Chiasmal Lesions Research Articles

An amplitude ratio of pattern visually evoked cortical potentials.

We evaluated the amplitude of steady state pattern visually evoked cortical potentials (St PVECP) by comparing the amplitude ratio to transient PVECP (Tr PVECP) with the latency of Tr PVECP in macular, optic nerve, and chiasmal lesions. PVECPs were obtained by pattern reversal stimulation of both 3 times and 12 times per second from normal subjects and patients. The peak latency of the P100 component of Tr PVECP and the amplitude ratio (St PVECP/ Tr PVECP) were studied. Ratio abnormalities were specifically found in patients with optic and chiasmal lesions who had normal Tr PVECP latency, but not in those with macular lesions. The ratio increased with visual improvement in optic nerve disease and chiasmal lesions. The amplitude ratio was useful in detecting and monitoring optic nerve and chiasmal lesions, and in differentiating optic nerve and chiasmal lesions from macular lesions.

Chiasmal decussation in tilted disc syndrome PVER in tilted disc

The tilted disc syndrome is a benign congenital abnormality of the optic nerve head. Since it can be confused with papilledema and chiasmal lesions, differential diagnosis is important. The tilting anomaly may be associated with other abnormalities along the optic nerve. Visual field defects may be similar to those in chiasmal lesions. In order to determine whether the normal crossover of nerve fibers at the chiasm is altered, the crossed and the uncrossed fibers were investigated using the pattern visual evoked responses (PVER) test. Thirty-four eyes of 17 patients diagnosed with tilted disc syndrome were evaluated for refraction, keratometry, color vision with Ishihara, visual field, and PVER. The presence of abnormal nerve fiber decussation was determined by recording PVER from the electrodes mounted on the scalp of both hemispheres. The amplitude and latency differences between the ‘crossed’ and ‘uncrossed’ fibers were not statistically significant (p>0.05). As a result, the tilting abnormality of papilla was found to be without chiasmal abnormal decussation.

The nasal circling phenomenon pattern of visual field loss on automated static perimetry Implications on the neuroanatomy of the optic chiasm

Purpose: Progressive chiasmal dysfunction can produce nasal quadrant visual field defects after the development of a temporal hemianopia. The study determined if preservation of the superior nasal visual quadrant (i.e., predominant inferior nasal quadrant defect) is restricted to inferior chiasmal compressive lesions. Methods: Seventeen consecutive patients with temporal hemianopia and nasal quadrant defect (termed the ‘nasal circling phenomenon’) were studied. Full-threshold automated static perimetry and neuroradiologic imaging were performed on all patients. The proportion of predominant superior and inferior nasal quadrant defects was calculated. A predominant superior or inferior nasal quadrant defect was defined as having at least twice as many defective points at p<0.05, and more defective points at p<0.005, when compared with the corresponding inferior or superior nasal quadrant in that eye. Results: Twenty-five (74%) inferior but only 12 (35%) superior nasal defects were identified among the 34 eyes tested. The inferior nasal quadrant defect was the predominant nasal defect in 19 (83%) of 23 eyes with predominant nasal defect, irrespective of the lesion being superior, inferior, or intrinsic to the optic chiasm. Conclusions: The redominance of inferior nasal quadrant defect when temporal hemianopia with the nasal circling phenomenon is present appears to be related to alteration of the normal chiasmal architecture following compression, demyelination, or atrophy.

Objective assessment of visual field defects using multifocal electroretinography

Multifocal electroretinography allows simultaneous recording of 61 focal electroretinographic signals from the retina of the posterior pole. The function of the outer retinal layers can be mapped for a visual field of 30.5 degrees radius. We herein describe the topography of such potentials in patients with hemianopic and concentric visual field defects. Six patients with visual field defects caused by chorioretinal and central visual pathways diseases were examined using multifocal ERG. In 30 normal volunteers in the entire 30 degrees visual field clear signals were obtained. In the patients with visual field defects caused by retinal diseases in areas with reduced light sensitivity diminished electroretinographical activity was found. In contrast, in patients with bitemporal hemianopsia due to a chiasmal lesion no correlation between visual field and magnitude of focal ERGs was seen. In retinal disorders defects in multifocal ERG presented the similar pattern as scotomata in perimetry. The patient with visual field defects due to disturbances in the chiasma exhibited a normal ERG-topography. In patients with visual field defects multifocal ERG supported differentiation of the location of the lesion.

