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Transcerebellar biopsy in the posterior fossa: 12 years experience
100
Surg Neurol 1987;28:100-4
Transcerebellar Biopsy in the Posterior Fossa: 12 Years Experience Juan R. Mathisen, M.D., Filipo Giunta, M.D., Giovanni Marini, M.D., and Erik-Olof Backlund, M.D., Ph.D. Department of Neurosurgery, University of Bergen School of Medicine, Haukeland Hospital, Bergen, Norway, and Division of Neurosurgery, Ospedale Civili, Brescia, Italy
Mathisen JR, Giunta F, Marini G, Backlund E-O. Transcerebellar biopsy in the posterior fossa: 12 years experience. Surg Neurol 1987;28:100-4.
Utilizing the Leksell stereotactic system, the transcerebellar approach was used for posterior fossa biopsies. During a period of 12 years, a total of 29 patients were operated on by this technique, among them 12 children. In the adult, the procedure was carried out with the patient awake and sitting upright; the pediatric patients required general anesthesia and the head was supported either manually or by a clamp. Representative specimens were obtained in all cases but one, showing a wide diagnostic spectrum. As a rule, the procedures were performed smoothly, with no serious side effects. Stereotactic biopsies in the posterior fossa, hitherto seldom performed, open new diagnostic perspectives, one of which is for use in obscure brain stem lesions. The transcerebellar approach has been proven to be easy, direct, and safe provided an appropriate technique is used, such as that described in the present paper. KEYWORDS: Stereotactic biopsy; Posterior fossa; Brain tumor
Stereotactic procedures are now completely integrated in the diagnosis and management of a variety o f intracranial lesions. Even a seemingly insignificant and minute specimen from a deeply located tumor can provide tissue for diagnosis by conventional histological methods or by the smear technique. Although simple, the technique may imply a therapeutic program for the individual patient, radically different from what was originally planned. In addition, stereotactic biopsy opens new perspectives for the characterization o f a tumor by other means, for example, biological markers, immunohistochemistry, and D N A measurements. Chemical and physical parameters o f the tumor in situ, such as oxygen
tension, pH, temperature, and impedance, can also be studied using a stereotactic technique. A number of papers on stereotactic tumor biopsies published during recent years now represent a significant pool of knowledge, accumulated in many centers [10]. In these reports, however, operations in the posterior fossa are mentioned only occasionally. An explanation for this may be the neurosurgeon's fundamental reluctance to manipulate, by an invasive procedure, precarious pressure conditions in the posterior fossa without simultaneously decompressing it. The axial structures caudal to the mesencephalon are furthermore seldom the object for surgical measures and are thus not included in most surgeons' operative paradigm. Many stereotactic systems make it difficult or impossible to approach the intracranial compartment from behind. The patient is fixed to the operating table in the supine position, according to the practice developed during stereotactic procedures of a more conventional character. In the occasional cases o f posterior fossa biopsy hitherto published, a transtentorial-transcerebral trajectory has been chosen [1,8,12], increasing the operating risk. This has recently been emphasized [9]. The stereotactic system used must be completely versatile, giving access to an operative approach from any direction. Using the Leksell stereotactic system, the senior author (E.-O. B.) performed his first posterior fossa biopsy in 1975. In the first case it became evident that the transcerebellar approach was a simple, direct, and safe way to reach any compartment of the posterior fossa. The present study, representing experiences since then and using the same technique at the Karolinska Hospital, Stockholm, Sweden; Ospedale Civile, Brescia, Italy; and Haukeland Hospital, Bergen, Norway, gives further support to the value of the transcerebellar approach. Material and Methods
Address reprint requests to: Professor Erik-Olof Backlund, Nevrokirurgisk avdelning, 5016 Hauke|and sykehus, Norway.
© 1987 by Elsevier Science Publishing Co., Inc.
