The actual management of tumor and vertebral compression fractures.

Tumor related fractures of the spine frequently dictate surgical management. The most critical factors influencing the need and type of surgery are degree of epidural cord compression, radiosensitivity of the tumor, presence of spinal instability and patient medical status/ estimated survivorship. There is a wide spectrum of therapeutic options: major en bloc resections in primary or oligometastatic disease; decompression and fusion in non-radiosensitive tumors with cord compression followed by adjuvant radiation therapy (RT); kyphoplasty/ vertebroplasty for stable compression fractures or minimally invasive corpectomy for more unstable fractures and RT- only for radiosensitive tumors not causing overt instability. Radiation therapy has always been essential component of the treatment algorithm although it has been displaced from principal treatment modality in the last 2 decades. However, the advent of more targeted and efficient forms of RT (radiosurgery) may be a new treatment paradigm for more radioresistant tumors and may obviate the need for major operations.

Meningiomas of the cerebellopontine angle.

BACKGROUND: Meningiomas of the cerebellopontine angle (CPA), although uniform in location, are diverse with regard to the site of dural origin and displacement of neurovascular structures. A study of patients with CPA meningiomas was undertaken to gain more information regarding the relationship between site of dural attachment, clinical presentation, operative approach, and outcome. METHODS: In this report, we retrospectively review 40 patients with CPA meningiomas managed surgically. RESULTS: Common clinical presentations were hearing loss, unsteadiness, and dysequilibrium. Findings upon physical examination included hearing loss (73%), cerebellar signs (32%), trigeminal neuropathy (16%), and facial nerve dysfunction (16%). The most common site of dural origin was the petrous ridge (anterior to the IAC [26%], posterior [21%], superior [18%], and inferior [16%]). Less common sites of dural origin included the tentorium (31%), the clivus (15%), the IAC (10%), and the jugular foramen (8%). Site of dural origin determined the direction of displacement of the facial/vestibulocochlear nerve bundle. The most common microsurgical complication was facial nerve dysfunction (30%). Gross total resection was achieved in 82% of cases, whereas 18% underwent subtotal resection. Two patients died. Follow-up ranged from three months to 13 years with three recurrences. CONCLUSIONS: CPA meningiomas displace the seventh and eighth cranial nerves in various directions depending on the site of dural origin. Total surgical excision can be accomplished in the majority of cases with acceptable morbidity.

Gap junctions: the "kiss of death" and the "kiss of life".

Cells expressing herpes simplex-thymidine kinase (HSV-tk) can be killed "in vitro" within 5 days of treatment with 20 microM ganciclovir (GCV) and transmit this toxicity to adjacent cells lacking HSV-tk; this phenomenon was termed "bystander effect" or "kiss of death". On testing a large number of cell lines in vitro, a wide range of sensitivity to GCV-mediated bystander killing has been reported. Although intercellular transfer of GCV metabolites through gap junction channels seems to be a likely mechanism for the "kiss of death", some studies suggest that other pathways may contribute to induced apoptosis of neighboring cells. To further investigate the mechanism underlying cell death mediated by HSV-tk and to evaluate the efficacy of gap junction channels formed by different connexins in this process, we have stably transfected a virtually uncoupled mouse neuroblastoma cell line (N2A cells) with different connexin-types expressed by neural cells (Cx32, Cx37, Cx40, Cx43) and co-cultured these cells with N2A cells stably transfected with Cx37 and HSV-tk. Here, we confirm our previous studies and those of others that the extent of cell death and sensitivity to GCV depend on the degree of connexin expression in transfectants. Further, we show that the bystander effect also depends on which connexin is expressed; reported disparities regarding the extent of GCV-mediated cellular apoptosis are likely due both to the degree of functional coupling and the type of connexin expressed. These results support the notion that gap junction hemichannels formed of certain connexins are more likely than others to pair functionally with Cx37, and suggest co-transfection strategies that might prove effective in sensitizing tumor cell populations to GCV. In addition, potential applications are discussed for use of the "good Samaritan effect", a mechanism by which bystander cells have been suggested to prevent cytotoxicity.

Temporal bone meningiomas.

