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ASNR: Thin T2 Coronal Study Useful In Understanding The Mechanism Of Visual Loss By Maria Bishop Special to DG News BOSTON, MA -- April 30, 2001 -- Visual loss-and therapeutic orientation-can be better understood with a careful examination of the optic chiasm, said French researchers at the 39th Meeting of the American Society of Neuroradiology (ASNR) in Boston, Massachusetts. A careful examination, they noted, includes thin T2 coronal study with magnetic-resonance (MR) imaging. Dr. Francoise Heran of the Fondation A. de Rothschild in Paris, France, described a systematic MR imaging protocol undertaken for 176 patients with visual loss in the optic anterior pathways (OAP); ophthalmologic loss of vision was excluded. Fifty-one patients had optic-chiasm abnormalities; 19 demonstrated hypersignal in T2 sequences. Most patients, moreover, had an abnormal morphology of the optic chiasm (atrophy, hypertrophy, displacement) that was either isolated or associated with an optic-nerve lesion. The main etiologies discovered were as follows: displacement/compression as the result of pituitary adenoma; atrophy as the after-effect of macroadenoma treatment or long-lasting multiple sclerosis; hypersignal on T2 as the result of a tumour (glioma, germinoma). The clinical correlation of these findings was good, noted Dr. Heran, and there were only a few cases of disagreement between unilateral visual-field alteration and lesion of the whole chiasm. The study of isolated optic chiasm lesions may help the medical community to understand the mechanism of visual alteration, noted Dr. Heran, who outlined the outcomes of the above findings. Atrophic optic chiasm has a poor visual prognosis. Visual outcome of hypersignal of a normal or hypertrophied optic chiasm depends on the duration of the compression and the efficacy of the compressive agent. Inflammatory lesions with atrophy (i.e., in late multiple sclerosis) lead to worsening of the visual loss. Evolution of tumour involvement depends on the type of tumour. This study emphasizes the need for careful examination of the optic chiasm-even when the visual deficit is unilateral. E-mail this page to a friend or colleague! To print, use this version