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Biomedical subjects

J C Horton

Publications and source records attributed to J C Horton.

At least 55 records · Page 3Linked to original sources
PubMed1991

Hemianopsia from occipital lobe abscess after dental care.

We treated four patients who developed a homonymous hemianopsia from a bacterial abscess in the occipital lobe of the brain. All four patients were treated successfully by surgical drainage of the abscess and administration of parenteral antibiotics for at least six weeks. Despite cure of the brain abscess, each patient was left with a permanent residual homonymous visual field defect. Cultures from the abscess fluid in three of the four patients grew oral flora. Moreover, each patient had a history of dental care two to four weeks before the onset of visual symptoms. A history of recent dental treatment in a patient with a new hemianoptic field defect should alert the ophthalmologist to the possibility of a bacterial abscess in the occipital lobe.

Adolescent↗
PubMed1991

The representation of the visual field in human striate cortex. A revision of the classic Holmes map.

We have tested the accuracy of Gordon Holmes' retinotopic map of human striate cortex by correlating magnetic resonance scans with homonymous field defects in patients with clearly defined occipital lobe lesions. Our findings indicate that Holmes underestimated the cortical magnification of central vision. In a revised map of the human striate cortex, we expand the area subserving central vision and reduce the area devoted to peripheral vision. These changes bring the map of human striate cortex into agreement with data reported for closely related nonhuman primate species.

Adult↗
PubMed1991

Quadrantic visual field defects. A hallmark of lesions in extrastriate (V2/V3) cortex.

We report 2 patients with homonymous quadrantic visual field defects. The first patient experienced scintillations in the left lower quadrant, leading to the discovery of an astrocytoma in the cuneus of the right occipital lobe. Postoperatively she had a left lower quadrantanopia that precisely respected the horizontal meridian. The second patient presented with a left lower quadrantanopia, sparing the central 10 degrees of vision that also respected the horizontal meridian. An astrocytoma was resected from the right upper peristriate cortex. We must explain how a lesion in extrastriate cortex produced a homonymous field defect with a sharp horizontal edge in these 2 patients. Areas V2 and V3 are each divided along the horizontal meridian into separate halves flanking striate cortex. Consequently, the upper and lower quadrants in extrastriate cortex are physically isolated on opposite sides of striate cortex. We propose that a lesion involving V2/V3 may be sufficient to create a visual field defect. Although the lesion may have irregular margins, if it crosses the representation of the horizontal meridian in extrastriate cortex, it will produce a quadrantic visual field defect with a sharp horizontal border because of the split layout of the upper and lower quadrants in V2/V3.

Adult↗
PubMed1991

Von Hippel-Lindau disease and erythrocytosis: radioimmunoassay of erythropoietin in cyst fluid from a brainstem hemangioblastoma.

A 59-year-old woman with von Hippel-Lindau disease developed erythrocytosis and a recurrent intracranial hemangioblastoma. Radioimmunoassay showed an elevated level of erythropoietin in her serum. Cyst fluid from the tumor also contained erythropoietin, concentrated a thousandfold relative to the serum level. Production of erythropoietin by hemangioblastomas may explain the erythrocytosis present in some patients with von Hippel-Lindau disease.

Brain Neoplasms↗
PubMed1990

Magnetic resonance imaging of the human lateral geniculate body.

We used magnetic resonance imaging to map the human lateral geniculate body. The optimal imaging plane was determined by obtaining axial and coronal scans in two normal brains obtained at autopsy. The brain specimens were then sectioned and individual slices were compared with matching magnetic resonance images. After the lateral geniculate body was identified using this correlative anatomic approach, the nucleus was imaged in four normal subjects.

Adult↗
PubMed1990

Arrangement of ocular dominance columns in human visual cortex.

