subsequent neurological deterioration or fatal hemorrhage. Direct surgical treatment has been attempted for cavernous angiomas of the brainstem, but the approaches are still limited to exophytic or surface Received September 7, 2001; Accepted November 30, 2001 lesions. 8,16,18) Thefloorofthefourthventriclecan be incised for safe entry routes to intra-axial lesions, 3,11,12,21) but the surgical fields are restricted by the surrounding neuronal structures such as the nuclei of the cranial nerves and the medial longitudinal fascicles. We treated two patients with pontine cavernous angiomas which were successfully removed through incision of the parenchyma of the lateral pontine surface without additional postoperative symptoms. These cases show that a small incision of the fascicles of the middle cerebellar peduncles allows intraaxial lesions to be approached safely, and indicate the usefulness of the presigmoid approach for pontine lesions. Image-guided navigation was helpful for the craniotomy as well as for removing the deepseated lesions in the brainstem, and a new technique for image-guided one-piece craniotomy is explained. Case Reports Case 1: A 41-year-old woman suffered diplopia and motor weakness in the left extremities progressing for 2 weeks before admission. Neurological examination showed paresis of the cranial nerves VI and 91

2 92 Y. Oiwa et al. Fig. 1 Case 1. A: Preoperative axial T 1 -weighted magnetic resonance (MR) image showing a hypointense round mass surrounded by a hyperintense lesion in the ventral part of the pons on the right side. B: Preoperative T 2 - weighted MR image of the same lesion showing mixed intensity, suggesting recurrent hemorrhage. C: Preoperative coronal T 1 -weighted MR image. D: Postoperative T 1 -weighted MR image showing a small cavity in the ventral part of the lower pons after total removal of the lesion. VII on the right and hemiparesis on the left at admission. Her hearing was impaired to 90 db on the right. No ataxia was defined in the trunk and extremities. MR imaging revealed a mixed intensity lesion on both T 1 -andt 2 -weighted images in the lower pons suggesting a cavernous angioma coexisting with recurrent hemorrhage (Fig. 1A C). Surgery using the presigmoid approach on the right was performed with the patient in the supine position. A heavy roll was placed under the right shoulder, and the head was then fixed with a Mayfieldpinheadrestandturned80degreestotheleftso that the right mastoid bone was uppermost. Combined temporo-occipital craniotomy, mastoidectomy, unroofing of the sigmoid sinus, and a partial petrosectomy were performed using a high-speed drill (Medtronic Midas Rex, Fort Worth, Tex., U.S.A.). The superior petrosal sinus was cut and the dura opened through the temporal area to the presigmoid area. The tentorium was divided, and Fig. 2 Schematic drawing of the operative view of the right presigmoid approach. The lateral surface of the pons can be exposed with minimum retraction. Small incisions are made on the lateral surface of the pons (black solid lines 1 and 2 in Cases 1 and 2, respectively). The surgery was actually performed on the left in Case 2. CN: cranial nerve. cerebrospinal fluid was then released from the cerebellopontine angle cistern so that the cerebellopontine angle was exposed with minimum retraction. The lateral surface of the pons was incised rostrally to the cranial nerve VII VIII complex (Fig. 2), and the hematoma was partially evacuated with a suction tube. The cavernous angioma was then removed from the cavity wall. No changes were observed in the auditory brainstem response (ABR) or somatosensory evoked potential (SEP) during the surgery. Postoperative MR imaging showed total removal of the lesion (Fig. 1D). Her neurological symptoms improved postoperatively and she was able to walk with a cane. Her hearing also improved to 45 db. Case 2: A 50-year-old woman presented with a medical history of left acoustic schwannoma surgically treated 8 years previously. She had paresis of the cranialnervesv,vii,andviiiaftersurgeryforthe acoustic schwannoma. Two months prior to admission, she developed dizziness while walking. Neurological examination showed truncal ataxia as an additional symptom. MR imaging showed a large mixed intensity mass occupying the center of the

