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At least 1,765 records · Page 98Linked to original sources
PubMed2000

Atypical and typical presentations of Alzheimer's disease: a clinical, neuropsychological, neuroimaging and pathological study of 13 cases.

There has been increasing awareness that some slowly progressive focal cortical syndromes can be the presenting features of Alzheimer's disease, but pathological evidence has been sparse. This clinico-pathological series presents our experience with pathologically proven atypical as well as typical Alzheimer's disease presentations. We report and compare four patterns of presentation: a typical pattern with initial amnesic syndrome (n = 4 cases), progressive visual dysfunction (n = 1), progressive biparietal syndrome (n = 2) and progressive aphasia (n = 6). The aphasic presentations include both fluent and non-fluent aphasic syndromes. The neuropsychological profiles and neuroimaging clearly reflect the presenting clinical features, and show a close relationship to the distribution of pathology in these cases. Of note was the sparing of medial temporal structures (hippocampus and/or entorhinal cortex) in several aphasic cases and the severe occipito-parietal involvement in those with prominent visuospatial disorders at presentation. Our data demonstrate the wide spectrum of Alzheimer's disease presentations. The recognition of atypical presentations of Alzheimer's disease is important when attempting to make an early accurate pre-morbid diagnosis of neurodegenerative disease.

Aged↗
PubMed1996

Utilizing latency for object recognition in real and artificial neural networks.

A consistent analysis of a visual scene requires the recognition of different objects. In vertebrate brains this could be achieved by synchronization of the activity of disjunct nerve cell assemblies. During such a process cross-talk between spatially adjacent image parts occurs, preventing efficient synchronization. Temporal differences, naturally introduced by stimulus latencies in every sensory system, were utilized in this study to counteract this effect and strongly improve network performance. To this end in our model the image is 'spread out' in time as a function of contrast-dependent visual latencies, and synchronization of cell assemblies occurs without mutual disturbance. The network model requires a direct link between visual latencies and the onset of synchronous oscillations in cortical cells. This was confirmed experimentally.

Cognition↗
PubMed1998

Carcinoma of the male breast metastatic to both orbits.

We report the case of a 43-year-old man who presented with painless proptosis of the right eye of 6 weeks' duration. Examination demonstrated a tense right orbit and decreased vision and extraocular motility bilaterally. Diagnostic evaluation included computed tomographic imaging of the head and orbits, a therapeutic trial of high-dose systemic corticosteroids, and orbital biopsy, which revealed the presence of metastatic adenocarcinoma. The primary tumor was found to be an estrogen-receptor-positive, infiltrating ductal adenocarcinoma of the right breast. Therapy included lumpectomy of the breast mass, orbital irradiation, and hormonal therapy. Metastatic carcinoma of the breast should be considered in the differential diagnosis of orbital neoplastic disease in the male patient.

Adult↗
PubMed2002

Blindness as a complication of Le Fort I osteotomy for maxillary distraction.

High Le Fort I osteotomy and maxillary distraction has become an accepted method for the treatment of maxillary retrusion in children and teenagers with cleft lip and palate or craniofacial anomalies. This procedure effectively corrects the dentofacial deformity in these patients. No major surgical morbidity has been reported. During the past 4 years, 94 cleft patients with maxillary hypoplasia received Le Fort I osteotomy and distraction osteogenesis at the authors' center. Two of them developed blindness after this operation. The first case was a girl with bilateral cleft lip and palate with median facial dysplasia. She received high Le Fort I osteotomy at age 12 years 4 months to correct maxillary retrusion. Right eye swelling and ecchymosis was found after surgery. The patient complained of vision loss in that eye 2 days later. Computed tomography showed subarachnoid hemorrhage and skull base hematoma. There were no atypical fractures in the orbit, pterygoid plates, sphenoid bone, and skull base. Angiogram revealed left ophthalmic and basilar artery aneurysm. The second case was a 12-year-old boy with left cleft lip and palate. He received Le Fort I osteotomy to correct maxillary retrusion. During surgery, abnormal pupil dilatation was found after the osteotomy and down-fracture of maxilla. Emergent computed tomography found no hemorrhage or atypical fractures. Examination revealed complete left optic neuropathy and partial right abducens nerve palsy with mydriasis. Magnetic resonance imaging, magnetic resonance angiography, and repeated computed tomography revealed no sign of orbital injury, vascular problem, or abnormal fractures. The cause of blindness was unknown. In both cases, a steroid was used. Maxillary distraction was continued. Recovery of meaningful visual sense did not occur after 3 and 2 years' follow-up, respectively. A review of the literature revealed five other patients who suffered from visual loss after Le Fort I osteotomy. Inadvertent skull base fractures were identified in two cases, but a cause for the blindness was not known in the others. Induced hypotension and indirect trauma may be responsible for the optic nerve injury. In none of the cases was meaningful visual sense recovered, although high-dose steroids were given. In conclusion, a total of seven cases developed blindness after Le Fort I osteotomy. Once blindness develops, the prognosis is poor. High Le Fort I osteotomy should be performed with extreme care, and perhaps the informed consent should include visual loss as a complication of the procedure.

Abducens Nerve Diseases↗
PubMed2004

Radionecrosis of the inferior occipital lobes with altitudinal visual field loss after gamma knife radiosurgery.

A patient had bilateral superior altitudinal visual field defects because of radionecrosis of the inferior occipital lobes after gamma knife radiosurgery for a recurrent atypical cerebellar meningioma. Although radionecrosis of the anterior visual pathway has been well-documented, this is the first report of visual field loss associated with occipital lobe radionecrosis. The treatment dose this patient received is within the range of predicted tolerable radiosurgical dosing, although this patient was at increased risk for radionecrosis secondary to previous external beam radiotherapy. By offering an effective, noninvasive treatment, radiosurgery has changed the management of intracranial lesions. Radiosurgery targets a discrete volume of tissue and relatively spares the surrounding normal tissue. Radiation injury, or radionecrosis, is the only significant complication of radiosurgery (). We present a case of bilateral occipital lobe radionecrosis after gamma knife surgery that resulted in bilateral superior altitudinal defects.

Brain Diseases↗
PubMed2006

Reversible visual loss in a patient with rheumatoid arthritis and the role of vascular imaging.

Spontaneous vertebral artery dissection is a condition that can have lethal consequences. The condition should be considered in young male patients who present with a stroke. At presentation, headaches, cerebral ischaemic episodes and oculosympathetic paresis are the most commonly encountered manifestations. The diagnosis is confirmed with angiography. Here, we present a middle-aged male gardener with rheumatoid arthritis and signs of vertebral artery dissection to highlight the importance of diagnosis and discuss the controversies in management.

Arthritis, Rheumatoid↗
PubMed1985

Extrapolating and interpolating surfaces in depth.

Random-dot stereograms were generated with a blank area placed in part of the right-hand image so making a patchwork of monocular and binocular areas. The perceived depth and shape of the monocular region, where depth was not explicitly marked, depended in part on the depth and surface orientation of adjacent binocular areas. Thus a monocular rectangle flanked by two binocular rectangles which were placed in different fronto-parallel planes was seen as a sloping surface spanning the depth between the binocular regions, and, under some conditions, the gradient of a sloping binocular plane extended into a neighbouring monocular area. Division of the monocular region into two by textural discontinuities or discontinuities of motion sometimes altered the shape of the extrapolated surface. Often, though, the shape was unchanged by such discontinuities implying that both two- and three-dimensional features are used to segment a scene into separate surfaces. Pictorial cues also contribute to the shape and apparent depth of the monocular surface. For instance, when subjects viewed a display consisting of portions of a cube of which two ends were shown stereoscopically and one side monocularly, the monocular side was seen in three dimensions filling the gap between the ends. When stereo cues were pitted against pictorial cues, sometimes pictorial cues and sometimes stereo cues dominated, and sometimes the surface contained sharp discontinuities enabling both to be accommodated.

