Petroclival meningiomas: update of current treatment and consensus by the EANS skull base section.

BACKGROUND: The optimal management of petroclival meningiomas (PCMs) continues to be debated along with several controversies that persist. METHODS: A task force was created by the EANS skull base section along with its members and other renowned experts in the field to generate recommendations for the management of these tumors. To achieve this, the task force reviewed in detail the literature in this field and had formal discussions within the group. RESULTS: The constituted task force dealt with the existing definitions and classifications, pre-operative radiological investigations, management of small and asymptomatic PCMs, radiosurgery, optimal surgical strategies, multimodal treatment, decision-making, and patient's counselling. CONCLUSION: This article represents the consensually derived opinion of the task force with respect to the management of PCMs.

Growth dynamics of meningiomas in patients with multiple sclerosis treated with interferon: report of two cases.

BACKGROUND: Although multiple sclerosis (MS) is a common disease of the central nervous system, the association of intraparenchymal tumour has been rarely reported and the potential relationship between intracranial meningioma and MS has not been seriously analysed. This report addresses the association of multiple sclerosis and intracranial meningioma and discusses the effect of interferon treatment on tumour progression. CLINICAL PRESENTATION: We report two cases with multiple sclerosis, who developed meningioma four and twenty years after the diagnosis of MS was made. Neither patient had a history of meningioma initially and both were being treated interferon when the meningioma was progressed. FINDINGS: Histological examination of two cases revealed meningothelial meningioma. The first patient's KI67 level was 2.5% and was positive for the progesterone and estrogen receptor. Chromosomal analysis showed some abnormalities. In the second case, mild atypical change by presence of nuclear enlargement and rare mitotic figures were noted and PCNA, KI67 levels were less than 2%. CONCLUSIONS: We reported the association of multiple sclerosis and intracranial meningioma and observed the progression of the meningiomas during interferon treatment. Although, we cannot exclude the coincidence between the two diseases we discussed suspicious relationship between the interferon treatment and the tumour progression.

Surgical seeding of chordomas.

OBJECT: Chordomas have a high propensity for local recurrence and progression, as well as for systemic and cerebrospinal fluid metastasis. The authors identified and analyzed a series of patients with chordomas, focusing on an underrecognized pathological entity-surgical seeding of tumor cells. METHODS: In a retrospective analysis of 82 patients with chordomas treated over a 10-year period (1990-2000), the authors found six patients (7.3%) in whom surgical seeding had occurred. In five (83%) of these patients the primary tumor was located at the clivus. In one (17%), the tumor was present at the cervical spine. There were two male (33%) and four female patients (67%) whose mean age was 34 years. The seeding sites, which were separate from the primary tumor, were located along the operative route or in the abdomen where fat was removed. The seeding was diagnosed 5 to 15 months (mean 12 months) after surgery. One seeding site was present in five patients, and 17 seeding sites were present in one patient. The involved tissues included mucosa, bone, dura, muscle, and fat. After resection, all seedings were confirmed histologically. CONCLUSIONS: Seeding of chordomas occurs along the operative route and at distant locations where tissue is harvested. Early diagnosis and aggressive surgery are recommended. Based on the results of this study, the authors suggest that surgical techniques, postoperative radiotherapy, neuroradiological follow-up protocol, and even research on chordomas should be reevaluated.

Chordomas of the craniocervical junction: follow-up review and prognostic factors.

OBJECT: Chordomas are rare tumors that arise from the remnants of the notochord. Because of their deep location, local infiltrative nature, and involvement of surrounding bone, treatment of chordomas is a challenge. In this study the authors analyze the data and prognostic factors obtained during the follow-up period (range 1-150 months, median 38 months) in 53 patients with craniocervical junction chordomas and 10 patients with chondrosarcomas. METHODS: Several surgical approaches were used, and some tumor excisions required staged procedures. Survival was calculated according the Kaplan-Meier method. Statistical analysis was performed using Fisher exact, log rank and Kruskal-Wallis tests. Radical/subtotal resection was achieved in 77.8% of the patients. The mortality rate during the follow-up period was 14.3%. In patients harboring chondrosarcoma better 5-year recurrence-free survival (RFS) rates were demonstrated than in those with chordoma (100% and 50.7%. respectively). Histological patterns (typical or chondroid chordomas) and patient age at onset of symptoms had no effect on the RFS rates. Radical/subtotal resections were associated with better RFS rates than partial resection. Adjuvant proton-beam therapy was shown to increase the RFS rates compared with conventional radiotherapy (90.9% and 19.4%, respectively, at 4 years posttreatment). Karyotypically abnormal tumors were associated with the worst RFS rates compared with karyotypically normal lesions (44.5% and 90.3%, respectively, at 3 years). Cases of cranial nerve palsy followed by those with cerebrospinal fluid leakages were the most frequent postoperative complications. Permanent postoperative neurological deficit was observed in 28.6% of the patients. CONCLUSIONS: A better prognosis was observed in patients with chondrosarcoma compared with those harboring chordoma. Histological pattern and patient age at symptom onset were not factors that influenced prognosis in cases of chordoma. Extensive resection and possibly adjuvant proton-beam therapy provided better prognoses for these patients.

