Basilar decompression via a far lateral transcondylar approach: technical note.

BACKGROUND: Treatments for symptomatic or unstable basilar invagination (BI) include posterior decompression, distraction/fusion, trans-nasal or trans-oral anterior decompression, and combined techniques, with the need for occipitocervical fusion based on the degree of craniocervical instability. Variations of the far lateral transcondylar approach are described in limited case series for BI, but have not been widely applied. METHODS: A single-institution, retrospective review of consecutive patients undergoing a far lateral transcondylar approach for odontoidectomy (± resection of the inferior clivus) followed by occipitocervical fusion over a 6-year period (1/1/2016 to 12/31/2021) is performed. Detailed technical notes are combined with images from cadaveric dissections and patient surgeries to illustrate our technique using a lateral retroauricular incision. RESULTS: Nine patients were identified (3 males, 6 females; mean age 40.2 ± 19.6 years). All patients had congenital or acquired BI causing neurologic deficits. There were no major neurologic or wound-healing complications. 9/9 patients (100%) experienced improvement in preoperative symptoms. CONCLUSIONS: The far lateral transcondylar approach provides a direct corridor for ventral brainstem decompression in patients with symptomatic BI. A comprehensive knowledge of craniovertebral junction anatomy is critical to the safe performance of this surgery, especially when using a lateral retroauricular incision.

Synergy of local, regional, and systemic non-specific stressors for host defense against pathogens.

The immune brinksmanship conceptual model postulates that many of the non-specific stressful components of the acute-phase response (e.g. fever, loss of appetite, iron and zinc sequestration) are host-derived systemic stressors used with the "hope" that pathogens will be harmed relatively more than the host. The concept proposes that pathogens, needing to grow and replicate in order to invade their host, should be relatively more vulnerable to non-specific systemic stress than the host and its cells. However, the conceptual model acknowledges the risk to the host in that the gamble to induce systemic self-harming stress to harm pathogens may not pay off in the end. We developed an agent-based model of a simplified host having a local infection to evaluate the utility of non-specific stress, harming host and pathogen alike, for host defense. With our model, we explore the benefits and risks of self-harming strategies and confirm the immune brinksmanship concept of the potential of systemic stressors to be an effective but costly host defense. Further, we extend the concept by including in our model the effects of local and regional non-specific stressors at sites of infection as additional defenses. These include the locally hostile inflammatory environment and the stress of reduced perfusion in the infected region due to coagulation and vascular leakage. In our model, we found that completely non-specific stressors at the local, regional, and systemic levels can act synergistically in host defense.

Mortality and cost of radiation therapy for oesophageal cancer according to hospital accreditation level: a nationwide population-based study.

This study examined and analysed the relationship between the cost-effectiveness and outcome of radiotherapy for oesophageal cancer among hospitals with varying accreditation levels. We selected 428 oesophageal cancer patients from medical and non-medical centres using the National Health Insurance Research Database, which is maintained by the Taiwanese National Health Research Institutes, and compared their medical expenditure and the outcome of their radiotherapy treatment. In this study cohort of patients with oesophageal cancer, 278 patients were treated in medical centres (mean age: 60.1 years) and 150 patients were treated in non-medical centres (mean age: 62.0 years, P = 0.16). The medical centre group exhibited significantly lower medical expenses, mortality and risk of death compared with the non-medical centre group (adjusted hazard ratio = 1.38, 95% confidence interval = 1.11-1.71). Our study determined that radiotherapy for oesophageal cancer costs significantly less, and medical centres had lower mortality rates than non-medical centres. These findings could provide professional organisations and healthcare policy makers with essential information for allocation of resources.

Intracranial hematolymphoid malignancies: A case series with molecular characterization.

