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The role of visually evoked potentials in the management of hemispheric arachnoid cyst compressing the posterior visual pathways
The role of visually evoked potentials in the management of hemispheric arachnoid cyst compressing the posterior visual pathways Vignesh Raja, MRCOphth,a Anupma Kumar, MRCOphth,a Jon Durnian, MRCOphth,a Richard Hagan, PhD,b Neil Buxton, FRCS,c and William Newman, FRCOphtha
We report a case of an occipital arachnoid cyst in an infant, managed on the basis of changes in visually evoked potentials (VEPs). A significant asymmetry of VEP responses prompted neurosurgical intervention, which improved visual behavior and electrical response to both pattern and flash stimuli.
Case Report
A
5-month-old girl with a confirmed antenatal diagnosis of an occipital arachnoid cyst measuring 3.3 2.8 3.9 cm (Figure 1A) was referred for ophthalmological evaluation. The cyst was located between the occipital poles, distorting the left side more than the right, with suspected compression of the left occipital cortex and optic radiations. On examination, she appeared to have good central fixation but was less interested in objects presented from the right side. Anterior segment and fundus examination of both eyes were unremarkable. No significant refractive error was noted. Pupillary responses were normal. There was no evidence of nystagmus or strabismus. On 3-channel flash visually evoked potential (VEP) testing (2 cds/m2 flash intensity delivered via a Ganzfeld bowl), binocular responses showed a consistent asymmetry with right occiput response significantly greater than left occiput recordings (Figure 2); the right occiput recording was also larger than the midline response. Binocular pattern reversal VEP showed a possible response to 500 checks and a repeatable response to 1000 checks (Figure 3), with the right occiput response greater than the left. The asymmetry in VEPs strongly suggested that the arachnoid cyst was compressing the optic radiations passing toward the left Author affiliations: aDepartment of Ophthalmology, Alder Hey Children’s Hospital, Liverpool, United Kingdom; bDepartment of Clinical Engineering, Royal Liverpool University Hospital, Liverpool; cDepartment of Paediatric Neurosurgery, Alder Hey Hospital, Liverpool Institution of study: The Royal Liverpool Children’s NHS Trust, Alder Hey Children’s Hospital, Eaton Road Liverpool, L12 2AP, United Kingdom. This work was presented as a poster at the 2009 Annual Congress of the Royal College of Ophthalmologists, Birmingham, May 19-21. The authors have no conflict of interests to disclose. Submitted June 13, 2009. Revision accepted October 11, 2009. Reprint requests: Vignesh Raja, MRCOphth, MRCS (Edin), Specialist Registrar— Ophthalmology, Alder Hey Hospital, Eaton Road, Liverpool, United Kingdom, L12 2AP (email: [email protected]). J AAPOS 2010;14:85-87. Copyright Ó 2010 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/2010/$36.00 1 0 doi:10.1016/j.jaapos.2009.10.010
Journal of AAPOS
occipital cortex. Based on these findings, the patient underwent an uneventful open marsupialization of the occipital arachnoid cyst. Postoperative scans showed improvement in the cerebrospinal fluid collection. Six months postoperatively, fixation was steady, and the patient seemed equally interested in objects presented from either side. On 3-channel flash VEP (F-VEP) testing, binocular responses were much larger on both right and left occiput, with improved latency on the left occiput (Table 1), although a noticeable asymmetry was still present (Figure 2). On monocular stimulation, there was no obvious lateralization. Pattern reversal VEP (PR-VEP) showed no obvious asymmetry on the lateral channels. The midline channel response increased in amplitude and decreased in latency (Figure 3), although responses to both F-VEP and PR-VEP could still be considered somewhat delayed (Table 1). Repeat computed tomographic (CT) imaging showed reduction in the size of the arachnoid cyst, to 1.3 1.5 1.2 cm (Figure 1B).