Chordomas of the skull base: follow-up review and prognostic factors.

OBJECT: Chordomas are rare tumors that arise from the remnants of the notochord. Because of their deep location, local infiltrative nature, and involvement of surrounding bone, treatment of chordoma is a challenge. The authors analyze the data and prognostic factors obtained during the follow-up period (range 1-150 months, median 38 months) in 53 patients with craniocervical junction chordoma and 10 patients with chondrosarcoma. METHODS: Several surgical approaches were used, and some tumor excisions required staged procedures. Survival was calculated according the Kaplan-Meier method. Statistical analysis was performed using the Fisher exact and Kruskal-Wallis tests. Radical/subtotal resection was achieved in 77.8% of the patients. The mortality rate during the follow-up period was 14.3%. In patients harboring chondrosarcoma better 5-year recurrence-free survival (RFS) rates were demonstrated than in those with chordoma (100% and 50.7%, respectively). Histological patterns (typical or chondroid chordoma) and patient age at onset of symptoms had no effect on the RFS rates. Radical/subtotal resections were associated with better RFS rates than partial resection. Adjuvant proton-beam radiotherapy was shown to increase the RFS rates compared with conventional radiotherapy (90.9% and 19.4%, respectively at 4 years posttreatment). Karyotypically abnormal tumors were associated with worst RFS rates as compared with karyotypically normal lesions (44.5% and 90.3%, respectively at 3 years). Cases of cranial nerve palsy, followed by CSF leakages were the most frequent postoperative complication. Permanent postoperative neurological deficit was observed in 28.6% of the patients. CONCLUSIONS: A better prognosis was observed in patients with chondrosarcoma compared with those harboring chordoma. Histological pattern and the patient's age at symptom onset were not factors that influenced prognosis in cases of chordoma. Extensive resection and possibly adjuvant proton-beam radiotherapy provided better prognosis for these patients.

Identification of isochromosome 1q as a recurring chromosome aberration in skull base chordomas: a new marker for aggressive tumors?

OBJECT: The authors conducted a study of 22 skull base chordomas. METHODS: A series of 22 skull base chordomas was analyzed with G banding. Subsequently, metaphase cells obtained from three tumors were reexamined using multicolor spectral karyotyping. Clonal chromosome aberrations were identified in 11 cases, all of which were recurrent tumors. Three tumors showed a remarkable similarity in cytogenetic features, and these features appear to characterize a recurring combination of nonrandom chromosome aberrations, including isochromosome 1q, gain of chromosome 7, and monosomy for chromosomes 3, 4, 10,13, and 18. Isochromosome 1q was identified as the sole recurring structural chromosome rearrangement in these tumors. The pattern of chromosome loss reported in the progression of lumbosacral chordoma also appears to be true of skull base chordomas with the additional findings of isochromosome 1q, gain of chromosome 7, and loss of chromosome 18. CONCLUSIONS: Skull base chordomas characterized by isochromosome 1q and monosomy 13 provide support for the concept of the loss of putative tumor suppressor loci on 1p and 13q and aggressive tumor behavior.

Surgical seeding of chordomas.

OBJECT: Chordomas have a high propensity for local recurrence and progression, as well as for systemic and cerebrospinal fluid metastasis. The authors identified and analyzed a series of patients with chordomas, focusing on an underrecognized entity--surgical seeding. METHODS: In a retrospective analysis of 82 patients with chordomas treated over a 10-year period (1990-2000) the authors found six patients (7.3%) in whom surgical seeding had occurred. In five (83%) of these patients the primary tumor was located at the clivus. In one (17%) the tumor was present in the cervical region. There were two male (33%) and four female patients (67%) with a mean age of 34 years. The seeding sites, which were separate from the primary tumor, were located along the operative route or in the abdomen where fat was removed. The seeding was diagnosed 5 to 15 months after surgery (mean 12 months). One seeding site was present in five patients and 17 seeding sites were present in one patient. The involved tissues included mucosa, bone, dura, muscle, and fat. After resection, all seedings were documented histologically. CONCLUSIONS: Seeding of chordomas occurs along the operative route and at distant locations where fat is harvested. Early diagnosis and aggressive surgical treatment are recommended. Based on the results of this study, it is suggested that surgical techniques, postoperative irradiation, the neuroradiological follow-up protocol, and even research on chordomas should be reevaluated.

