Brain calcification in hypoxic-ischemic lesions: an autopsy review

Editor's Highlight: Spatiotemporal Progression and Remission of Lesions in the Rat Brain Following Acute Intoxication With Diisopropylfluorophosphate

Similar to organophosphate (OP) nerve agents, diisopropylfluorophosphate (DFP) rapidly and irreversibly inhibits acetylcholinesterase, leading to convulsions that can progress to status epilepticus (SE). However, in contrast to the OP nerve agents, the long-term consequences of DFP-induced SE are not well known. Thus, we characterized the spatiotemporal profile of neuropathology during the first 2 months following acute DFP intoxication. Adult, male Sprague Dawley rats administered pyridostigmine bromide (0.1 mg/kg, im) 30 min prior to successive administration of DFP (4 mg/kg, sc), atropine sulfate (2 mg/kg, im), and 2-pralidoxime (25 mg/kg, im), exhibited moderate-to-severe seizure behavior, yet survived until euthanized at 0.5 to 60 days post exposure. Analyses of brains and hearts stained with hematoxylin-eosin, or of brains immunostained for neuronal nuclei (NeuN), glial fibrillary acidic protein (GFAP), or ionized binding adapter molecule 1 (IBA1), revealed progressive neuronal cell death, neuroinflammation, and tissue remodeling across limbic brain regions and the cerebral cortex, with no detectable pathology in the cerebellum or the heart. The lesion type and progression varied according to brain region and time after exposure. Across multiple brain regions, neuronal necrosis peaked after the first week, and neuroinflammation persisted at least 2 months after intoxication. Notably, mineralization was observed at later times in the thalamus, and to a more limited extent, in the hippocampus. Lesion severity was influenced by the initial seizure severity, and spontaneous recurrent seizures were associated with more severe brain damage. These findings parallel descriptions of neuropathology in preclinical models of acute intoxication with OP nerve agents, and other seizurogenic chemicals, suggesting conserved mechanisms of pathology downstream of chemical-induced SE.

From the Cover: MagneticResonance Imaging Reveals Progressive Brain Injury in Rats Acutely Intoxicated With Diisopropylfluorophosphate

Acute intoxication with organophosphates (OPs) can trigger seizures that progress to status epilepticus, and survivors often exhibit chronic neuropathology, cognitive impairment, affective disorders, and/or electroencephalographic abnormalities. Understanding how acute injury transitions to persistent neurological sequelae is critical to developing medical countermeasures for mitigating damage following OP-induced seizures. Here, we used in vivo magnetic resonance imaging (MRI) to monitor the spatiotemporal patterns of neuropathology for 1 month after acute intoxication with diisopropylfluorophosphate (DFP). Adult male Sprague Dawley rats administered pyridostigmine bromide (0.1 mg/kg, im) 30 min prior to successive administration of DFP (4 mg/kg, sc), atropine sulfate (2 mg/kg, im), and 2-pralidoxime (25 mg/kg, im) exhibited moderate-to-severe seizure behavior. T2-weighted and diffusion-weighted MR imaging prior to DFP exposure and at 3, 7, 14, 21, or 28 days postexposure revealed prominent lesions, tissue atrophy, and ventricular enlargement in discrete brain regions. Lesions varied in intensity and/or extent over time, with the overall magnitude of injury strongly influenced by seizure severity. Importantly, lesions detected by MRI correlated spatially and temporally with histological evidence of brain pathology. Analysis of histogram parameters extracted from frequency distributions of regional apparent diffusion coefficient (ADC) values identified the standard deviation and 90th percentile of the ADC as robust metrics for quantifying persistent and progressive neuropathological changes. The interanimal and interregional variations observed in lesion severity and progression, coupled with potential reinjury following spontaneous recurrent seizures, underscore the advantages of using in vivo imaging to longitudinally monitor neuropathology and, ultimately, therapeutic response, following acute OP intoxication.

Patterns and pathways of calcification in the developing brain

AIM

To determine specific cell types and pathways involved in calcification of the developing brain.

METHOD

We examined the detailed histopathology of samples from 28 autopsied brains aged from 22 weeks' gestation to 14 years. The samples were selected because they showed calcification associated with a range of different diseases. Samples were examined with routine stains as well as stains to show calcification and specific markers for endothelium and macrophages.

RESULTS

Our observations indicate that calcification develops via two main pathways: dystrophic and vascular. Dystrophic calcification results from membrane disruption and uncontrolled calcium entry into necrotic (dead) cells in ischaemia and infections. Vascular calcification appears to be initiated in protein globules, sometimes intracellular, but outside the endothelium of small vessels. One case with mutation of the occludin gene, implicating impaired endothelial integrity, showed this pattern, but identical vascular calcification was seen in other conditions, including Sturge-Weber syndrome. Another form of vascular calcification involved the adventitia of arteries; the endothelium was always spared.