OBJECTIVE: Central nervous system (CNS) manifestations of hematologic malignancies are uncommon and often have a poor prognosis. As hematologic neoplasms are typically chemotherapy- and radiotherapy-sensitive, surgical resection is usually not indicated; thus, opportunities for in-depth characterization of CNS hematologic tumors are limited. Here, we report four cases of rare intracranial hematologic tumors requiring surgical intervention, allowing for histopathologic and genomic characterization. METHODS: The clinical course, genetic perturbations, and histopathological features are described for a case of 1) primary marginal zone B-cell lymphoma of the dura as well as cases of brain metastases of 2) cutaneous T-cell lymphoma, 3) acute myeloid leukemia/myeloid sarcoma, and 4) multiple myeloma. Targeted DNA sequencing, fluorescence in situ hybridization, cytogenetic analysis, flow cytometry and immunohistochemical staining were used to assess the lesions. RESULT: Molecular and histopathological characterizations of four unusual presentations of hematolymphoid diseases involving the CNS are presented. Genetic abnormalities were identified in each lesion, including chromosomal aberrations and single nucleotide variants resulting in missense or nonsense mutations in oncogenes. CONCLUSIONS: Our case series provides insight into unique pathological phenotypes of hematologic neoplasms with atypical CNS involvement. We offer targets for future studies by identifying potentially pathogenic genetic variants in these lesions, as the full implications of the novel molecular abnormalities described remain unclear.

Transsulcal parafascicular brain path-assisted approach to subcortical lesions: 2-dimensional operative video.

BACKGROUND: Approaches to subcortical lesions have traditionally been limited by the morbidity of white matter dissection and fixed blade retraction required to reach these targets. Visualization of deep surgical fields with a traditional operating microscope is also poor. Coordinated use of intra-operative image guidance, a tubular retractor (BrainPath®, Nico Corp, Indianapolis, Indiana), a high-definition exoscope (Vitom®, Karl Storz Endoscopy America, Inc, El Segundo, California), and a low-profile resection device (Myriad®, Nico Corp) facilitates atraumatic access to and resection of subcortical lesions including primary brain tumors, brain metastases, and intracerebral hemorrhages.[1] Use of pre-planned transsulcal and parafascicular trajectories based on magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) can further mitigate damage to white matter tracts with this technique. CASE DESCRIPTION: We herein present details of the transsulcal parafascicular BrainPath®-assisted approach to subcortical lesions and demonstrate the utility of this technique using two patient examples: a spontaneous deep left posterior temporal lobe hematoma in a 41-year-old male and a left hippocampal glioblastoma in a 54-year-old female. Key steps include selection of appropriate patients with non-skull base subcortical lesions, preoperative trajectory and tube depth planning based on MRI (including diffusion-weighted imaging and DTI), patient positioning and operating room setup to facilitate pre-planned trajectories and surgeon ergonomics, and use of low-profile instruments with a two-handed surgical technique. CONCLUSION: Given recent data demonstrating the utility of this approach for hematoma evacuation and a likely increased future usage of this technique,[2] surgeon familiarity with the above steps will be of increasing importance.

Surgical Relevance of the Suprameatal Tubercle During Superior Petrosal Vein-Sparing Trigeminal Nerve Microvascular Decompression.

BACKGROUND: An enlarged suprameatal tubercle (SMT) can obscure visualization of the trigeminal nerve and require removal during microvascular decompression (MVD) surgery, especially when the superior petrosal vein (SPV) complex is preserved. OBJECTIVE: To define the incidence and important variables affecting the need for SMT removal with an SPV-sparing trigeminal nerve MVD. METHODS: Retrospective single-institution review identified patients who underwent a first-time, SPV-sparing MVD for trigeminal neuralgia (TGN) over a 26-mo period. SMT length (SMT-L), SMT width (SMT-W), and peri-trigeminal cerebellopontine cisternal thickness (CT) were measured from axial high-resolution magnetic resonance images. Need for SMT removal and use of endoscopic assistance was recorded. Data were analyzed using unpaired t-tests, and receiver operating characteristic (ROC)/area under the curve testing. RESULTS: A total of 43 MVD surgeries for TGN on 42 patients (mean age 52.7 ± 14.4 yr) were analyzed. Mean SMT-L, SMT-W, and CT were 9.8 ± 1.6, 2.0 ± 0.8, and 4.2 ± 1.5 mm, respectively. SMT removal via drilling was required in 4/43 cases (9.3%). Endoscopic assistance was used in 3 cases (2 SMT removed and 1 SMT preserved). SMT-W was the biggest predictor of the need for SMT removal on ROC analysis (area under the curve 0.97, 0.92-1.0 95% CI). The combined thresholds of SMT-W ≥ 3.2 mm and CT ≤ 3.5 mm demonstrated 100% sensitive and 100% specificity for the need to remove the SMT on optimal cutoff analysis. CONCLUSION: SMT drilling is necessary in nearly 10% of SPV-sparing MVDs for TGN. The combination of SMT width and cerebellopontine cistern thickness is predictive of the need for SMT removal.