3 Presigmoid Approach for Pontine Cavernous Angioma 93 Fig.3 Case2. A:PreoperativeaxialT 1 -weighted magnetic resonance (MR) image showing a large hyperintense mass indicating methemoglobin of subacute hemorrhage in the center of the pons. B: Preoperative T 2 - weighted MR image showing a heterogeneous mixed intensity lesion surrounded by hypointense rims indicating hemosiderin deposits. C: Preoperative midsagittal T 1 - weighted MR image. D: Postoperative T 1 - weighted MR image showing total removal of the lesion. E: Postoperative computed tomography scans showing cosmetic reconstruction of the mastoid bone. Open arrowheads indicate the reconstructed bone flap. Closed arrowheads indicate the previous suboccipital craniectomy for the acoustic schwannoma. pons (Fig. 3A C), suggesting de novo formation of a cavernous angioma. The surgical procedures for the left presigmoid approach were basically the same as those used for the first patient, but image-guided surgery was performed as described previously. 2,7) Briefly, computed tomography (CT) data were acquired for registration using fiducial markers placed on the scalp on the day before surgery. Three-dimensional (3-D) reconstructed MR imaging data were transferred to the operating room computer workstation (Stealth Station; Medtronic Sofamor Danek, Minneapolis, Minn., U.S.A.) and then superimposed on the CT images. The reference arc of the image-guided navigation system was fixed to a Mayfield headrest for registration of the fiducial markers. Reflective spheres to reflect infrared light to the camera array (SureTrak; Medtronic Sofamor Danek) were attached to the high-speed drill (Medtronic Midas Rex) so that the position and direction of the drill tip were determined by the system. The relationship between the drill tip and the corner of the sigmoid sinus was visualized on the MR images. The inner table of the cortical bone adjacent to the sinus was drilled with a small diamond-bar tip and then combined temporooccipital craniotomy, mastoidectomy, and partial petrosectomy was safely performed with a one-piece bone flap (Fig. 4). After the lateral part of the petrous bone was drilled out, microsurgery was performed under image guidance with registration of the focal point of the surgical microscope (OME8000; Olympus, Tokyo) (Fig. 5). Care was taken to avoid excessive stretching of the petrosal vein, when the lateral surface of the pons was incised caudally to the cranial nerve V (Fig. 2). The hematoma was then encountered at a depth of 5 mm and evacuated by suction. The wall of the hematoma cavity was investigated under image-guided navigation to identify and totally remove the cavernous angioma. Cosmetic reconstruction of the skull was performed using titanium plates (Bioplate; Codman and Shurtleff, Raynham, Mass., U.S.A.) (Fig. 3E). No changes in ABR or SEP were induced by the surgical procedures. Postoperatively, she showed no deterioration of neurological symptoms and MR imaging showed complete removal of the lesion (Fig. 3D). Discussion Brainstem cavernous angiomas are commonly found in the cavities of hematoma. After aspiration of the hematoma, the cavernous angioma can be identified in the empty space, separated from the surrounding tissues and resected without additional injury to the neuronal structures. The lesion must be removed gently from the gliotic tissues without neuronal injury. Therefore, cavernous angiomas can be resected easily once exposed. The location of the

4 94 Y. Oiwa et al. Fig. 4 Case 2. Schematic drawing of one-piece craniotomy for the presigmoid approach. The mastoid bone is incised along the red line and removed with the temporo-occipital bone flap. The high-speed drill has reflective spheres attached for navigation when used for the mastoid craniotomy. The green line shows the bone incision for the conventional combined temporo-occipital craniotomy. Fig. 5 Case 2. Intraoperative display of the image-guided navigation and surgical microscope view (right lower panel). Fig. 6 Schematic drawing of the pons and neuronal structures involved in the presigmoid approach to the intra-axial lesion (red arrow). CN: cranial nerve, ML: medial lemniscus, Py: pyramidal tract, RN: red nucleus, Sp: spinothalamic tract. cavernous angioma or the hematoma on the surface of the brainstem should be considered as the entry window for removing the lesion. 