1/9. Stereotactic radiosurgery, X: clinical isodosimetry of gamma knife versus linear accelerator X-knife for pituitary and acoustic tumours.Several review articles have compared gamma unit versus linear accelerator (linac)-based radiosurgery systems, concluding that the dose gradient 'fall-off' at the margin of the target (expressed as the distance between isodoses) is very similar for both techniques as far as single isocentre treatment volumes up to 1.5 cm diameter are concerned, and that the two radiosurgical systems are, in general, comparable. 'Fine tuning' of the gamma unit can be carried out by using multiple isocentre plans, the differential use of small collimator sizes (down to 4 mm) and field weightings, and adroit use of the gamma angle, and selective beam blocking. Multiple isocentre plans, beam modification, restriction of gantry angles and arc lengths, and microcollimation can similarly improve the isodose gradients from linac units. In both instances, the dosimetric advantages occur along selected aspects of the target perimeter border. However, the more frequent use of multiple isocentred 'shots' on the gamma unit achieves greater conformity indices for more complex target volumes, but at the expense of steeper internal dose gradients. We studied two patients with tumours close to or arising from radiosensitive special sensory nerves (optic and cochlear) to compare and contrast fine tuning of the two technologies. In a previously irradiated patient with a pituitary adenoma, the dose gradient achieved at the rostral margin, adjacent to the optic chiasma, was steeper on the gamma unit (due to the concentration of small collimator shots rostrally and beam blocking), which was therefore the dosimetrically preferred technique. In contrast, the vastly smaller internal dose gradient (11% for linac/X-knife versus 100% for Gamma Knife) and the ability to fractionate on the X-knife system, gave a large dosimetric advantage to the X-knife plan in the treatment of an acoustic neuroma, where the intracanalicular component of the cochlear nerve traversed the target volume. This advantage also pertains to the cochlear ramus of the internal auditory (labyrinthine) artery and the facial nerve. Our published work on X-knife radiosurgery of acoustic neuroma has documented improvement of hearing after therapy and may be relevant in this regard. That there are advantages in physical dose distribution and fractionation, producing a reduction in the biological dose in normal tissue, argues for the use of linac technology in acoustic neuromas. Craniopharyngiomas enveloping the optic nerve/chiasma will similarly be better treated by the linac X-knife system. It is apparent that different radiosurgery systems may be indicated in particular neuro-oncological situations.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
2/9. Miniaturised ultrasonic aspiration handpiece for increased applicability.OBJECTIVE: At present, ultrasonic aspiration is routinely used in several fields of surgery, especially in brain and spinal micro-surgery for tumour removal. In order to broaden the access to difficult surgical sites, it is important to design highly miniaturised but still efficient handpieces. The internal resonant system, always made of high-grade materials, must be optimally dimensioned. Normally this is done semi-empirically, by successively improving the design during many iterative test steps. This method however involves several additional difficulties when the degree of miniaturisation increases. For example, small transducer weights exacerbate heat-dissipation problems and make design optimisation important. methods: To resolve these problems we have produced modelling software that makes it possible to simulate and automatically tune each individual interacting section of the design before it is actually manufactured, thereby assuring optimal efficiency. RESULTS: Using a new mini-handpiece, designed via the software, two cases of dissection of acoustic neurinomas were successfully performed. CONCLUSION: Using conventional physical steps for improving ultrasonic aspiration handpieces, several problems arise when the grade of miniaturisation increases, due to increasing demands. We have designed computer software for handpiece simulation. Using this model it has been possible to manufacture a highly efficient miniaturised handpiece.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
3/9. Acoustic neuromas with normal pure tone hearing levels.From 1966 through 1983, 408 patients underwent primary removal of an acoustic neuroma at the Mayo Clinic. Of these, 21 had preoperative pure tone hearing levels of 25 dB hearing loss or better at 500, 1000, and 2000 Hz, which for this study was defined as normal pure tone hearing. Fourteen patients (67%) had dysequilibrium and 13 (62%) had subjective hearing impairment. Nystagmus was the most common physical finding. Five patients (23%) had completely symmetric pure tone hearing levels through all frequencies tested. The mean speech discrimination score was 90%. Mean tumor size was 2.4 cm. brain stem evoked response audiometry was the most helpful of the special tests in the evaluation of these patients with normal pure tone hearing levels. Our results suggest that 5% of patients with acoustic neuromas have normal pure tone hearing levels. A careful history, a thorough physical examination, and an appropriate selection of tests will identify these patients.- - - - - - - - - - ranking = 2keywords = physical (Clic here for more details about this article) |
