Glutamate-induced energetic stress in hippocampal slices: evidence against NMDA and glutamate uptake as mediators

The introduction of exogenous glutamate to normally respiring hippocampal slices produced substantial reductions in ATP, phosphocreatine (PCr) and intracellular pH (pHi) when the concentration exceeded 1 mM. These changes were not prevented by addition of MK-801 (an NMDA receptor antagonist), nor were they mimicked by NMDA or high potassium. In addition, the glutamate-induced metabolic alterations were not prevented by addition of aspartate-b-hydroxymate or sodium substitution by choline, both of which should inhibit high-affinity sodium-dependent glutamate uptake. These results suggest that glutamate alone can produce marked energetic stress in neural tissue, even when glucose and oxygen are maintained at control levels; and that the energetic stress does not appear to be specifically mediated by NMDA-induced depolarization, or by high-affinity uptake of glutamate.

Protein kinase C activity in permanent focal cerebral ischemia

Protein kinase C (PKC) activity was investigated in a model of focal stroke in the rat. Following 6 h of left middle cerebral artery occlusion, rat brains were frozen in situ. In the peripheral ischemic zone, total PKC activity declined by close to two-thirds (1.07 +/- 0.35 vs 2.77 +/- 0.12 nmol/min/mg protein; p less than 0.05, n = 4), and the proportion of total activity associated with the particulate fraction decreased from 33.3 +/- 1.5% to 16.2 +/- 1.4% (p less than 0.01, n = 4). Thus, overall particulate PKC activity in the ischemic zone was less than 20% of control. The cerebral energy metabolite profile of tissue from the ipsilateral hemisphere, corresponding to the region where samples were obtained for PKC activity assay, suggests that this tissue may have been part of the ischemic penumbra before further deterioration.

Use of the delayed mask for improved demonstration of aneurysms on intraarterial DSA

PURPOSE

We retrospectively explored the use of the delayed mask technique for intraarterial digital subtraction angiography (IADSA) to demonstrate the anatomy of aneurysm necks.

METHODS

The delayed mask technique was utilized in 22 patients who had craniotomies for aneurysms demonstrated at angiography. The operative notes were compared to the angiographic findings of both the traditionally masked IADSA and the delayed mask IADSA. In addition, an in vitro model was constructed to examine the relationship between the size of the aneurysm neck and the ability to indirectly define its anatomy by demonstrating the flow jet.

RESULTS

In 12 of 22 cases, the delayed mask technique demonstrated a systolic jet that was not demonstrated by traditional subtraction techniques. In nine of 12 cases, the delayed mask technique gave more specific information regarding the size, location, and orientation of the aneurysm neck.

CONCLUSION

The delayed mask technique can add important information regarding the anatomy of aneurysm without adding time or risk to the procedure.

Rapid metabolic failure in spontaneously hypertensive rats after middle cerebral artery ligation

The metabolic characteristics of the penumbral region were examined in spontaneously hypertensive rats one hour after permanent middle cerebral artery occlusion. The effect of hyperglycemia on this region was examined by providing a glucose load prior to occlusion. The depressed concentrations of adenosine triphosphate and elevated levels of lactate in the penumbral region were similar to those found in the ischemic focus. The purported neuroprotective effect of hyperglycemia in the penumbral region was not reflected in an increased high-energy phosphate level in the penumbral region. The rapid deterioration of the metabolic status of this region in this strain of rat suggests that the increased consistency of infarction may come at the expense of the penumbral region, and thus this model may not be well suited for the study of metabolic changes and perhaps even therapeutic intervention.

Improvement of pituitary function after surgical decompression for pituitary tumor apoplexy

Hypopituitarism is a major manifestation of pituitary adenoma apoplexy. We postulated that the acute deterioration in pituitary function may be caused by compression of portal vessels and the pituitary stalk, secondary to a sudden increase in intrasellar contents. If this were the case, one would predict improvement in pituitary function to occur after surgical decompression. We studied pituitary function in eight patients presenting with the clinical syndrome of pituitary adenoma apoplexy before and on multiple occasions after urgent surgical decompression. Partial or complete hypopituitarism was seen in all subjects at the time of presentation. Serum cortisol levels were inappropriately low (5.9 +/- 1.4 micrograms/dL; 162.8 +/- 38 nmol/L) for the degree of stress in seven patients and appropriately elevated in only one subject (55.3 micrograms/dL; 1525.7 nmol/L). High normal increments in cortisol levels were noted in three subjects given test doses of cosyntropin. Patients were given glucocorticoids before, during, and for 2 days after surgery. Serum cortisol concentrations measured on or after the third day when glucocorticoids had already been stopped were normal in seven subjects and consistently low in one. These seven subjects were discharged on no replacement and were subsequently documented by dynamic testing to have normal pituitary-adrenal function. Gonadal function improved in two of four men and in one of two women who had hypogonadism on presentation. Improvement in thyroid function was documented in two of three subjects with preoperative hypothyroidism. Gradual improvement and almost complete resolution of the neuroophthalmological abnormalities occurred days to weeks after decompression. These observations demonstrate that urgent surgical decompression after pituitary tumor apoplexy was associated with improvement not only in neurological defects but also in pituitary function. The rapid improvement in pituitary function indicates not only that the hypopituitarism was reversible, but also that it might be caused by compression of the portal circulation and pituitary stalk by the sudden increase in intrasellar contents.

Intracranial aneurysms: evaluation by MR angiography

The purpose of this study was to compare the accuracy of a volume gradient-echo MR angiography (MRA) technique with that of intraarterial digital subtraction angiography (IA DSA) in the identification of intracranial aneurysms. The intracranial vasculature was examined in 47 patients by MRA and compared with IA DSA findings in 19 of these patients who had saccular or giant intracranial aneurysms. The remaining 28 patients, in whom no aneurysm was found, served as a control group. MRA was performed with the use of a velocity-compensated gradient-echo sequence (TR = 40-50/TE = 7-15) with a 15 degrees flip angle. The sensitivity and specificity were calculated for the evaluation of the cine 3D reconstructions (cine MRA) only, cine MRA + inspection of the individual partitions, and cine MRA + individual partitions + spin-echo studies. Of 21 aneurysms, of which three were missed in two patients, the sensitivity varied from 67% for cine MRA only to 86% for the cine MRA + partitions + spin-echo studies; of the 19 patients, among whom it was assumed that the diagnosis of any one aneurysm in a patient would lead to angiography and detection of additional aneurysms, the sensitivity varied from 73% for the cine MRA only to 95% for the cine MRA + partitions + spin-echo studies. The results of this study suggest that MRA can define the circle of Willis sufficiently to allow detection of intracranial aneurysms as small as 3-4 mm. MRA holds promise as a truly noninvasive screening examination of intracranial vasculature in patients at risk for aneurysms.

Intracranial aneurysms: evaluation by MR angiography

The purpose of this study was to compare the accuracy of a volume gradient-echo MR angiography (MRA) technique with that of intraarterial digital subtraction angiography (IA DSA) in the identification of intracranial aneurysms. The intracranial vasculature was examined in 47 patients by MRA and compared with IA DSA findings in 19 of these patients who had saccular or giant intracranial aneurysms. The remaining 28 patients, in whom no aneurysm was found, served as a control group. MRA was performed with the use of a velocity-compensated gradient-echo sequence (TR = 40-50/TE = 7-15) with a 15 degree flip angle. The sensitivity and specificity were calculated for the evaluation of the cine 3D reconstructions (cine MRA) only, cine MRA + inspection of the individual partitions, and cine MRA + individual partitions + spin-echo studies. Of 21 aneurysms, of which three were missed in two patients, the sensitivity varied from 67% for cine MRA only to 86% for the cine MRA + partitions + spin-echo studies; of the 19 patients, among whom it was assumed that the diagnosis of any one aneurysm in a patient would lead to angiography and detection of additional aneurysms, the sensitivity varied from 73% for the cine MRA only to 95% for the cine MRA + partitions + spin-echo studies. The results of this study suggest that MRA can define the circle of Willis sufficiently to allow detection of intracranial aneurysms as small as 3-4 mm. MRA holds promise as a truly noninvasive screening examination of intracranial vasculature in patients at risk for aneurysms.

Impairment of metabolic recovery with increasing periods of middle cerebral artery occlusion in rats

We examined the consequences of reflow on metabolic recovery following increasing periods of focal ischemia. The middle cerebral artery of 21 Sprague-Dawley rats was occluded with a snare ligature for 1, 2, or 6 hours followed by 5, 4, or 0 hours of reflow, respectively (seven rats in each group). All animals were injected with neutral red for visual confirmation that the affected regions were reperfused. The brains were frozen in situ, and the concentrations of adenosine triphosphate, phosphocreatine, glycogen, and lactate were determined in those areas corresponding to the normally perfused medial ipsilateral cortex, the perifocal region, and the ischemic focus. Values for the 6 hours' occlusion with no reflow group served as a control to demonstrate restoration of metabolite concentrations. In both groups with reflow, the levels of high-energy phosphates were greater than control, but this effect of reflow was primarily significant for the group with 1 hour's occlusion (p less than 0.05). The levels of glycogen and lactate provided additional evidence that the extent of metabolite restoration was graded; following 2 hours of occlusion, metabolite recovery was compromised (p less than 0.05). Our data strongly support the concept that the window of opportunity for effective treatment of focal ischemia by reperfusion is narrow (of short duration).

