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Biomedical subjects

L Steiner

Publications and source records attributed to L Steiner.

At least 19 recordsLinked to original sources
PubMed1996

Histological changes in the normal rat brain after gamma irradiation.

Radiation-induced changes in the parietal cortex of Wistar rats were observed at various time points after gamma surgery. Maximum dosages of 50, 75, and 120 Gy were given at the iso-center of the radiation using a 4-mm collimator. Conventional histochemical and immunocytochemical analyses, and computer-assisted videomicroscopy were utilized to examine perfusion-fixed brain tissue. Irradiation at a dosage of 50 Gy elicited morphological changes of astrocytes in the parietal cortex at 3 months. Vasodilatation became obvious at 12 months; fibrin deposition was observed in the dilated capillary wall. Neither leakage of Evans Blue from the vasculature into the tissue nor necrosis was observed across the 12 month observation period. Irradiation at a dosage of 75 Gy resulted in morphological changes of astrocytes within 1 month. Dilatation of vessels and capillary thickening were observed at 3 months. Evans Blue leakage and necrosis were observed at 4 months after 75 Gy irradiation. At this time, the walls of arterioles became thickened by subintimal accumulation of fibrin and hyaline substance; this sometimes resulted in occlusion of the lumen. Significant hemispheric swelling was observed at 4 months. Irradiation at a dosage of 120 Gy elicited changes in astrocytic morphology within 3 days. Evans Blue leakage into the tissue was observed by 3 weeks. Vasodilation became marked at this time point and rarefaction was observed in the irradiated cortex. Necrosis was observed at 4 weeks, however, no significant swelling was observed. Taken together, these findings demonstrate time-dependent and dosage-dependent changes in normal cerebral tissue after Gamma Knife irradiation. These results provide a basis for gauging the impact of gamma surgery in regions of eloquent tissue. An enhanced understanding of the cellular responses to radiosurgery will contribute to developing and evaluating future applications for gamma surgery.

Animals↗
PubMed1996

Neuroimaging studies of postobliteration nidus changes in cerebral arteriovenous malformations treated by gamma knife radiosurgery.

BACKGROUND: Following radiosurgical treatment, the majority of patients with arteriovenous malformations (AVMs) are periodically examined by means of computed tomography (CT) and magnetic resonance imaging (MRI) to assess the attainment of nidus obliterations, as well as adverse radiation effects in the surrounding brain. However, few neuroimaging studies of the long-term results following complete obliterations, confirmed by angiography, have been published to date. METHODS: CT, MRI, magnetic resonance (MR) angiographic and angiographic images, obtained after angiographic confirmation of complete nidus obliteration, were reviewed in 11 AVM patients treated with gamma knife radiosurgery. The period between angiographic confirmation of nidus obliteration and these most recent examinations was 12-84 months (mean, 29 months). RESULTS: In ten patients who were assessed by CT, the obliterated nidus was shown to be isodense (eight cases). A significant time-related decrease in contrast enhancement was observed within 1 to 2 postobliteration years (five/seven cases). Eight patients were evaluated by MRI. On T1-weighted imaging, the nidus was shown to be hypointense (six cases) or a mixture of hypointense and isointense areas (two cases). On T2-weighted imaging, nidus intensity varied more than than observed on T1-weighted imaging, and time-related intensity increases were observed (two/seven cases). No flow-signal void was demonstrated in any of these cases. In four of the seven cases, in which serial postobliteration follow-up MRI studies were conducted, significant gadolinium enhancement persisted 3 years or more after obliteration (maximum of 7 years). No vascular abnormalities were demonstrated in seven patients who were assessed by conventional angiography and/or MR angiography. CONCLUSIONS: Radiosurgery-induced changes in a nidus may continue for several years after angiography has shown complete AVM obliteration.

Adolescent↗
PubMed1996

Effect of Gamma Knife surgery on the risk of rupture prior to AVM obliteration.

The incidence for hemorrhage in non-obliterated arteriovenous malformations (AVM) during the first two years following Gamma Knife (GK) surgery was compared to the calculated incidence in untreated patients. There was a decrease in the incidence of hemorrhage as compared to the natural course. This difference was statistically significant. The actual number of hemorrhages during the first two years was 49 in a series of 1604 patients. Additionally, 41 hemorrhages occurred beyond the two years following treatment over the entire follow up time span of up to 24 years. For the first two years the calculated incidence was roughly two times higher than the observed incidence. This impact on the natural history was detectable already within six months after the treatment for the malformations totally covered with at least 25 Gy. The relation between a high minimum and a high average dose on the one hand and a lower risk for hemorrhage on the other hand was statistically significant. Low treatment doses and high age correlated to a higher risk. Neither hemorrhage prior to treatment nor time interval between presenting hemorrhage and treatment seemed to influence the risk for post treatment hemorrhage. The risk for permanent neurological deficit or death due to AVM rupture during the latency period between the time of treatment and total nidus obliteration was less than 0.5% for small AVM and 2-4% for large ones during the first two years. Of the 24 patients with sequelae following AVM rupture after treatment 14 died and 10 remained with neurological deficit of different degrees. However, all survivors were self sufficient.