4/9. False negative MRI scan in an acoustic neuroma.The clinical picture determines the workup of the patient. The referring physicians' high index of suspicion for an acoustic tumor compelled them to persist with the evaluation and referral of this patient, despite a normal MRI. No one can argue that MRI is a technological breakthrough, but it has its limitations like any other test. The quality of the MRI study depends on the cooperation of the patient, and the capabilities of both the machine and physicians. The fact that it depends on completely different physical and chemical properties than conventional radiography suggests to us that it will be an important adjunct rather than a replacement for CT scanning.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
5/9. Massive hemorrhage into intracranial neurinomas.Massive bleeding into an intracranial neurinoma is a rare event. The 12th case of this particular occurrence, which was precipitated by weight lifting, is described and a review of the literature is presented. risk factors for bleeding appear to be tumor size and vascularity. Presenting symptomatology is abrupt and includes headache, nausea, vomiting, and depressed consciousness. Preexisting symptoms referrable to and marked dysfunction of the cranial nerve of origin are present. Deficits of neighboring cranial nerves are frequent. Computed tomography demonstrates the hemorrhages and the tumors. Mild head injury and physical exertion were precipitating factors in two cases. One-fourth of the patients died, while the others made good recoveries.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
6/9. Acoustic tumors: atypical features and recent diagnostic tests.About one-third of patients with acoustic tumor (AT) initially seek medical attention for nonaudiologic complaints. The nonspecific early symptoms of AT require the inclusion of AT in many neurologic differential diagnoses. Advances in electrophysiologic and radiographic tests have allowed earlier diagnosis of AT at a time when abnormal physical findings other than hearing loss are present in less than half of patients. The availability of brainstem auditory evoked response testing, fourth-generation CT, and air-CT cisternography have changed the approach to the diagnosis of AT. Neurologists should be cognizant of recent diagnostic advances.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
7/9. Auditory perceptual and visual-spatial characteristics of gaze-evoked tinnitus.Auditory perceptual and visual-spatial characteristics of subjective tinnitus evoked by eye gaze were studied in two adult human subjects. This uncommon form of tinnitus occurred approximately 4-6 weeks following neurosurgery for gross total excision of space-occupying lesions of the cerebellopontine angle and hearing was lost in the operated ear. In both cases, the gaze-evoked tinnitus was characterized as being tonal in nature, with pitch and loudness percepts remaining constant as long as the same horizontal or vertical eye directions were maintained. tinnitus was absent when the eyes were in a neutral head-referenced position with subjects looking straight ahead. The results and implications of ophthalmological, standard and modified visual-field assessment, pure-tone audiometric assessment, spontaneous otoacoustic emission testing and detailed psychophysical assessment of pitch and loudness are discussed.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
8/9. Appropriateness of magnetic resonance imaging in sudden sensorineural hearing loss.Idiopathic sudden sensorineural hearing loss is an enigmatic condition of unknown cause. Although the treatment for sudden sensorineural hearing loss is controversial, the evaluation for a cause should not be. All patients are evaluated with a complete history, physical examination, audiologic examination, and blood draw to evaluate complete blood count, general chemistry screen, thyroid function test results, erythrocyte sedimentation rate, and fluorescent treponemal antibody absorbance. magnetic resonance imaging with gadolinium contrast is essential in the evaluation of idiopathic sudden sensorineural hearing loss, even if there is a complete response to either treatment or no treatment. During the last year we treated 16 patients for idiopathic sudden sensorineural hearing loss with our protocol of intravenous dextran/Hypaque or oral high-dose steroids. Fifteen patients were evaluated immediately before treatment with a magnetic resonance imaging scan. An additional patient had been treated successfully with high-dose steroids at an outside institution and came in for an evaluation. Of these 16 patients, 3 (18.75%) were found to have significant pathologic conditions on magnetic resonance imaging scan. The patient who had been treated successfully on the outside was noted to have a 5-mm intracanalicular acoustic neuroma, the second patient was found to have a multiple sclerosis lesion at the level of the superior olive, and the third patient, who had had a normal magnetic resonance imaging scan 18 months previously, was now found to have a large 4- to 5-cm meningioma in the cerebellopontine angle. We believe it is essential that all patients with idiopathic sudden sensorineural hearing loss be evaluated at some point during their treatment with a magnetic resonance imaging scan with gadolinium contrast.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
9/9. cerebellopontine angle meningiomas with primary otologic symptoms.The majority of cerebellopontine angle (CPA) tumors are acoustic neuromas (AN). However, an intracranial meningioma may occur at this site and will produce symptoms similar to an AN. The most common presenting symptoms of CPA meningiomas are hearing loss, tinnitus, dizziness and dysequilibrium. It cannot be easily distinquished from an AN only on the history and physical examination. Even with an audiogram, evoked response audiometry (ERA) and vestibular function tests, it still cannot be distinquished. CT scan and MRI are helpful in differentiating these two tumors radiographically. In this article, we report two cases of CPA meningiomas which presented with otologic symptoms. The diagnosis and treatment of CPA meningioma is discussed.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |