Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 17  |  Issue : 1  |  Page : 30-33

Neuroimaging in optic neuropathy: Role of computed tomography


1 Department of Radiology, University of Benin Teaching Hospital, Benin City, Nigeria
2 Department of Radiology, Irrua Specialist Teaching Hospital, Irrua, Edo State, Nigeria

Date of Web Publication7-Jan-2015

Correspondence Address:
Ehimwenma Ogbeide
Department of Radiology, University of Benin Teaching Hospital, Benin City, Edo State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2276-7096.148689

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  Abstract 

Background: There are many different conditions that can lead to optic neuropathy. The purpose of this article is to evaluate retrospective data on computed tomographic findings in patients presenting with optic neuropathy at a southern Nigerian teaching hospital.
Methodology: A retrospective review of patients with clinical examination finding of optic atrophy who presented for cranial Computed Tomography (CT) scan at the University of Benin Teaching Hospital, Benin City, Nigeria from July 2009 to June 2012 was undertaken. SPSS version 16 software was used for data analysis.
Results: The request forms and CT reports of 13 patients which comprised of 7 males and 6 females were reviewed. The mean age of the patients was 37.2 ΁ 13.5 years (age range 16 to 55 years). There was bilateral presentation in 12 (92.3%) of cases while the only unilateral case was left sided.
Computed tomography finding of tumor was the most common finding in five cases. In one patient the only finding of note was an atrophic left optic nerve.
Conclusion: Computed tomography is a useful tool in the management of patients with optic neuropathy providing information regarding etiology.

Keywords: Computed tomography, optic neuropathy, tumor


How to cite this article:
Ogbeide E, Theophilus AO. Neuroimaging in optic neuropathy: Role of computed tomography. J Med Trop 2015;17:30-3

How to cite this URL:
Ogbeide E, Theophilus AO. Neuroimaging in optic neuropathy: Role of computed tomography. J Med Trop [serial online] 2015 [cited 2019 Oct 24];17:30-3. Available from: http://www.jmedtropics.org/text.asp?2015/17/1/30/148689


  Introduction Top


Optic neuropathy is a condition in which there is a loss of optic nerve fibers which lead to poor vision, and it is an important sign of advanced optic nerve disease. [1] Afferent nerve fibers are numbering about 1.2 million originate from the retinal ganglion cells and are carried in about 600 bundles as the optic nerve, with majority synapsing at the lateral geniculate ganglion. Optic neuropathy, also commonly referred to as optic atrophy is an end-stage condition in which any of a number of pathologies causes compromise to ganglion cell function. Axonal loss occurs with filling of the spaces by astrocytes and a resultant pale appearance of the optic disc on fundoscopy. Axons of the optic nerve once damaged cannot be replaced thus early detection of optic neuropathy is important.

Optic neuropathy is diagnosed on clinical grounds and the history often points to possible etiology. [2] Compressive and hereditary optic neuropathies usually present with a protracted history over years. [2] In compressive optic neuropathy, the lesion may be found between the orbital segment of the optic nerve and the lateral geniculate ganglion. Radiological imaging has evolved to occupy a prominent position in diagnostic evaluation of many medical and dental conditions providing clinicians with a versatile tool for diagnosis, treatment planning, monitoring progression or outcome of different conditions and also the possibility of intervention. Cross-sectional imaging with computed tomography (CT) and magnetic resonance imaging (MRI) are the most useful techniques in imaging the orbits and its contents. [3],[4] The confined space of the orbits with the contained structures of varied attenuation coefficients make it ideal for CT evaluation. [3] The optic nerves are clearly visualized on CT and MRI. For most neuro - ophthalmic disorders, MRI is superior to CT. [4],[5] MRI is the recommended study in inflammatory, infiltrative and compressive optic neuropathies, with fat suppression technique useful in excluding intraorbital optic nerve enhancement. However, CT is superior in traumatic optic neuropathy for canal fractures. [4] Confirmation of optic neuropathy is made by optical coherence tomography (OCT). OCT is a noninvasive noncontact imaging system that is analogous to ultrasound imaging except that it uses light instead of sound waves. [1],[6] It provides high-resolution images of the vitreous, retina, and optic nerves. [1] The purpose of this article is to evaluate the findings in patients presenting with optic neuropathy referred to the Radiology department for CT scanning.


  Methodology Top


A retrospective case series study of patients aged 16-55 years with optic neuropathy was undertaken. The study setting was the Radiology Department of the University of Benin Teaching Hospital. The hospital is a tertiary health facility which serves as a referral center, especially for special radiological investigations like CT. Most of the patients were referred from the Ophthalmology Department of the hospital. Data reviewed were from the request forms and CT reports of the patients, and included age, sex, indication for the CT scan and the CT findings. The CT machine used for the scans was either a Siemens 1998 Somatom ART or a General Electric Bright Speed 2007 machine. A lateral scanogram was obtained, and slice thicknesses of 5 mm were employed with the patient in the supine position prior to and after intravenous injection of contrast medium. Where necessary coronal slices were obtained with the patient in the prone position. The images were evaluated on soft tissue and bone window settings. The data were analyzed with the use of SPSS version 16.0 Chicago: SPSS Inc.