Adult↗
PubMed1995

Calreticulin--the potential autoantigen in celiac disease.

Monoclonal antibodies to gliadin were recently found to cross-react with epitopes on rat enterocytes. Two molecules of mol. mass 62 and 66 kDa were isolated from enterocyte lysates by affinity chromatography using antigliadin monoclonal antibodies. The N-terminal amino acid sequence of the 62-kDa protein was determined to be XXXIYFKEQFLD. This amino acid sequence corresponds to amino acid sequence of rat calreticulin. The presence of calreticulin in enterocyte lysates was further confirmed using anticalreticulin serum. Anticalreticulin serum was also used to investigate the reactivity of isolated rat calreticulin. To analyze whether gliadin and calreticulin share similar epitopes recognized by anticalreticulin antibodies, synthetic dodecapeptides derived from the amino acid sequence of alpha gliadin were used in competitive ELISA assay. Two gliadin peptides, QEQVPLVQQQQF and YQLLQELCCQHL, were found to inhibit the binding of rabbit anti-rat calreticulin sera to rat calreticulin. The significant correlation was detected between IgA anticalreticulin and antigliadin antibodies (r = 0.827; P < 0.001) in celiac patients.

Amino Acid Sequence↗
PubMed1995

Enhanced magnetic resonance imaging of the rat brain using a stereotactic device with a small head coil: technical note.

A stereotactic device (SDM) was developed for performing consistent magnetic resonance imaging (MRI) of the rat brain. The SDM was developed by adapting a radiofrequency transmit/receive head coil of 4.4 cm inner diameter (quadrature birdcage head coil), and utilizing partial acrylic construction for the positioning elements. The small head coil provides improved resolution and accuracy of the image, while the stereotactic holder permits repeatable and accurate imaging of identified brain structures. This system provides several advantages over existing experimental MRI devices. The SDM ensures that the head is always placed in the center of the coil in a uniform fashion. Standardized positioning of the skull optimizes image quality and provides a consistent orientation of the brain. In addition, a widely-utilized coordinate system described by Paxinos and Watson can be employed to assist in the identification of structures and to facilitate surgical planning. The SDM is compatible with a recently-developed stereotactic device for radiosurgery with the Gamma Knife, thus permitting the planning and performance of experimental radiosurgery using the same coordinate system. The SDM also provides the ability to perform MRI and radiosurgery at different times, thus avoiding the need for prolonged anesthesia during an experimental study. Finally, the SDM allows repeated MRI of the same, identifiable positions in the brain during longitudinal experimental studies. The utility of this device is demonstrated here by examining the time course of cerebral damage that evolved within a radiosurgical focus after gamma irradiation.

Animals↗
PubMed1995

Failure in management of pituitary tumors discussion of 3 cases.

Three patients with pituitary adenomas (ACTH-secreting, non-secretory, and multi-secretory) with unfavorable course, in spite of repeated microsurgery, drug therapy, as well as radiotherapy and radiosurgery, are presented. Each case was re-evaluated for possible flaws in management. Two of the invasive tumors continued to grow, in spite of correct management. The third patient with a pituitary adenoma underwent microsurgical resection, and later following a false positive finding of recurrence, received radiotherapy and underwent radiosurgery. The lesion actually was chronic inflammatory tissue.

Adult↗
PubMed1995

Gamma knife surgery for craniopharyngioma.

We present our results of Gamma Knife surgery for craniopharyngioma in nine patients. The current status of surgery, radiation therapy, intracavitary instillation of radionucleides and Gamma Knife surgery in the management of craniopharyngiomas is discussed.

Adolescent↗
PubMed1995

Gamma Knife radiosurgery in cerebral arteriovenous malformations: postobliteration nidus changes observed on neurodiagnostic imaging.

