Eur. Neurol. 14: 17-28 (1976)

Visual Evoked Responses and Their Dispersion Pattern in Frontal Lobe Tumours E. C righel . C. A rseni and M. M atei1 Institute of Neurology and Psychiatry and the Neurosurgical Clinics of the Marinescu Hospital, Bucharest

Key Words. Averaged evoked responses (AVER) • Dispersion pattern (DP) • Frontal lobe • Cerebral tumours • Visual acuity Abstract. In patients with frontal lobe tumours the averaged visual evoked res­ ponses (AVER) and their dispersion pattern (DP) in visual areas were investigated before and at different periods after operation. Important changes in AVER (in amplitude and latency) were found in the patients with tumours on the midline or in one of the frontal lobes. The DP was abnormal in all the cases. There was no relation to visual acuity, tumour location and existence of intracranial hyperten­ sion. After operation, despite the clinical improvement, the alterations of AVERs or DPs were very marked and in some cases became even more important than before. The role of the frontal lobe in the organization of the responses to peri­ pheral stimuli in the visual areas is discussed.

Introduction Little has been said about the visual evoked responses (VER) in spa­ ce-occupying lesions situated in cerebral regions which are not directly involved in the visual function. Such investigations were performed by B ergamini and co-workers [1, 2], D rechsler [12], J onkman [quoted by 14] but the results are still inconclusive. Bearing in mind the role of the frontal lobe in visual orienting [3] and in visual recovery [15] functions, we were interested especially in VER changes induced by frontal lobe lesions. 1 We wish to thank Mrs. G. D umitru and S. Chicus for their collaboration and very competent technical assistance.

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Received: April 2, 1975; accepted: April 21, 1975.

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C righel/A rseni/M atei

Previous investigations in normal subjects [8, 10] and in patients with cerebrovascular strokes [9] or with epilepsy [11] showed the im­ portance of studying the dispersion pattern of VER (DP). In these pap­ ers we stated that in healthy adult subjects the VER of a series of stimu­ li showed an independent variability at each time point locked to the sti­ mulus onset, resulting in a typical dispersion pattern [D = f(t)]; the nor­ mal DP, investigated along 400-600 msec after the stimulus onset and on 15 samples, is characterized by an initial period of high dispersion, followed by a very constant small dispersion and then there appeared a third period, inconstant along the 400-600 msec analysis time, of high dispersion, but of smaller amplitude of dispersion than the first period. Between DP and averaged visual evoked responses (AVER) or back­ ground EEG no correlation was found. Important DP changes, offering a statistically significant correlation, were found in pathological and in some special physiological conditions [8, 9, 11]. These results pointed to the conclusion that the DP of VER is a more reliable index to the func­ tional capacity of an investigated structure than the AVER is. The aim of the present paper is to investigate in patients with fron­ tal lobe tumours the functional capacity of the visual areas by the study of the AVERs and DPs before and after operation.

The investigations were performed on 20 patients with frontal lobe tumours, aged between 20 and 50. Eleven were investigated before operation only, the other nine at different time intervals after operation also. Midline tumours were found in eight patients, in ten the tumours involved the convexity and/or the deep re­ gions of one frontal lobe and two were orbital tumours compressing the orbital areas of the frontal lobe. The results found in the patients with frontal lobe tumours were compared with those found in 27 control subjects from another paper [10] and with ten new controls within the same age range as the patients. The control subjects were so­ matically, neurologically and mentally normal. The patients and the controls were investigated lying on their backs, in a quiet dark room, with their eyes closed throughout the examination. The VERs were re­ corded using bipolar leads: one of the electrodes was located in a point T situated 1.5 cm rostral to the inion, the second in the vertex ‘V’ or in P3 or P, according to the international scheme for EEG recordings. Bright flashes, delivered by a si­ lent photostimulator, were used for photostimulation. The bulb of the photostimu­ lator was situated 50 cm in front of the patient’s eyes. The AVER [M = f(t)] and the DP of VER [D = f(t)] and of background activity were computed by a digital

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Material and Method

A v e r and DP in Frontal Lobe Tumours

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Fig. 1. Patient B. V. Glioma of the right frontal lobe. Visual acuity: right = O; left = very poor hémianopsie perception of light. Epileptic seizures. Recordings before operation; left side curves = I-P 4; right side curves = I-P3. Top = DP; bottom = AVER. Note the high amplitude of AVER and their asymmetry; the DP amplitude is higher on the tumour side and shows an ascending pattern.

computer, according to the method described in previous papers (8, 10]. Concomi­ tantly EEG recordings were performed by a Nihon-Kohden EEG machine.

Averaged Visual Evoked Responses (A VER) Before the operation 16 of the 20 patients showed a normal, polyphasic AVER. In 6 cases the latencies at the pike of the first deflection were less than 100 msec and in 10 cases the latency exceeded 110 msec. In tumours involving only one frontal lobe, with extant AVERs (10 cases) there was amplitude asymmetry in 8 cases: in 5 cases the AVER was higher on the tumour side (fig. 1) and in three contralaterally

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Results

C righei./A rsf.ni/M atf.i

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I 1 40

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1 I 1 | 120

100

1 i

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1 | 1 r 1 i

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160 200 240 280 320 360 400 140 180 220 260 300 340 380

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(fig. 6); in two cases the AVERs were equal bilaterally. Latency asym­ metry was found only in 4 cases: in 3 the latency was longer contralatcrally and in one homolaterally to the tumour. Absence of AVER before operation was noted in 4 cases: three with midline tumours and one with right frontal tumour; two cases with a very important loss of vision, con-

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Fig. 2. Superimposition of nine DPs of the nine control subjects with a normal dispersion pattern. In this graph the amplitude scale in /

Visual evoked responses and their dispersion pattern in frontal lobe tumours.

In patients with frontal lobe tumours the averaged visual evoked responses (AVER) and their dispersion pattern (DP) in visual areas were investigated ...
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