12,16,18) However, cavernous angioma deeply seated in the brainstem will require incision of the parenchymal layer of the brainstem with the risk of additional neuronal damage. The floor of the fourth ventricle provides one of the zones for safe access to intra-axial pontine lesions. 3,11,12,21) The triangle bordered by the medial longitudinal fascicle medially, the genu of the fascicle of the cranial nerve VII caudally, and the inferior cerebellar peduncle laterally, is the main landmark for the entry. Lesions in the lower pons can be approached via the smaller triangle bordered by the medial longitudinal fascicle, the striae medullares, and the caudal margin of the fascicle of the cranial nerve VII. Direct electrical stimulation is actually needed for mapping of the cranial nerve VII to identify neuronal structures if the normal anatomical topography is altered by the lesion. 5,10,14) Moreover, the medial longitudinal fascicles can be easily injured when the midline structure is incised or retracted. Therefore, only lesions located unilaterally and dorsally in the pons can be treated by this approach. The presigmoid approach, variously called the presigmoid petrosal approach or the retrolabyrinthine petrosal approach, is a microsurgical route for access to the midline of the ventral brainstem. Ver-

5 Presigmoid Approach for Pontine Cavernous Angioma 95 tebrobasilar artery aneurysms close to the midline or neoplasms situated in the medial petrosal or clival region are commonly treated with this approach. 1,20) We employed the presigmoid approach for the intraaxial lesions located in the central to ventral regions of the pons in our patients. The lateral aspect of the pons was exposed with minimum retraction of the cerebellum or stretching of the cranial nerves VII and VIII (Fig. 2). The deep-seated lesions were approached through the small window of the lateral surface. The center of the pons in which the reticular formation is approximately located is less eloquent compared to the dorsal brainstem. The most significant structures, in which injury may become symptomatic, are the corticospinal tracts located ventrally and the middle cerebellar peduncles (brachium pontis) located laterally in the pons (Fig. 6). Dissection of the middle cerebellar peduncle to approach the mesencephalic lesions causes no or only transient aggravation of cerebellar ataxia. 15) Our results also suggest that the middle cerebellar peduncles, if cut longitudinally to the fascicles in the lateral surface of the pons, do not show significant morbidity with a small incision. Therefore, we conclude that intra-axial lesions in the pons can be treated safely with the presigmoid approach. In addition, this approach allows access to large lesions extending bilaterally as shown in our Case 2. The presigmoid approach is useful for other intrinsic neoplasms of the brainstem. Brainstem gliomas, for example, can be classed in the subcategories as other tumors, namely diffuse, focal, cystic, or dorsal exophytic. Focal and exophytic tumors include low-grade astrocytomas for which direct surgery may be recommended. However, aggressive surgery is only recommended when mass reduction may be beneficial and adjuvant therapy is appropriate. 8,16,22) The recent development of computer-assisted neurosurgery allows interactive surgical navigation guided with 3-D image representations of CT or MR imaging. 2,7) The image-guided navigation system demonstrates the location and direction of the surgical instrumentation on the route to the target, safely leading to deep-seated lesions or neurologically eloquent areas. However, the accuracy of the image guidance may be reduced by brain tissue shift due to leakage of the cerebrospinal fluid or resection of the mass lesions. Brain shift occurs quite often in patients with supratentorial lesions, so real-time updating of the images is now used during the course of the surgical procedure by intraoperative CT or MR imaging. In our Case 2, the brainstem lesion was shown with minimal shift on the MR imaging representation and the location of the surgical manipulation could be monitored precisely. We also used the image-guided navigation system for the presigmoid craniotomy that is commonly performed by separate craniotomy with the temporo-occipital and mastoid bone (Fig. 4). 