Discussion Arachnoid cysts are intra-arachnoid fluid collections that account for about 1% of all intracranial space-occupying lesions.1 Although most arachnoid cysts are static throughout life, some grow and exert a mass effect on adjacent structures. Arachnoid cysts can cause a variety of clinical signs and symptoms, including headache, weakness, seizure, hydrocephalous, scoliosis, cognitive decline, and vision loss.2 Nonsurgical treatment options for asymptomatic patients include observation through serial radioimaging for asymptomatic patients. Surgical options for symptomatic patients include shunt placements, craniotomy, endoscopic fenestration, and stereotactic aspiration.2 VEPs offer an objective noninvasive method to assess the vision of infants and young children. The electrode montage used at our center is ground at Fpz, common reference at Fz, and recording electrodes at Oz (midline), O1 (left occiput), and O2 (right occiput) (Jasper 10-20 system). The F-VEP is seen as the most robust stimulus3 and is often easier to perform in less cooperative children.4 While intersubject variability is high for the F-VEP, the intertrial variability for the same subject is good, with 15% variability of latency.5 PR-VEPs are much less variable4 and intersubject standard deviation between trials for the same subject has been reported as 1.51 ms.6 This low variability makes PR-VEP a more sensitive and specific tool for assessing visual pathway dysfunction. The use of pattern
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FIG 1. A, CT scan at presentation: parafalcine arachnoid cyst, measuring 3.3 2.8 3.9 cm, between the occipital poles compressing left side. B, CT scan 6 months after surgery: cyst reduced in size, measuring 1.3 1.5 1.2 cm.
FIG 2. Binocular FVEP responses before and after surgery. Figure shows clear repeatable asymmetry, with improved response from each occiput, although a noticeable asymmetry is still present.
reversal with variable check sizes has been shown to be better than flash stimulus in patients in detecting latency shifts and hints for visual function correlating to visual acuity.7
The usual waveform is an initial negative peak (N1 or N75) followed by a large positive peak (P1 or P100) and then another negative peak (N2 or N145). The P100 is
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FIG 3. Left, the midline response to a 500 and 1000 check pattern reversal presurgical intervention (2 runs). Right, the midline response after surgical intervention (2 runs). Table 1. Response amplitudes and latencies before and after surgical intervention FVEP Visit
Rocc
Locc
PRVEP to 100’ Mocc
Preop Postop
18.6uV@ 153ms 53uV@ 158ms
9.4uV@ 183ms 19.3uV@ 155ms
4.5uV @199ms 7.8uV @155ms
Rocc, right occipital lobe; Locc, left occipital lobe; Mocc, monocular.
generated largely in the striate cortex as a response to the central region of the visual field. The latency and amplitude of the P100 are the main parameters of study. Although VEPs are more sensitive for patients with anterior visual pathway lesions, their role in assessing occipital lobe lesions has been established.8 In our patient, the role of the VEP was to identify significant loss of function from the left occiput, suggesting poor visual response in the right visual field: these results seemed to correlate with the clinical findings. The F-VEPs reinforced clinical findings and proved a physiological deficit over and above that identified by the CT scan. There was a remarkably asymmetric VEP to flash (rudimentary) and pattern (more complex visual processing) stimuli. After surgery, the PR-VEP improved on all 3 recorded channels, with no obvious asymmetry; amplitude became larger, and waveform became symmetrical.
Journal of AAPOS
It is possible that VEPs improved in part with age from the time of presentation: latency of VEPs tends to improve with myelination and age. In our case, the pre- and postintervention latencies from both sides were still delayed, most likely because of the cyst and its effect on the development of the posterior visual pathway. References 1. Cincu R, Agrawal A, Eiras J. Intracranial arachnoid cysts: Current concepts and treatment alternatives. Clin Neurol Neurosurg 2007;109: 837-43. 2. Pradilla G, Jallo G. Arachnoid cysts: Case series and review of the literature. Neurosurg Focus 2007;22: E7. 3. Halliday AM. Evoked potentials in clinical testing. 2nd ed. New York: Churchill Livingstone; 1993. p. 57-113. 4. Kriss A, Thompson D. Visual Electrophysiology. In: Taylor D, editor. Paediatric ophthalmology. 1st ed. Oxford, UK: Blackwell Science Ltd; 1990. p. 93-121. 5. Contamin F, Cathala HP. Responses electro-corticales de l’homme normal eveille a des eclairs lumineux: Resultats obtenus a partir d’enregistrements sur le cuir chevelu, a l’aide d’un dispositif d’integration. Electroencephalogr Clin Neurophysiol 1961;13:674-94. 6. Skuse NF, Burke D, McKeon B. Reproducibility of the visual evoked potential using a light-emitting diode stimulator. J Neurol Neurosurg Psychiatry 1984;47:623-9. 7. Wenzel D, Brandl U, Beck JD, Cedzich C, Albert F. Visual evoked potentials in tumors from orbita to occipital lobe in childhood. Neurosurg Rev 1988;11:279-86. 8. Streletz LJ, Bae SH, Roeshman RM, Schatz NJ, Savino PJ. Visual evoked potentials in occipital lobe lesions. Arch Neurol 1981;38:80-85.