INTERPRETATION

Calcification in the developing brain that is not associated with tissue necrosis is initiated in cells associated with blood vessels. Calcium incrustation of blood vessels imposes rigidity, reduced vascular compliance, and altered permeability. This would explain associated atrophy, gliosis, and (in the developing brain) malformations of the cortex. Our findings suggest that pericytes initiate non-dystrophic brain calcification, but further studies are needed to explore this possibility.

Detection of calcifications in vivo and ex vivo after brain injury in rat using SWIFT

Calcifications represent one component of pathology in many brain diseases. With MRI, they are most often detected by exploiting negative contrast in magnitude images. Calcifications are more diamagnetic than tissue, leading to a magnetic field disturbance that can be seen in phase MR images. Most phase imaging studies use gradient recalled echo based pulse sequences. Here, the phase component of SWIFT, a virtually zero acquisition delay sequence, was used to detect calcifications ex vivo and in vivo in rat models of status epilepticus and traumatic brain injury. Calcifications were detected in phase and imaginary SWIFT images based on their dipole like magnetic field disturbances. In magnitude SWIFT images, calcifications were distinguished as hypointense and hyperintense. Hypointense calcifications showed large crystallized granules with few surrounding inflammatory cells, while hyperintense calcifications contained small granules with the presence of more inflammatory cells. The size of the calcifications in SWIFT magnitude images correlated with that in Alizarin stained histological sections. Our data indicate that SWIFT is likely to better preserve signal in the proximity of a calcification or other field perturber in comparison to gradient echo due to its short acquisition delay and broad excitation bandwidth. Furthermore, a quantitative description for the phase contrast near dipole magnetic field inhomogeneities for the SWIFT pulse sequence is given. In vivo detection of calcifications provides a tool to probe the progression of pathology in neurodegenerative diseases. In particular, it appears to provide a surrogate marker for inflammatory cells around the calcifications after brain injury.

Bevacizumab-induced tumor calcifications as a surrogate marker of outcome in patients with glioblastoma

Therapy-induced calcifications in glioblastoma are rarely recognized. They may represent regressive changes in the tumor tissue, but their occurrence and possible predictive or prognostic value have not been systematically assessed. The observation of hyperintense lesions on precontrast T1-weighted magnetic resonance images (MRIs) in 2 index patients with glioblastoma after therapy with bevacizumab, subsequently identified as calcifications on computed tomographs (CTs), prompted us to prospectively screen for these radiographic changes. Therefore, 36 patients with recurrent glioblastoma prospectively treated with bevacizumab in an observational trial were examined every 8 weeks by MRI and, if clinically necessary, by CT. In 22 patients (61.1%), T1 hyperintense lesions became apparent after bevacizumab treatment. The median time to detection of these lesions was 55 days. In 14 (63.6%) of 22 patients, CTs were available and confirmed the existence of tumor calcifications. No substantial changes in T1 hyperintense lesions or calcifications were recognized on additional MRI or CT scans. Interestingly, the patients with therapy-induced T1 hyperintense lesions had better durations of progression-free survival than patients without these changes (median, 5.8 vs 3.5 months; P< .001), and the duration of overall survival was also superior (median, 9.7 vs 5.0 months; P= .006). There was a striking correlation between the appearance of therapy-induced T1 hyperintense lesions and overall response to bevacizumab. Therefore, this phenomenon is a rather early and time-limited event during the first weeks of treatment and appears to be response related. In summary, T1 hyperintense lesions are common in patients with glioblastoma who have been exposed to bevacizumab, may represent a novel biomarker of response and outcome, and seem to correspond to tumor calcifications.

Nature against nurture: calcification in the right thalamus in a young man with anorexia nervosa and obsessive-compulsive personality disorder

This report describes the case of a young man with a large calcification in the right thalamus that was first diagnosed at 9 years of age. Case history reveals specific eating rituals and other obsessive-compulsive personality traits during the patient's childhood and adolescence, fulfilling diagnostic criteria of obsessive-compulsive personality disorder. After a critical life event the patient develops anorexia nervosa. We suggest that our case and further literature provide evidence for an involvement of specific thalamic structures, such as the dorsomedial nucleus, in the development of anorexia nervosa. Furthermore, the treatment of the patient by a combined psychotherapeutic and pharmacotherapeutic approach is described. We focus on the beneficial effect of the atypical antipsychotic olanzapine, which can induce weight gain by an increase of leptin levels.

Neuropathogical features of a rat model for perinatal hypoxic-ischemic encephalopathy with associated epilepsy

Hypoxic-ischemic (HI) encephalopathy is an important neurological problem of the perinatal period. Little is known of the long-term progression of HI insults or the maladaptive changes that lead to epilepsy. Using rats with unilateral carotid occlusion followed by hypoxia at postnatal day 7, this study provides an initial analysis of the epilepsy caused by a perinatal HI insult with chronic and continuous behavioral monitoring. The histopathology was investigated at postnatal day 30 and later at > or =6 months of age using cresyl violet, Timm, and rapid Golgi staining and immunocytochemistry. The resultant epilepsy showed an increase in seizure frequency over time, with a preponderance for seizure clusters and behavioral features of an ipsilateral cerebral syndrome. In addition to parasagittal infarcts and porencephalic cysts in severe lesions, columnar neuronal death was found with cytomegaly in isolated groups of dysmorphic cortical neurons. Cortical dysgenesis was seen in the form of deep laminar cell loss, microgyri, white matter hypercellularity, and blurring of the white and gray matter junction. Mossy fiber sprouting was not only detected in the atrophied ipsilateral dorsal hippocampus of HI rats with chronic epilepsy, but was also found in comparable grades in spared ipsi- and contralateral ventral hippocampi. The cortical lesions in this animal model show histological similarities with those found in humans after perinatal HI. The occurrence of cortical abnormalities that are associated with epilepsy in humans correlates with the consequent detection of spontaneous recurrent seizures.

Early appearance of functional deficits after neonatal excitotoxic and hypoxic-ischemic injury: fragile recovery after development and role of the NMDA receptor

We sought to determine whether neonatal rats that sustain unilateral cerebral hypoxic-ischemic or excitotoxic insults (1) manifest contralateral sensorimotor deficits during development or in adulthood and (2) recover from those deficits. Seven-day-old (P7) rats received a right intrastriatal injection of the glutamate analog N-methyl-D-aspartate (NMDA). Unilateral hypoxia-ischemia (HI) was induced by right carotid ligation followed by 1.5 h in 8% O2. Both procedures produce neuronal loss in the striatum and sensorimotor cortex. Nonlesioned controls were included. We scored percent forepaw placement on the edge of a horizontal surface, with lateral vibrissa stimulation, from P9 to P19, and at P33 and P50. Then, on P50, rats were treated with the NMDA antagonist MK-801 to determine whether deficits could be reinstated. NMDA- and HI-lesioned rats exhibited a deficit in contralateral vibrissa-stimulated forepaw placing that emerged during the second week of life. Yet, by P33 and P50, the lesioned groups and controls were indistinguishable. MK-801 injection on P50 resulted in transient reinstatement of the placing deficit. After unilateral neonatal excitotoxic or HI brain injury, contralateral sensorimotor deficits are detected, but in many animals, these deficits have resolved by adulthood. Thus, timing of sensorimotor tests may influence their sensitivity for detection of focal neuropathology originating in the neonatal period.

Demonstration of acute ischemic lesions in the fetal brain by diffusion magnetic resonance imaging

The possibility of detecting acute hypoxic-ischemic brain lesions by prenatal magnetic resonance imaging or ultrasound is low. We present a case of a fetus with a vein of Galen arteriovenous malformation in whom prenatal diffusion-weighted magnetic resonance imaging at 33 weeks of gestation clearly detected cerebral acute ischemic lesions, associated with remarkable decrease of the average apparent diffusion coefficient, whereas T2-weighted imaging was still not informative.

Calcium precipitation in acute and chronic brain diseases

In rat brain, calcification associated with excitotoxicity has been proposed to play a protective role, whereas in human brain, nonartherosclerotic calcification is present in several pathological conditions without any clear significance. To determine if calcification can be viewed as a protective step of calcium homeostasis during chronic and acute neuronal suffering, cerebral cortex and hippocampus of patients with Alzheimer's disease, vascular dementia and neonatal hypoxia-ischemia were investigated. To investigate the human specificity, these two areas were also studied in dogs with established cognitive deficits. In all groups, calcium precipitates were observed in the cerebral parenchyma associated with neuronal damage. The cerebral cortex presented a higher degree of calcification than the hippocampus. The neonatal hypoxia-ischemia group was characterised by a higher degree of calcification, whereas the groups with lowest calcification were the Alzheimer's patients and dogs. As shown by X-ray microanalysis, in the precipitates, calcium is mainly associated with phosphorus in a form that resembles hydroxyapatites. Thus, intracellular calcium concentration associated with neuronal suffering may reduce the energy extrusion. We propose that, to help overcome excitotoxicity, calcium precipitation acts in CNS of vertebrates as a new compartment of the calcium homeostasis in which free cytoplasmic calcium ions are inactivated by phosphate ones.

Perinatal human hypoxia-ischemia vulnerability correlates with brain calcification

Deregulation of intracellular calcium homeostasis is widely considered as one of the underlying pathophysiological mechanisms of hypoxic-ischemic brain injury. Whether this alteration can result in cerebral calcification was investigated in basal ganglia, cerebral cortex, and hippocampus of human premature and term neonates together with glial reaction. In all samples nonarteriosclerotic calcifications were observed, their number and size were area-specific and increased in term neonates. Basal ganglia always presented the highest degree of calcification and hippocampus the lowest, located mainly in the CA1 subfield. In all cases, neuronal damage was associated with astroglial reaction and calcium precipitates, with microglial reaction only in basal ganglia and cerebral cortex, and argues for the participation of excitatory amino acid receptors in hypoxia-ischemia damage. These data correlate with hypoxia-ischemia vulnerability in the perinatal period. The clinical relevance of these precipitates and the neuroprotective interest of non-NMDA receptor manipulation are discussed in the light of our results.

Calcified brain metastases from ovarian carcinoma

A case of calcified brain metastases from ovarian carcinoma is reported. Lesions developing during chemotherapy were thought on Ct to be parasitic and, to avoid dissemination of pathogens, biopsy was postponed. When neurological deficits progressed, MRI showed perifocal oedema and contrast enhancement. It also showed a new noncalcified focus which was biopsied, proving to be a metastasis.

Stroke is an emergency

Stroke is an emergency. Ischemic stroke is similar to myocardial infarction in that the pathogenesis is loss of blood supply to the tissue, which can result in irreversible damage if blood flow is not restored quickly. Public education is needed to emphasize the warning signs of stroke. Patients should seek medical help immediately, using emergency transport systems. Therapy geared toward minimizing the damage from an acute stroke should be started without delay in the emergency room. This includes measures to protect brain tissue, support perfusion pressure, and minimize cerebral edema. Strategies for improving recovery should also begin immediately. All major medical centers need stroke teams and stroke units. Stroke prevention should be given high priority as a public health strategy. Risk factor management should be part of general health care and should begin in childhood, with emphasis on nutrition, exercise, weight control, and avoidance of tobacco. Health screening and early treatment of hypertension and hypercholesterolemia has decreased the incidence of stroke and heart disease, but these efforts need to be expanded to reach all segments of the population. Basic research has opened the door to new therapies aimed at re-establishing blood flow and limiting tissue damage. Clinical trials have already led to changes in stroke prevention, including studies of carotid endarterectomy and ticlopidine and warfarin therapy (for patients with atrial fibrillation). Trials in progress are testing the usefulness of ancrod, neuroprotective agents, antioxidant agents, anti-inflammatory agents, low-molecular-weight heparin, thrombolytic drugs, and angioplasty. Any delay starting therapy after an acute stroke will result in progressive, irreversible loss of brain tissue. Clinicians should remember that for a stroke patient, time is brain tissue.

Discordant infantile encephalopathy with symmetrical thalamic calcifications in identical twins

Connatal thalamic calcifications in apparently uneventful pregnancies have been described in various case reports and in a single report in two sibs. On the other hand, this lesion is known to occur after a hypoxic-ischemic accident in the immature brain. In the present report infantile encephalopathy with symmetrical thalamic calcifications is observed in one sib of a monozygous twin pair. This observation adds to the evidence that the condition is acquired, most probably on the basis of hypoxia-ischemia, and provides strong evidence against autosomal-recessive inheritance.

Neuropathology of remote hypoxic-ischemic damage in the immature rat

This study was undertaken to determine: (a) the duration of hypoxia required to produce brain damage in immature rats with unilateral carotid artery ligation (Levine technique); (b) the regions of immature brain most vulnerable to hypoxia-ischemia (HI); and (c) the neuropathology of the remote HI insult. To this end, 7-day postnatal rats, subjected to unilateral carotid artery ligation combined with hypoxia of varying durations (45, 60, 75 or 90 min), were killed at 30 days of postnatal age and their brains examined by light microscopy. The results indicated that a longer duration of HI was more likely to produce brain lesions and that the extent and severity of the lesions closely correlated with the length of HI. Shorter intervals of HI primarily damaged the cerebral cortex and hippocampus, while longer periods resulted in more extensive damage and were often associated with cavitary lesions of the cerebral hemisphere. Comparison of HI brain damage produced by the Levine technique in immature and adult rats suggested that in immature rats: (a) the cavitary lesions were common; (b) the non-cavitary cortical lesions had a tendency to show a vertical band-like distribution - a pattern never seen in adults; and (c) the lesions often showed mineralization. The similarities between these experimentally produced HI cerebral lesions and those observed in the developing human brain, such as ulegyria and porencephaly, are discussed.