Immune therapeutic strategies using optimal controls with L1 and L2 type objectives.

Therapeutic strategies to correct an excessive immune response to pathogenic infection is investigated as an optimal control problem. The control problem is formulated around a four dimensional mathematical model describing the inflammatory response to a pathogenic insult with two therapeutic control inputs which have either a direct pro- or anti-inflammatory effect in the given system. We use Pontryagin's maximum principle and discuss necessary optimality conditions. We consider both an L1 type objective functional as well as an L2 type objective. For the former, the presence of singular control will be addressed. For each case, numerical simulations using a nonlinear programming optimization solver to acquire different drug treatment strategies are presented and discussed. The results provide insight for possible treatment strategies and the methods could be a relevant tool for future practice to assist in better prediction of clinical outcomes and subsequently better treatment for patients.

The Safety and Feasibility of Image-Guided BrainPath-Mediated Transsulcul Hematoma Evacuation: A Multicenter Study.

BACKGROUND: Subcortical injury resulting from conventional surgical management of intracranial hemorrhage may counteract the potential benefits of hematoma evacuation. OBJECTIVE: To evaluate the safety and potential benefits of a novel, minimally invasive approach for clot evacuation in a multicenter study. METHODS: The integrated approach incorporates 5 competencies: (1) image interpretation and trajectory planning, (2) dynamic navigation, (3) atraumatic access system (BrainPath, NICO Corp, Indianapolis, Indiana), (4) extracorporeal optics, and (5) automated atraumatic resection. Twelve neurosurgeons from 11 centers were trained to use this approach through a continuing medical education-accredited course. Demographical, clinical, and radiological data of patients treated over 2 years were analyzed retrospectively. RESULTS: Thirty-nine consecutive patients were identified. The median Glasgow Coma Scale (GCS) score at presentation was 10 (range, 5-15). The thalamus/basal ganglion regions were involved in 46% of the cases. The median hematoma volume and depth were 36 mL (interquartile range [IQR], 27-65 mL) and 1.4 cm (IQR, 0.3-2.9 cm), respectively. The median time from ictus to surgery was 24.5 hours (IQR, 16-66 hours). The degree of hematoma evacuation was ≥90%, 75% to 89%, and 50% to 74% in 72%, 23%, and 5.0% of the patients, respectively. The median GCS score at discharge was 14 (range, 8-15). The improvement in GCS score was statistically significant ( P < .001). Modified Rankin Scale data were available for 35 patients. Fifty-two percent of those patients had a modified Rankin Scale score of ≤2. There were no mortalities. CONCLUSION: The approach was safely performed in all patients with a relatively high rate of clot evacuation and functional independence.

Redox properties of the diheme cytochrome c4 from Azotobacter vinelandii and characterisation of the two hemes by NMR, MCD and EPR spectroscopy.

From biphasic stopped-flow kinetic studies it has been established that the two heme centres of cytochrome c4 from Azotobacter vinelandii undergo redox change with [Co(terpy)2]3+/2+ (260 mV) at different rates. Rate constants for oxidation and reduction at pH 7.5 give reduction potentials for the two heme centres in agreement with previous values from spectrophotometric titrations (263 and 317 mV). From NMR studies on the fully reduced protein two sharp methyl methionine resonances are observed at -3.16 and -3.60 ppm, consistent with axial methionine coordination. On titration with [Fe(CN)6]3- the -3.16 ppm resonance is the first to disappear, and is assigned to the less positive reduction potential. Line-broadening effects are observed on partial oxidation, which are dominated by intermolecular processes in an intermediate time-range exchange process. The hemes of the oxidised protein are distinguishable by EPR g-values of 3.64 and 3.22. The former is of interest because it is at an unusually low field for histidine/methionine coordination, and has an asymmetric or ramp shape. The latter assigned to the low potential heme is similar to that of a cytochrome c551. The MCD spectra of the fully oxidised protein are typical of low-spin Fe(III) heme centres, with a negative peak at 710 nm characteristic of methionine coordination, and an NIR peak at 1900 nm characteristic of histidine/methionine (axial) coordination. Of the four histidines per molecule only two undergo diethyl pyrocarbonate (DEPC) modification.