Loss of Vision Alone May Result in Seesaw Nystagmus

A patient is described who developed seesaw nystagmus (SSN) associated with progressive severe vision loss due to cone-rod dystrophy. She was otherwise neurologically normal, and findings on magnetic resonance imaging of the brain were normal, including optic chiasm, meso-diencephalic junction, and brainstem. The literature is reviewed on neurologically normal patients with SSN and ocular vision loss, and the hypothesis is presented that SSN may become manifest as a result of vision loss alone, even in patients with chiasmal lesions, without disruption of central ocular motility pathways.

Juvenile Pilocytic Astrocytoma Masquerading as Amblyopia

A healthy 13-year-old girl, previously diagnosed with amblyopia in her right eye, was seen in consultation after her vision continued to decrease. A complete ophthalmologic examination including visual field testing and optic nerve photography was performed in the neuro-ophthalmologic clinic. Magnetic resonance imaging study was also obtained. Visual sensory deficits and pale optic nerves were noted on clinical examination. Visual field testing showed a chiasmatic junctional defect. Magnetic resonance imaging verified a large chiasmatic mass, histologically proven to be a juvenile pilocytic astrocytoma. Early recognition of signs and symptoms of chiasmatic lesions is essential for preventing visual loss.

Visual evoked potential abnormalities in compressive chiasmal lesions: the relevance of central visual field defects

In healthy subjects, the pattern visual evoked potential (VEP) arises predominantly from the stimulation of the central 5 degrees of the visual field. This central-field paradigm is well confirmed in VEP studies of retrochiasmal lesions, but it appears to be more ambiguous in patients with compressive lesions of the chiasm. To further clarify how central and peripheral visual field defects affect VEP, we compared the Goldmann perimetric charts with the frequency and type of VEP abnormalities in 25 patients in whom a compressive chiasmal lesion had been confirmed by CT. Perimetric findings were compared with the full-field and half-field VEP records with regard to the presence or absence of defects within the 0-5 degrees of the visual field. Full-field VEP abnormalities were present in all eyes with absolute, in 81% of the eyes with relative central visual field defects, and in 59% of the eyes with no impairment of the central visual field. Half-field VEP abnormalities were found in all half-fields with absolute, in 89% of half-fields with relative central visual field defect, and in 77% of half-fields that manifested visual field defects without macular involvement. We also found abnormalities in 36% of half-field VEP recordings, obtained by stimulation of apparently normal visual half-fields. The analysis of the types of VEP abnormalities showed that Pi00 amplitude attenuation typically reflected the central field defect, while Pi00 asymmetry, Pi00 prolongation, and Pi35 appearance could be detected in both the presence or absence of the central field impairment. Our results confirm that central visual field defects are associated with VEP abnormalities. However, the high proportion of VEP abnormalities in eyes with field defects not affecting the central 5 degrees, and the VEP half-field abnormalities even in an absence of visual field defect indicate that compressive chiasmal lesions may be reflected in abnormal VEP well before the appearance of central-field defects in the Goldmann perimetric tests.

Vision defects in patients with peri-chiasmal lesions.

Patients with chiasmal lesions frequently suffer loss of vision, but some may be visually asymptomatic and have little, if any, visual field loss. This study addressed two questions about the nature of such loss: (1) which tests are best able to detect visual loss and (2) what is the relation between the size of a lesion and the degree and type of visual loss. Visual acuity (VA), Goldmann perimetry, pattern evoked potentials, contrast sensitivity (CS), and color vision (CV) were assessed, in addition to a full ophthalmologic examination. Thirty-five patients were recruited from neurology, endocrinology, and ophthalmology departments; 31 had pituitary tumors and 4 had tumors of other origin (1 secondary) close to the chiasm. For analysis, patients were classified (1) according to whether they had visual symptoms on presentation and (2) according to lesion size. Seventeen patients had visual symptoms; all had visual field defects and all but one had two or more additional abnormal test results. Of the 18 visually asymptomatic patients, 12 had visual field defects and 14 had at least 2 abnormal test results; 7 had tumors with less than 5 mm of suprasellar extension, of whom 5 had field loss or at least 2 abnormal test results. CS was abnormal most often (85% of patients), followed by Goldmann perimetry (80%), visual evoked potentials (VEPs) (57%), CV (49%), and VA (26%). Our results support previous reports that asymptomatic patients and those with intrasellar tumors or only small amounts of suprasellar extension may have demonstrable visual dysfunction. Perimetry did not appear to be significantly worse than other more recently developed tests, which have often been regarded as being more sensitive, for detecting vision loss. However, VA and clinical observation of pupil reactions had poor sensitivity.