Meningiomas involving the temporal bone may originate from arachnoid cell nests present within the temporal bone (intratemporal), but more frequently originate from arachnoid cell nests of the posterior or middle cranial fossa with secondary invasion of the TB (extratemporal). In this study, we retrospectively reviewed the charts of 13 patients with meningiomas involving the temporal bone who underwent surgery. Tumors of the posterior fossa with only temporal bone hyperostosis, but without invasion, were excluded. Patients presented primarily with otologic symptoms and signs. The tumors originated in the temporal bone (5/13), jugular foramen (4/13), petroclival region (2/13), the asterion (1/13) or the internal auditory meatus (1/13). All of the intratemporal meningiomas had the radiological appearance of en-plaque menigiomas. The tumor extended into the middle ear (11/13), eustachian tube (5/13), and/or the labyrinth (3/13). A gross total resection was achieved in 11 patients and a subtotal resection in 2 patients. The lower cranial nerves were infiltrated by tumor in 4 patients, and were sacrificed. At a mean follow-up of approximately 6 years, 12 patients are currently alive and doing well and 1 died from tumor progression. Six patients showed tumor recurrence and were reoperated on (5/6) or followed conservatively (1/6). Surgical treatment of temporal bone meningiomas is associated with high recurrence rate due to indiscreet tumor margins. Combined surgical approaches (temporal craniotomy and mastoidectomy) by neurosurgical and otological teams are recommended for meningiomas originating in the temporal bone.

Gene therapy of neoplastic meningosis.

Gene therapy of neoplastic meningosis is a promising new approach that relies on introduction of 'suicide' genes into cancer cells. The most commonly used gene has been the herpes virus thymidine kinase gene (HSV-tk) which has been delivered to cancer cells via retroviral or adenoviral vectors. A bystander cytocidal effect to non-transduced tumor cells has been documented and is dependent upon intercellular communication via gap junctions. A variety of gene therapy approaches using the HSV-tk system have been used in experimental models of neoplastic meningosis with promising results. Optimizing vector design and bystander cytotoxicity is a prerequisite for successful gene therapy in patients with neoplastic meningosis.

Asterion meningiomas.

Asterion meningiomas arise from the posterior petrous ridge at the junction of the transverse and sigmoid sinuses (sinodural angle). The authors retrospectively reviewed the charts of seven patients with asterion meningiomas who underwent a Simpson I tumor resection by either the petrosal or suboccipital approach. Patients presented with headaches, dizziness, ataxia, or seizures. Preoperative angiograms and intraoperative observations confirmed occlusion of the transverse and sigmoid sinuses by tumor, thrombus, or both in four of the patients. In all cases, tumor infiltrated the sinuses and the sinuses were ligated without adverse sequelae. Temporal bone invasion was seen in one patient who had the only tumor recurrence. Postoperatively, there were two transient CSF leaks. Asterion meningiomas can be completely resected with a low incidence of major morbidity. In this small series, a patent transverse/sigmoid sinus was resected in three patients without sequelae. We believe that in young patients with asterion meningiomas a nondominant transverse/sigmoid sinus should be resected if the torcula is patent. More research is needed to determine the safety of resecting a patent dominant transverse/sigmoid sinus.

The bystander effect exerted by tumor cells expressing the herpes simplex virus thymidine kinase (HSVtk) gene is dependent on connexin expression and cell communication via gap junctions.

To elucidate the role gap junctions play in the bystander effect, we examined the cytotoxic effect of herpes simplex virus thymidine kinase (HSVtk) modified tumor cells on gap junction communication-deficient tumor cells and their connexin transfectants. Communication competent Walker 256 tumor cells engineered to express the HSVtk gene (Walker-tk+) when cocultured with N2A mouse neuroblastoma and PC12 rat pheochromocytoma cells with absent endogenous junctional conductance showed no bystander cytotoxicity. Transfection of N2A cells with the rat connexin37 gene (5Q) and PC12 cells with the human connexin43 gene rendered them susceptible to bystander cell death. Additionally, communication-deficient N2A cells transfected with the HSVtk gene failed to exert a bystander effect, whereas N2A transfectants coexpressing the connexin37 and HSVtk genes (5Qtk+ cells) exerted bystander cytotoxicity on gap junction communication-competent 5Q but not on communication-deficient N2A cells in vitro. In vivo experiments also showed tumor growth inhibition of communication-competent 5Q but not communication-incompetent N2A cells by 5Qtk+ cells. In conclusion, these results indicate that in several cellular environments the bystander effect is dependent on connexin expression and gap junctional communication between HSVtk-positive and HSVtk-negative cells.