The evolution of focal ischemic damage: a metabolic analysis

Focal cerebral ischemia in the rat was induced by left middle cerebral artery occlusion. The area of ischemia was determined by infusion of a qualitative perfusion indicator, neutral red. The temporal evolution of alterations in regional energy metabolism was assessed by direct microquantitative histochemical analysis of high-energy phosphates, glucose, glycogen, and lactate content of the tissue. Perfusion analyses demonstrated a perifocal region of diminished, but not absent perfusion up to 6 hr after occlusion. By 24 hr, there was an abrupt demarcation between perfused and nonperfused regions. Profound metabolic alterations were seen as early as 20 min after occlusion. Although there was an area of intermediate metabolic derangement in the more medial portions of the lateral ipsilateral cortex up to 6 hr, by 24 hr there was an abrupt transition from normal to abnormal cortex. No evidence of metabolic recovery was seen in this model of permanent occlusion.

Magnetic resonance angiography of the extracranial carotid arteries and intracranial vessels: a review

MRI is uniquely suited for evaluation of vascular structures due to its sensitivity to a variety of flow-related phenomena. Recent work has demonstrated that high quality magnetic resonance angiograms (MRA) of the carotid arteries and intracranial vasculature can be achieved by using gradient-echo techniques with short echo times. These MRAs are displayed like conventional arteriograms, but are acquired in a noninvasive fashion with a minimal increase in examination time. We used MRA to visualize 50 of 54 carotid bifurcations tested, with good correlation to the intra-arterial angiograms. We examined the intracranial vasculature in over 40 patients, and demonstrated aneurysms, vascular malformations, and occlusions.

Intracranial circulation: preliminary clinical results with three-dimensional (volume) MR angiography

The authors assessed the clinical utility of a magnetic resonance angiography technique in the evaluation of intracranial circulation. Eighteen patients with a low likelihood of cerebrovascular disease (control group) and 40 patients with suspected cerebrovascular disease were imaged with a FISP (fast imaging with steady precession) sequence (repetition time of 50 msec, echo time of 15 msec, velocity compensation in the read and section-select directions with acceleration compensation in the read direction, 15 degrees anisotropic volume, and a 1.25-mm partition thickness). Ninety-four percent of images in the control group and 72% of images in the group with cerebrovascular disease were considered useful for diagnosis. This technique can provide accurate images of intracranial circulation and can be performed in conjunction with two-dimensional spin-echo or gradient-echo imaging. It was most useful in the evaluation of patent intracranial aneurysms, vessel displacement, and large-vessel occlusive disease. Disadvantages included limited field of view, persistent signal voids, limited spatial resolution, and inadequate depiction of lesions with slow flow.

Three-dimensional (volume) gradient-echo imaging of the carotid bifurcation: preliminary clinical experience

This study was designed to test the accuracy of magnetic resonance (MR) imaging with a FLASH (fast low-angle shot) 40 degrees volume pulse sequence by comparing it with intraarterial digital subtraction angiography (DSA) in patients with suspected carotid artery stenoses. Fifteen patients referred for evaluation of anterior circulation in cerebrovascular disease composed the pilot group. Twelve patients underwent correlative intraarterial DSA examinations. The FLASH volume sequence, with an echo time of 7.7 seconds, produced high-signal-intensity vascular images for 28 of 30 bifurcations. Of the 24 carotid bifurcations studied with DSA, 22 were depicted with MR angiography. Among the depicted bifurcations, 21 showed good correlation with the DSA images. These included four of four normal bifurcations, three of three with mild stenosis, four of four with moderate stenosis, eight of nine with severe stenosis, and two of two with occlusions. With respect to ulceration, three of four MR angiographic studies showed good correlation with DSA images. This preliminary experience indicates that the method is reproducible and capable of delineating carotid lesions in patients and that it can be performed in conjunction with conventional spin-echo imaging of the brain with only a small increase in patient examination time.

Herniation of the suprasellar visual system and third ventricle into empty sellae: morphologic and clinical considerations

Intrasellar herniation of the optic nerve, optic chiasm, optic tract (suprasellar visual system, SVS), and anteroinferior third ventricle can occur into primary or secondary empty sellae. The anatomic part of this study evaluated the appearance of the SVS in subjects with normal sellae (n = 52), the patterns and prevalence of SVS herniation in enlarged primary empty sellae (n = 24), and the patterns of intrasellar herniation of the SVS in secondary empty sellae (n = 8). The clinical part of this study was to correlate the visual status with the anatomic patterns of the intrasellar herniated SVS. High-resolution MR and CT were used to define the anatomy. MR was superior to CT in all groups in defining accurately the SVS relationship to the sella turcica. In the normal group, the SVS invariably had a straight-line appearance formed by the optic nerve, optic chiasm, and floor of the third ventricle and was above the sella. The SVS was herniated in three of 24 enlarged primary empty sellae. A difference in the appearance of the hypothalamic and infundibular recesses in the primary empty sella group with SVS herniation (dilated recesses and formation of an obtuse angle) and in the secondary empty sella group with SVS herniation (nondilated recesses and formation of an acute angle) was observed. Visual disturbances in primary empty sellae with SVS herniation were present in two of three subjects. Visual disturbances may be absent or minimal in primary empty sellae and secondary empty sellae with herniation of the SVS. Progression of the symptoms--visual field defects, optic atrophy, and loss of vision--is not inevitable. There was no correlation between the severity of visual symptoms and the degree of herniation of the SVS in either the primary or secondary sellae. We found that intrasellar herniation of the SVS into a primary or secondary empty sella is well delineated with MR, and MR should facilitate decisions concerning surgery or therapy. Visual disturbances proved to be an unreliable indicator of herniation.

Visually defined zones of focal ischemia in the rat brain

A technique to guide brain tissue sampling in experimental focal ischemia is described. This technique allows visual identification for accurate metabolic analysis of regions with variable tissue perfusion. After 2.5 hours of unilateral middle cerebral artery occlusion (MCAO) in the rat, intravenous infusion of the vital dye, neutral red (NR), identified three distinct regions: (a) an intensely stained region consisting of the entire contralateral hemisphere and the medial ipsilateral hemisphere; (b) a blanched region in the lateral ipsilateral hemisphere; and (c) a zone of intermediately stained tissue interposed between the medial and lateral ipsilateral regions. Close regional correlation between NR staining and the iodoantipyrine intensity of adjacent brain slices suggests that NR distribution is a qualitative indicator of brain perfusion. Using the NR staining pattern to guide tissue dissection for metabolite analysis of high energy phosphates (adenosine triphosphate and phosphocreatine) and glucose-related metabolites showed that the blanched region contained ischemic tissue, whereas values from the contralateral cortex resembled those of control tissue. The intermediately stained region exhibited a gradient of metabolic perturbation. Tissue near intensely stained regions resembled control tissue, and tissue near blanched regions resembled ischemic tissue. These results confirm the concept of a metabolic penumbra. When present, it occupies only the most medial area of the intermediate region at 2.5 hours after MCAO.

Large pituitary gland adenomas evaluated with magnetic resonance imaging

Magnetic resonance imaging (MRI), computed tomographic (CT) scanning, and angiography or digital subtraction angiography (DSA) were used preoperatively to evaluate 16 surgically proven cases of sellar tumor with extrasellar extension. There were 15 pituitary tumors and 1 schwannoma. The capabilities of MRI in evaluating these tumors were compared with CT scanning and angiography. Bone destruction and tumor calcification were better detected by CT scanning than by MRI. MRI was as effective as CT scanning in detecting a cyst or variation in tumor consistency. Neither MRI nor CT scanning was capable of distinguishing specific tumor types. In every case, MRI was superior to CT scanning for delineating spatial relationships of the tumor to the 3rd ventricle, the optic apparatus, adjacent brain, and parasellar vasculature. Vessel encasement by tumor was clearly seen on MRI when there was no direct indication of this on other studies. Cavernous sinus invasion was not demonstrated by CT scanning, but was indicated by MRI in 5 cases and was surgically confirmed in 3. MRI can provide more precise spatial information on extrasellar tumor extension. Vascular encasement and cavernous sinus invasion may be determined preoperatively. Treatment expectations and operative approaches can be guided by this information. When MRI is available, it is the test of choice for the preoperative evaluation of patients with suspected large pituitary gland (sellar region) tumors. Contrast-enhanced CT scanning and angiography can be used as supplementary studies to add information inherently unique to these techniques.