PS-8-9 Effects of chiasmatic lesion on binocular interactions of flash visual evoked potentials

PS-8-9 Effects of chiasmatic lesion on binocular interactions of flash visual evoked potentials

Electrodiagnostics of chiasmal compressive lesions

Recording of visual evoked potentials (VEPs) is not yet a routine test in patients with suspected chiasmal compressive lesions, but has proved useful to a clinician in assessing and following-up visual pathway dysfunctions. Abnormalities of VEPs can be found even in patients without clinical evidence of the visual impairment: VEP delays and alterations of the waveform, asymmetric distribution in one eye or in both eyes (crossed asymmetry) can indicate chiasmal compressive lesion. Simultaneous recording of pattern electroretinograms (PERGs) can additionally provide useful information about the patient's cooperation as well as about eventual retrograde degeneration of the ganglion cells. Electrophysiologic tests can be regarded as an integral part of diagnostic procedures — ocular diagnostic tests and neuroimaging — in suspected compressive lesions of the optic chiasm.

Computer-assisted interpretation of resolution visual fields from patients with chiasmal and retrochiasmal lesions.

Computer-assisted interpretation of resolution visual fields was performed in 147 normal subjects and 174 consecutive patients with known chiasmal or retrochiasmal lesion. The program identified 99% of normal subjects, and provided support for the correct diagnosis in 64% of patients with chiasmal and 83% of patients with retrochiasmal lesions. In conclusion, computer-assisted interpretation of resolution visual fields can provide considerable support to the final diagnostic decision in patients with lesions of the visual pathways.

The treatment and long-term prognosis of children with intracranial tumors: A study of 610 cases, 1950–1981

Six hundred and ten children aged under 16 years with intracranial tumors were referred for radiotherapy between 1950 and 1981: 579 were new cases and 31 had recurrent disease after primary treatment elsewhere. Radiotherapy was completed in 93% of all cases. The actuarial survival rate for all new cases was 53% at 5 years, 46% at 10 years, 40% at 20 years, and 39% at 30 years. The oldest children (10–15 years) had the best survival and the youngest (0–2 years) had the worst survival. Children treated with megavoltage x-ray equipment (1970 to 1981) had a significantly greater survival than those treated with orthovoltage X rays (1950–1969). Overall, a direct correlation was found between survival and maximum radiotherapy dose. Children having a total excision of the tumor prior to radiotherapy showed a greater survival than those treated by a subtotal or partial tumor removal. Children treated by radiotherapy alone had a survival comparable to those treated by sub-total excision and radiotherapy. There is a striking difference in survival expectation depending on initial functional category (I to III). The overall survival rates of 428 children completing treatment for glioma were 49% at 5 years, 43% at 10 years, and 40% at 15 years. The results according to certain specific tumor sites within the cerebral hemispheres are reported. Age is an important prognostic factor in low grade and also high grade astrocytomas, children having longer survivals than adults. Sub-total or partial excision of Canopharyngiomas combined with radical radiotherapy appears to give the best long-term results. Of 73 new cases, the 5-, 10-, and 15-year survival rates were 92%, 84%, and 79%. Recurrent craniopharyngiomas treated by surgery alone can be salvaged by further conservative surgery and radical radiotherapy. Optic gliomas are slow growing low grade astrocytomas. Survival rates at 5, 10, and 15 years for 20 children with mostly chiasmal lesions were 89%, 89%, and 78%, respectively. In 73 children with brain stem tumors, 17% remained alive for up to 15 years. The risk of CNS seeding from intracranial ependymomas depends on site of origin and grade of malignancy, with 50% incidence occurring in cases with high grade lesions situated in the posterior fossa. Survivals at 5, 10, and 15 years in 51 children were 51%, 40%, and 31%. Adjuvant chemotherapy improves survival. One hundred and forty-three children with medulloblastoma completing radiotherapy had survival rates of 42%, 33%, and 29% at 5, 10, and 15 years. Adjuvant chemotherapy has a profound effect on their survival. In a sample of 62 children treated and evaluated, 3–20 years after treatment, 15% had I.Q. scores of under 70 whereas in 60% the scores were average or above average. Seventy-three per cent were at normal school, at university or in full-time employment.