Dose-dependent inhibition of theophylline metabolism by disulfiram in recovering alcoholics.

The influence of disulfiram on theophylline metabolism was studied in 20 recovering alcoholics. Ten of the patients, who were selected at random, received 250 mg of disulfiram daily. The other 10 patients received 500 mg of disulfiram daily. Two single-dose studies of theophylline kinetics were performed--one as a baseline control and the other after 1 week of treatment with disulfiram. With disulfiram pretreatment, the plasma clearance of theophylline was decreased from 105.7 +/- 10.2 (mean +/- SEM) to 83.1 +/- 8.1 ml/kg per hour (p less than 0.001) in the 250 mg group and from 94.3 +/- 13.3 to 65.4 +/- 10.7 ml/mg per hour (p less than 0.001) in the 500 mg group. The elimination half-life was prolonged significantly in both groups. The percent reduction in theophylline clearance was greater in the 500 mg group (32.5 +/- 3.1; range, 21.6 to 49.6) than it was in the 250 mg group (21.2 +/- 1.7; range, 14.6 to 29.6; p less than 0.01). Disulfiram decreased the formation of all theophylline metabolites in smokers in both treatment groups. In each group, the hydroxylation pathway was affected more than the demethylation pathway. These data indicate that at therapeutic doses disulfiram exerts a dose-dependent inhibitory effect on theophylline metabolism. Depending on the dose of disulfiram, a dose reduction of theophylline by as much as 50% may be necessary to minimize the risk of toxicity.

Immunohistochemical evaluation of HER-2/neu expression in pancreatic adenocarcinoma and pancreatic intraepithelial neoplasms.

Although several morphological and molecular genetic studies have implicated various grades of pancreatic duct hyperplasia as precursor lesions to infiltrating pancreatic adenocarcinoma, the identity of preinvasive pancreatic neoplasms remains controversial. In the present study, the authors examined the expression of the epidermal growth factor receptor homologue, HER-2/neu (c-erbB-2), in pancreatic duct lesions adjacent to infiltrating pancreas cancers in a series of 19 cases of pancreatic duct adenocarcinoma. HER-2/neu expression was examined because it has been identified in a proportion of infiltrating pancreas cancers and because it may provide early neoplasms with a growth advantage over adjacent nonneoplastic epithelium. In normal pancreatic ducts and ductules, HER-2/neu expression was absent in all but one case. By contrast, HER-2/neu was expressed in 82% (P = .008 vs normal ) of ducts with flat mucinous hyperplasia, 86% (P = .03 vs normal) of ducts with papillary mucinous hyperplasia without atypia, 92% (P = .001 vs normal) of ducts with atypical papillary mucinous hyperplasia, and all specimens with carcinoma in situ. HER-2/neu expression was observed in 69% (P = .002 vs normal) of the moderately differentiated infiltrating carcinomas and none of the poorly differentiated infiltrating carcinomas. These data establish HER-2/neu as a potential mediator of growth factor-related signal transduction in pancreatic duct lesions, and provide additional support for the hypothesis that lesions formerly regarded as various grades of hyperplasia instead may represent intraepithelial neoplasms with the potential for subsequent invasion and metastasis.

Fatal fat embolism syndrome after numerous vertebral body compression fractures in a lung transplant recipient.

