Optic Nerve Sheath Complex Research Articles

Practical Approach to Orbital Lesions by Anatomic Compartments.

A wide range of pathologic conditions can originate in the orbit. While it is common to approach the differential diagnosis based on disease categories, such as neoplastic and inflammatory, segmenting the orbit into anatomic compartments can direct the radiologist toward the most common pathologic conditions for each manifestation and space. The orbit can be divided into intraconal, conal, and extraconal compartments. Additionally, the optic nerve sheath complex and lacrimal apparatus can be partitioned into separate compartments due to their unique functions and pathologic features. By using this anatomic approach, the authors review the most common pathologic conditions affecting the orbit and discuss clinical and imaging findings that can guide the differential diagnosis for lesions with similar appearances. Published under a CC BY 4.0 license. Supplemental material is available for this article.

Normative measurements of orbital structures on magnetic resonance images; a cross-sectional study with mini review of the literature.

Awareness of normative values of extra orbital structures would provide useful information to interpret the radiological images better and use them for diagnostic purposes. This study aimed to reveal the average values of major extraocular structures measured on magnetic resonance images. In this retrospective cross-sectional study, magnetic resonance (MR) images of 256 orbits of 128 patients were re-interpreted regarding the measurements of major orbital structures. Extraocular muscles, superior ophthalmic vein, and optic nerve-sheath complex were measured on orbital MR images of these patients. The data distributions were presented by box-plot analyses for each parameter, and the measurement results were analyzed regarding gender and age groups. Lateral rectus muscle thickness (LR), inferior rectus muscle thickness (IR), globe position (GP), and interzygomatic line (IZL) values were higher in the male group than in the female group (p values were < 0.001, 0.003, 0.020, and < 0.001 respectively). LR, the thickness of the superior group muscles (SUP GR), IR, superior oblique muscle thickness (SOBL), and the thickness of optic nerve-sheath complex (ON) values indicated a significant relationship between age groups. There was a significant, positive, and low-level correlation between age and LR, SUP GR, and IR values (p values were < 0.001, 0.001, and < 0.001, respectively). This study provides quantitative data on normative values of orbital structures with gender and age group comparisons. Clinicians or surgeons can easily use the measured values to gather diagnostic information from the orbital region.

Measurement of Optic Nerve and Optic Nerve Sheath Diameter in MRI Brain

Introduction: Many diseases affect the size of the optic nerve and optic nerve sheath, measurement of which is important for the diagnosis and treatment of different pathologies of the brain and orbit. This study aimed to measure the diameter of the optic nerve and optic nerve sheath in MRI brain examinations. We also studied their variation according to age, gender, and laterality. Methods: This cross-sectional, quantitative study was performed in the Radiology Department of Tribhuvan University Teaching Hospital (TUTH). The diameter of the optic nerve and optic nerve sheath were measured in the T2 weighted Dixon Turbo Spin Echo axial images. The diameter was measured at the level of 3mm and 8mm behind the eye globe. The study was completed over a period of 3 months (August 2023 to October 2023). Results: The mean diameters of the optic nerve were 2.187±0.35 mm/2.14 ± 0.35 mm at 3 mm behind the eye globe and 2.056 ± 0.334 mm/2.11 ± 0.35 mm at 8 mm behind the globe for the right/left sides respectively. The optic nerve sheath of the right/left sides measured 4.50 ± 0.60 mm/4.46 ± 0.56 mm at 3 mm behind the eye globe and 4.16 ± 0.50 mm/ 4.14 ± 0.47 mm at 8mm behind the eyeball. Conclusion: The measurements for the diameter of the optic nerve and optic nerve sheath complex were similar in both the right and left eyes. There was no significant difference in optic nerve and optic nerve sheath diameters with the age and gender of the participants.

Abstract 162: Indirect Carotid Cavernous Fistula with Oculomotor Nerve Palsy Secondary to Trauma