We report a case of an occipital arachnoid cyst in an infant, managed on the basis of changes in visually evoked potentials (VEPs). A significant asymmetry of VEP responses prompted neurosurgical intervention, which improved visual behavior and electrical response to both pattern and flash stimuli.
Case Report
A
5-month-old girl with a confirmed antenatal diagnosis of an occipital arachnoid cyst measuring 3.3 2.8 3.9 cm (Figure 1A) was referred for ophthalmological evaluation. The cyst was located between the occipital poles, distorting the left side more than the right, with suspected compression of the left occipital cortex and optic radiations. On examination, she appeared to have good central fixation but was less interested in objects presented from the right side. Anterior segment and fundus examination of both eyes were unremarkable. No significant refractive error was noted. Pupillary responses were normal. There was no evidence of nystagmus or strabismus. On 3-channel flash visually evoked potential (VEP) testing (2 cds/m2 flash intensity delivered via a Ganzfeld bowl), binocular responses showed a consistent asymmetry with right occiput response significantly greater than left occiput recordings (Figure 2); the right occiput recording was also larger than the midline response. Binocular pattern reversal VEP showed a possible response to 500 checks and a repeatable response to 1000 checks (Figure 3), with the right occiput response greater than the left. The asymmetry in VEPs strongly suggested that the arachnoid cyst was compressing the optic radiations passing toward the left Author affiliations: aDepartment of Ophthalmology, Alder Hey Children’s Hospital, Liverpool, United Kingdom; bDepartment of Clinical Engineering, Royal Liverpool University Hospital, Liverpool; cDepartment of Paediatric Neurosurgery, Alder Hey Hospital, Liverpool Institution of study: The Royal Liverpool Children’s NHS Trust, Alder Hey Children’s Hospital, Eaton Road Liverpool, L12 2AP, United Kingdom. This work was presented as a poster at the 2009 Annual Congress of the Royal College of Ophthalmologists, Birmingham, May 19-21. The authors have no conflict of interests to disclose. Submitted June 13, 2009. Revision accepted October 11, 2009. Reprint requests: Vignesh Raja, MRCOphth, MRCS (Edin), Specialist Registrar— Ophthalmology, Alder Hey Hospital, Eaton Road, Liverpool, United Kingdom, L12 2AP (email: [email protected]). J AAPOS 2010;14:85-87. Copyright Ó 2010 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/2010/$36.00 1 0 doi:10.1016/j.jaapos.2009.10.010
Journal of AAPOS
occipital cortex. Based on these findings, the patient underwent an uneventful open marsupialization of the occipital arachnoid cyst. Postoperative scans showed improvement in the cerebrospinal fluid collection. Six months postoperatively, fixation was steady, and the patient seemed equally interested in objects presented from either side. On 3-channel flash VEP (F-VEP) testing, binocular responses were much larger on both right and left occiput, with improved latency on the left occiput (Table 1), although a noticeable asymmetry was still present (Figure 2). On monocular stimulation, there was no obvious lateralization. Pattern reversal VEP (PR-VEP) showed no obvious asymmetry on the lateral channels. The midline channel response increased in amplitude and decreased in latency (Figure 3), although responses to both F-VEP and PR-VEP could still be considered somewhat delayed (Table 1). Repeat computed tomographic (CT) imaging showed reduction in the size of the arachnoid cyst, to 1.3 1.5 1.2 cm (Figure 1B).
Discussion Arachnoid cysts are intra-arachnoid fluid collections that account for about 1% of all intracranial space-occupying lesions.1 Although most arachnoid cysts are static throughout life, some grow and exert a mass effect on adjacent structures. Arachnoid cysts can cause a variety of clinical signs and symptoms, including headache, weakness, seizure, hydrocephalous, scoliosis, cognitive decline, and vision loss.2 Nonsurgical treatment options for asymptomatic patients include observation through serial radioimaging for asymptomatic patients. Surgical options for symptomatic patients include shunt placements, craniotomy, endoscopic fenestration, and stereotactic aspiration.2 VEPs offer an objective noninvasive method to assess the vision of infants and young children. The electrode montage used at our center is ground at Fpz, common reference at Fz, and recording electrodes at Oz (midline), O1 (left occiput), and O2 (right occiput) (Jasper 10-20 system). The F-VEP is seen as the most robust stimulus3 and is often easier to perform in less cooperative children.4 While intersubject variability is high for the F-VEP, the intertrial variability for the same subject is good, with 15% variability of latency.5 PR-VEPs are much less variable4 and intersubject standard deviation between trials for the same subject has been reported as 1.51 ms.6 This low variability makes PR-VEP a more sensitive and specific tool for assessing visual pathway dysfunction. The use of pattern
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Volume 14 Number 1 / February 2010
FIG 1. A, CT scan at presentation: parafalcine arachnoid cyst, measuring 3.3 2.8 3.9 cm, between the occipital poles compressing left side. B, CT scan 6 months after surgery: cyst reduced in size, measuring 1.3 1.5 1.2 cm.