1,4,18,19) Using the navigation system, the mastoidectomy and partial petrosectomy were easily performed with a one-piece bone flap without injury to the sigmoid sinus. One-piece presigmoid craniotomy allows better cosmetic reconstruction of the mastoid bone. The surgical indications for direct approaches to intra-axial brainstem lesions can now be based on accurate anatomical identification of brainstem lesions with MR imaging. Small incision of the middle cerebellar peduncle does not cause serious neurological symptoms, so the lateral aspect of the pons is a safe zone to access intra-axial lesions. Therefore, the presigmoid approach can lead safely to the entry zone. However, pre-existing neurological deficits must be taken into consideration among the surgical indications in individual patients. In addition, image-guided navigation is a useful tool for presigmoid one-piece craniotomy as well as for removing lesions of the brainstem. References 1) Al-Mefty O, Fox JL, Smith RR: Petrosal approach for petroclival meningiomas. Neurosurgery 22: , ) BathJS,WarnickRE:Chapter46:Image-guidedneurosurgery, in Schmidek A, Sweet WH (eds): Operative Neurosurgical Techniques. Indications, Methods, and Results. Philadelphia, WB Saunders, 2000, pp ) Cantore G, Missori P, Santoro A: Cavernous angiomas of the brain stem: intra-axial anatomical pitfalls and surgical strategies. Surg Neurol 52: 84 94, ) Couldwell WT, Fukushima T: Cosmetic mastoidectomy for the combined supra/infratentorial transtemporal approach. JNeurosurg79: , ) Eisner W, Schmid UD, Reulen H-J, Oeckler R, Olteanu-Nerbe V, Gall C, Kothbauer K: The mapping and continuous monitoring of the intrinsic motor nuclei during brain stem surgery. Neurosurgery 37: , ) Fritschi JA, Reulan HJ, Spetzler RF, Zabramski JM: Cavernous malformations of the brain stem. A review of 139 cases. Acta Neurochir (Wien) 130: 35 46, ) Golfinos JG, Fitzpatrick BC, Smith LR, Spetzler RF: Clinical use of a frameless stereotactic arm: results of 325 cases. J Neurosurg 83: , ) Heffez DS, Zinreich SJ, Long DM: Surgical resection of intrinsic brain stem lesions: An overview. Neurosurgery 27: , ) Isamat F, Conesa G: Cavernous angioma of the brain

6 96 Y. Oiwa et al. stem. Neurosurg Clin N Am 4: , ) Katsuta T, Morioka T, Fujii K, Fukui M: Physiological localization of the facial colliculus during direct surgery on an intrinsic brain stem lesion. Neurosurgery 32: , ) Kyoshima K, Kobayashi S, Gibo H, Kuroyanagi T: A study of safe entry zones via the floor of the fourth ventricle for brain-stem lesions. J Neurosurg 78: , ) LeDoux MS, Aronin PA, Odrezin GT: Surgically treated cavernous angiomas of the brain stem: report of two cases and review of the literature. Surg Neurol 35: , ) Moriarity JL, Wetzel M, Clatterbuck RE, Javedan S, Sheppard JM, Hoenig-Rigamonti K, Crone NE, Breiter SN, Lee RR, Rigamonti D: The natural history of cavernous malformations: a prospective study of 68 patients. Neurosurgery 44: , ) Morota N, Deletis V, Lee M, Epstein FJ: Functional anatomic relationship between brain stem tumors and cranial motor nuclei. Neurosurgery 39: , ) Ogata N, Yonekawa Y: Paramedian supracerebellar approach to the upper brain stem and peduncular lesions. Neurosurgery 40: , ) Pechstein U, Zentner D, Roost DV, Schramm J: Surgical management of brain-stem cavernomas. Neurosurg Rev 20: 87 93, ) Pozzati E, Acciarri N, Tognetti F, Marliani F, Giangaspero F: Growth, subsequent bleeding, and de novo appearance of cerebral cavernous angiomas. Neurosurgery 38: , ) Sakai N, Yamada H, Tanigawara T, Asano Y, Andoh T, Tanabe Y, Takada M: Surgical treatment of cavernous angioma involving the brainstem and review of the literature. Acta Neurochir (Wien) 113: , ) Sasaki T, Taniguchi M, Suzuki I, Kirino T: En bloc petrosectomy using a Gigli saw for petroclival lesions. Technical note. J Neurosurg 83: , ) Sekhar LN, Kalia KK, Yonas H, Wright DC, Ching H: Cranial base approaches to intracranial aneurysms in the subclinoid space. Neurosurgery 35: , ) Symon L, Jackowski A, Bills D: Surgical treatment of pontomedullary cavernomas. Br J Neurosurg 5: , ) Vandertop WP, Hoffman HJ, Drake JM, Humphreys RP: Focal midbrain tumors in children. Neurosurgery 31: , ) Weil SM, Tew JM Jr: Surgical management of brain stem vascular malformations. Acta Neurochir (Wien) 105: 14 23, 1990 Address reprint requests to: Y.Oiwa,M.D.,Departmentof Neurological Surgery, Wakayama Medical University, Kimiidera, Wakayama , Japan. oiwa@wakayama-med.ac.jp. Commentary on this paper appears on the next page.