Computers↗
PubMed2000

Multifractal wavelet filter of natural images.

Natural images are characterized by the multiscaling properties of their contrast gradient, in addition to their power spectrum. In this Letter we show that those properties uniquely define an intrinsic wavelet and present a suitable technique to obtain it from an ensemble of images. Once this wavelet is known, images can be represented as expansions in the associated wavelet basis. The resulting code has the remarkable properties that it separates independent features at different resolution level, reducing the redundancy, and remains essentially unchanged under changes in the power spectrum. The possible generalization of this representation to other systems is discussed.

Fractals↗
PubMed2004

Optic nerve signals in a neuromorphic chip I: Outer and inner retina models.

We present a novel model for the mammalian retina and analyze its behavior. Our outer retina model performs bandpass spatiotemporal filtering. It is comprised of two reciprocally connected resistive grids that model the cone and horizontal cell syncytia. We show analytically that its sensitivity is proportional to the space-constant-ratio of the two grids while its half-max response is set by the local average intensity. Thus, this outer retina model realizes luminance adaptation. Our inner retina model performs high-pass temporal filtering. It features slow negative feedback whose strength is modulated by a locally computed measure of temporal contrast, modeling two kinds of amacrine cells, one narrow-field, the other wide-field. We show analytically that, when the input is spectrally pure, the corner-frequency tracks the input frequency. But when the input is broadband, the corner frequency is proportional to contrast. Thus, this inner retina model realizes temporal frequency adaptation as well as contrast gain control. We present CMOS circuit designs for our retina model in this paper as well. Experimental measurements from the fabricated chip, and validation of our analytical results, are presented in the companion paper [Zaghloul and Boahen (2004)].

Action Potentials↗
PubMed2004

Optic nerve signals in a neuromorphic chip II: Testing and results.

Seeking to match the brain's computational efficiency, we draw inspiration from its neural circuits. To model the four main output (ganglion) cell types found in the retina, we morphed outer and inner retina circuits into a 96 x 60-photoreceptor, 3.5 x 3.3 mm2, 0.35 microm-CMOS chip. Our retinomorphic chip produces spike trains for 3600 ganglion cells (GCs), and consumes 62.7 mW at 45 spikes/s/GC. This chip, which is the first silicon retina to successfully model inner retina circuitry, approaches the spatial density of the retina. We present experimental measurements showing that the chip's subthreshold current-mode circuits realize luminance adaptation, bandpass spatiotemporal filtering, temporal adaptation and contrast gain control. The four different GC outputs produced by our chip encode light onset or offset in a sustained or transient fashion, producing a quadrature-like representation. The retinomorphic chip's circuit design is described in a companion paper [Zaghloul and Boahen (2004)].

Action Potentials↗
PubMed1995

Aspergillus sphenoid sinusitis-induced orbital apex syndrome in HIV infection.

BACKGROUND: Orbital apex syndrome due to aspergillus sphenoid sinusitis is a rare condition. Human immunodeficiency virus (HIV) infection has recently been reported in aspergillus orbital abscess. To the authors' knowledge this is the first reported association of HIV with the orbital apex syndrome. METHODS: A 37-year-old HIV-infected man presented with headache, reduced vision and progressive ophthalmoplegia in the right eye. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed sphenoid sinusitis. Sphenoid sinus biopsy was performed. RESULTS: Light microscopy revealed infiltrative branching septate fungal hyphae. Fungal culture isolated Aspergillus fumigatus. CONCLUSION: Atypical fungal infection such as Aspergillus fumigatus sphenoid sinusitis should be suspected in HIV-infected patients with orbital apex syndrome.

Adult↗
PubMed1995

Haemorrhagic-ischaemic lesions of the neonatal brain: correlation between cerebral visual impairment, neurodevelopmental outcome and MRI in infancy.