FIG 2. Binocular FVEP responses before and after surgery. Figure shows clear repeatable asymmetry, with improved response from each occiput, although a noticeable asymmetry is still present.
reversal with variable check sizes has been shown to be better than flash stimulus in patients in detecting latency shifts and hints for visual function correlating to visual acuity.7
The usual waveform is an initial negative peak (N1 or N75) followed by a large positive peak (P1 or P100) and then another negative peak (N2 or N145). The P100 is
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Volume 14 Number 1 / February 2010
Raja et al
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FIG 3. Left, the midline response to a 500 and 1000 check pattern reversal presurgical intervention (2 runs). Right, the midline response after surgical intervention (2 runs). Table 1. Response amplitudes and latencies before and after surgical intervention FVEP Visit
Rocc
Locc
PRVEP to 100’ Mocc
Preop Postop
18.6uV@ 153ms 53uV@ 158ms
9.4uV@ 183ms 19.3uV@ 155ms
4.5uV @199ms 7.8uV @155ms
Rocc, right occipital lobe; Locc, left occipital lobe; Mocc, monocular.
generated largely in the striate cortex as a response to the central region of the visual field. The latency and amplitude of the P100 are the main parameters of study. Although VEPs are more sensitive for patients with anterior visual pathway lesions, their role in assessing occipital lobe lesions has been established.8 In our patient, the role of the VEP was to identify significant loss of function from the left occiput, suggesting poor visual response in the right visual field: these results seemed to correlate with the clinical findings. The F-VEPs reinforced clinical findings and proved a physiological deficit over and above that identified by the CT scan. There was a remarkably asymmetric VEP to flash (rudimentary) and pattern (more complex visual processing) stimuli. After surgery, the PR-VEP improved on all 3 recorded channels, with no obvious asymmetry; amplitude became larger, and waveform became symmetrical.
Journal of AAPOS
It is possible that VEPs improved in part with age from the time of presentation: latency of VEPs tends to improve with myelination and age. In our case, the pre- and postintervention latencies from both sides were still delayed, most likely because of the cyst and its effect on the development of the posterior visual pathway. References 1. Cincu R, Agrawal A, Eiras J. Intracranial arachnoid cysts: Current concepts and treatment alternatives. Clin Neurol Neurosurg 2007;109: 837-43. 2. Pradilla G, Jallo G. Arachnoid cysts: Case series and review of the literature. Neurosurg Focus 2007;22: E7. 3. Halliday AM. Evoked potentials in clinical testing. 2nd ed. New York: Churchill Livingstone; 1993. p. 57-113. 4. Kriss A, Thompson D. Visual Electrophysiology. In: Taylor D, editor. Paediatric ophthalmology. 1st ed. Oxford, UK: Blackwell Science Ltd; 1990. p. 93-121. 5. Contamin F, Cathala HP. Responses electro-corticales de l’homme normal eveille a des eclairs lumineux: Resultats obtenus a partir d’enregistrements sur le cuir chevelu, a l’aide d’un dispositif d’integration. Electroencephalogr Clin Neurophysiol 1961;13:674-94. 6. Skuse NF, Burke D, McKeon B. Reproducibility of the visual evoked potential using a light-emitting diode stimulator. J Neurol Neurosurg Psychiatry 1984;47:623-9. 7. Wenzel D, Brandl U, Beck JD, Cedzich C, Albert F. Visual evoked potentials in tumors from orbita to occipital lobe in childhood. Neurosurg Rev 1988;11:279-86. 8. Streletz LJ, Bae SH, Roeshman RM, Schatz NJ, Savino PJ. Visual evoked potentials in occipital lobe lesions. Arch Neurol 1981;38:80-85.