[Clinical applications of visual evoked potentials for detection of chiasmal and postchiasmal lesions (author's transl)]

The electrophysiological tests in the early detection of the visual pathway dysfunction in patients with microadenoma

PURPOSE

To evaluate the validity of electrophysiological tests in the early diagnosis of a ganglion cells and/or optic nerve dysfunction in patients with pituitary microadenoma.

METHODS

66 eyes, from 33 patients with microadenoma with no evidence of the optic chiasm compression in magnetic resonance imaging (MRI) and the visual impairment in the routine ophthalmological examination, standard static perimetry (24-2 white on white) and optical coherence tomography (HD-OCT), were analysed. The pattern electroretinogram (PERG), standard pattern visual evoked potentials (PVEPs) and multichannel visual evoked potentials (mVEPs) (ISCEV standards) were performed. The results obtained from the electrophysiological tests were compared to the same number of age-matched healthy controls.

RESULTS

Statistically significant differences between the patients with microadenoma and healthy controls were detected in all electrophysiological tests (p < 0.001). The most frequent abnormalities were observed in mVEPs (25/33 patients, 75.8%; 43/66 eyes, 65.2%). The most frequent features registered in this test were: (1°4')-an increase in the P100wave latency from uncrossed fibres (13/33 patients, 39.39%; 21/66 eyes, 31.8%) and (0°16')-an amplitude reduction of this wave from the crossed fibres (11/33 patients, 33.33%; 19/66 eyes, 28.8%). The changes in PVEPs (15/33 patients, 45.5%; 25/66 eyes, 37.9%) and PERG (10/33 patients, 30.3%; 15/66 eyes, 22.7%) were also registered. Of all the tests and parameters analysed in the study, the greatest diagnostic value in detecting the visual pathway dysfunction in this group of patients was the amplitude of P100 wave from the crossed fibres of the mVEPs (1°4') with a sensitivity of 60.6% and a specificity of 93.8%. These parameters suggest that this type of dysfunction is downstream to the chiasm and can also indicate the visual pathway dysfunction severity.

CONCLUSIONS

In patients with microadenoma, the abnormalities in the electrophysiological tests are registered even without clinical evidence of visual impairment from the routine ophthalmological examination, SAP, OCT and chiasmal compression in MRI. The mVEPs have the most significant role in the diagnosis of the visual pathway dysfunction in patients with microadenoma.

Visual evoked potentials in tumors from orbita to occipital lobe in childhood

68 infants and children with proven tumours along the visual pathway visually evoked potentials with pattern reversal and flash were investigated. Subdivided in 5 locational groups (orbital, optic nerve, chiasmatic, retrochiasmatic and occipital lobe) best results were obtained by stimulation with pattern reversal using variable checksizes (91.2%) versus 61.8% by using flash evoked responses. Furthermore, using patterned stimuli not only latency shifts are best detected but also hints for visual function correlating to visual acuity could be given also in nonverbal or disabled children. For long term follow-up studies in known space-occupying lesions along the visual pathway, the use of pattern VEP is extraordinary because of its high sensitivity and complete harmlessness. Pattern VEP are even more sensitive than visual acuity testing in cooperative patients. The close interdisciplinary follow-up controls in these children between pediatric neurophysiologists and neurosurgeons are, therefore, strongly recommended.