Use of cranial surface anatomic fiducials for interactive image-guided navigation in the temporal bone: a cadaveric study.

OBJECTIVE: Because of the intricate anatomy of the temporal bone, we examined the feasibility and reliability of cranial surface anatomic fiducials to register computed tomographic images of the temporal bone by using a frameless image-guided system. METHODS: One-millimeter thick computed tomographic slices and the smallest possible field of view were used to register 10 dry and 10 fresh temporal bones from cadavers. The fiducials used for registration included the umbo of the tympanic membrane, emissary foramina, the asterion, various sutures, the tip of the mastoid process, and Henle's spine. RESULTS: Mean initial fiducial registration error ranged from 0.6 to 0.7 mm, and was reduced to 0.5 and 0.4 mm for the dry cranial and cadaveric studies, respectively, by eliminating or reregistering inexact fiducials. Mean target localization error ranged from 0.91 to 2.44 mm for superficial structures of the temporal bone in the dry cranial specimens and from 0.71 to 1.52 mm for deep structures such as the facial nerve, semicircular canals and ossicles in the cadaveric study. CONCLUSION: Interactive image-guided navigation in the temporal bone is possible with registration of cranial surface anatomic fiducials. It may be useful to the neurosurgeon and otologist in identifying critical anatomic structures of the temporal bone encountered during the translabyrinthine, retrolabyrinthine presigmoid, and suboccipital approaches.

Image-interactive orientation in the middle cranial fossa approach to the internal auditory canal: an experimental study.

Approaches through the middle cranial fossa directed at reaching the internal auditory canal (IAC) invariably employ exposure of the geniculate ganglion, the superior semicircular canal (SSC) or the epitympanum. This involves risk to the facial nerve and hearing apparatus. To minimize this risk, we conducted a laboratory study on 9 cadaver temporal bones by using an image-interactive guidance system (StealthStation) to provide topographic orientation in the middle fossa approach. Surface anatomic fiducials such as the umbo of the tympanic membrane, Henle's spine, the root of the zygoma and various sutures were used as fiducials for registration of CT-images of the temporal bone. Accurate localization of the IAC was achieved in every specimen. Mean target localization error varied from 1.20 to 1.38 mm for critical structures in the temporal bone such as the apex of the cochlea, crus commune, ampula of the SSC and facial hiatus. Our results suggest that frameless stereotaxy may be used as an alternative to current methods in localizing the IAC in patients with small vestibular schwannomas or intractable vertigo undergoing middle fossa surgery.

Preservation of the bystander cytocidal effect of irradiated herpes simplex virus thymidine kinase (HSV-tk) modified tumor cells.

In vitro and animal experiments have demonstrated the potential efficacy of using the bystander effect alone in the treatment of brain tumors. A known problem in some in vitro and in vivo experiments is that a fraction of cells engineered to express the herpes simplex virus thymidine kinase (HSV-tk) gene survive ganciclovir (GCV) treatment and undergo cell division. To prevent the recurrent growth of HSV-tk+ cells in the presence of GCV we examined the potential use of lethal or sublethal irradiation of Walker 256 carcinosarcoma cells selected for expression of the HSV-tk gene (Walker-tk+). Western blot analysis of Walter-tk+ cells showed similar levels of HSV-tk protein expression at 0, 1, 3, 6 and 9 days after lethal gamma-irradiation. In vitro, there was no difference in the bystander effect exerted by non-irradiated, sublethally irradiated or lethally irradiated Walker-tk+ cells on wild-type Walker cells in the presence of GCV. In vivo experiments demonstrated long-term survival (100 days) in rats implanted intrathecally with sublethally or lethally irradiated Walker-tk+ cells with GCV treatments. Intrathecal implantation of irradiated Walker-tk+ cells either pre-mixed with Walker cells or used in in situ treatment of established Walker tumors resulted in prolonged animal survival compared to controls (p < 0.05). These experiments suggest that the bystander tumoricidal effect is preserved despite gamma-irradiation of the HSV-tk modified tumor cells and that irradiation could be an effective method to prevent long-term resistance to GCV in HSV-tk+ tumor cells.

Microsurgical anatomy of the infratemporal fossa as viewed laterally and superiorly.

OBJECTIVE: Benign tumors involving cavernous sinus, trigeminal nerve, and middle cranial fossa occasionally extend to the infratemporal fossa (ITF). In this study, we describe the microsurgical anatomy and dissection of the ITF, as viewed laterally and superiorly. We also describe a new bypass graft to the supraclinoid internal carotid artery using the internal maxillary artery (IMA), which is found in the ITF. METHODS: Twelve cadaver specimens were used. Dissection required zygomatic arch osteotomy, downward displacement of the temporalis muscle, extensive subtemporal craniectomy, and mild elevation of the temporal lobe together with the dura. RESULTS: The anatomic relationships between the lateral and medial pterygoid muscles and the neurovascular bundle of the ITF are demonstrated. The neurovascular bundle contains the IMA, which runs horizontally, and the main branches of the mandibular nerve, which run vertically. The course and anatomic variations of the IMA and inferior alveolar, lingual, auriculotemporal, and buccal nerves are shown. The distal IMA was quite tortuous and, when the artery straightened, we were able to perform a tension-free in situ IMA graft to the supraclinoid carotid artery in 9 of 12 specimens. CONCLUSIONS: Knowledge of the anatomy of the ITF is a prerequisite for tumor resection in this area. The IMA may serve as a bypass graft to the supraclinoid internal carotid artery if the cavernous or petrous carotid artery is involved by tumor and needs to be sacrificed.

Tumor cells expressing the herpes simplex virus-thymidine kinase gene in the treatment of Walker 256 meningeal neoplasia in rats.

A promising strategy in the treatment of neoplastic meningitis involves the use of herpes simplex virus-thymidine kinase (HSV-tk)-modified cells. In these experiments the authors used cells expressing HSV-tk to treat meningeal carcinomatosis in the rat Walker 256 model. Intrathecal injection of 2 x 10(5) Walker cells resulted in a median survival time of 15 days. Up to 80% of animals implanted with HSV-tk-modified Walker cells (Walker-tk+) and treated with ganciclovir showed long-term survival (120 days or more), whereas the remaining animals died from tumor growth between 37 and 44 days after implantation. Tumor cells from an animal in which the treatment failed were cultured in vitro and were shown to be still sensitive to ganciclovir. However, continuous ganciclovir administration for 6 weeks rather than 2 weeks did not improve survival. Histopathological studies confirmed leptomeningeal infiltration in the untreated Walker or Walker-tk+ animals. Walker-tk+ cells were mixed with Walker cells in 1:1, 10:1, or 50:1 ratios, respectively, and implanted intrathecally; the animals were treated with ganciclovir. All groups of treated animals had long-term survivors, with 40% of the rats in the 10:1 and 50:1 groups demonstrating long-term survival and absence of microscopic tumors in the brain or spinal cord. Similarly, murine fibroblast HSV-tk virus-producer cells improved survival. Walker-tk+ cells were better than fibroblast-producer cells in improving the survival of animals with Walker tumors at low (1:1) but not at high (10:1) effector-to-target cell ratios. Repeated intrathecal administration of Walker-tk+ cells resulted in inhibition of established Walker tumors. The authors conclude that Walker-tk+ cells are at least as effective as murine virus-producer cells and could be used in the treatment of meningeal neoplasia.

A more potent bystander cytocidal effect elicited by tumor cells expressing the herpes simplex virus-thymidine kinase gene than by fibroblast virus-producer cells in vitro.