7 Presigmoid Approach for Pontine Cavernous Angioma 97 Commentary Dr. Oiwa and his colleagues present in this report the approach and resection of cavernomas located ventrally in the pons through the presigmoid approach aided by an intraoperative navigational system. Our experience corroborates the utility and superiority of this approach to ventral brain stem lesions. The entry between the cranial nerves V and VII is known to be a safe entry into the pons as they have also demonstrated. The use of a navigational system in the brain stem is very helpful, particularly as little shift is encountered at the brain stem itself especially in the presigmoid approach that requires no cerebellar retraction. We commend the authors on presenting this technique and exposure with removal of cavernomas and tumors through this approach and support their conclusions. Ossama AL-MEFTY, M.D. Department of Neurosurgery University of Arkansas College of Medicine Little Rock, Arkansas, U.S.A. The authors report the successful surgical removal of two brainstem cavernomas in patients in whom the lesion has produced intraparenchymal hemorrhage. Since the vascular malformation has been removed totally in both instances and there were no additional neurological deficits, the patients may be considered practically cured. The authors may be congratulated for their technical skillfulness. Nevertheless, I cannot agree with the authors' surgical strategy of applying the presigmoid approach in these two cases. During the past six years I have treated surgically 30 patients harboring a brainstem cavernoma. The majority of the lesions were located within the pons, and several of them were quite similar to the lesions described in the present report. In none of them have I encountered the necessity of using the presigmoid approach, even in anterolaterally located pontine cavernomas. This skull base approach is applied at my institution predominantly for exposing large petroclival meningiomas. Oiwa and coworkers have stated that the presigmoid approach provides a safe route to intraaxial lesions in the pons, suggesting that this constitutes the optimal access route to such lesions. Indeed, the presigmoid approach is most useful in lesions with a broad-based attachment to the petroclival area and with an extensive anatomical relationship to the surface of the pons. To expose such lesions, a wide area of the brainstem must be visualized during surgery. However, to expose a totally intrapontine lesion such as a cavernoma, necessitates only a limited exposure of the brainstem or a limited surgical window, since opening of the brainstem does not exceed 8 10 millimeters in the vast majority of cases. The exact site of this opening may vary from case to case and depends upon the relationship between lesion and surface of the brainstem as depicted on preoperative imaging. To chose the optimal access route, the surgeon must define the exact viewing direction or the access trajectory for the removal of the intrinsic lesion. In anterolateral pontine cavernomas as described in the present report, a subtemporal transtentorial route is sufficient and has advantages over the presigmoid approach: it is less time-consuming and implies no complications related to drilling the petrous bone. Even though the authors have not encountered such complications, these may occur in a larger group of patients or in less experienced hands. For large intrapontine cavernomas even two different trajectories can be achieved with two small standard approaches such as the subtemporal combined with the retrosigmoid route, as we have recently described in detail (see the reference, published in 2001 in the journal Neurosurgical Review, Online First). 