This study consisted of 29 patients; 18 males and 11 females (12 patients were children, 15 years of age or 0090-3019/87/$3.50
Transcerebellar Biopsy
Surg Neurol 1987;28:100-4
101
A
B
younger). The Leksell stereotactic system [ 16] was used, and the stereotactic coordinates were, as a rule, determined by computed tomography (CT) [17]. General anesthesia was used for the pediatric patients only. The biopsy was performed using a transcerebellar approach, with the patient sitting upright. The awake patient was placed on an ordinary chair beside an operating table, which was elevated to function as a comfortable armrest in front of the patient. The surgeon could conveniently sit or stand behind (Figure 1). In the pediatric patients under general anesthesia, the head was supported by hand or with a Mayfield clamp or Garder-Wells skull traction tongs, tightened just enough to hold the head. To prevent air embolism the pins should not be allowed to penetrate more than the outer table of the skull (Figure 2). In the most recent patients, the burr hole over the cerebellar hemisphere was performed separately prior to the stereotactic biopsy procedure (see the Discussion). The customary surgical attention was given to the risks for possible air embolism, but no special equipment was used for embolus detection. The biopsy cannulas used were the standard instruments of the Backlund biopsy kit of the Leksell system [2,5], and the aim was always to obtain specimens for both embedding and sectioning and for smears. To prevent air embolism, the biopsy cannula should be "shut"
Figure I. The Leksell system offers alternative positioning of the patient during the biopsy procedure. The awake patient can be sitting upright, the surgeon sitting or standing behind (A). In children and other patients in need of general anesthesia, the head is supported by a Mayfield clamp (B). by its stylet or the aspiration syringe, respectively, during the procedure. Results It was possible to obtain more than one specimen from each biopsy target. As a rule, smears for cytology were also obtained. Except in one case, there were no difficulties in interpreting the preparations. (Some of the material in the present study was taken from an extensive study published earlier [11].) The diagnostic spectrum found in the present series is shown in Table 1. Two patients, one being the first in the series, was found to have cysts containing cerebrospinal fluid (CSF). One cyst was in the tegmental area and the other was located in the cerebellar peduncle. Shunts were introduced into both by the stereotactic technique using a special cannula for catheter placement [3]. The four acoustic tumors mirror a special treatment protocol that is used at the Karolinska Hospital when biopsies from selected pontine angle tumors are performed (Figure 3) in connection with treatment by stereotactic radiosurgery [18].
102
Surg Neurol 1987;28:100-4
Mathisen et al
A
Figure 2. In this case, a preoperative C T scan shows a tumor in the right brachium pontis. The stereotactic C T image, used for coordinate determination, is shown in (A). The biopsy target is indicated by the cursor. Smears for cytology (B) show the tumor to be an anaplastic astrocytoma (Giemsa stain, × 280, courtesy of Professor Sverre Moerk).
The procedures were usually performed without difficulty. The adult patients only received local anesthesia. No side effects were seen except in one case. A small boy with a pontine glioma, who before the operation had a left-sided hemiparesis, showed a more pronounced disability after the procedure. Furthermore, a suggestive adverse reaction occurred in a 48-year-old man with an oat-cell carcinoma metastasis in the cerebellar peduncle. Because the burr hole was made too close to the transverse sinus, a small sinus tear occurred when the dura mater was cut. The surgeon had to compress a small venous bleeding point for a while using Gelfoam (The Up john Company, Kalamazoo, MI). Meanwhile, the patient suddenly began coughing and felt uncomfortable. The operation was stopped for some time and the symptoms gradually subsided. The procedure then was continued without further problems. A plausible explanation for this reaction would be air embolism. All the patients were mobilized on the first postoperative day, when most of them could also be discharged.
Discussion When lesioning of the dentate nucleus was attempted for the treatment of cerebral palsy, stereotactic destruc-
tion was performed via the transcerebellar route [14]. The present study indicates that this route is also the proper approach to obtain stereotactic biopsy specimens from lesions in any region of the posterior fossa. In benign cystic lesions, which are often only lined with meningeal structures, the clinical problems usually encountered are due to the expansive character of the cyst [13]. Aggressive surgery, with attempts at radical removal of the cyst, is seldom indicated. Stereotactic diagnostic puncture followed by shunt insertion during the same procedure and using the transcerebellar approach is the treatment of choice. The area between the infra- and supratentorial compartments, the mesencephalic region, may also be approached from above, with the burr hole near the bregma, This approach is used for the implantation of electrodes
Table 1. Histology~Cytology Glioma Acoustic neurinoma Metastasis CSF cyst One each of pinealoma, germinoma, medulloblastoma, ependymoma, spontaneously obliterated AVM, and hematoma Not conclusive
14 4 2 2 6
1
Abbreviations:AVM,arteriovenousmalformation;CSF, cerebrospinalfluid.