Introduction Intriguing and uncommon, we present a fascinating case of carotid‐cavernous fistula (CCF) following ocular trauma. Delving into medical nuances and outcomes, this reported case offers valuable insights for clinicians and researchers in the field of ophthalmology and interventional Neurology. Methods An elderly patient presented to the emergency department with diplopia and left eyelid ptosis two weeks after left ocular trauma. The patient had exotropia and hypotropia with restricted movement in all directions but mostly during adduction and infraduction which led to the diagnosis of oculomotor nerve palsy. Computer Tomography (CT) head was obtained which showed mild left proptosis with the prominence of the optic nerve sheath complex, CT angiography revealed asymmetric prominence of the left ophthalmic veins and enlarged left cavernous sinus with outward convex borders. CT face and mandible with IV contrast did not show any bony deformity. The patient underwent cerebral angiography that showed an indirect type 4 cavernous‐carotid fistula. Results A precise incidence of CCF fistula has not been reported so far in the literature but it is estimated to be present in 0.2 % of patients presenting with traumatic brain injury with an increased incidence of 4 % with basilar skull fractures. They can occur spontaneously or following closed skull injury, skull base fractures, or iatrogenically after craniotomies, endoscopic transsphenoidal or sinus surgery, and endovascular procedures. They can be classified based on angiographic arterial architecture (direct or indirect), hemodynamics (high flow or low flow), and etiology (spontaneous or traumatic). Type A are direct fistulas, whereas types B, C, and D are indirect fistulas. Direct CCFs often present with pulsatile exophthalmos, orbital bruit, chemosis, diplopia, ocular redness, orbital pain, swelling, swishing or buzzing sounds, headache, or vision loss. Indirect low‐flow CCFs may be asymptomatic and insidious in onset and mostly present with chemosis and conjunctival injection. Conclusion Indirect carotid‐cavernous fistula rarely occurs secondary to a head trauma without any bony deformity and it's even rare to have an oculomotor nerve palsy on presentation, it should be considered as an etiology when evaluating patients for ocular nerve palsies.

Pictorial Review of Post COVID-19 Acute Invasive Fungal Sinusitis: Clinical Radiologists' Perspective.

Acute invasive fungal sinusitis (AIFS) is a rapidly progressive infection predominantly seen in immunocompromised patients. There is an increasing incidence of AIFS post COVID-19 infection. Yet, there is sparse literature regarding spectrum of cross-sectional imaging findings (CT and MRI) in these patients, which is prudent for appropriate timely surgical intervention. This study aims to highlight spectrum of imaging findings in patients with post-COVID-19 AIFS integrating the clinical details from presentation to follow-up. We retrospectively reviewed the demographics, clinical details and radiological imaging of 31 histopathological proven cases of post COVID-19 AIFS. MR and CT images of these patients were retrieved from the PACS and analysed. 90-day follow-up of these patients was obtained. Statistical analysis was performed using descriptive statistics. Cross-sectional imaging showed nasal cavity involvement in all patients, bilateral in (15, 48%) cases; predominant involvement of maxillary (31, 100%) followed by ethmoid sinuses (29, 93.5%) was seen. MR showed patchy/complete loss of normal mucosal enhancement in the turbinates and sinuses as predominant imaging finding. Maxillary sinus walls erosions were seen in 28 cases (90%). Rhino-orbital and rhino-orbito-cerebral mycosis was seen in 24 (77%) and 14 (45%) respectively. Optic nerve-sheath complex was involved in 15 (48%) cases. Cerebral involvement was seen in form of meningeal enhancement, cerebritis, ischemic changes, cavernous sinus and intracranial arterial thrombosis and aneurysms. Comprehensive knowledge of imaging features of AIFS and recognition of extent of their spread allows radiologists to play pivotal role in alerting the clinician for appropriate therapy to avoid protracted and fatal outcome.

Evaluation of optic nerve sheath complex by magnetic resonance imaging in patients with idiopathic normal pressure hydrocephalus

Background: We aimed to evaluate the optic nerve and optic nerve sheath diameter of patients with idiopathic normal pressure hydrocephalus with magnetic resonance imaging and to compare with the normal population. Methods: Magnetic resonance images and clinical records of the patients were retrospectively evaluated between 01.01.2015 and 01.01.2020. Twenty one patients in the normal pressure hydrocephalus group and 47 patients in the control group were included. Measurements were performed from the images obtained by creating multiplanar reconstructions from thin-slice Fast Spin Echo T2-weighted images. Measurements were made of optic nerve from the 3 mm posterior to the optic globe, on the plane which is oriented perpendicular to the nerve. Results: There was no difference between the two groups in terms of optic nerve diameters. Optic nerve sheath diameters are significantly higher in the normal pressure hydrocephalus group (p&lt;0.0001). Conclusion: Morphological analysis of the optic nerve sheath complex which contains cerebrospinal fluid will contribute to the diagnosis and understanding chronic effects of normal pressure hydrocephalus, a disease in which changes in brain compliance and cerebrospinal fluid absorption are suspected in its etiology.