Computed tomographic (CT), magnetic resonance (MR), MR angiographic and angiographic images, obtained after complete nidus obliteration had been angiographically confirmed, were reviewed in 9 patients who had undergone Gamma Knife treatment for cerebral arteriovenous malformations (AVMs). The period between angiographic confirmation of nidus obliteration and the most recent examinations was 12-84 months (mean 29 months). The patients ranged in age from 9 to 54 years (mean 22 years). There were 6 females and 3 males. In 8 patients, the obliterated nidus was shown on CT to be isodense. Calcification was identified in 3 patients, 1 of whom had not shown calcification on CT before treatment. Contrast enhancement of the nidus was seen in 6 patients, in 5 of whom a significant time-related decrease in contrast enhancement was observed following nidus obliteration. In 6 patients, T1-weighted MR imaging showed a hypointense nidus in 4 cases, both hypo- and isointense in 1 and isointense in 1. T2-weighted imaging showed a more varied nidus intensity than was seen on T1-weighted imaging. No flow signal void was demonstrated in any of these cases. After gadolinium administration, the nidus was enhanced in all cases, markedly in 4 and moderately in 2. In 5 of the 6 cases a time-related decrease in gadolinium enhancement was observed following nidus obliteration. This change was, however, less significant than that observed on contrast-enhanced CT. Angiography and/or MR angiography showed no vascular abnormalities in 7 patients. These results show that radiosurgery-induced changes in a nidus may continue for several years after angiography has shown complete AVM obliteration. These late changes can be considered to involve further obliteration of the remaining or recanalizing vessels, reflecting an ongoing process from coagulation necrosis to liquefaction necrosis.

Adolescent↗
PubMed1994

A stereotactic guide for microsurgery. Technical note.

A stereotactic guide for microsurgery is presented. The guide consists of a weak helium neon laser projecting a red beam towards the target when the arc carrying the beam has been set on the Leksell frame according to the stereotactic co-ordinates of the target calculated on the pre-operative imaging studies. The device allows free manoeuverability of the operating microscope.

Brain Diseases↗
PubMed1994

Alternate-site testing. Consider the analyst.

The ability to perform accurate and precise testing in sites outside the main clinical laboratory is more dependent on the quality of the individual performing the alternate-site testing (AST) than on any other factor. Most of these individuals have little or no laboratory training or experience. The central laboratory must take responsibility for training AST analysts, monitoring their performance (testing, QC, PT, and QA), and certifying their competence. Regular retraining and recertification must be performed.

Clinical Laboratory Techniques↗
PubMed1993

Isolation of a shark immunoglobulin light chain cDNA clone encoding a protein resembling mammalian kappa light chains: implications for the evolution of light chains.

The time of emergence of immunoglobulin kappa and lambda light (L) chains in evolution is unknown. An L chain cDNA clone was isolated from the nurse shark (Ginglymostoma cirratum), a cartilaginous fish, whose predicted variable (V) region amino acid sequence has up to 60% sequence identity to mammalian V kappa domains. Genomic analyses suggest a cluster-type gene organization for this L chain locus, similar to the shark lambda-like immunoglobulin L chain loci rather than mammalian kappa loci. We propose that divergence of the ancestral L chain into isotypes likely occurred before the emergence of elasmobranchs 400-450 million years ago. Similarities in gene organization between the two isotypes in sharks may reflect the gene organization utilized by the ancestral L chain.

Amino Acid Sequence↗
PubMed1993

Gamma knife surgery of cerebral arteriovenous malformations: serial MR imaging studies after radiosurgery.

PURPOSE: To investigate the temporal sequence of post radiosurgery magnetic resonance imaging changes in cerebral arteriovenous malformations. METHODS AND MATERIALS: Eighteen patients were regularly followed up after gamma knife surgery. The follow-up intervals ranged from one day to 44 months. High signal lesion in or around arteriovenous malformations on T2-weighted magnetic resonance images corresponding to the treatment volume and developing after radiosurgery were defined as the adverse reaction of the irradiation. This high signal and the regression of arteriovenous malformations nidus after radiosurgery were evaluated. RESULTS: Adverse reaction of irradiation was observed in nine cases. Seven of them were symptomatic. The reactions presented as focal high signal in three cases and focal high signal with extension along the neural tracts in six cases. The reactions were seen either immediately after treatment (one case), between 3 and 14 months (seven cases), and 40 months after treatment (one case). The regression of the adverse reaction was observed to start 5 +/- 3 months after its appearance. Regression of the arteriovenous malformations' nidus was found in 16 cases. In two cases the AVMs became invisible on magnetic resonance images but the angiogram still demonstrated abnormal shunts. In another one case with angiogram showing total obliteration, the nidus was erroneously interpreted as incomplete obliteration on magnetic resonance images. CONCLUSION: It is concluded that magnetic resonance imaging is a sensitive in vivo method for detecting cerebral radiation injury. Magnetic resonance imaging offers a method for evaluating the regression of arteriovenous malformations' nidus, but the diagnosis of complete obliteration of the nidus after radiosurgery still relies on the angiogram.