Fiber dissection technique: lateral aspect of the brain.

OBJECTIVE: The fiber dissection technique involves peeling away the white matter tracts of the brain to display its three-dimensional anatomic organization. Early anatomists demonstrated many tracts and fasciculi of the brain using this technique. The complexities of the preparation of the brain and the execution of fiber dissection have led to the neglect of this method, particularly since the development of the microtome and histological techniques. Nevertheless, the fiber dissection technique is a very relevant and reliable method for neurosurgeons to study the details of brain anatomic features. METHODS: Twenty previously frozen, formalin-fixed human brains were dissected from the lateral surface to the medial surface, using the operating microscope. Each stage of the process is described. The primary dissection tools were handmade, thin, wooden spatulas with tips of various sizes. RESULTS: We exposed and studied the myelinated fiber bundles of the brain and acquired a comprehensive understanding of their configurations and locations. CONCLUSION: The complex structures of the brain can be more clearly defined and understood when the fiber dissection technique is used. This knowledge can be incorporated into the preoperative planning process and applied to surgical strategies. Fiber dissection is time-consuming and complex, but it greatly adds to our knowledge of brain anatomic features and thus helps improve the quality of microneurosurgery. Because other anatomic techniques fail to provide a true understanding of the complex internal structures of the brain, the reestablishment of fiber dissection of white matter as a standard study method is recommended.

Venous consideration in petrosal approach: microsurgical anatomy of the temporal bridging vein.

OBJECTIVE: The technical difficulty of using the petrosal approach and the likelihood of encountering venous complications depend on the particular temporal venous anatomy. To reduce such potential risks, neurosurgeons must have adequate knowledge of the variations in the anatomy of the temporal venous drainage system, particularly of the temporal bridging veins. METHODS: In 20 cadaveric specimens, the temporal bridging veins were examined with the aid of an operating microscope. The anatomic location of their termination and of the tributaries of these bridging veins was noted. RESULTS: Forty-four terminations and 109 tributaries of the temporal bridging veins were identified in our specimens. The temporal bridging veins were divided into three groups according to the anatomic location of their terminations: 1) the transverse sinus group (seen in all 20 hemispheres), with drainage into the lateral part of the cerebellar tentorium, to which most of the vein of Labbé belongs; 2) the tentorial group (seen in 50% of the 20 hemispheres), with drainage into the medial part of the tentorium, which is composed mainly of the middle and posterior temporobasal veins; and 3) the petrosal group (seen in 55% of the 20 hemispheres), with entry around the superior petrosal sinus, which may limit mobility of the temporal lobe in the petrosal approach. On the basis of this anatomic information, we propose a new classification of the temporal venous drainage system and discuss the clinical implications of these findings. CONCLUSION: In planning the petrosal approach, great care should be taken not only with the vein of Labbé but also with the petrosal bridging veins. Knowledge of this venous anatomy can reduce venous complications during the lateral cranial base approach.

Arteries of the insula.

OBJECT: The insula is located at the base of the sylvian fissure and is a potential site for pathological processes such as tumors and vascular malformations. Knowledge of insular anatomy and vascularization is essential to perform accurate microsurgical procedures in this region. METHODS: Arterial vascularization of the insula was studied in 20 human cadaver brains (40 hemispheres). The cerebral arteries were perfused with red latex to enhance their visibility, and they were dissected with the aid of an operating microscope. Arteries supplying the insula numbered an average of 96 (range 77-112). Their mean diameter measured 0.23 mm (range 0.1-0.8 mm), and the origin of each artery could be traced to the middle cerebral artery (MCA), predominantly the M2 segment. In 22 hemispheres (55%), one to six insular arteries arose from the M1 segment of the MCA and supplied the region of the limen insulae. In an additional 10 hemispheres (25%), one or two insular arteries arose from the M3 segment of the MCA and supplied the region of either the superior or inferior periinsular sulcus. The insular arteries primarily supply the insular cortex, extreme capsule, and, occasionally, the claustrum and external capsule, but not the putamen, globus pallidus, or internal capsule, which are vascularized by the lateral lenticulostriate arteries (LLAs). However, an average of 9.9 (range four-14) insular arteries in each hemisphere, mostly in the posterior insular region, were similar to perforating arteries and some of these supplied the corona radiata. Larger, more prominent insular arteries (insuloopercular arteries) were also observed (an average of 3.5 per hemisphere, range one-seven). These coursed across the surface of the insula and then looped laterally, extending branches to the medial surfaces of the opercula. CONCLUSIONS: Complete comprehension of the intricate vascularization patterns associated with the insula, as well as proficiency in insular anatomy, are prerequisites to accomplishing appropriate surgical planning and, ultimately, to completing successful exploration and removal of pathological lesions in this region.

A role for telomeric and centromeric instability in the progression of chromosome aberrations in meningioma patients.

BACKGROUND: The primary chromosome aberration in meningiomas is monosomy or deletion of chromosome 22. Common secondary aberrations include losses or deletions of chromosomes 1p, 14q, and 10q and unstable chromosome aberrations including rings, dicentrics, and telomeric associations. Despite the analysis of several hundred tumors by cytogenetic and molecular techniques, the mechanisms involved in the progression of chromosome aberrations in meningioma remain poorly understood. METHODS: Sixty-seven meningiomas were cultured successfully using a short term in situ technique and harvested incorporating a high resolution G-banding technique with ethidium bromide. RESULTS: Twenty-six tumors (39%) showed normal karyotypes, whereas 41 tumors (61%) showed clonal chromosome aberrations. The most frequently observed aberration was the loss of chromosome 22 or structural aberrations involving 22q12, which occurred in 30 tumors (45%). The second most common aberrations were whole arm translocations involving the centromeric breakpoint at 1q10, resulting in the loss of the entire 1p chromosome in 12 tumors (18%). Two tumors showed a new, recurring, unbalanced, whole arm translocation der(1;2)(q10;q10). A third aberration, telomeric associations, were observed in 16 tumors (24%), occurring transiently in 11 tumors and recurring clonally in 5 tumors. Dicentric chromosome 22 was found in 7 tumors (10%), with the progressive loss of chromosome 22q material being found in 2 tumors. CONCLUSIONS: The chromosome instability demonstrated in the current series of tumors suggests that the progression of chromosome aberrations in meningioma is mediated in some respects by both telomeric and centromeric instability. These two types of instability may be early events in the progression of chromosome aberrations in meningioma and each can account for at least some of the loss of heterozygosity of chromosomes 22q and 1p detected by molecular analysis.

Ventral foramen magnum meninigiomas.

OBJECT: Ventral foramen magnum meningiomas (VFMMs) are rare lesions that account for more than 3% of all meningiomas. These are among the most challenging of all meningiomas to treat. The authors comprehensively analyzed multiple features in a series of VFMMs. METHODS: A retrospective study was performed of 18 patients who harbored a meningioma in the ventral foramen magnum (mean follow-up period, 40 months) and underwent surgery via a transcondylar approach. Sixteen patients underwent surgery for the first time: 12 underwent gross-total (75%), two near-total (12.5%), and two subtotal (12.5%) tumor removal. The remaining two patients were treated for a recurrent tumor. After obtaining postoperative Karnofsky Performance Scale (KPS) scores at follow up, statistically significant improvement was demonstrated compared with the preoperative scores. The extent of surgery and higher preoperative KPS scores were variables that showed statistically significant favorable influence on outcome. Ninth and 10th cranial nerve deficits were the most common complications contributing to a prolonged hospital stay. There were no perioperative deaths. Four patients died during the follow-up period. The first patient died of multiple myeloma. The second patient, in whom surgery was performed to treat a recurrent tumor, died 3 years after the surgery of new tumor recurrence at the age of 80 years. The remaining two patients died 1.5 and 5 months postsurgery of pulmonary embolus and endocarditis, respectively. CONCLUSIONS: Ventral foramen magnum meningiomas can be radically resected in a majority of patients, with frequent but transient morbidity caused by lower cranial nerve deficits. Radical removal of a recurrent tumor provides a relatively long, stable postoperative course. In patients presenting with a low KPS score a poor prognosis is demonstrated, and early diagnosis and treatment are recommended to avoid it.