Noninvasive intracranial pressure assessment by optic nerve sheath diameter: Automated measurements as an alternative to clinician-performed measurements.

Optic nerve sheath diameter (ONSD) has shown promise as a noninvasive parameter for estimating intracranial pressure (ICP). In this study, we evaluated a novel automated method of measuring the ONSD in transorbital ultrasound imaging. From adult traumatic brain injury (TBI) patients with invasive ICP monitoring, bedside manual ONSD measurements and ultrasound videos of the optic nerve sheath complex were simultaneously acquired. Automatic ONSD measurements were obtained by the processing of the ultrasound videos by a novel software based on a machine learning approach for segmentation of the optic nerve sheath. Agreement between manual and automated measurements, as well as their correlation to invasive ICP, was evaluated. Furthermore, the ability to distinguish dichotomized ICP for manual and automatic measurements of ONSD was compared, both for ICP dichotomized at ≥20 mmHg and at the 50th percentile (≥14 mmHg). Finally, we performed an exploratory subgroup analysis based on the software's judgment of optic nerve axis alignment to elucidate the reasons for variation in the agreement between automatic and manual measurements. A total of 43 ultrasound examinations were performed on 25 adult patients with TBI, resulting in 86 image sequences covering the right and left eyes. The median pairwise difference between automatically and manually measured ONSD was 0.06 mm (IQR -0.44 to 0.38 mm; p = 0.80). The manually measured ONSD showed a positive correlation with ICP, while automatically measured ONSD showed a trend toward, but not a statistically significant correlation with ICP. When examining the ability to distinguish dichotomized ICP, manual and automatic measurements performed with similar accuracy both for an ICP cutoff at 20 mmHg (manual: AUC 0.74, 95% CI 0.58-0.88; automatic: AUC 0.83, 95% CI 0.66-0.93) and for an ICP cutoff at 14 mmHg (manual: AUC 0.70, 95% CI 0.52-0.85; automatic: AUC 0.68, 95% CI 0.48-0.83). In the exploratory subgroup analysis, we found that the agreement between measurements was higher in the subgroup where the automatic software evaluated the optic nerve axis alignment as good as compared to intermediate/poor. The novel automated method of measuring the ONSD on the ultrasound videos using segmentation of the optic nerve sheath showed a reasonable agreement with manual measurements and performed equally well in distinguishing high and low ICP.

Computed Tomographic Thickness of Retrobulbar Optic Nerve Is Decreased in Glaucoma Patients and Is Negatively Correlated With Disease Severity.

Purpose The purpose of the study was toquantitatively measure the width of the retrobulbar optic nerve-sheath complex by computed tomography (CT) in glaucoma and evaluate its relationship with optic nerve changes and visual field loss parameters. Methods Sixty-six eyes of 33 patients with bilateral asymmetric glaucomatous optic nerve damage and 20 eyes of 20 age- and sex-matched control subjects without glaucoma were included. Axial retrobulbar optic nerve-sheath complex was measured by CT in the eyes with advanced glaucomatous damage (group 1); in the fellow eyes of the same patients with moderate glaucomatous damage (group 2); and in control subjects (group 3). Measurements were obtained at three different points: just behind the globe, near the optic canal, and in the middle. Results Mean age and sex distribution between groups were comparable (p>0.05). The mean diameters of the retrobulbar optic nerve at three measurement points in group 1 (4.00±0.42mm, 3.49±0.44mm, 3.18±0.45mm) were significantly (for each, p<0.05) lower when compared with the corresponding points of group 2 eyes (4.24±0.41mm, 3.77±0.47nn, 3.47mm±0.44mm) and normal controls (4.58±0.44mm, 4.15±0.45mm, 3.92±0.48mm). Optic disc changes and visual field parameters were negatively correlated with retrobulbar optic nerve diameter (for each, p < 0.05). Conclusion Radiological alterations of the retrobulbar optic nerve in glaucomatous eyes revealed a decreased optic nerve diameter which correlated with disease severity. Optic nerve dimensions below the lower limit for normal individuals may be considered pathologically reduced and, therefore, CT measurements of the retrobulbar nerve may be additive to the traditional triad of raised intraocular pressure, field defects, and optic disc changes in some cases with opaque optic media preventing the fundus examination or with optic nerve anomalies.

Orbital structures in the pediatric age group: A normative assessment using magnetic resonance imaging

PurposeMany diseases of traumatic, infectious, endocrinologic and neoplastic origin can lead to orbital involvement and related morphological changes. In the present study, we aimed to determine the age-based normal orbital measurements using magnetic resonance imaging (MRI) in pediatric patients. MethodsOur retrospective study included 186 patients with normal orbital MRI findings. The patients were divided into the following five groups based on their age. Group 1: 1–24 months; Group 2: 25–60 months; Group 3: 61–120 months; Group 4: 121–168 months; and Group 5: 169–216 months. Globe position relative to interzygomatic line (IZL) and orbital rim, optic nerve-sheath complex, extraocular muscle diameters, were measured. ResultsThe differences among the age groups for the distances between cornea and sclera in relation to IZL, for the distances between cornea and sclera relative to orbital rim, and for the extraocular muscle diameters were statistically significant. In terms of the extraocular muscle diameter, it was found that the thinnest muscle of all groups was the lateral rectus muscle while the thickest was the medial rectus muscle. ConclusionIn pediatric patients who were divided into five groups based on their age, the positions of bulbus oculi relative to IZL or orbital rim and the normal diameter ranges of extraocular muscles and of the optic nerve-sheath complex in orbital MRI were determined. We are of the opinion that the presence of such a scale could be a guide in the evaluation of orbital MRI in pediatric patients.

Normative orbital measurements in an Australian cohort on computed tomography

ABSTRACT Purpose To determine the normal diameters of the extraocular muscles (EOMs) and optic nerve sheath complex (ONSD) and correlate with patient demographics in an Australian cohort. Methods Consecutive patients who underwent contrast enhanced computed tomography (CT) orbits between December 2017 and March 2021 were included. Patients with bilateral disease, previous orbital surgery, or poor scan quality were excluded. Normal orbit was used in patients with unilateral orbital disease. Results Two hundred one orbits from 201 patients were included. Normal measurements (mean ± SD) were as follows: medial rectus (MR) 4.22 0.56 mm; inferior rectus (IR) 4.20 0.70 mm; lateral rectus (LR) 3.40 0.56 mm; superior muscle group (SMG) 4.13 0.72 mm; superior oblique (SO) 2.60 0.43 mm; inferior oblique (IO) on quasi-sagittal plane 2.19 0.42 mm, and the ONSD 5.62 0.82 mm. The mean diameters of the LR, SMG, IR, SO, and ONSD were significantly larger in male than female patients (p < .05). Statistically significant correlation was found between age and the diameters of the LR (r = 0.29, p < .01), SMG (r = 0.22, p < .01), IO on a coronal plane (r = −0.18, p < .01), and ONSD (r = 0.16, p = .02). Conclusion This normative data may be used to diagnose pathological enlargement of the optic nerve and extraocular muscles, including involvement of the oblique muscles.

Low-Field Magnetic Resonance Imaging Findings in 18 Dogs With Presumed Optic Neuritis.

Canine optic neuritis has been attributed to a focal or disseminated form of granulomatous meningoencephalitis (GME) amongst other etiologies. Magnetic resonance imaging (MRI) has been proven to help differentiate the structures within the optic nerve sheath and therefore could aid the diagnosis of optic neuritis in dogs. The objectives of this study were to describe and compare the MRI abnormalities affecting the optic nerve sheath complex and optic chiasm in dogs with clinically suspected optic neuritis as a component of meningoencephalitis of unknown etiology (MUE) or as an isolated form (I-ON). Retrospective evaluation of patient details, clinical signs, cerebrospinal fluid (CSF) analysis, and MRI findings of dogs with clinically suspected optic neuritis between January 2011 and May 2018 was performed. Eighteen dogs met the inclusion criteria. MRI findings included contrast enhancement of both optic nerves (11/18) and optic chiasm (6/18), changes within the CSF volume surrounding the optic nerve (10/18), changes to the optic disc (10/18), changes of size or signal affecting the optic chiasm (10/18), changes in the Short TI inversion recovery (STIR) signal of the optic nerve (7/15), retrobulbar changes (3/18), and concurrent brain lesions (13/18). A variety of subtle MRI features may indicate optic nerve involvement and low-field MRI is a sensitive method to detect changes within the optic nerve sheath complex in dogs with optic neuritis as an isolated form (I-ON) or as an extension of MUE.