Transcerebellar Biopsy
in the periaqueductal gray matter [ 15] or for stereotactic reconstruction of the aqueduct [6]. This anterior approach should also always be used when obtaining biopsy specimens from a tumor well above the tentorial notch. Large mesencephalic and pineal region tumors may however grow along or into the tegmental area, and if an infratentorial extension is present, as in two patients of the present series, the biopsy may well be done via the transcerebellar route. Careful attention should be paid to the preoperative angiograms (carotid and vertebral), the venous phase in particular. Any trajectory implying risk o f injury to the important vessels in the mesencephalic region must be avoided, irrespective of approach. The present study directs attention to some details in the operative technique, which are partly of a precautionary character: 1. The stereotactic frame should be tilted to make the projection of the stereotactic CT scan as similar as possible to that of the preoperative CT studies. This facilitates the selection of the biopsy target and the position of the needle trajectory in relation to critical anatomical structures. The position of the burr hole, over the cerebellar hemisphere, can be selected similarly.
Surg Neurol 1987;28:100-4
103
Figure 3. The straight approach through the cerebellar hemisphere is illustrated by this lateral x-ray from an acoustic neurinoma biopsy ~from Backlund [4]). 2. During the operation, the patient's head must be maximally flexed in relation to his neck and shoulders. The ideal position is when the straight sinus is congruent with the horizontal plane. With a patient in a sitting position, this means more flexion o f his neck than is usually assumed. The awake patient can cooperate, but when a patient is under general anesthesia with the aid of a Mayfield clamp, careful attention should be paid to the position of the patient's head. 3. As is the rule for supratentorial stereotactic operations, any approach in, or close to the midsagittal plane should be avoided. A trajectory through the central part of the cerebellar hemisphere, never through the vermis, may thus be considered the safest procedure for most purposes. The main reason for this is the arrangement of the vessels of the posterior fossa. 4. It is preferable to make the burr hole as a separate procedure before the stereotactic frame is applied. The patient can then be placed in a lying and prone position, which minimizes the risk for air embolism in case venous sinuses are accidentally opened.
104
Surg N e u r o l 1987;28:100-4
A second argument for the trephination to be performed separately is that the neck muscles of a patient occasionally may be very thick, making the preparation of even a single burr hole well below the transverse sinus more difficult than is the case in other parts of the skull. When the burr hole is completed, and the dura mater incised crosswise, the extracranial soft tissues are sutured. In principle they may be opened again for the biopsy. However, correct placement of the sutures at all levels during this initial phase of the operation may allow the definite biopsy sampling during the stereotactic part of the procedure to be done without opening more than a single suture. To have the burr hole "covered" by soft tissues thus further minimizes the risk for air embolism.
Conclusions For many years, the value of stereotactic biopsy as a diagnostic procedure in many cases of intracranial pathology has been self-evident. The nervous system within the posterior fossa has not often been the subject of stereotactic exploration however, some recent reports [7,9] indicate an interest in this region. The present study, reporting more than a decade of experience, proves the value of the transcerebellar approach to the infratentorial compartment and shows that any intracranial area can be safely approached for stereotactic biopsy if an appropriate technique, such as the one presented here, is used.
We thank Professors Lars Granholm and Torgny Greitz for access to chart files and x-ray material at the Karolinska Hospital. We also thank Dr. Georg Noren for his permission to include some of his cases and Dr. Jeremy Ganz for valuable criticism of the English language.