The fat embolism syndrome is an uncommon clinical disorder that typically occurs as a complication of severe trauma. We report the case of a 60-year-old single-lung transplant recipient who died of massive fat emboli. Before lung transplantation, the patient had been treated with corticosteroids for at least 1 year because of chronic obstructive pulmonary disease caused by centrilobular emphysema and asthmatic bronchitis. After receiving his lung transplant, he was treated with triple-drug immunosuppression, which included 25 mg of prednisone per day. He was discharged from the hospital 2 months after transplantation only to be readmitted 2 weeks later with cytomegalovirus pneumonia, from which he recovered. Concomitantly, he had new lumbar compression fractures with severe back pain and lost approximately 3 cm in height during a 3-week period. On the eleventh day after hospital readmission, he suddenly had a "sepsis-like" illness without a known infectious cause, numerous petechiae and ecchymoses, marked pulmonary edema with worsening diffuse pulmonary infiltrates, profound hypoxemia, decreased mentation, and mild thrombocytopenia. He died 3 days later. With the exception of a positive sputum culture for cytomegalovirus, all cultures were negative. The postmortem examination showed severe osteoporosis, multiple vertebral compression fractures, and widespread massive fat emboli. This is the first reported case of fat emboli as the cause of death in a lung transplant recipient, and the case suggests that the fat embolism syndrome should be considered in the differential diagnosis of a sepsis-like illness in patients who have received steroids during a long period, particularly in the setting of vertebral compression fractures.

Cranial base surgical techniques for large sphenocavernous meningiomas: technical note.

OBJECTIVE: Large meningiomas arising from the dura covering the sphenoid ridge present surgical challenges because of frequent involvement of the carotid artery and its branches, the optic nerve and tract, the superior orbital fissure, and cavernous sinus structures. To circumvent the inherent difficulties of a traditional approach strategy, cranial base approaches were applied to: 1) isolate and interrupt the major blood supply as an initial step, 2) minimize brain retraction, and 3) isolate the neurovascular structures exiting the tumor at the cranial base to protect and better separate them. METHODS: Six patients were treated with such a strategy in the past 2 years (five women and one man, ages 34-69 yr). All tumors measured at least 5 cm in their greatest diameter and arose at the sphenoid ridge. All tumors extended posteriorly to involve the cavernous sinus to varying degrees. In two patients a frontotemporal bone flap was used; in two patients, a transzygomatic approach was used; and in the remaining two patients, an orbitozygomatic strategy was used. Extensive bone removal at the cranial base was performed in all cases. RESULTS: Four patients had gross total resections, and two were subtotal owing to invasion of the cavernous sinus or the middle cerebral artery. There were no permanent cranial nerve deficits; however, two patients sustained transient IIIrd nerve paresis. Two patients postoperatively developed transient cerebral edema that required intensive treatment. All six patients had good outcomes, resuming independent activity by 3 months after surgery. CONCLUSION: Contemporary cranial base surgical techniques have a role in the treatment of large sphenoid ridge meningiomas. These strategies result in safe resection with low morbidity and obviate the need in most cases for preoperative embolization. The anatomic foundation for using these approaches is discussed.

Two simple devices for microneurosurgery: automatic drip irrigating needle and a suction retractor.

During microneurosurgical procedures, frequent intermittent irrigation and/or suction are often necessary. We describe two simple devices: the automatic drip irrigating needle and the suction retractor. We have confirmed their usefulness through our routine use of these simple devices since 1982.

Neurological surgery at the University of Vienna.

ANTON VON EISELSBERG was the first to resect a cerebral tumor at the First Surgical Clinic at the General Hospital in Vienna in 1904. He successfully removed a cerebral glioma, the first of no fewer than 15,000 tumors operated on at that hospital to date. von Eiselsberg and his successors, Egon Ranzi and Leopold Schönbauer, as heads of the First Surgical Clinic, devoted themselves intensively to brain surgery, and neurosurgery developed to be an integral part of Viennese surgery. During the first decades, a prominent neurologist, Otto Marburg, and a world-famous anatomist, Julius Tandler, were members of the neurosurgical operating team. This approach changed in the 1950s, when the brain surgeons aimed at becoming independent of the basic sciences. The founding of an independent neurosurgical department at the University of Vienna in 1964 under Herbert Kraus also marked the beginning of the formation of specialized sections for pediatric and stereotactic neurosurgery. After 1968, the operating microscope was greatly emphasized. As of 1970, cerebral tumors and cerebrovascular lesions were treated microneurosurgically. Many operations were performed by surgeons who were experienced in neurosurgery. This again changed in 1978 under the new head of the department, Wolfgang Koos, who regarded the neurosciences as the basis for neurosurgical training as well as neurosurgical activity. The reorganization of the neurosurgical institution coincided with the construction of a large modern building with state-of-the-art equipment for microneurosurgery, radiosurgery (gamma knife), neurodiagnostics, laboratories, etc. Many details of the construction plans, the equipment, and the organization of the department have their roots in the years that the present head of the department spent in the United States; this is also the reason for the close connection and cooperation of Vienna neurosurgery with many neurosurgeons in the United States.