Neuroimaging Neuro-Ophthalmology

Computed tomographic scanning is an excellent modality for evaluation of most orbital and intracranial tumors and strokes. However, MR scanning is definitely superior to CT when evaluating for multiple sclerosis, posterior fossa lesions (evaluation of gaze palsies, internuclear ophthalmoplegia, and downbeat nystagmus), or when assessing an area where sagittal scanning is important (chiasmal lesions). Magnetic resonance has increased specificity when the CT is equivocal. Although MR and CT may be complementary in the information they provide, many clinical studies have shown MR to be superior to CT in evaluating cerebral infarctions, hematomas, the intracanalicular optic nerve, optic chiasm, sella turcica, and the cavernous sinus. Magnetic resonance generally has replaced metrizamide CT cisternography as the procedure of choice for evaluating the suprasellar cistern and posterior fossa. Computed tomography is still preferable for major trauma, especially involving acute fractures and hematomas, although MR is more sensitive to the more subtle intracerebral lesions, such as shear injuries and subdural hematomas, that may provide prognostic information. Computed tomography also is preferred in situations where detecting small amounts of calcification is important for the differential diagnosis. As the development of MR imaging continues with faster scan times, finer spatial resolution, the use of paramagnetic contrast agents, and with increased availability and decreased cost, MR imaging may become preferable to CT as the imaging modality of choice for the CNS and orbit.

Multi-channel visual evoked potentials in early compressive lesions of the chiasm.

The sensitivity of transient, pattern-reversal visual evoked potentials in the detection of early compressive lesions of the chiasm is controversial in the literature. There have been claims that the technique is capable of detecting an abnormality in the absence of any demonstrable visual field loss, and conversely that VEPs are not reliable for the detection of chiasmal lesions even when a bitemporal hemianopsia is clearly recordable. Using nine patients with pituitary adenoma we attempted to quantify the extent of visual field loss and correlate the diagnostic capabilities of topographically recorded potentials following full- and half-field stimulus presentations of various field and check sizes. Differential light thresholds were measured and quantified according to one investigator's graticule for the neural representation of visual space. Results show a strong correlation between the degree of information loss and the diagnostic value of the visual evoked potential. The technique was, however, capable of detecting abnormality in the absence of recordable field loss when large field and check sizes were used.

To image or not to image

An 8-year-old girl was first seen at the age of 4 with nystagmus and hypoplastic discs. Subsequent follow-up demonstrated poor visual acuity and optic atrophy. A CT scan showed a chiasmal or perichiasmal mass. The presumptive diagnosis of an optic chiasmal glioma is being considered. The use of neuroimaging in chiasmal or perichiasmal lesions and the natural history and treatment of optic nerve and chiasmal gliomas are discussed.

CT of cerebral abnormalities in precocious puberty.

True precocious puberty occurs as a result of the premature release of luteinizing hormone-releasing hormone from the hypothalamus, which stimulates the secretion of the pituitary gonadotropins, which in turn stimulate the gonadal sex steroids. The differential diagnosis of true precocious puberty includes cerebral and idiopathic categories. This differentiation, which cannot be made endocrinologically due to similarities in pituitary gonadotropin and sex steroid levels, may be facilitated by high-resolution CT. A CT study of 90 children (73 girls and 17 boys) with true precocious puberty was performed at the NIH to detect cerebral causes of their precocious puberty. Thirty-four cerebral abnormalities were demonstrated in 32 children, 16 boys and 16 girls. These included hypothalamic hamartomas (17), hypothalamic astrocytoma (one), optic chiasm lesions (six), ventricular abnormalities (eight), arachnoid cyst (one), and teratoma (one). The CT appearance of these cerebral abnormalities is discussed and related to the endocrinologic findings and natural history of true precocious puberty. A practical neuroradiologic approach to the evaluation of children with precocious puberty is presented.