Mathisen et al
References 1. Apuzzo MLJ, Zelman V, Chandrasoma P. Observations with the utilization of the Brown-Robert-Wells stereotactic system in the management of intracranial mass lesions. Acta Neurochir 1984;Suppl 33:261-3. 2. Backlund EO. A new instrument for stereotactic brain tumor biopsy. Acta Chit Scand 1971;137:825-7. 3. Backlund EO. Stereotactic cystoventricular shunting--a new technique. Neurol Res (to be published). 4. Backlund EO. Stereotactic radiosurgery in intracranial tumors and vascular malformations. In: Krayenbuhl H, ed. Advances and technical standards. Vol. 1. Wien, New York: Springer Verlag, 1979:3-37. 5. Backlund EO, Johansson L, Sarby B, et al. Studies on craniopharyngiomas II. Treatment by stereotaxis and radiosurgery. Acta Chit Scand 1972;138:749-59. 6. Backlund EO, Grepe A, Lunsford D. Stereotactic reconstruction of the aqueduct of Sylvius. J Neurosurg 1981;55:800-10. 7. Bosch DA, Beute GN. Successful stereotactic evacuation of an acute pontomedullary haematoma. J Neurosurg 1985 ;62:153 -6. 8. Broggi G, Franzini A, Migliavacca F, Allegranza A. Stereotactic biopsy of deep brain tumors in infancy and childhood. Child's Brain 1983;10:92-8. 9. Coffey RJ, Lunsford LD. Stereotactic surgery for mass lesions of the midbrain and pons. Neurosurgery 1985;17:12-9. 10. Conway LW. Stereotactic biopsy of deep intracranial tumors. In: Schmidek HH, Sweet WH, eds. Operative neurosurgical techniques. Vol. I. New York: Grune & Stratton, 1982:389-401. 11. Edner G. Stereotactic biopsy of intracranial space occupying lesions. Acta Neurochir 1981;57:213-34. 12. Galanda M, Nadvornik P, Sramka M, Basandova M. Stereotactic biopsy of brainstem tumors. Acta Neurochir 1984 ;Suppl 33:213-7. 13. Galassi E, Tognetti F, Frank F, Fagioli L, Nasi MT, Gaist G. Infratentorial arachnoid cysts. J Neurosurg 1985;63:210-7. 14. Heimburger RF, Whitlock CC. Stereotactic destruction of the human dentate nucleus. Confin Neurol 1965;26:346-58. 15. Hosobuchi Y, Adams JE, Linchitz. Pain relief by electrical stimulation of the central gray matter and its reversal by naloxone. Science 1977;197:183-6. 16. Leksell L. Stereotaxis and neurosurgery. Springfield, IL: CC Thomas, 1972:5-68. 17. Leksell L, Jernberg B. Stereotaxis and tomography. Acta Neurochir 1980;52: I-7. 18. Noren G, Collins VP. Stereotactic biopsy in acoustic tumors. Appl Neurophysiol 1980;43:189-97.
Surg Neurol 1987;28:100-4
Transcerebellar Biopsy in the Posterior Fossa: 12 Years Experience Juan R. Mathisen, M.D., Filipo Giunta, M.D., Giovanni Marini, M.D., and Erik-Olof Backlund, M.D., Ph.D. Department of Neurosurgery, University of Bergen School of Medicine, Haukeland Hospital, Bergen, Norway, and Division of Neurosurgery, Ospedale Civili, Brescia, Italy
Mathisen JR, Giunta F, Marini G, Backlund E-O. Transcerebellar biopsy in the posterior fossa: 12 years experience. Surg Neurol 1987;28:100-4.
Utilizing the Leksell stereotactic system, the transcerebellar approach was used for posterior fossa biopsies. During a period of 12 years, a total of 29 patients were operated on by this technique, among them 12 children. In the adult, the procedure was carried out with the patient awake and sitting upright; the pediatric patients required general anesthesia and the head was supported either manually or by a clamp. Representative specimens were obtained in all cases but one, showing a wide diagnostic spectrum. As a rule, the procedures were performed smoothly, with no serious side effects. Stereotactic biopsies in the posterior fossa, hitherto seldom performed, open new diagnostic perspectives, one of which is for use in obscure brain stem lesions. The transcerebellar approach has been proven to be easy, direct, and safe provided an appropriate technique is used, such as that described in the present paper. KEYWORDS: Stereotactic biopsy; Posterior fossa; Brain tumor
Stereotactic procedures are now completely integrated in the diagnosis and management of a variety o f intracranial lesions. Even a seemingly insignificant and minute specimen from a deeply located tumor can provide tissue for diagnosis by conventional histological methods or by the smear technique. Although simple, the technique may imply a therapeutic program for the individual patient, radically different from what was originally planned. In addition, stereotactic biopsy opens new perspectives for the characterization o f a tumor by other means, for example, biological markers, immunohistochemistry, and D N A measurements. Chemical and physical parameters o f the tumor in situ, such as oxygen