  Results Top


A total of 13 patients were evaluated in this study. They comprised of 7 males and 6 females giving a male to female ratio of 1.17-1 [Figure 1]. There was bilateral presentation in 12 (92.3%) cases and one unilateral case, which was left sided as shows in [Table 1].
Figure 1: Sex distribution of patients

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Table 1: Age, sex, side and radiological findings in 13 cases of optic atrophy


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[Table 1] shows a summary of the CT findings in all 13 patients. In the six patients with CT evidence of abnormality, five had intracranial mass lesions while in one patient an atrophic left optic nerve was the only finding of note. Four of the five cases of intracranial mass lesions were neoplasms, while one patient had CT diagnosis of aneurysm as shows in [Table 1].{Table 1}

There were two cases with the primary diagnosis of pituitary adenoma with evidence of enlargement of the sella and suprasellar extension in both cases. Two cases of suspected meningioma were seen with one located in the cerebellopontine angle on the right and the other in the anterior cranial fossa [Table 1]. The mass lesion diagnosed as internal carotid aneurysm appeared as a hyperdense mass with evidence of bony erosion of the anterior clinoid and right optic canal narrowing.{Table 1}


  Discussion Top


Optic atrophy exists when a pale optic disc is accompanied by visual loss as distinct from optic disc pallor, which may be observed in otherwise normal patients without visual impairment. It may be diffuse or sectoral depending on the cause and level of the lesion. [1] Unilateral optic atrophy results from lesions anterior to the optic chiasm and it is the more common presentation. Band atrophy is the form that occurs in lesions of the optic chiasm or tract and is caused by involvement of fibers entering the optic disc nasally and temporally with sparing of the superior and inferior portions. [1] The patients in our present study however had clinical evidence of bilateral optic atrophy in the vast majority comprising 12 (92%) of cases with only one unilateral case. This could partly be attributed to the fact that unilateral cases may go unnoticed by the patient, occasionally being detected incidentally.

The five mass lesions detected in this study were in locations related to the visual pathway comprising two pituitary masses, one anterior cranial fossa mass, and one cerebellopontine angle mass. Lesions involving the optic chiasm and optic tract may present as bilateral atrophy. The optic chiasm lies directly above the pituitary gland and pituitary neoplasms such as pituitary adenoma if large enough may compress the optic chiasm from below frequently leading to progressive visual impairment possible visual symptoms include diplopia, bitemporal visual field loss, ophthalmoplegia and color changes (color desaturation).

Differential considerations of a suprasellar mass include pituitary macroadenoma, craniopharyngioma, meningioma, chiasmatic gliomas and aneurysmal carotid artery. Pituitary adenoma is the most common neoplasm in the sellar region. [7] It is the most common cause of the chiasmal syndrome, majority of which are due to compressive pathologies. [8] The etiology of chiasmal syndrome may be intrinsic or extrinsic, with the latter implying compression by some other structure. [8] Post gadolinium contrast enhancement was observed by Grimm et al. when a hypertrophied anterior clinoid process in a patient with fibrous dysplasia caused compression of the optic nerve. [9] Chromophobe adenoma is the most common primary intracranial tumor to produce neuro ophthalmic features. [1] On high-resolution CT pituitary adenomas typically appear as a hypodense mass compared with the normal gland on unenhanced and contrast - enhanced scans. [7] The "snowman appearance" has been described and is attributed to the compression of the relatively soft pituitary adenoma by the diaphragm sella. [10] Expansion of the pituitary fossa as found in the two cases of suspected pituitary adenoma in our study may occur with macroadenomas. In these two cases, there was also evidence of significant suprasellar extension of the mass [Table 1].{Table 1}

Craniopharyngioma may present in adults with visual field defect and is a major differential of suprasellar masses. They can be cystic, solid or mixed cystic/solid and unless very large do not usually expand the pituitary fossa. [7] The solid portion of the tumor shows contrast enhancement and may be partially calcified. [7]

Meningioma was the primary consideration in two patients with one located in the anterior cranial fossa and the other in the cerebellopontine angle. The patient in the latter case was a 53-year-old female who presented with bilateral optic atrophy and jerk nystagmus, with CT finding of a huge hyperdense right cerebellopontine angle mass, which showed contrast enhancement. The cerebellopontine angle is a site of meningioma although not as common as other notable locations such as the falx and over the convexities. Meningiomas on CT are spontaneously hyperdense in about 60% and show intense homogenous contrast enhancement except the uncommon cystic and densely calcified types. [7]