1) In both patients of the present report, the pons was incised at a site between the exit zone of the cranial nerves V and VII/VIII. The authors have not mentioned whether the pons was bulging due to the compressive effect of the intraparenchymal hematoma or discolorated in this area. The preoperative images suggest that this was the case. In my own series, I have encountered both a bulging, elastic surface of the pons either discolorated or not by the underlying hematoma, this area constituting the zone of entrance into the brainstem, and an apparently intact brainstem surface with no bulging or discoloration, either laterally or at the floor of the fourth ventricle. In my opinion, the discussion about ``safe entry zones to the brainstem'' makes sense only in the latter cases where the brainstem is apparently healthy and the lesion cannot be visualized directly. To conclude my comment, I recommend the surgeons who treat similar brainstem lesions not to overuse the skull base approaches propagated in the literature which certainly have their specific indications, but rather to apply an individually tailored access route with the least amount of invasiveness, whenever possible. Reference 1) Bertalanffy H, Benes L, Miyazawa T, Alberti O, Siegel AM, Sure U: Cerebral cavernomas in the adult. Review of the literature and analysis of 72 surgically treated patients. Neurosurg Rev DOI /s Available from: URL: Helmut BERTALANFFY, M.D. Department of Neurosurgery

8 98 Y. Oiwa et al. Philipps-University Marburg, Germany The symptoms and signs of brainstem cavernomas are not of progressive character during the later weeks, but rather the opposite: the symptoms and signs are most severe at the onset (bleeding) and then decrease in intensity. It can be also the opposite when successive bleedings occur. It is also true that the diagnosis of a cavernoma can be made on the basis of MR imaging. There is no doubt that the best treatment for cavernomas is complete surgical removal. However, it is very difficult, if not impossible, to accept ``the aggressive policy'' that all cavernomas should be operated. It is no doubt much better to follow incidentally found small cavernomas in the brainstem. The strategy is, of course, different when a cavernoma has bled. However, again these lesions should be studied in relation to the size of the lesion, amount of the bleeding, the number of the bleedings, and the neurological status of the patient. Having experience with more than 100 patients with brainstem cavernomas, I still believe that direct surgical removal of the cavernoma and blood clot can be safely achieved only when the lesion has reached the surface of the brainstem. It is very difficult to advocate the safe entry point(s) toward the intra-axial cavernomas when the lesion does not extend to the surface of the brainstem. One should keep in mind that the intra-axial lesion with additional bleeding is exerting pressure in all directions of the cavernoma and hematoma cavity. And due to this pressure, the thin layer of brainstem tissue over the cavernoma represents the ``compressed'' normal tissue, and hence the cutting of this tissue does destroy the remaining functions(s). I do hope that the authors agree that NO neuro-navigation can provide the surgeon with data on how many neurons are to be destroyed while cutting such a ``condensed'' neural tissue. In my opinion, I think that a cavernoma even if it is a larger one, and also with hematoma can be operated and completely resected without causing additional neurological deficits in cases when the cavernoma reaches the surface of the brainstem. On the contrary, cavernomas which do not extend to the surface, and when there is still a normal layer of the tissue over the lesion, surgery may not be more beneficial for the patient than conservative treatment. In the end, it should be mentioned also that the approach should be adjusted toward the point on the surface of the brainstem, where the cavernoma is reaching the surface. Hence the presigmoid approach is only one of the approaches which can be used. And, after all, surgical reports on treatment of whatever pathology are not the best places for the advertisement of neurosurgical equipment such as high-speed drills,surgicalmicroscopes,bioplates,andequipment for neuro-navigation. The reader may start believing that without this specific equipment one cannot operate on such kinds of lesions. No doubt, we are still far from the final solution to the treatment of all brainstem cavernomas. Further microanatomical, neurophysiological, and clinical neurological studies are necessary to be coupled with the specific monitoring during surgery, according to the different locations of the cavernomas in the brainstem. Vinko V. DOLENC, M.D. Department of Neurosurgery University Hospital Center Ljubljana, Slovenia