Radiculomeningeal vascular malformations of the spine: MR imaging

Three patients (two men, one woman; 63-81 years old) with radiculomeningeal vascular malformations of the spine were examined using high-resolution surface coil magnetic resonance (MR) imaging at 1.5 T. The findings included previously described high-velocity signal loss within the vessels of the malformation as well as previously unreported signal-intensity changes within the cord (long T1/long T2) distal to the malformation. The MR images correlate well with previous reports of location and pathophysiology of these dural lesions.

Advances in neuroradiologic imaging of the pituitary gland: changing concepts

A review of pituitary imaging is presented based on the history of neuroradiologic definition of the sellar contents as well as modern diagnostic techniques. The importance of normal pituitary and seller anatomy is stressed in an attempt to determine the limitations of defining abnormal sellar contents with the imaging techniques of computed tomography and magnetic resonance imaging. The sensitivity and specificity of these techniques are illustrated with histopathologic correlation.

Lead encephalopathy presenting as a posterior fossa mass. Case report

✓ A case of lead encephalopathy with clinical and computerized tomography evidence of a midline posterior fossa mass is presented. The pathophysiology and the predilection for posterior fossa involvement are discussed.

The occurrence of dural invasion in pituitary adenomas

This report describes 60 dural specimens from patients with pituitary adenomas treated by transsphenoidal microsurgery, and attempts to define more precisely the clinical and pathological correlation of microscopic dural invasion. Analysis of the adenomas was based on four characteristics; size, surgical invasiveness (based on the surgeon's assessment of involvement by tumor of bone, dura, or cavernous sinus), histological evidence of invasion, and immunohistochemical staining characteristics. The incidence of surgical invasiveness (24 cases, 40%) was greater than previously reported, but most important was the frequent occurrence of microscopic dural invasion (51 cases, 85%). There was a clear progression of microscopic evidence of dural invasion with increasing tumor size: 69%, 88%, and 94% of the dural specimens from microadenomas, macroadenomas, and tumors with suprasellar extension, respectively, showed microscopic dural invasion. A correlation of invasiveness with immunohistochemical classification of tumor type was not evident.

Cerebrospinal fluid penetration of moxalactam in ventriculostomy patients

The cerebrospinal fluid penetration of moxalactam was simultaneously investigated in three patients with presumed bacterial meningitis. When ratios of simultaneously drawn ventriculostomy to serum moxalactam levels of 1, 2, 3, and 4 h were examined, the penetration ratios were 7.8 +/- 2.4, 11.2 +/- 1.3, 14.2 +/- 2.5, and 15.0 +/- 4.9%, respectively. These ratios were not statistically different from the penetration of moxalactam calculated by the area under the concentration-time curve technique (8.97 +/- 1.89%).

Naloxone therapy during focal cerebral ischemia evaluation in a primate model

Conflicting reports have appeared in the literature regarding the effect of the opiate antagonist naloxone on ischemic neurologic deficits. We report the results of a study using naloxone in our model of focal cerebral ischemia in the awake primate. A total of 14 adult baboons were subjected to six-hour occlusion of the left middle cerebral artery (MCA). Seven animals served as controls and seven received treatment with naloxone (5 mg/kg) beginning 30 min after MCA occlusion and continuing until two hours after reperfusion. All animals developed profound hemiparesis and homonymous hemianopsia within seconds of inflating the MCA occluder. Acutely, therapy with naloxone partially reversed ischemic neurologic deficits in five of the seven treatment animals. Within minutes of receiving the loading dose of naloxone, responding animals were more alert and demonstrated improvements in motor function. Naloxone did not affect mortality: Three animals in the treatment group and two in the naloxone group died secondary to malignant intracranial pressure within 48 hours of the ischemic episode. In animals surviving the ischemic insult however, treatment with naloxone significantly improved neurologic outcome at 10 days (p less than 0.05). Neuropathologic examinations in these animals revealed amelioration of ischemic tissue damage, with three of the five suffering only small focal areas of infarction. (All control animals suffered large infarcts of the MCA territory.) Our results verify that naloxone can reverse ischemic deficits, and more importantly may improve the outcome from focal ischemic insults.

Liver abscess: complication of a ventriculoperitoneal shunt

Liver abscess is a previously unreported complication of ventriculoperitoneal shunting. We present such a case, which was diagnosed by computed tomography (CT) and managed by CT-guided percutaneous catheter drainage of the liver abscess, appropriate antibiotics, and shunt externalization.

New lumboperitoneal shunt catheter

A new catheter is described for percutaneous lumboperitoneal shunts. The method of introduction and indications for this shunt are reviewed.