Case Series on Chiasmal Lesions with Ocular Manifestations seen at the Eye Center of a Tertiary Government Hospital in Philippines

The Optic chiasm is an essential structure to vision, located in the anterior inferior recess of the third ventricle. Fibers from the nasal half of the retina decussate in the chiasm and join the uncrossed temporal fibers of the retina to form the optic tract giving characteristic visual field defects that respect the vertical horizon². The etiology of chiasmal lesions varies from congenital, traumatic, iatrogenic causes to extrinsic or intrinsic lesions. The most common intrinsic lesion is the pituitary adenoma which may promote compression of the optic chiasm causing visual disturbances.³

In a retrospective study done by Kitthaweesin et al.⁴, the ocular manifestations documented among patients with suprasellar tumors were visual loss (86%), eye pain (9%), diplopia (4%), and ptosis (1%). Ocular signs including relative afferent pupillary defect was detected in 31 patients (45%) and optic disc atrophy in 26 patients (38%). The most commonly encountered VFD was bitemporal hemianopia (49%), 14% had quadrantanopia and 7% with a 3 or greater quadrant loss of visual field.

Signs of chiasmal injury include a characteristic pattern of optic atrophy called “band” optic atrophy. Optic disc atrophy occurs over weeks to months, and the absence of optic atrophy should not preclude additional evaluation of patients with visual loss⁵. Additional effects could arise from compression of adjacent structures such as extension of the mass to the cavernous sinus causing disorders of extra ocular motility. 

Nystagmus may occur in patients with suprasellar tumors. See-saw nystagmus is an uncommon form of nystagmus with a finding of an alternating elevation and intorsion of one eye along with depression and excyclotorsion of the other eye.⁶

Most common non ocular manifestation of chiasmal syndrome include headache and systemic signs secondary to hormonal imbalance.

Epilepsy can occur under circumstances similar to cranial nerve lesions, and its frequency was reported by Poppen (1963)⁷pre-operatively with an incidence of 1-7%. If hemorrhage into a pituitary tumor occurs, that is, pituitary apoplexy, patients may present with varying combinations of sudden onset of severe headache, cranial neuropathy, visual impairment, and hypopituitarism. If very large, pituitary tumors may cause hydrocephalus and signs of increased intracranial pressure⁸.

Primary objective is to determine the common clinical symptoms and signs of patients with chiasmal lesions.

Specific Objectives Include:

1. To identify ocular and non-ocular symptoms among patients diagnosed with chiasmal lesions presenting to our OPD clinic.

2. To describe visual field defects seen among this group.

3. To compare size of lesion as documented on neuroimaging studies to the signs and symptoms of the patients.

At present, there is limited information available on chiasmal lesions presenting to ophthalmologists and this would be the first local study done. The results of this study may contribute to the diagnostic approach for patients with blurring of vision presenting to ophthalmologists.  

This study was approved by IRB ethics committee of Rizal medical center in November 2018 and followed the tenets of declaration of Helsinski. The examinations and testing done were fully explained to the patients and each provided informed written consent. Each patient was informed that all data gathered in relation with the study is confidential and will be used exclusively for purposes of the study only. 

A total of 12 patients diagnosed with Chiasmal lesions were included in this case series with a mean age of 39 years (10 to 62 years). We had 6 females and 6 male in this study, thus a 1:1 M:F ratio.

Table 2 summarises the patient demographics. Most of these patients were walk in to the RMC Eye Training & Facilities Center (83.33%) and 3 were referrals from the other clinical departments (Internal Medicine, General Surgery, Neurosurgery). 2 out of the 8 walk in patients were initially evaluated by other ophthalmologic subspecialty (Glaucoma, Oculoplastic, lacrimal & orbits) before being referred to the Neuro-ophthalmology service. In most of the cases, diagnosis was performed in our eye center and in only 2 cases, diagnosis were already known prior to consultation at the ophthalmology department as seen in table 3

Automated Visual Field perimetry in all 12 cases of chiasmal le-sions revealed similar output as confrontation testing. Junctional scotoma was seen in 7 cases, bitemporal hemianopia in 4 cases and Generalized scotoma in 1 case. There was no atypical visual field defects such as peripheral constriction or homonymous hemianopia encoun-tered in this study.

The average Mean Deviation of 22 eyes is 21.79dB (8.3 to 38.45dB). Majority of eyes had MD of more than 10 dB as seen in table 5

It is notable that in this case series a higher number of patients with junctional scotoma was observed compared to the bitemporal hemianopia cases in other studies ²⁹,³⁰

Neuroimaging(Cranial MRI or CT Scan)revealed pituitary lesions in 9 cases, two (2) cases of craniopharyngioma and Optic nerve glioma with extension to the chiasma.

The size of chiasmal lesions was measured in neuroimaging in dimensions and computed in volume using the Cavalieri’s principle. Mean volume of mass in 12 cases was 25.46cm³ (6.89 to 98.55cm³). Pituitary lesions (n = 9) have a mean size of 11.3cm³ (6.89 to 67.30cm³), Craniopharyngioma cases are larger at 38-98.55cm³ and the Optic nerve glioma with extension to the chiasma at 11.30cm³ as seen in table 6

A retrospective study done by Astorga-Carballo et al⁹ with a larger population than ours (n = 104) observed a slight female predominance (1:1.47) and a median age of 52 years (4-86 years) among patients with diagnosis of chiasmal syndrome attending their ophthalmological institution. In our case series, the mean age is 39 years, with a 1:1 M:F ratio.

Most walk in patients to our Eye center had blurring of vision in the average of around 16 months prior to consultation (6 to 60 months), while those referred from other services noted BOV earlier at around 10 months prior to referral (3-24 months) as seen in table 7

Irrespective of etiology of mass, blurring of vision was the main complaint in 10 of our 12 cases, involving one or both eyes. This main complaint was associated with headache in all cases, diplopia in 3 (25%)and symptoms secondary to hormonal imbalance in 2 (16.66%).

Chiasmal syndrome can have a variety of clinical manifestations with low vision as the initial presentation in most cases¹,³. In our case series, most complained of asymmetrical, gradually progressive blurring of vision in both eyes, often poorly described in the aspect of involved location except in 2 cases.

The duration of BOV prior to consultation among this set of patients was 14.75 months on the average, which is delayed compared to other studies at 12 months (4 days to 5 years)⁴, which is probably the reason for advanced disease at presentation. Considering that among these cases, patient may consult late in onset when macular fibres become affected, since an early peripheral field defect usually goes unnoticed by patients.¹⁰Also, having a good vision in one eye may have precluded consulting earlier.

The best corrected visual acuity (BCVA) of 24 eyes ranged from 6/6 to NLP. Bilateral blurring of vision was observed in 8 cases (66.67%) and was asymmetrical in 9 cases (75%) with corresponding relative afferent pupillary defect, in accordance to a study done by Jonathan et al.¹¹

Visual Field defects were intially identified by performing confrontation testing which corresponded well with AVF perimetry results. According to Lenworth et al¹², sensitivities for confrontation testing for posterior visual field defects, were high for detecting homonymous hemianopsias at 76% (19 of 25) and junctional scotomas at 75%, but low for bitemporal hemianopsias at 50% (6 of 12). This low sensitivity might have occurred because these visual field defects were often relative rather than near absolute scotomas.

Dyschromatopsia as tested using Ishihara color plates was seen in all cases (100%), involving 22 eyes. This is higher compared to a study by Astorga⁹, affecting only 62.5% of their cases, which probably is due to the fact that most of the patients presented in the late course of the disease.

Diplopia was an ocular symptom observed in 3 cases (25%). 1 case was restrictive ophthalmoplegia and 2 cases were not associated with any ocular motility defect. These 2 nonparetic diplopia cases have related VFD of bitemporal hemianopia and junctional scotoma, which resulted to retinal hemifield slide.¹³,¹⁴

There were no complaints of eye pain or problem in depth perception.

Optic nerve was described as unremarkable in 12 eyes (50%), pale (diffuse or temporal pallor) in 10 eyes (41.67%), and was swollen in 2 eyes (8.33%). This finding was slightly different with others, that Optic nerve palor was observed frequently (63% to 64.4%) among patients with perichiasmal tumors¹⁰,¹². This may be due to the more asymmetrical involvement in our cases. The 2 eyes with swollen optic nerves was found in a patient with a large chiasmal mass associated with supratentorial hydrocephalus with moderate transependymal edema, which can be considered as an unusual manifestation of a chiasmal mass¹⁵.

In all 12 cases, Junctional scotoma was the most common (58.33%) visual field defect reported using the Automated Visual Field Perimeter, followed by bitemporal hemianopia (33.3%) and Generalized scotoma in 1 case. This is different with other studies citing bitemporal hemianopia as the most frequent VFD observed¹,¹³,¹⁴,¹⁶. 7cases (77.78%) presenting with asymmetrical BOV had a VFD of Junctional scotoma and 2 with bitemporal hemianopic defect in Automated Visual Field Perimetry. There was no atypical visual field defects such as peripheral constriction or homonymous hemianopia encountered in this study.

Considering only the Pituitary adenoma cases (n=9), Junctional scotoma was the mostly observed VFD (5 cases), bitemporal hemi-anopsia in 3 cases and one case with generalized depression. This is different with other studies citing bitemporal hemianopia as the most frequent VFD observed among those observed with pituitary adenoma cases ^{14, 16}.

Headache is the most common non-ocular manifestation seen in all 12 of our cases. It was described as non-specific in character that is mild to severe in intensity in most cases. Headache among patients with brain tumors was described by Kirby et al¹⁷, as intermittent, moderate to severe in intensity with variable character described as dull, aching, throbbing or shooting and usually more severe in the morning. Headache is a common manifestation of brain tumor according to a local study1, occurring in 39.1% of patients. Among patients with chiasmal syndrome, headache was the presenting symptom of 10 patients among 104 studied (9.61%). In our case series, headache was the main complaint in only 1 case, but was an associated symptom in all the remaining cases. This was expected since they are presenting to ophthalmologists.