The primary diagnosis in one patient in this study was internal carotid artery aneurysm with the mass located in the anterior cranial fossa and showing contrast enhancement. About 90% of intracranial aneurysms arise from the carotid circulation and on CT appear as rounded enhancing lesions. [11]

Five patients had normal CT scans and other etiologies have to be considered in the differential diagnosis of optic atrophy in this group. Possible causes of optic atrophy include nonarteritic anterior ischemic optic neuropathy (NAION), and optic neuritis. These may however not show features on CT except in some cases evidence of change in size of the optic nerve, a common end point of optic neuropathy of various etiologies. Hickman et al. found that atrophic optic nerves had smaller cross-sectional area when compared with either the unaffected eye or eye of control subjects. [12]

Lee et al. in a retrospective observational case series reported patients with intracranial lesions who presented with acute optic neuropathy, thus masquerading as optic neuritis or NAION. The authors identified certain atypical features in patients initially misdiagnosed as optic neuritis or NAION which should warrant consideration for neuroimaging. For both optic neuritis and NAION these atypical features included a progressive course and optic atrophy at presentation. [13]

This article provides insight into a condition that has not received much attention with regard to CT findings in our center. To the best of our knowledge, this is the first such study and the paucity of data-informed our evaluation. From the foregoing it is important to note that CT may provide very useful information in patients with optic atrophy. However because there are many possible causes of optic atrophy, proper patient selection through history taking, clinical examination (including full neurological evaluation) and other investigations is mandatory to avoid unnecessary use of the technology.

 
  References Top

1.
Kanski JJ. Neuroophthalmology. In: Kanski JJ, editor. Clinical Ophthalmology. A Systematic Approach. 6 th ed. Philadelphia: Elsevier Limited; 2007. p. 786-837.  Back to cited text no. 1
    
2.
Behbehani R. Clinical approach to optic neuropathies. Clin Ophthalmol 2007;1:233-46.  Back to cited text no. 2
    
3.
Massoud TF, Cross JJ. The orbit. In: Adam A, Dixon AK, editors. Grainger and Allison's Diagnostic Radiology. 5 th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2008. p. 1393-1408.  Back to cited text no. 3
    
4.
Lee AG, Brazis PW, Garrity JA, White M. Imaging for neuro-ophthalmic and orbital disease. Am J Ophthalmol 2004;138:852-62.  Back to cited text no. 4
    
5.
Kim JD, Hashemi N, Gelman R, Lee AG. Neuroimaging in ophthalmology. Saudi J Ophthalmol 2012;26:401-7.  Back to cited text no. 5
    
6.
Fujimoto JG, Pitris C, Boppart SA, Brezinski ME. Optical coherence tomography: An emerging technology for biomedical imaging and optical biopsy. Neoplasia 2000;2:9-25.  Back to cited text no. 6
    
7.
Jager RH, Caseiras GB, Rich PM. Benign and malignant intracranial tumors in adults. In: Adam A, Dixon AK, editors. Grainger and Allison's Diagnostic Radiology. 5 th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2008. p. 2152-75.  Back to cited text no. 7
    
8.
Foroozan R. Chiasmal syndromes. Curr Opin Ophthalmol 2003;14:325-31.  Back to cited text no. 8
    
9.
Grimm MA, Hazelton T, Beck RW, Murtagh FR. Postgadolinium enhancement of a compressive neuropathy of the optic nerve. AJNR Am J Neuroradiol 1995;16:779-81.  Back to cited text no. 9
    
10.
Choi SH, Kwon BJ, Na DG, Kim JH, Han MH, Chang KH. Pituitary adenoma, craniopharyngioma, and Rathke cleft cyst involving both intrasellar and suprasellar regions: Differentiation using MRI. Clin Radiol 2007;62:453-62.  Back to cited text no. 10
    
11.
Rich PM, Jager RH. Cerebrovascular disease and nontraumatic intracranial hemorrhage. In: Adam A, Dixon AK, editors. Grainger and Allison's Diagnostic Radiology. 5 th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2008. p. 2176-217.  Back to cited text no. 11
    
12.
Hickman SJ, Wheeler-Kingshott CA, Jones SJ, Miszkiel KA, Barker GJ, Plant GT, et al. Optic nerve diffusion measurement from diffusion-weighted imaging in optic neuritis. AJNR Am J Neuroradiol 2005;26:951-6.  Back to cited text no. 12
    
13.
Lee AG, Lin DJ, Kaufman M, Golnik KC, Vaphiades MS, Eggenberger E. Atypical features prompting neuroimaging in acute optic neuropathy in adults. Can J Ophthalmol 2000;35:325-30.  Back to cited text no. 13
    


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