Search PubMed⌕ Search

Biomedical subjects

G D Silverberg

Publications and source records attributed to G D Silverberg.

At least 37 records · Page 2Linked to original sources
PubMed1990

Stereotactic heavy-charged-particle Bragg-peak radiation for intracranial arteriovenous malformations.

BACKGROUND: Heavy-charged-particle radiation has several advantages over protons and photons for the treatment of intracranial lesions; it has an improved physical distribution of the dose deep in tissue, a small angle of lateral scattering, and a sharp distal falloff of the dose. METHODS: We present detailed clinical and radiologic follow-up in 86 patients with symptomatic but surgically inaccessible cerebral arteriovenous malformations that were treated with stereotactic helium-ion Bragg-peak radiation. The doses ranged from 8.8 to 34.6 Gy delivered to volumes of tissue of 0.3 to 70 cm3. RESULTS: Two years after radiation treatment, the rate of complete obliteration of the lesions, as detected angiographically, was 94 percent for lesions smaller than 4 cm3, 75 percent for those of 4 to 25 cm3, and 39 percent for those larger than 25 cm3. After three years, the rates of obliteration were 100, 95, and 70 percent, respectively. Major neurologic complications occurred in 10 patients (12 percent), of whom 8 had permanent deficits. All these complications occurred in the initial stage of the protocol, before the maximal dose of radiation was reduced to 19.2 Gy. In addition, hemorrhage occurred in 10 patients from residual malformations between 4 and 34 months after treatment. Seizures and headaches were less severe in 63 percent of the 35 and 68 percent of the 40 patients, respectively, who had them initially. CONCLUSIONS: Given the natural history of these inaccessible lesions and the high risks of surgery, we conclude that heavy-charged-particle radiation is an effective therapy for symptomatic, surgically inaccessible intracranial arteriovenous malformations. The current procedure has two disadvantages: a prolonged latency period before complete obliteration of the vascular lesion and a small risk of serious neurologic complications.

Adolescent↗
PubMed1990

Occult vascular malformations of the optic chiasm: magnetic resonance imaging diagnosis and surgical laser resection.

Angiographically occult vascular malformations of the optic nerve and chiasm are extremely rare. Before the advent of magnetic resonance imaging (MRI), it was difficult to diagnose these lesions preoperatively. We report MRI scan findings of optic chiasm cavernous angiomas in two patients with chiasmal syndrome. MRI was useful in localizing the vascular malformation and delineating its characteristics, especially chronic hemorrhage. One patient underwent biopsy of the lesion. The other patient underwent complete microsurgical resection of the malformation with the carbon dioxide laser with preservation of vision. Occult vascular malformations of the optic nerve and chiasm may be a more common cause of visual deterioration than previously recognized. The MRI scan is the imaging modality of choice for diagnosing and following these lesions. In certain patients, these vascular malformations may be amenable to complete surgical removal with stabilization or improvement of visual function.

Adult↗
PubMed1989

Mixed gangliocytoma-adenoma: a distinct neuroendocrine tumor of the pituitary fossa.

A mixed gangliocytoma-adenoma occurring in the pituitary fossa of a patient who presented with acromegaly, galactorrhea, and headaches is described. Immunohistochemical studies demonstrated the gangliocytic portion of the tumor to be composed nearly entirely of ganglion cells enmeshed in their neuritic processes and disclosed focal presence of growth hormone and prolactin-secreting cells in the adenoma. Ultrastructurally, some of the larger ganglion cells contained (and were often filled with) zebra-like bodies, while the adenoma was shown to be sparsely granulated with numerous fibrous bodies. These findings support the term of mixed gangliocytoma-adenoma for these rare intrasellar tumors and provide additional support for their nature as independent neuroendocrine units.

Adenoma↗
PubMed1989

Noradrenaline (gamma) and ATP responses of innervated and non-innervated rat cerebral arteries.