Retrovirus-mediated herpes simplex virus-thymidine kinase (HSV-tk) gene therapy is a promising approach in the treatment of brain tumors. Previous in vitro and in vivo studies have demonstrated a bystander effect in which nonmodified tumor cells in proximity to HSV-tk-modified tumor cells are killed with the modified cells in the presence of ganciclovir. In the present study the authors assessed the contribution of infectious HSV-tk retrovirus made by producer cells to the bystander cytocidal effect in tissue culture using Walker 256 rat breast carcinosarcoma cells, which represent an established model for carcinomatous meningitis. The authors observed ganciclovir-dependent growth inhibition even when only one HSV-tk-positive Walker cell was mixed with 1000 HSV-tk-negative Walker cells and showed that the bystander cytocidal effect is not mediated by toxic cell lysis products. Walker cells engineered to produce HSV-tk retrovirus with titers ranging from 10(3) to 10(5) colony-forming units/ml exert no greater cytocidal effect than nonviral producer HSV-tk-positive Walker cells in vitro. Murine fibroblast-producer cells with viral titers ranging from 10(6) to 10(7) colony-forming units/ml exerted a stronger cytocidal effect than nonviral producer HSV-tk-positive murine fibroblasts. Despite the high viral titers of fibroblast producer cells, HSV-tk-modified Walker cells performed better than fibroblast producer cells in their cytotoxic effect on wild-type Walker tumor cells. Given that HSV-tk-modified tumor cells can become ganciclovir resistant, we tested gamma-irradiation as a means to overcome resistance. Lethal gamma-irradiation of the HSV-tk-positive Walker cells did not abolish their bystander effect on Walker HSV-tk-negative cells. One can infer from these results that HSV-tk-modified tumor cells, irradiated or not, may be a better alternative to murine fibroblast producer cells in the treatment of central nervous system neoplasia.

Bystander tumoricidal effect in the treatment of experimental brain tumors.

The retrovirus-mediated transfer of the herpes simplex virus-thymidine kinase (HSV-tk) gene into tumor cells renders them sensitive to the cytocidal effect of the antiviral drug ganciclovir. This method has shown promising results as a treatment for experimental brain tumors. These experiments indicate that a major mechanism for the effectiveness of HSV-tk retroviral gene therapy may be the bystander tumoricidal effect. The bystander effect was hypothesized to explain tumor eradication, given that the efficacy of in vivo gene transfer to tumor cells was less than 100%. We demonstrate, in this report, that the bystander tumoricidal effect is a major contributor to the tumoricidal effect of ganciclovir in cell culture experiments using the mouse K1735 C19 cerebral melanoma line, thereby expanding the observation of the bystander phenomenon to a broader range of tumor types. The bystander effect was studied in vitro by coculturing wild-type C19 melanoma cells with HSV-tk-expressing C19 (C19-STK) cells. A maximal tumoricidal effect was seen when only 1 in 10 tumor cells expressed the HSV-tk gene. This suggests that in effect, 1 tumor cell with the HSV-tk gene, when given ganciclovir, will destroy 10 neighboring or bystander cells. The destruction of bystander cells does not appear to be mediated by a soluble factor(s) released into the media but, rather, requires close cell proximity or cell contact. In addition, HSV-tk-expressing C19 cells can exert an antitumoral effect not only on wild-type C19 cells but also on cells from a variety of different tumor cell lines, including a human glioblastoma multiforme cell line, indicating that the bystander effect is not a cell line-specific phenomenon. Finally, we observed that the bystander tumoricidal effect could be harnessed directly without using retrovirus-producing cells to increase survival in the mouse C19 brain tumor model. The potential implications of our findings in treating human brain tumors are discussed.

Anti-GM2 monoclonal antibodies induce necrosis in GM2-rich cultures of a human glioma cell line.