tension, pH, temperature, and impedance, can also be studied using a stereotactic technique. A number of papers on stereotactic tumor biopsies published during recent years now represent a significant pool of knowledge, accumulated in many centers [10]. In these reports, however, operations in the posterior fossa are mentioned only occasionally. An explanation for this may be the neurosurgeon's fundamental reluctance to manipulate, by an invasive procedure, precarious pressure conditions in the posterior fossa without simultaneously decompressing it. The axial structures caudal to the mesencephalon are furthermore seldom the object for surgical measures and are thus not included in most surgeons' operative paradigm. Many stereotactic systems make it difficult or impossible to approach the intracranial compartment from behind. The patient is fixed to the operating table in the supine position, according to the practice developed during stereotactic procedures of a more conventional character. In the occasional cases o f posterior fossa biopsy hitherto published, a transtentorial-transcerebral trajectory has been chosen [1,8,12], increasing the operating risk. This has recently been emphasized [9]. The stereotactic system used must be completely versatile, giving access to an operative approach from any direction. Using the Leksell stereotactic system, the senior author (E.-O. B.) performed his first posterior fossa biopsy in 1975. In the first case it became evident that the transcerebellar approach was a simple, direct, and safe way to reach any compartment of the posterior fossa. The present study, representing experiences since then and using the same technique at the Karolinska Hospital, Stockholm, Sweden; Ospedale Civile, Brescia, Italy; and Haukeland Hospital, Bergen, Norway, gives further support to the value of the transcerebellar approach. Material and Methods
Address reprint requests to: Professor Erik-Olof Backlund, Nevrokirurgisk avdelning, 5016 Hauke|and sykehus, Norway.
© 1987 by Elsevier Science Publishing Co., Inc.
This study consisted of 29 patients; 18 males and 11 females (12 patients were children, 15 years of age or 0090-3019/87/$3.50
Transcerebellar Biopsy
Surg Neurol 1987;28:100-4
101
A
B
younger). The Leksell stereotactic system [ 16] was used, and the stereotactic coordinates were, as a rule, determined by computed tomography (CT) [17]. General anesthesia was used for the pediatric patients only. The biopsy was performed using a transcerebellar approach, with the patient sitting upright. The awake patient was placed on an ordinary chair beside an operating table, which was elevated to function as a comfortable armrest in front of the patient. The surgeon could conveniently sit or stand behind (Figure 1). In the pediatric patients under general anesthesia, the head was supported by hand or with a Mayfield clamp or Garder-Wells skull traction tongs, tightened just enough to hold the head. To prevent air embolism the pins should not be allowed to penetrate more than the outer table of the skull (Figure 2). In the most recent patients, the burr hole over the cerebellar hemisphere was performed separately prior to the stereotactic biopsy procedure (see the Discussion). The customary surgical attention was given to the risks for possible air embolism, but no special equipment was used for embolus detection. The biopsy cannulas used were the standard instruments of the Backlund biopsy kit of the Leksell system [2,5], and the aim was always to obtain specimens for both embedding and sectioning and for smears. To prevent air embolism, the biopsy cannula should be "shut"
Figure I. The Leksell system offers alternative positioning of the patient during the biopsy procedure. The awake patient can be sitting upright, the surgeon sitting or standing behind (A). In children and other patients in need of general anesthesia, the head is supported by a Mayfield clamp (B). by its stylet or the aspiration syringe, respectively, during the procedure. Results It was possible to obtain more than one specimen from each biopsy target. As a rule, smears for cytology were also obtained. Except in one case, there were no difficulties in interpreting the preparations. (Some of the material in the present study was taken from an extensive study published earlier [11].) The diagnostic spectrum found in the present series is shown in Table 1. Two patients, one being the first in the series, was found to have cysts containing cerebrospinal fluid (CSF). One cyst was in the tegmental area and the other was located in the cerebellar peduncle. Shunts were introduced into both by the stereotactic technique using a special cannula for catheter placement [3]. The four acoustic tumors mirror a special treatment protocol that is used at the Karolinska Hospital when biopsies from selected pontine angle tumors are performed (Figure 3) in connection with treatment by stereotactic radiosurgery [18].
102
Surg Neurol 1987;28:100-4
Mathisen et al
A
Figure 2. In this case, a preoperative C T scan shows a tumor in the right brachium pontis. The stereotactic C T image, used for coordinate determination, is shown in (A). The biopsy target is indicated by the cursor. Smears for cytology (B) show the tumor to be an anaplastic astrocytoma (Giemsa stain, × 280, courtesy of Professor Sverre Moerk).
The procedures were usually performed without difficulty. The adult patients only received local anesthesia. No side effects were seen except in one case. A small boy with a pontine glioma, who before the operation had a left-sided hemiparesis, showed a more pronounced disability after the procedure. Furthermore, a suggestive adverse reaction occurred in a 48-year-old man with an oat-cell carcinoma metastasis in the cerebellar peduncle. Because the burr hole was made too close to the transverse sinus, a small sinus tear occurred when the dura mater was cut. The surgeon had to compress a small venous bleeding point for a while using Gelfoam (The Up john Company, Kalamazoo, MI). Meanwhile, the patient suddenly began coughing and felt uncomfortable. The operation was stopped for some time and the symptoms gradually subsided. The procedure then was continued without further problems. A plausible explanation for this reaction would be air embolism. All the patients were mobilized on the first postoperative day, when most of them could also be discharged.
Discussion When lesioning of the dentate nucleus was attempted for the treatment of cerebral palsy, stereotactic destruc-
tion was performed via the transcerebellar route [14]. The present study indicates that this route is also the proper approach to obtain stereotactic biopsy specimens from lesions in any region of the posterior fossa. In benign cystic lesions, which are often only lined with meningeal structures, the clinical problems usually encountered are due to the expansive character of the cyst [13]. Aggressive surgery, with attempts at radical removal of the cyst, is seldom indicated. Stereotactic diagnostic puncture followed by shunt insertion during the same procedure and using the transcerebellar approach is the treatment of choice. The area between the infra- and supratentorial compartments, the mesencephalic region, may also be approached from above, with the burr hole near the bregma, This approach is used for the implantation of electrodes
Table 1. Histology~Cytology Glioma Acoustic neurinoma Metastasis CSF cyst One each of pinealoma, germinoma, medulloblastoma, ependymoma, spontaneously obliterated AVM, and hematoma Not conclusive
14 4 2 2 6
1
Abbreviations:AVM,arteriovenousmalformation;CSF, cerebrospinalfluid.
Transcerebellar Biopsy
in the periaqueductal gray matter [ 15] or for stereotactic reconstruction of the aqueduct [6]. This anterior approach should also always be used when obtaining biopsy specimens from a tumor well above the tentorial notch. Large mesencephalic and pineal region tumors may however grow along or into the tegmental area, and if an infratentorial extension is present, as in two patients of the present series, the biopsy may well be done via the transcerebellar route. Careful attention should be paid to the preoperative angiograms (carotid and vertebral), the venous phase in particular. Any trajectory implying risk o f injury to the important vessels in the mesencephalic region must be avoided, irrespective of approach. The present study directs attention to some details in the operative technique, which are partly of a precautionary character: 1. The stereotactic frame should be tilted to make the projection of the stereotactic CT scan as similar as possible to that of the preoperative CT studies. This facilitates the selection of the biopsy target and the position of the needle trajectory in relation to critical anatomical structures. The position of the burr hole, over the cerebellar hemisphere, can be selected similarly.
Surg Neurol 1987;28:100-4
103
Figure 3. The straight approach through the cerebellar hemisphere is illustrated by this lateral x-ray from an acoustic neurinoma biopsy ~from Backlund [4]). 2. During the operation, the patient's head must be maximally flexed in relation to his neck and shoulders. The ideal position is when the straight sinus is congruent with the horizontal plane. With a patient in a sitting position, this means more flexion o f his neck than is usually assumed. The awake patient can cooperate, but when a patient is under general anesthesia with the aid of a Mayfield clamp, careful attention should be paid to the position of the patient's head. 3. As is the rule for supratentorial stereotactic operations, any approach in, or close to the midsagittal plane should be avoided. A trajectory through the central part of the cerebellar hemisphere, never through the vermis, may thus be considered the safest procedure for most purposes. The main reason for this is the arrangement of the vessels of the posterior fossa. 4. It is preferable to make the burr hole as a separate procedure before the stereotactic frame is applied. The patient can then be placed in a lying and prone position, which minimizes the risk for air embolism in case venous sinuses are accidentally opened.