1. The distribution of sympathetic adrenergic nerves on the rat middle cerebral artery and on the arterioles which originated from it was determined by use of gloxylic histochemistry. 2. Whereas the middle cerebral artery and proximal arterioles arising from this artery received a sympathetic innervation, the distal regions of the same arterioles were devoid of innervation. 3. The arteries and arterioles which were innervated were depolarized by noradrenaline in the combined presence of alpha- and beta-adrenoceptor antagonists. Those which were not innervated were not depolarized by noradrenaline. 4. ATP depolarized all arteries and arterioles examined. 5. These observations are discussed with respect to the similarities and differences between gamma-adrenoceptors and P2 purinoceptors.

Adenosine Triphosphate↗
PubMed1988

Inward rectification in rat cerebral arterioles; involvement of potassium ions in autoregulation.

1. The resting membrane potentials of proximal and distal segments of the arterioles which arise from the rat middle cerebral artery were determined. Proximal segments had stable membrane potentials with a mean value of -69 mV. The membrane potentials of distal segments were less negative and often unstable. 2. When the extracellular concentration of potassium ions [( K+]o) was increased proximal segments of arteriole were depolarized whereas distal ones were hyperpolarized. When [K+]o was decreased both proximal and distal segments were depolarized, the changes being more marked in proximal arterioles. 3. The membranes of proximal segments of arteriole displayed inward rectification at potentials near rest; inward rectification in distal segments of arteriole, when detected, was less pronounced. 4. The activation curve for inward rectification in proximal segments of arteriole was changed by changing the extracellular concentration of K+. A reduction in [K+]o caused the activation curve to move to such negative potentials that the inward rectifier no longer contributed to the resting conductance. 5. Increasing [K+]o changed the activation curve for inward rectification in distal segments of arteriole so that more K+ current flowed at potentials near resting. At the same time the membrane potential hyperpolarized. 6. The results are discussed in relation to autoregulatory changes which occur following changes in the K+ concentration of cerebrospinal fluid.

Animals↗
PubMed1986

The action potential and underlying ionic currents in proximal rat middle cerebral arterioles.

The active and passive electrical properties of isolated segments (length 120-220 microns, diameter 60-150 micron) of proximal rat middle cerebral arterioles (less than 1 mm from parent artery) were analysed using a single-electrode current or voltage clamp. The voltage response to a current step exhibited an exponential time course. The mean resistance and time constant was 102 M omega and 265 ms corresponding to approximate specific resistance and capacitance of 60 k omega/cm and 4 micro F/cm2. Membrane resistance was constant in the range -55 to -80 mV. At potentials more negative than -80 mV there was a decrease in membrane resistance resulting in activation of an inward rectifier. At membrane potentials less negative than -50 mV the membrane resistance decreased; larger depolarizations (greater than -40 mV) initiated small regenerative responses. External application of tetraethylammonium chloride caused membrane depolarization (10-15 mV), spontaneous discharge of action potentials and rhythmic arteriolar constriction. Action potentials studied with the membrane held at -60 mV had a large rapid depolarizing component, an after-depolarization and a small slower after-hyperpolarization. Tetrodotoxin (TTX) had no effect on the action potential. However, both the fast and slow components of the action potential were suppressed by extracellular removal of calcium ions and/or addition of cobalt ions, nifedipine or verapamil. Voltage-clamp studies demonstrated an inward rectifying current at membrane potentials more negative than -80 mV. At depolarized potentials at least four separate currents were activated; two separate calcium currents and two outward currents.

Action Potentials↗
PubMed1986

Sympathetic innervation and excitability of arterioles originating from the rat middle cerebral artery.