M. Gazi Yasargil: the time in Little Rock.

Microneurosurgery is Professor Yasargil's legacy. Its impact on patient outcomes, surgeons' abilities, the field of neurosurgery in particular, and the art of surgery in general is great, profound, and everlasting. Professor Yasargil led a revolution that has transformed neurosurgery into the fine art we practice today. His ingenuity, devotion, energy, and masterful technique have made his contributions so salient that they have earned him recognition as Neurosurgery's Man of the Century. It has been an honor, a great opportunity, and a phenomenal experience to spend the last 5 years with him at the University of Arkansas for Medical Sciences in Little Rock. There, he represents the very best in knowledge, expertise, dexterity, and, above all, devotion to advancing the field of neurosurgery. Most enjoyable have been his stimulating intellect and inspiring vision.

Management of intracranial meningiomas secondarily involving the infratemporal fossa: radiographic characteristics, pattern of tumor invasion, and surgical implications.

OBJECTIVE: Intracranial meningiomas extending into the infratemporal fossa (ITF) are uncommon. This series describes the radiographic characteristics, histological pattern of invasion, and implications for surgical treatment of intracranial meningiomas. METHODS: Nine patients (median age, 52 yr) underwent resection of a transcranial meningioma extending into the ITF. Five patients (56%) had undergone a previous resection; however, none had involvement of the ITF. Four patients (44%) had received prior radiation therapy to the area. RESULTS: Preoperative neuroradiography uniformly showed erosion of the middle fossa floor and extension of the tumor through cranial base foramina. Histological results indicated tumor invasion of the middle fossa floor and skeletal muscle in all patients. Perineural invasion was present in four patients. Mucosal invasion was observed in six patients. A middle fossa/zygomatic approach provided access to the intra- and extracranial components of the tumor, as well as the cavernous sinus, ITF structures, paranasal sinuses, and nasopharynx. Reconstruction was performed using the temporalis muscle, which provides a vascularized flap between exposed mucosa and the carotid artery and intradural structures. A gross total resection was performed in seven patients (78%). Postoperative complications included soft tissue ischemia (one patient), worsening of preoperative cranial neuropathy (two patients), and lower extremity deep vein thrombosis (two patients). One patient died 2 months postoperatively from a pulmonary embolus. Two patients had recurrence of intracranial meningiomas extending into the ITF at 2 and 3 years postoperatively, necessitating further resection. CONCLUSION: Understanding the pertinent clinical and morphological aspects of meningioma transcranially involving the ITF is essential to surgical treatment of patients with this condition.

Inside-outside technique for posterior occipitocervical spine instrumentation and stabilization: preliminary results.

OBJECT: The authors present a series of 16 patients who underwent inside-outside occipital and posterior cervical spine stabilization. METHODS: In this technique, the screw was placed from the inside of the occiput to the outside. An articular (lateral) mass plate was contoured to the shape of the occipital bone and the cervical spine and affixed to the occiput with a flat-headed screw or stud placed through a burr hole in the calvaria with the flat head of the screw in the epidural space and the threads facing outward. The bone plate was then secured with a nut to the occipital screw and the cervical plate was attached to the spine with a bone screw that coursed through the plate and into the articular pillar. Our series included six children and 10 adults. In five patients, previous fusion had failed; in two patients spinal instability was secondary to Down's syndrome; two patients' instability was related to developmental anomalies; and in five patients spinal instability was due to the presence of tumor. One patient with rheumatoid arthritis had undergone a transoral procedure. Two patients had suffered traumatic fracture. Three patients died of causes unrelated to the procedure, one patient died of metastatic cancer, and one patient died in a long term care facility of cardiopulmonary complications. One patient with renal failure suffered a hemorrhage from an arteriovenous fistula after being treated with dialysis. In one child, a nut backed off after 3 months. The nut was reseated, and a maturing arthrodesis was present. CONCLUSIONS: The authors conclude that the inside-outside occipitocervical fixation is an effective technique for stabilizing the cervical spine.

Benign nonmeningeal tumors of the cavernous sinus.