Normative Orbital Measurement Based on Computed Tomography Imaging in Tertiary Care Hospital, Bangalore, Karnataka

Introduction: The orbit is an anatomically complex region. Clear idea of the normal orbital measurements is needed for the diagnosis and management of the various diseases that may affect the orbit like optic neuritis, optic nerve glioma, meningioma, proptosis and exophthalmos. Aim: To evaluate normative orbital measurement at tertiary care hospital in Bangalore, Karnataka in Indian population based on Non Enhanced Computed Tomography (NECT) imaging. Materials and Methods: A cross-sectional observational study of 100 patients referred to a tertiary care centre for NECT of the brain for diseases other than those of the orbits was conducted. Patients having any orbital disorder, surgery or trauma and having metallic implants were excluded from the study. The patients of all age groups and either sex were included. The horizontal orbital diameter, vertical orbital diameter, orbital index, optic nerve complex, globe position, interorbital diameter and interzygomatic line measurements were calculated for 100 patients, i.e., total of 200 orbits using both axial and direct coronal CT images. Mean measurements of these parameters were calculated. Scans were performed on Siemens Somatom Perspective 128 slice multi- detector CT scanner. All statistical analysis was performed using Statistical Package for The Social Sciences (SPSS) for windows software (SPSS Inc. Illinois, Chicago, USA). Results: The mean orbital index was 118.6 and 118.3 for right and left orbit, respectively. It was derived from mean horizontal orbital diameter of 32.5 mm and 31.7 mm of right and left orbit, respectively and mean vertical orbital diameter of 38.4 mm and 37.4 mm of right and left orbit, respectively. Mean optic nerve sheath complex diameter was 5.2 mm and 5.4 mm for right and left orbit, respectively, while mean globe position measurements 6.7 mm and 6.8 mm of right and left orbit, respectively. Average interorbital distance was 22.9 mm and average interzygomatic distance 97.1 mm. Conclusion: The present study has given normative mean measurements for various orbital structures that are essential to ophthalmologists and radiologists to differentiate normal from abnormal dimensions which is likely to be helpful in accurate assessment of various orbital pathologies.

Computed tomography imaging-based normative orbital measurement in Indian population.

Purpose:This study aims to evaluate normal orbital structures with nonenhanced computed tomography (NCCT) and determine normative data for the Indian population.Methods:CT images of the orbits of 100 patients were retrospectively reviewed on a work station to record the normative data of the orbits. Clinical details of all patients were reviewed to ensure that they did not have ocular/orbital diseases. Both axial and coronal images were utilized to record the data.Results:The mean age of the population evaluated was 34.07 years, with male to female ratio of 1.77. The average orbital index for the left orbit was 97 and for the right side was 103. The mean thickness of left inferior rectus, lateral rectus, medial rectus, and the superior rectus was 3.36 mm, 3.14 mm, 3.80 mm, and 3.75 mm, respectively. The right inferior rectus, lateral rectus, medial rectus, and the superior rectus measured 3.46 mm, 3.14 mm, 3.83 mm, and 3.78 mm, respectively. The optic nerve sheath complex diameter varied between 3.05 mm and 7.17 mm for the left eye and 3.05 mm and 7.0 mm for the right eye.Conclusion:The study provides normative data on various orbital structures in an Indian population. This data is likely to be useful for diagnosing various orbital pathologies and in planning surgical orbital procedures.

Orbital tumours and tumour-like lesions: exploring the armamentarium of multiparametric imaging.

Although the orbit is a small anatomical space, the wide range of structures present within it are often the site of origin of various tumours and tumour-like conditions, both in adults and children. Cross-sectional imaging is mandatory for the detection, characterization, and mapping of these lesions. This review focuses on multiparametric imaging of orbital tumours. Each tumour is reviewed in relation to its clinical presentation, compartmental location, imaging characteristics, and its histological features. We herein describe orbital tumours as lesions of the globe (retinoblastoma, uveal melanoma), optic nerve sheath complex (meningioma, optic nerve glioma), conal-intraconal compartment (hemangioma), extraconal compartment (dermoid/epidermoid, lacrimal gland tumours, lymphoma, rhabdomysarcoma), and bone and sinus compartment (fibrous dysplasia). Lesions without any typical compartmental localization and those with multi-compartment involvement (veno-lymphatic malformation, plexiform neurofibroma, idiopathic orbital pseudotumour, IgG4 related disease, metastases) are also reviewed. We discuss the role of advanced imaging techniques, such as MR diffusion-weighted imaging (DWI), diffusion tensor imaging, fluoro-2-deoxy-D-glucose positron emission tomography CT (FDG-PET CT), and positron emission tomography MRI (MRI PET) as problem-solving tools in the evaluation of those orbital masses that present with non-specific morphologic imaging findings.Main messages/Teaching points• A compartment-based approach is essential for the diagnosis of orbital tumours.• CT and MRI play a key role in the work-up of orbital tumours.• DWI, PET CT, and MRI PET are complementary tools to solve diagnostic dilemmas.• Awareness of salient imaging pearls and diagnostic pitfalls avoids interpretation errors.