The densities of the adrenergic innervation of the internal carotid and middle cerebral arteries and their extracerebral branches have been determined using fluorescence histochemistry. The density of the nerve plexus on the internal carotid artery was greater than that of the middle cerebral artery. The density of the plexus on the middle cerebral artery decreased with increasing distance from its origin. The density and the peripheral extent of the nerve fibre plexus on the arterioles arising from the carotid artery were greater than those arising from the middle cerebral artery. On any arteriole the density of innervation decreased with increasing distance from its origin. The passive electrical properties of proximal and distal middle cerebral arteriolar segments were compared. Both proximal and distal arteriolar segments had similar resistances and time constants in the order of 100 M omega and 250 ms respectively. Small regenerative responses could be elicited in all proximal middle cerebral arteriolar segments but only in a proportion of corresponding distal segments. The addition of external tetraethylammonium ions (TEA) provided much larger regenerative responses. Action potentials in proximal middle cerebral arteriolar segments had larger peak amplitudes and faster rise times than those of corresponding distal segments. Distal carotid arteriolar segments had similar voltage-dependent excitability as proximal segments of middle cerebral arterioles but generated less inward current for a given voltage step. There was a direct correlation between the density of innervation and the voltage-dependent excitability of arteriolar smooth muscle cells. The possibility that the presence of nerves is correlated with the density of calcium channels is discussed.

Action Potentials↗
PubMed1985

Tumors of the central nervous system studied by computed tomography and ultrasound.

Intraoperative ultrasound (US) was compared to computed tomography (CT) in 41 intracranial and 6 spinal cord tumors. The studies correlated closely except for primary gliomas. Eight of the 22 primary intracranial gliomas (37%), including 1 low-grade and 7 anaplastic tumors, were larger and more extensive on US than on CT. Margins of non-enhanced primary astrocytomas were shown by US but not CT. Four anaplastic tumors (19%) exhibited echogenicity extending beyond the enhanced area. In 4 patients an enhanced lesion contained a lucent center which proved to be echogenic. Low-grade astrocytomas were relatively homogeneous on US, while anaplastic astrocytomas were more inhomogeneous. Cysts could be found in both types of astrocytomas and were often small and multiple. The echo pattern was not helpful in differentiating metastases from primary tumors, although all of them had sharp margins. Sonography of the central nervous system can provide valuable information about tumor morphology and margins.

Astrocytoma↗
PubMed1985

Regulation of growth hormone release from cultured human pituitary adenomas by somatomedins and insulin.

GH secretion is stimulated by hypothalamic GH-releasing factor (GHRH) and inhibited by somatostatin. Since GH induces the production of insulin-like growth factors (IGF) in liver and other tissues, it is of interest to learn whether IGF alters GH release through long loop feedback inhibition. Pituitary adenomas which had been removed from six acromegalic patients were processed for dispersed cell cultures and/or cell membrane preparations. Binding studies using 125I-labeled IGF-I, IGF-II, and insulin revealed specific hormone binding for each ligand to cell membranes derived from four somatotropinomas. A partially purified somatomedin preparation inhibited basal and/or GHRH-stimulated GH release from cultured pituitary cells derived from three of four adenomas; there was no effect of somatomedin in one tumor. In a single tumor, insulin also partially inhibited GHRH-stimulated GH release. Additionally, in one nonadenomatous pituitary removed from a patient with diabetes mellitus, insulin and somatomedin inhibited GHRH-stimulated GH release, and insulin inhibited basal GH secretion. These results indicate that specific cell membrane receptors for somatomedin peptides and insulin may be found on cell membranes from GH-secreting tumors, and that somatomedins and insulin can inhibit GH release in cultured human somatotropinoma cells. Thus, these data suggest that somatomedins may exert feedback inhibition of GH secretion in some patients with acromegaly.

Acromegaly↗
PubMed1983

Reappraisal of cardiopulmonary bypass with deep hypothermia and circulatory arrest for complex neurosurgical operations.