Direct microsurgery of dural arteriovenous malformation type carotid-cavernous sinus fistulas: indications, technique, and results.

OBJECTIVE: There is a subgroup of patients with Barrow Type D carotid-cavernous sinus fistulas (CCFs) who have progressive neurological deficits despite endovascular attempts at obliteration. To effectively arrest the progression of neurological deficits, especially visual loss, these patients require direct operative intervention. We have used a direct approach to such lesions, which comprehensively occludes all fistulous connections of the CCF. METHODS: We present a series of nine patients with Type D CCFs for which attempts at endovascular embolization failed and that, because of persistent symptoms, required surgical intervention. These lesions characteristically had extensive multiple external carotid artery feeders, often bilateral, in addition to the internal carotid artery feeders. The operative approach used was a combined extra- and intradural full exposure of the cavernous sinus and its contents, with identification and direct obliteration of all arterial input and selective ablation of the venous outflow from the cavernous sinus. RESULTS: All nine patients experienced resolution of their symptoms, and complete ablation of the lesions, as demonstrated by postoperative angiography, was achieved. Transient diplopia and trigeminal hypesthesia was observed in all nine patients, which resolved by 6 months postoperatively. One patient suffered from a temporary hemiparesis and another from permanent hemiparesis. There were no deaths related to surgery in this series. CONCLUSIONS: Patients with Type D CCFs who have persistent, progressive neurological deficits after failed endovascular attempts at obliteration may be treated by a direct surgical approach to ablate the fistulas. The pertinent anatomic concepts, indications for surgery, and operative techniques that are different from previously described methods are discussed.

The surgical management of trigeminal neuromas.

OBJECTIVE: Trigeminal neuromas are rare tumors that may involve any part of the nerve complex, including peripheral divisions of the nerve. These rare lesions are treated primarily surgically. We present our series of 38 patients who were treated surgically since 1981, with special emphasis on surgical approach. METHODS: We have surgically treated 38 patients with 39 trigeminal neuromas since 1981. This series of patients was reviewed with regard to clinical presentation, tumor characteristics, surgical approach, and outcome. RESULTS: Sixteen women and 22 men (mean age, 48 yr) all presented with some abnormality of trigeminal dysfunction. Twenty-eight patients presented with trigeminal hypesthesia, 10 with hypesthesia also had facial pain, 3 presented with only facial pain, and 7 presented with diplopia. Eighteen patients had tumors originating from the ganglion, nine from the posterior fossa nerve root, two from the ophthalmic division, and one from the mandibular division, and nine had tumors involving both posterior and middle fossae (dumbbell type). Eighteen tumors were large (>3 cm), 16 were medium sized (2-3 cm), and 5 were small (<2 cm). Tumor location was the prime determinant of surgical approach. Patients with peripheral and ganglion type lesions were treated via an entirely extradural temporopolar approach. Lesions confined to the posterior fossa were approached via a lateral suboccipital approach. Dumbbell-shaped lesions required a combined petrosal strategy. Total resection of tumor was accomplished in 30 patients. Three patients with subtotal resection displayed malignant histology. Postoperatively, 30 patients remained with some degree of trigeminal hypesthesia, two had facial pain (one persistent and one new), and five were left with total trigeminal anesthesia. Four patients were relieved of diplopia, five were relieved of headache, and two were relieved of ataxia. There were no perioperative deaths. CONCLUSION: Trigeminal neuroma is a surgically treatable disease that may be operated on, in many cases, via an entirely extradural approach. These lesions may be successfully resected with low morbidity and a very low rate of recurrence.

Anatomic position of the asterion.