Adolescent↗
PubMed1993

A stereotactic device for experimental gamma knife radiosurgery in rats. A technical note.

A rat stereotactic device was designed for use in Gamma Knife radiosurgery. Experimental radiosurgical lesions were made in superficial and deep cerebral structures to verify the accuracy of the coordinate system, which is based on a standard rat stereotactic atlas. Calculated dosages were shown to be accurate utilizing thermoluminescence dosimetry. Two additional features of the device permit the surgical positioning and placement of electrodes, and postmortem slicing of the brain according to the same coordinate system. This new apparatus allows precise and repeatable gamma irradiation of the rat brain without the need for expensive and time-consuming imaging techniques. Studies of this type will provide a rapid means for examining the effects of radiosurgery on the central nervous system.

Animals↗
PubMed1993

Postradiation volume changes in gamma unit-treated cerebral arteriovenous malformations.

Postradiation changes in angiographically determined nidus volume were quantitatively studied in 22 arteriovenous malformation (AVM) cases treated by gamma unit radiosurgery. The postradiosurgical decrease was statistically significant by post-treatment year 2 (p < .05). In children, AVMs tended to be obliterated more quickly than in adults. Volume reduction was more rapid in nidi receiving 25 Gy or more than in those receiving less than 25 Gy (p < .01). However, there were no significant differences in nidus volume decrease between these two dose groups at the second or third postradiosurgical year. Dose response curves were obtained 1, 2, and 3 years following treatment.

Adolescent↗
PubMed1993

Stereotactic microsurgical resection of cerebral lesions.

We describe our experience with stereotactic microsurgical resection of 27 lesions using the Leksell frame in 23 patients; 7 had cerebral metastases, 6 had gliomas, 6 had vascular malformations, 3 had meningiomas and 1 had radiation necrosis. Gross total removal of the lesion was accomplished in every case. All lesions were between 1.0 and 3.5 cm in greatest diameter and located either deep within the cerebral (n = 7) or superficially in areas of functional cortex (n = 20). There was no operative mortality and only minimal morbidity. Average length of operating time including frame application, imaging and resection was 4.4 h and most patients were discharged on the second postoperative day. The indications, advantages and limitations of stereotactic craniotomy are discussed and technical modifications that extend the usefulness and safety of this technique are described.

Adolescent↗
PubMed1993

The dosimetric consequences of weighted fields using the same isocenter in radiosurgery.

One handicap in achieving ideal dosimetry with the Gamma Knife is the limited number of standard collimator sizes (4, 8, 14 and 18 mm). We report an approach that makes possible the creation of 50% or higher isodose lines, corresponding to collimator sizes from 4 to 18 mm. This technique, which uses the same icocenter, but with different sized and weighted collimators, improves matching for given isodose lines to the diameter of the lesion in a defined plane. However, when combination fields, designed to reproduce the 50% isodose diameter of the 8- and 14-mm collimators, are compared to the standard sizes, there are significant differences in the three-dimensional dosimetry.

Brain Neoplasms↗
PubMed1993

Extracranial absorbed doses with Gamma Knife radiosurgery.

Radiosurgery is used with increasing frequency, not only for the treatment of cerebral arteriovenous malformations (AVMs), but also for the treatment of other well-defined lesions including acoustic neuromas, meningiomas, pituitary adenomas as well as solitary metastases. Although investigators have addressed dosimetric aspects of stereotactic radiosurgery in terms of target volume, little if any attention has been focused on the absorbed doses received at extracranial sites. Therefore, absorbed doses to the eye, thyroid, sternum and gonads were measured in 111 patients (100 adults and 11 children) using thermoluminescent dosimetry (TLDs). For the 100 adults, the average maximum target absorbed dose was 35 +/- 8 Gy. The measured absorbed dose in selected organs of adults from Gamma Knife radiosurgery using one or more isocenters was 9 +/- 8 cGy for the eye, 15 +/- 7 cGy for the thyroid, 20 +/- 10 cGy for the sternum and 3 +/- 2 cGy for the gonads. The absorbed doses received by the children (13 years and younger) was similar with the exception of a marked increase in gonadal dose. The use of multiple isocenters is associated with higher absorbed doses to extracranial sites.

Adolescent↗