The effects of four anti-GM2 monoclonal antibodies (DMAb-1, DMAb-2, DMAb-3, and DMAb-5) were studied on spheroid cultures from a human glioma cell line (D-54 MG) that is known to express high levels of GM2. The spheroids developed central necrosis 48 h after antibody exposures at concentrations greater than 6 micrograms/ml. No necrosis was found with antibodies that had been absorbed with GM2 prior to exposure or with unrelated cytotoxic antibodies. Immunohistochemistry showed that the necrosis started shortly after the antibodies were evenly distributed throughout the spheroids. Light and transmission electron microscopy revealed that a small portion of the cells, mainly in the periphery of the spheroids, was unaffected by antibody exposure. New monolayer cultures established from antibody-treated cells expressed a 50% lower GM2 content as shown by flow cytometry and determination of ganglioside content throughout at least 12 passages. Thus, the GM2-rich D-54 MG cell line has subpopulations of cells with lower GM2 content. Spheroids obtained from this subpopulation developed only minor necrosis after antibody treatment. These results show that GM2 antibodies cause severe necrosis of GM2-containing glioma cells in vitro, but the effect depends on the concentration of antigen, and a threshold number of GM2 molecules is required.

Five new epitope-defined monoclonal antibodies reactive with GM2 and human glioma and medulloblastoma cell lines.

In order to investigate GM2 expression in gliomas, the GM2-positive human glioma cell line (HGL) D-54 MG, which contains 0.6 nmol GM2/mg protein, representing 77% of the total monosialoganglioside fraction, was used as an immunogen for the production of anti-GM2 monoclonal antibodies. For ganglioside designations, see IUPAC-IUB (Eur. J. Biochem., 79: 11-21, 1977) and Svennerholm (J. Neurochem., 10: 613-623, 1963). Five IgM monoclonal antibodies (DMAb-1 through DMAb-5) specifically recognizing the GalNAc beta1-4(NeuAc alpha 2-3)Gal-terminal epitope common to GM2 and GalNAC-GD1a are reported. The antibodies did not react with GM1, GM3, GD2, GD3, GD1a, GD1b, and GQ1b. Purified anti-GM2 MAbs were used to define the expression of the "GM2" terminal epitope by cultured human malignant and normal cells by radioimmunoassay and membrane immunofluorescence. Among neuroectodermal tissue-derived cell lines, DMAb-3, at an optimal concentration of 5 micrograms/ml, showed high reactivity (radioimmunoassay binding ratios greater than 20) with 9 of 19 HGLs, 3 of 5 medulloblastoma, 4 of 5 neuroblastoma, and 1 of 3 melanoma lines. Moderate reactivity (binding ratio, 10-20) was exhibited by 3 HGL, 2 medulloblastoma, and 1 neuroblastoma lines and low reactivity (binding ratio, 3-10) by 5 HGL lines; no reactivity was detected with 2 HGL and 2 melanoma lines. Densitometric evaluation of monosialoganglioside extracts from human glioma and medulloblastoma cell lines in conjunction with immunostaining on thin-layer chromatograms showed that GM2 represents the major monosialoganglioside in 8 of 10 HGL and in 3 of 4 Med lines. In these lines the amount of GM2 ranged from less than 0.1 to 0.6 nmol/mg protein. These results indicate that GM2 represents a proportionally increased ganglioside of most glioma, medulloblastoma, and neuroblastoma cells in vitro.

A new ganglioside of the lactotetraose series, GalNAc-3'-isoLM1, detected in human meconium.

A monoclonal antibody produced by immunization with cells of the human glioma cell line D-54 MG reacted with ganglioside GM2. The binding epitope of the antibody was found to be GalNAc beta 1-4(NeuAc alpha 2-3)Gal. Immunological detection of glycolipid antigens on thin-layer plates with this monoclonal antibody, DMAb-1, revealed the presence of a new ganglioside. This ganglioside, co-migrating with NeuAc alpha 2-6Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer(6'-LM1) and GalNAc beta 1-4(NeuAc alpha 2-3)Gal beta 1-3GalNAc beta 1-4Gla beta 1-4Glc beta 1-1Cer (GalNAc-isoGM1) at chromatographic separation was isolated from human meconium. Its structure was determined by permethylation and fast atom bombardment-mass spectometry analyses. The new ganglioside was found to be a combination of the lacto and ganglio series gangliosides, and the structure found to be GalNAc beta 1-4(NeuAc alpha 2-3)Gal beta 1-3GlcNAc alpha 1-3Gal beta 1-4Glc beta 1-1Cer(GalNAc-3'-isoLM1).