In a 15 year retrospective study done in Jamaica by Cawich et al¹⁸, nonspecific headaches accounted the most (72.3%) common clinical manifestation of pituitary adenoma, with cranial nerve palsies (16%) and pituitary apoplexy (5%). These, however, were not observed in any of the 12 cases in this case series.

Pituitary adenoma was the most considered etiology of chiasmal lesion on this case series (75%) based on neuroimaging, which is similar to those found in the literature regarding chiasmal lesions³,¹⁶,¹⁹. Pituitary adenoma accounts for 12-15% of all intracranial neoplasms and it is estimated that 25% of the population have pituitary adenoma, most of which are incidentally found.²⁰

Table 8 summarises the common causes of Lesions affecting the chiasm including extrinsic and intrinsic causes.

Eight (8) patients included in this study, radiologically considered with pituitary adenoma had an average age of 44.5 years (range of 31-61 years old) that is similar with findings of other studies (mean age of 43-51 years¹⁴,²¹) and a female preponderance of 1:3.5 M:F ratio, no different to other studies (1:2, 1:3.8)¹⁴,²¹

Apart of pituitary adenomas the rest of our cases (25%) were in paediatric age group (range of 10-18 years). Craniopharyngioma was the etiology in 2 cases (16.67%) and Optic nerve glioma with chiasmal extension in one. These etiologies other than pituitary adenoma were also among the common etiologies reported in other studies affecting the chiasm ³,¹²,¹⁶,¹⁹,²²

Craniopharyngiomas constitute to 5-10% of tumours of childhood²³. Craniopharyngioma accounts for 56% of sellar and suprasellar tumors in children²⁴.Our 2 cases of Craniopharyngioma have an average age of 15.5 years (13-18), similar to the results of a retrospective study of 45 patients by Kennedy et al²⁵, wherein more than half presented in the first two decades of life. The US-Central Brain Tumor Registry of the United States (CBTRUS), observed a bimodal age of distribution: one in childhood (0-19²⁴, 5-14²⁶years) and in adulthood (45-84²⁴, 50-75²⁶years), higher peak for ages 65-74²⁸.

The chiasm was secondarily involved in the case of a 10 year old boy diagnosed with neurofibromatosis type 1 (NF1) with an optic nerve glioma. He presented later than what was reported in the literature at 6²⁷ to 8.8²⁸ years. This case was similar to those described in a chart review study by Segal²⁷, wherein nearly a third (36%) of NF1 patients with Optic nerve glioma (13% of the 331 NF1 patients) presented past the age of 6 years and 18% are symptomatic (decreased vision or precocious puberty) demonstrating chiasmal or retrochiasmal tumor in addition to nerve involvement.

The largest mass measuring 98.55cm³and the smallest mass measuring 6.89cm³both had a BCVA of the poorer eye (>2 logMAR units). Also, the largest mass had one eye with normal vision showing the asymmetrical visual involvement. (see table 9).

Mean deviation (MD) from Automated Visual Field Perimetry performed were gathered only from 22 eyes. The Average mean deviation of 22 eyes is 21.79 dB, with majority having a MD above >10 and <40dB (19 eyes). There are only 3 eyes with mean deviation less than 10 dB (see Table 10).

Considering AVF perimetry Mean Deviation and size of the lesion (in cm³), an eye of the patient with a large lesion (67.30cm³) had a MD of <10 dB, while an eye with MD of more than 30 dB had a small lesion (6.89cm³).

Table 11 summarizes MD of 22 eyes with size of lesions. Our results does not support studies regarding severity of VFD and visual loss in relation to tumor size. This maybe explained by the higher number of patients with junctional scotoma in this series compared to the bitemporal hemianopia cases in previous studies²⁹,³⁰.

To further compare size of lesion with BCVA in LogMAR and AVF Perimetry, non pituitary lesions were excluded as seen in table 12 and table 13. Majority of the cases (16 eyes) have pituitary lesions with volume measuring less than 20 cm³. The largest pituitary lesion volume measured at 67.3 cm³, had one eye with vision classified to be in the normal range, whereas the other eye was blind. This asymmetry was also seen in the group with pituitary lesions measuring less 20 cm³ (16 eyes), with equal number of eyes with normal vision and blindness (7 eyes each).

The average AVF Perimetry MD of the 18 eyes with pituitary lesion is 21.86 dB, with the majority of eyes (14 eyes) having an average MD higher than 20 dB, as shown in table 13. The eyes with lesion measuring more than 30cm had the lowest average AVF Perimetry MD as compared to lesions measuring smaller than 20 cm³, not supporting the findings in other studies.²⁹, ³⁰

Except for one case, most of the cases collected as chiasmal mass would not have histopathological confirmation and classification of the type of mass. There are no statistical test done to correlate tumor vol-ume with logMAR BCVA or AVF Perimetry MD. Also, stereo acuity was not determined in this study.