Beeinträchtigung der Sehbahn bei Glaukomen

Zusammenfassung

Bei Glaukomen ist die Darstellung der Sehbahn mittels Diffusionsbildgebung und metabolischer MRT möglich; es findet sich mit zunehmendem Alter eine Atrophie der Sehstrahlung, welche das Ausmaß der physiologischen Hirnvolumenminderung deutlich übersteigt. Bei den unterschiedlichen Glaukomsubtypen erlaubt die qualitative Auswertung der Diffusionsbildgebung mit Berechnung von fraktionaler Anisotropie (FA) und radialer Diffusivität (RD) die Beurteilung der axonalen Integrität entlang der Sehbahn. Es finden sich bei Glaukomen bereits im Anfangsstadium der Erkrankung deutliche FA- und RD-Veränderungen sowohl entlang der Sehbahn wie auch in weiteren Hirnregionen außerhalb der Sehbahn, die nahelegen, dass es sich beim Glaukom um eine komplexe neurodegenerative Erkrankung handelt. Die metabolische MRT wird uns künftig weitere Einblicke in die Pathophysiologie verschiedener Glaukomformen geben und damit zum Therapiemonitoring beitragen und die Diagnostik verbessern.

Abstract

MR Diffusion Tensor Imaging (DTI) enables visualisation of the visual system in glaucoma; it has been shown that the atrophy of the optic radiation is more pronounced in glaucoma than in age-matched controls. The atrophy of the optic radiation thereby correlates with OCT and visual field measures. Diffusion tensor imaging permits quantification of the axonal integrity of the optic radiation by calculation of fractional anisotropy (FA) and radial diffusivity (RD). Both within and also outside the visual system, there are substantial changes in FA and RD, changes suggesting a complex neurodegenerative disease. Metabolic MRI by specific Na⁺-coils and by the CEST-technique (CEST: chemical exchange saturation transfer) will enable visualisation of neuronal cell death and pathological protein accumulation in the visual system. It is proposed that glaucomatous atrophy of the visual system may be induced by antero- and retrograde axonal degeneration. In normal tension glaucoma and PEX glaucoma, retrograde degeneration is induced by ischemic lesions or pathological protein accumulation within the cerebral portion of the visual system. Magnetic resonance imaging of the visual system with DTI and metabolic imaging will potentially improve therapeutic monitoring and diagnosis of glaucoma.

Schlüsselwörter

Glaukom - Neuroophthalmologie - Diffusions-Tensor-Bildgebung - metabolisches MRT

Key words

diffusion tensor imaging - metabolic MRI - glaucoma

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