OBJECTIVE: The asterion is defined as the junction of the lambdoid, parietomastoid, and occipitomastoid sutures. The asterion has been used as a landmark in lateral approaches to the posterior fossa. However, its reliability as a landmark comes into question considering the apparent variability of its position. This study was performed to determine the reliability of the asterion as a surgical landmark. METHODS: One hundred dried skulls were obtained for study. A 2-mm drill hole was placed at the asterion on each side. The position of the drill hole on the inner surface of the skull was next determined and recorded. RESULTS: The asterion was located over the posterior fossa dura in 32% on the right and 25% on the left. Its position was over the transverse or sigmoid sinus complex in 61% on the right and 66% on the left. The landmark was located above the transverse-sigmoid sinus complex in 7% on the right and 9% on the left. CONCLUSIONS: The asterion is not a strictly reliable landmark in terms of locating the underlying posterior fossa dura. Its location is very often directly over the transverse-sigmoid sinus complex. Burr holes placed at the asterion may often open the bone directly over the sinus, leading to potential damage.

Microanatomical study of the extradural middle fossa approach to the petroclival and posterior cavernous sinus region: description of the rhomboid construct.

The extradural middle fossa transpetrosal approach has been used to access lesions of the petroclival and posterior cavernous sinus regions by several neurosurgical groups, including our own. This is a technically demanding approach that provides a relatively wide extradural corridor interposed between the 5th cranial nerve and the cranial nerve VII-VIII complex, which minimizes brain retraction. We performed a microanatomical study to determine the limits of this exposure and in particular how the removal of the petrous bone could be maximized through this approach. Dissection of 15 fixed human cadaveric heads and 8 isolated temporal bones was performed to yield 38 sides studied. We identified a rhomboid-shaped construct of middle fossa landmarks that serve as a guide to maximally removing the petrous apex. The points defining this construct are as follows: 1) the junction of the greater superficial petrosal nerve and the trigeminal nerve; 2) the lateral edge of the porus trigeminus; 3) the intersection of the petrous ridge and arcuate eminence; and 4) the intersection of the lines extended along the axes of the greater superficial petrosal nerve and arcuate eminence. A morphometric analysis determined the average lengths of the respective sides of the complex to be 13.2 mm +/- 2.6 x 22.2 mm +/- 2.8 x 16.4 mm +/- 3.4 x 16.6 mm +/- 1.5 (beginning at "1" and proceeding sequentially), with an approximate area of the construct equal to 2.9 square centimeters.(ABSTRACT TRUNCATED AT 250 WORDS)

Microsurgical anatomy of the inner surface of the petrous bone: neuroradiological and morphometric analysis as an adjunct to the retrosigmoid transmeatal approach.

The retrosigmoid transmeatal technique remains the approach of choice for hearing preservation during the removal of acoustic neuromas that protrude from the porus acusticus. However, encroachment into the bony labyrinth in an effort to remove the tumor in the lateral end of the internal auditory canal (IAC) continues to compromise hearing in certain cases. The limits in the safe removal of the posterior wall of the IAC are not generally agreed on. To address this problem, we have performed a morphometric analysis of 32 fixed cadaveric temporal bones by microsurgical dissection and measurement with fine-cut bone window computed tomographic (CT) scans. The morphometric relationships of identifiable surface landmarks were first determined. Fine cut bone window CT scans were next performed on each bone and the distances between the fundus, the vestibule, and the common crus (CC) with the internal auditory meatus (IAM) were determined. Additionally, the thickness of the bone overlying the posterior semicircular canal at the CC was measured. From a retrosigmoid trajectory, employing a 4-cm craniotomy, the posterior wall of the IAC was removed with a high-speed drill, limiting removal to the distance from the vestibule to the IAM, as determined by CT measurement. Preservation of the integrity of deep structures was confirmed by inspection. The length of the actual IAC unroofed was measured and was compared with the IAC length, from IAM to fundus, measured by CT. The average canal length by CT measured 10.0 mm +/- 1.8 (range, 6.6-14.0). The length of the canal uncovered averaged 5.9 mm +/- 1.4 (4.0-8.5).(ABSTRACT TRUNCATED AT 250 WORDS)