OBJECTIVE: Resection of benign cavernous sinus tumors with minimum morbidity and mortality is increasingly more common. Although meningiomas have dominated most discussions, numerous nonmeningeal tumors also deserve attention because they are generally more amenable to radical surgical resection. METHODS: We reviewed the records of 40 patients (19 female and 21 male patients) who were treated surgically during a 15-year period for benign, nonmeningeal tumors of the cavernous sinus. Invasive pituitary adenomas (14 cases) and trigeminal schwannomas (13 cases) comprised the majority of tumors; the remaining tumor types were hemangioma, neurofibroma, juvenile angiofibroma, dermoid tumor, giant cell tumor, chondromyxofibroma, and chondroma. Patient age ranged from 7 to 65 years (mean, 37 yr). RESULTS: All patients underwent surgery, the intent being total resection. Total resection was achieved in 33 (82.5%) of the 40 patients. Follow-up was achieved via a combination of direct patient visit or phone interview or via the referring physician. Eight patients had undergone previous surgery elsewhere, which correlated closely with complications and neurophthalmological outcomes but did not affect resectability. Postoperatively, 89.7% of the patients had either stable or improved extraocular muscle function compared with their preoperative statuses. Forty percent of the patients experienced improvement of their preoperative extraocular muscle deficits. Complications included cerebrospinal fluid leak (three cases), postoperative hemorrhage (one case), fat embolism (one case), perforator distribution infarct (one case), hydrocephalus requiring ventriculoperitoneal shunting (two cases), transient hemiparesis (one case), and diabetes insipidus (one case). CONCLUSION: We conclude that benign nonmeningeal tumors of the cavernous sinus can be safely and radically removed and result in good long-term neuro-ophthalmological function and low morbidity and mortality. Furthermore, when compared with our previously reported results for cavernous sinus meningiomas, benign nonmeningeal tumors of the cavernous sinus carry a better chance of total removal, a lower incidence of postoperative ocular dysfunction, and a higher rate of recovery of preoperative cranial nerve deficits.

Topographic anatomy of the insular region.

OBJECT: The insula is one of the paralimbic structures and constitutes the invaginated portion of the cerebral cortex, forming the base of the sylvian fissure. The authors provide a detailed anatomical study of the insular region to assist in the process of conceptualizing a reliable surgical approach to allow for a successful course of surgery. METHODS: The topographic anatomy of the insular region was studied in 25 formalin-fixed brain specimens (50 hemispheres). The periinsular sulci (anterior, superior, and inferior) define the limits of the frontoorbital, frontoparietal, and temporal opercula, respectively. The opercula cover and enclose the insula. The limen insula is located in the depths of the sylvian fissure and constitutes the anterobasal portion of the insula. A central insular sulcus divides the insula into two portions, the anterior insula (larger) and the posterior insula (smaller). The anterior insula is composed of three principal short insular gyri (anterior, middle, and posterior) as well as the accessory and transverse insular gyri. All five gyri converge at the insular apex, which represents the most superficial aspect of the insula. The posterior insula is composed of the anterior and posterior long insular gyri and the postcentral insular sulcus, which separates them. The anterior insula was found to be connected exclusively to the frontal lobe, whereas the posterior insula was connected to both the parietal and temporal lobes. Opercular gyri and sulci were observed to interdigitate within the opercula and to interdigitate the gyri and sulci of the insula. Using the fiber dissection technique, various unique anatomical features and relationships of the insula were determined. CONCLUSIONS: The topographic anatomy of the insular region is described in this article, and a practical terminology for gyral and sulcal patterns of surgical significance is presented. This study clarifies and supplements the information presently available to help develop a more coherent surgical concept.

Hyperostosis associated with meningioma of the cranial base: secondary changes or tumor invasion.

OBJECTIVE: Hyperostosis associated with intracranial meningiomas is a well-described entity. The cause, management, and prognosis of these bony changes have long been a point of controversy. Some authors have postulated that hyperostotic changes are secondary to the formation of the tumor and do not constitute invasion of the tumor into the bone. Determining this point has direct implications in the treatment of these patients, especially regarding surgical considerations. To more thoroughly evaluate this question, a study correlating the morphology to the radiology is necessary. METHODS: In this study, 51 patients underwent resection for meningiomas involving the cranial base. Preoperative radiographic evaluation using magnetic resonance imaging and/or computed tomography was performed, and areas of hyperostosis were identified. During the resection of the tumor, biopsies from these hyperostotic regions were sent for histological evaluation regarding the presence or absence of tumor invasion of the bone. RESULTS: Preoperative neuroradiological assessment identified 26 patients with radiographic evidence of hyperostosis. Histological examination of the resected bone showed tumor invasion in 35 patients, including the area of radiographically identified hyperostosis in 25 of the 26 patients. The floor of the middle fossa was a specific area of low sensitivity for preoperative assessment of associated hyperostosis. CONCLUSION: These results indicate that hyperostosis associated with meningiomas involving the cranial base are caused by tumor invasion of the bone histologically.