The relationship between the degree of cerebral visual impairment, established using the acuity card procedure, and the extent of neurological sequelae was assessed in 65 at-risk neonates in a prospective follow-up study. MRI and CT scans were performed in all infants with severe neurological sequelae. 11 of 12 children with an acuity at or below the 10th centile at 18 months developed cerebral palsy: the underlying condition was extensive cystic leukomalacia in all. An acuity above the 10th centile was no guarantee of normal development, as 10 out of 52 such infants developed cerebral palsy. MRI and CT scans showed that periventricular high signal intensity in the occipital area was a non-specific finding with regard to visual function. Extensive periventricular white matter loss and involvement of the striate/parastriate cortex was found in the most severely visually impaired infants.

Brain Ischemia↗
PubMed2004

Relation between static and dynamic aspects of vergence, estimated with a subjective test using flashed dichoptic nonius lines.

The psychophysical technique for measuring vergence with dichoptic nonius lines was used to investigate dynamic responses to step vergence stimuli. Liquid crystal shutter glasses were operated with a cathode ray tube monitor to present convergent or divergent step stimuli of 32 min arc at t = 0. The resulting initial vergence response was estimated with nonius lines that appeared for 80 ms at a fixed delay of 400 ms after the vergence step stimulus. The vergence state reached 400 ms after the step depended on the vergence accuracy assumed before the step, i.e. baseline fixation disparity (FD). The following physiologically plausible results were found: (i) the amount of dynamic vergence changes within 400 ms tended to be negatively correlated between the convergent and divergent direction; (ii) subjects with a smaller convergent dynamic change had a steeper proximity-FD curve measured with static fusion targets as a function of viewing distance; (iii) FD was more eso or more exo depending on whether the vergence change was larger in the convergent or divergent direction respectively.

Convergence, Ocular↗
PubMed2006

End-box scoring artefact evaluation of the Farnsworth-Munsell 100-Hue colour vision test.

The scoring artefact in the Farnsworth-Munsell 100-Hue test, arising from the grouping of the caps into four boxes, was investigated. The traditional method of scoring performed with the numbers of the anchor caps disregarded and the alternative scoring performed with the numbers of the anchor caps employed, were compared. For the traditional method of scoring, we revealed an increase of the error score of the outside (end-box) caps when the total error score was above 240. On the contrary for scoring performed with the numbers of the anchor caps employed, the difference between the error score of the outside caps and the average error per cap is not significant. To mitigate the end-box artefact and to improve the reliability of the Farnsworth-Munsell 100-Hue test, corrections to the traditional method of scoring are proposed.

Adolescent↗
PubMed2004

Pneumocephalus and presumed meningitis following inconspicuous penetrating periocular trauma.

PURPOSE: To report a case of serious intracranial complications in an adolescent youth following a seemingly trivial periocular injury. METHODS: An adolescent youth was examined and discharged after a small penetrating injury to his left medial canthus. He later presented with blurred vision, nausea and mild pyrexia and underwent a computed tomography (CT) scan of the head and orbits as well as a lumbar puncture. RESULTS: The CT scan revealed a fracture in the cribriform plate of the ethmoid bone and the medial orbital wall, as well as pneumocephalus. The lumbar puncture revealed 3000 white cells/mm3 in the cerebrospinal fluid (CSF). After treatment with meningitic doses of intravenous antibiotics, a significant improvement was noted. CONCLUSIONS: A CT scan, instead of an ordinary head radiograph, may be considered as a first-choice mode of diagnosis in evaluating even inconspicuous penetrating periocular wounds. Early administration of meningitic doses of antibiotics may significantly improve prognosis.

Adolescent↗
PubMed1998

Visual form of Alzheimer's disease and its response to anticholinesterase therapy.

In a 60-year-old woman with the visual variant of Alzheimer's disease, single photon emission computed tomography abnormalities were most marked in the parieto-occipital regions of the brain. After treatment with donepezil, improvement is noted on neuropsychological testing and on brain SPECT, including increased perfusion (metabolism) in the occipital lobes.

Alzheimer Disease↗