104
Surg N e u r o l 1987;28:100-4
A second argument for the trephination to be performed separately is that the neck muscles of a patient occasionally may be very thick, making the preparation of even a single burr hole well below the transverse sinus more difficult than is the case in other parts of the skull. When the burr hole is completed, and the dura mater incised crosswise, the extracranial soft tissues are sutured. In principle they may be opened again for the biopsy. However, correct placement of the sutures at all levels during this initial phase of the operation may allow the definite biopsy sampling during the stereotactic part of the procedure to be done without opening more than a single suture. To have the burr hole "covered" by soft tissues thus further minimizes the risk for air embolism.
Conclusions For many years, the value of stereotactic biopsy as a diagnostic procedure in many cases of intracranial pathology has been self-evident. The nervous system within the posterior fossa has not often been the subject of stereotactic exploration however, some recent reports [7,9] indicate an interest in this region. The present study, reporting more than a decade of experience, proves the value of the transcerebellar approach to the infratentorial compartment and shows that any intracranial area can be safely approached for stereotactic biopsy if an appropriate technique, such as the one presented here, is used.
We thank Professors Lars Granholm and Torgny Greitz for access to chart files and x-ray material at the Karolinska Hospital. We also thank Dr. Georg Noren for his permission to include some of his cases and Dr. Jeremy Ganz for valuable criticism of the English language.
Mathisen et al
References 1. Apuzzo MLJ, Zelman V, Chandrasoma P. Observations with the utilization of the Brown-Robert-Wells stereotactic system in the management of intracranial mass lesions. Acta Neurochir 1984;Suppl 33:261-3. 2. Backlund EO. A new instrument for stereotactic brain tumor biopsy. Acta Chit Scand 1971;137:825-7. 3. Backlund EO. Stereotactic cystoventricular shunting--a new technique. Neurol Res (to be published). 4. Backlund EO. Stereotactic radiosurgery in intracranial tumors and vascular malformations. In: Krayenbuhl H, ed. Advances and technical standards. Vol. 1. Wien, New York: Springer Verlag, 1979:3-37. 5. Backlund EO, Johansson L, Sarby B, et al. Studies on craniopharyngiomas II. Treatment by stereotaxis and radiosurgery. Acta Chit Scand 1972;138:749-59. 6. Backlund EO, Grepe A, Lunsford D. Stereotactic reconstruction of the aqueduct of Sylvius. J Neurosurg 1981;55:800-10. 7. Bosch DA, Beute GN. Successful stereotactic evacuation of an acute pontomedullary haematoma. J Neurosurg 1985 ;62:153 -6. 8. Broggi G, Franzini A, Migliavacca F, Allegranza A. Stereotactic biopsy of deep brain tumors in infancy and childhood. Child's Brain 1983;10:92-8. 9. Coffey RJ, Lunsford LD. Stereotactic surgery for mass lesions of the midbrain and pons. Neurosurgery 1985;17:12-9. 10. Conway LW. Stereotactic biopsy of deep intracranial tumors. In: Schmidek HH, Sweet WH, eds. Operative neurosurgical techniques. Vol. I. New York: Grune & Stratton, 1982:389-401. 11. Edner G. Stereotactic biopsy of intracranial space occupying lesions. Acta Neurochir 1981;57:213-34. 12. Galanda M, Nadvornik P, Sramka M, Basandova M. Stereotactic biopsy of brainstem tumors. Acta Neurochir 1984 ;Suppl 33:213-7. 13. Galassi E, Tognetti F, Frank F, Fagioli L, Nasi MT, Gaist G. Infratentorial arachnoid cysts. J Neurosurg 1985;63:210-7. 14. Heimburger RF, Whitlock CC. Stereotactic destruction of the human dentate nucleus. Confin Neurol 1965;26:346-58. 15. Hosobuchi Y, Adams JE, Linchitz. Pain relief by electrical stimulation of the central gray matter and its reversal by naloxone. Science 1977;197:183-6. 16. Leksell L. Stereotaxis and neurosurgery. Springfield, IL: CC Thomas, 1972:5-68. 17. Leksell L, Jernberg B. Stereotaxis and tomography. Acta Neurochir 1980;52: I-7. 18. Noren G, Collins VP. Stereotactic biopsy in acoustic tumors. Appl Neurophysiol 1980;43:189-97.