Although cardiopulmonary bypass (CPB) with hypothermia and circulatory arrest is routinely used for certain cardiovascular procedures, its advantages have infrequently been applied for other unusual surgical problems. Fourteen patients (six men and eight women, average age 48 years, range 29 to 74 years) underwent 15 operations over a 4-year period beginning in November 1978. Preoperative diagnosis included giant middle cerebral aneurysm (n = 8), internal carotid aneurysm (3), basilar artery aneurysm (2), and medullary hemangioblastoma (2). All patients had lesions that were considered inoperable by standard neurosurgical techniques. Operative technique consisted of peripheral cannulation with a long and short femoral vein cannula for venous return (24 to 28F) and a single femoral arterial cannula (18 to 24F). CPB flows ranged from 1 to 3.5 L/min, and the total CBP times averaged 146 minutes (range 66 to 282 minutes). Circulatory arrest times averaged 21 minutes (range 5 to 51 minutes), with two patients having no period of circulatory arrest. Lowest core temperature ranged from 16 degrees to 20 degrees C, with cooling and rewarming aided by Brown-Harrison heat exchangers placed in a countercurrent fashion within the venous return line. The heart spontaneously defibrillated in six patients, and external countershock was required in nine patients. No difficulty was encountered with cardiac distention. The intended operation was accomplished in all cases with 13 of 14 patients being discharged from hospital, having had a good neurosurgical result. One patient sustained a hemorrhagic infarction of the cerebellum and pons and is presently recovering. Our experience indicates that peripheral CPB with induced hypothermia and circulatory arrest is a safe technique for approaching otherwise inoperable neurosurgical lesions.

Adult↗
PubMed1982

Lack of alpha-adrenoreceptor binding of [125I]BE2254 to rat basilar artery membranes.

Rat basilar arteries do not contain classical alpha- or beta-adrenoreceptors as assessed by electrophysiological techniques even though these arteries are innervated by catecholamine-containing perivascular nerves. These arteries were therefore examined for their ability to selectively bind an alpha-adrenoceptor radioligand, [125I]BE2254 (2/beta/4-hydroxyphenyl)-ethylaminomethyl)-tetralone). For comparison, rat tail arteries were also studied as these are known to contain functional alpha-adrenoreceptors. It was found that basilar artery membranes had only one-third of the specific binding of tail artery membranes and this finding collaborates the electrophysiological data.

Animals↗
PubMed1982

Noradrenaline receptors on the rat basilar artery.

1. Intracellular recordings were obtained from the arterial smooth muscle cells of rat basilar artery during perivascular nerve stimulation and during the application of adrenoceptor agonists and antagonists. 2. Perivascular nerve stimulation evoked excitatory junction potentials. Increased stimulation resulted in action potentials which were associated with arterial constriction. 3. Bath-applied noradrenaline did not cause constriction but at high concentrations caused membrane depolarization. The depolarization caused by a given dose of noradrenaline was larger in the presence of cocaine. 4. Neither the depolarizations obtained by nerve stimulation nor those obtained by bath-applied noradrenaline were blocked by adrenoceptor blocking agents. 5. Unlike alpha-receptors, the receptors on the rat basilar artery were activated equally well by dopamine, adrenaline, and both optical isomers of noradrenaline. 6. Excitatory junction potentials could be obtained in the presence of high bath concentrations of noradrenaline.

Adrenergic Agonists↗
PubMed1981

Pathophysiology and management of raised intracranial pressure.

The mechanism of cerebral homeostasis is reviewed, paying particular attention to the way blood-brain barrier, cerebrospinal fluid and cerebral blood flow contribute to the maintenance of normal intracranial pressure. The pathophysiology of raised intracranial pressure is outlined delineating the different types of cerebral oedema. Guidelines for the management of patients with raised intracranial pressure are presented as well as the techniques of intracranial pressure monitoring.

Animals↗
PubMed1981

Balloon catheter occlusion for cavernous carotid artery injury during transsphenoidal hypophysectomy. Case report.

During transsphenoidal hypophysectomy for pituitary ablation in a patient with disseminated breast cancer, brisk arterial hemorrhage occurred during separation of adhesions between the pituitary gland and the wall of the cavernous sinus. Hemorrhage was controlled by placement of a Prolo balloon catheter into the internal carotid artery (ICA) that occluded the site of hemorrhage. The patient experienced no neurological sequelae. The cervical ICA was easily exposed for insertion of this double-lumen catheter. With the image intensifier already in position, injection of contrast material through the arteriography lumen allowed precise localization of the site of injury and directed positioning of the balloon for control of the hemorrhage.

Carotid Artery Injuries↗