Metrizamide computed tomographic cisternography: A high-yield diagnostic procedure for chiasmal syndromes with equivocal computed tomographic or magnetic resonance scans

Eight patients with chiasmal syndromes that could not be characterized despite high-resolution computed tomographic (CT) evaluation of the chiasm and suprasellar cistern were evaluated by metrizamide computed tomographic cisternography (MCTC). In all cases, the MCTC was essential in establishing the presence or absence of a structural chiasmal lesion. Although Magnetic Resonance Imaging (MRI) has largely supplanted MCTC as the procedure of choice in CT-negative chiasmal syndromes, the utility of intrathecal contrast computed tomography with cerebrospinal fluid analysis in evaluating chiasmal involvement in pituitary adenomas, craniopharyngiomas, gliomas, and particularly in unusual inflammatory lesions of the chiasm, make it a useful procedure to retain in one's diagnostic armamentarium.

Contribution of pattern reversal foveal and half-field stimulation to analysis of VEP abnormalities in multiple sclerosis

Multichannel pattern reversal visual evoked potentials (PRVEPs) from full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation were recorded in 112 mildly disabled multiple sclerosis (MS) patients with the aim of evaluating the contribution of HF and CF stimulation in this disease. CF stimulation was marginally more sensitive in detecting abnormalities (75% of patients) than FF stimulation (71% of patients). However, more importantly the two techniques were found to be complementary with the maximum number of abnormalities (79% of patients) resulting from a combination of the results. Abnormal FF responses were further evaluated by HF responses. P100 latency prolongation indicative of conduction delay was the most common finding but one-third of abnormalities consisted of disturbances of wave from relating to conduction block predominantly in macular fibres. Furthermore 34% of patients had an absent or indeterminate response to CF stimulation thus providing electrophysiological confirmation of the preferential involvement of macular fibres in MS. Although electrophysiological abnormalities were localised to the optic nerve in the majority of cases, some patients also had evidence of retrochiasmatic and chiasmatic lesions. In the majority of cases CF stimulation proved to be a useful alternative to HF stimulation in evaluating FF responses with abnormal wave forms. The study also suggested that an important factor determining whether a central scotoma will disturb the morphology of the FF VEP in the midline recording channel is the position of the macular representation in the occipital cortex. It is concluded that with multichannel recording and the additional use of CF and HF stimulation it is possible to increase the yield of PRVEP abnormalities found in MS and to define their nature with considerably greater precision.

The spectrum of the visual field defects in the tilted disc syndrome Clinical study and review

The tilted disc syndrome is a common ocular anomaly characterized by dysversion of the optic disc, congenital crescent, situs inversus of the retinal vessels, and ectasia and depigmentation of the fundus. The anomaly causes visual field defects that can mimic the defects produced by other neuro-ophthalmological diseases, particularly chiasmal lesions. This paper deals with the visual field defects of the tilted disc syndrome in an attempt to classify them and to find differential features as regards similar defects of other origin. Four types of visual field were charted in patients with tilted disc syndrome: normal field, altitudinal, quadrantanopia-like and hemianopia-like defects. These latter two defects tend to cross the vertical meridian, point towards the blind spot, and are partly surrounded by an arc of vision. A correspondence exists between the type of visual field defect and the position of the depigmented/ectatic area of the fundus.

Computed tomography in the evaluation of the optic chiasm

Computed tomography (CT) is the procedure of choice for initial evaluation of patients suspected of having chiasmal or perichiasmal lesions. Over 1000 patients were examined with high resolution CT, using axial and coronal scans, contrast enhancement, multiplanar reformations, and, when indicated, metrizamide CT cisternography. The normal anatomic appearance of the chiasm and neighboring structures is demonstrated, as are various pathologic conditions. CT criteria suggesting chiasmal disease are: (1) symmetric or asymmetric enlargement of the chiasm; (2) areas of abnormal density, without or with contrast enhancement, in the chiasm or perichiasmal region; (3) alteration of the suprasellar cistern; and (4) distortion of the anterior-inferior third ventricle.