The arrangement of the ocular dominance columns in the human primary visual cortex was studied by examining cytochrome oxidase activity in autopsy specimens of occipital lobes obtained from two patients who became blind in one eye before death. By artificially flattening the cortex before processing, it was possible to reconstruct the pattern formed by the ocular dominance columns throughout most of the primary visual cortex. The columns form a mosaic of irregular parallel stripes about 500 microns to 1000 microns wide (right eye column plus left eye column measures 1 to 2 mm), oriented at right angles to the boundary of the primary visual cortex. The columns are wider near the boundary of the primary visual cortex and within the representation of the peripheral visual field, the ocular dominance columns of the ipsilateral eye become fragmented until they disappear altogether at the border of the monocular crescent representation. The arrangement of ocular dominance columns in the human visual cortex is very similar to the pattern reported in the macaque monkey, although the columns in humans are wider.

Aged↗
PubMed1990

Pregnancy and the risk of hemorrhage from cerebral arteriovenous malformations.

We conducted a retrospective analysis of 451 women with an arteriovenous malformation (AVM) of the brain to determine whether pregnancy is a risk factor for cerebral hemorrhages. A total of 540 pregnancies occurred among our patient population, resulting in 438 live births and 102 abortions. There were 17 pregnancies complicated by a cerebral hemorrhage. The hemorrhage rate during pregnancy for women with an unruptured AVM was 0.035 +/- 0.005 per person-year. The hemorrhage rate for nonpregnant women of childbearing age with an unruptured AVM was 0.031 +/- 0.002 per person-year. Pregnancy did not increase significantly the rate of first cerebral hemorrhage from an AVM (P = 0.35). We found that women with an AVM face a 3.5% risk of hemorrhage during pregnancy. Pregnancy is not a risk factor for hemorrhage in women without a previous hemorrhage. This conclusion assumes no selection bias exists in our study population; a bias would be introduced if the risk of fatal outcome after a hemorrhage were greater in pregnant women than in nonpregnant women.

Adolescent↗
PubMed1990

Aneurysm mimicking intracranial growth of optic nerve sheath meningioma.

A patient with a 30-year history of blindness in the right eye developed progressive temporal visual loss in the left eye. Examination showed right optic atrophy with optociliary shunts and left band atrophy. These clinical findings suggested that the visual deficit was caused by a right optic nerve sheath meningioma that had grown intracranially to involve the chiasm. Magnetic resonance imaging and surgical exploration revealed a perioptic meningioma extending from the orbit through the optic canal and over the tuberculum sellae. The tumor did not impinge on the optic chiasm or the left optic nerve. The chiasm was compressed by a thrombosed giant right internal carotid artery aneurysm.

Blindness↗
PubMed1984

Sex-linked hereditary bilateral anophthalmos. Pathologic and radiologic correlation.

A 27-year-old man had X-linked true anophthalmos. No evidence of optic globe, nerves, or chiasm was found. Rudimentary structures suggesting optic tracts were present. Lateral geniculate nuclei were present but gliotic. Calcarine cortex was thinner but had usual lamination. The normal patches of cytochrome oxidase activity in layers II and III of visual cortex were absent.

Adult↗
PubMed1984

Receptive field properties in the cat's lateral geniculate nucleus in the absence of on-center retinal input.

In the cat, lateral geniculate neurons and retinal ganglion cells can almost all be categorized as on-center (excited by light stimuli) or off-center (excited by dark stimuli). We have investigated how these cells are affected when a drug is applied to the retina that, in the mudpuppy, inactivates on-bipolar cells (Slaughter, M. M., and R. F. Miller (1981) Science 211: 182-185). This drug, D,L-2-amino-4-phosphonobutyric acid (APB), is an analogue of glutamate. After injecting APB into the vitreous of the eye, we could record in the optic tract from fibers of off-center retinal ganglion cells that appeared normal in their responses, but we could find no fibers from on-center cells in the injected eye. In the lateral geniculate nucleus (LGN), the outcome was similar. Of a sample of 144 cells studied quantitatively, 13 had extremely poor responses and could not be characterized as on-or off-center. The remaining 131 cells had off-centers and appeared largely normal. Their receptive field organization was unaltered: the field center was excited by dark (off) stimuli and inhibited by light, whereas the surround was inhibited by off stimulation. Of particular interest was the fact that the surrounds of many off-center cells could still be excited by light stimuli; thus, despite the probable inactivation of on-bipolar cells, not all on-responses in the LGN were abolished. As a group, off-center cells were somewhat less responsive then in control experiments. Except for this change, APB appeared to affect only on-center cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