Monocular Vision Loss and Headache in a 60-Year-Old Liver Transplant Patient

Monocular Vision Loss and Headache in a 60-Year-Old Liver Transplant Patient

Normative Measurements of the Chinese Extraocular Musculature by High-Field Magnetic Resonance Imaging

To establish the normal measurements of diameter and cross-sectional area of the Chinese extraocular muscles (EOMs) and optic nerve-sheath complex (ON) as seen on high-field (3-Tesla; 3T) magnetic resonance imaging (MRI). Coronal 3T MRI of the orbit (TR, 700 ms; TE, 15 ms; FOV, 160 mm; matrix, 256 x 256; slice thickness, 1 mm; and slice gap, 0) was performed on 80 normal Chinese volunteers. T1-weighted images were analyzed with computer-assisted segmentation. The diameter and the cross-sectional area of EOMs and the ON were measured from the image plane at the posterior aspect of the globe and at 7 mm behind the globe. The maximum diameter of EOM was measured from their respective reconstructed images. The normal measurement (mean +/- SD) of diameter at the posterior aspect of the globe: medial rectus (MR), 3.6 +/- 0.4 mm; inferior rectus (IR), 3.7 +/- 0.8 mm; lateral rectus (LR), 2.3 +/- 0.5 mm; superior oblique (SO), 2.4 +/- 0.6 mm; and the ON, 5.4 +/- 0.7 mm. The normal measurement of diameter 7 mm behind the globe: MR, 3.2 +/- 0.6 mm; IR, 3.9 +/- 0.8 mm; LR, 4.0 +/- 0.8 mm; SO, 2.2 +/- 0.7 mm; and ON, 4.2 +/- 0.5 mm. The normal measurement of cross-sectional area at the posterior aspect of the globe: superior muscle group (SMG), 28.2 +/- 6.5 mm(2); MR, 25.5 +/- 3.2 mm(2); IR, 26.9 +/- 7.2 mm(2); LR, 17.3 +/- 3.9 mm(2); SO, 10.5 +/- 3.5 mm(2); and ON, 27.6 +/- 6.1 mm(2). The normal measurement of cross-sectional area 7 mm behind the globe: SMG, 24.1 +/- 6.6 mm(2); MR, 19.1 +/- 4.6 mm(2); IR, 29.5 +/- 6.6 mm(2); LR, 32.3 +/- 6.5 mm(2); SO, 9.7 +/- 3.9 mm(2); and ON, 17.1 +/- 2.9 mm(2). The normal measurement of maximum diameter: SMG, 4.8 +/- 1.1 mm; MR, 5.1 +/- 0.9 mm; IR, 5.4 +/- 1.0 mm; and LR, 4.5 +/- 0.9 mm. The Chinese 3T MRI EOMs and ON normative data may be useful in determining pathologic enlargement of the EOMs and ON in various orbital conditions. (ClinicalTrials.gov number, NCT00348413.).

MAGNETIC RESONANCE IMAGING OF THE CANINE OPTIC NERVE

We describe the magnetic resonance (MR) imaging aspects of normal canine optic nerve, the diameter of the optic nerve as measured on MR images, and optimal MR sequences for the evaluation of the optic nerve using a 0.2T MR unit. Three millimeter contiguous slides of the normal canine orbital region were acquired in transverse and dorsal oblique planes using a variety of tissue weighting sequences. It was apparent that detailed anatomic assessment of the optic nerve can be performed with low-field MR imaging, but none of the sequences provided unequivocal superior image quality of the optic nerve. The mean diameter of the optic nerve sheath complex was 3.7mm and of the optic nerve 1.7 mm. The intraorbital and intracanalicular parts of the optic nerve are consistently visible and differentiation between the optic nerve and optic nerve sheath complex is possible using low-field MR systems.

Normative measurements of Korean orbital structures revealed by computerized tomography.

The purposes of this study were to establish criteria for the diameters of normal extraocular muscles, the width of the optic nerve, and the globe position as revealed by CT, and to investigate the effects of age and sex on these parameters in the Korean population. Diameters of extraocular muscles (medial, lateral, superior complex, and inferior rectus), distance from the interzygomatic line to the posterior margin of the globe, width of the optic nerve-sheath complex, and length of the interzygomatic line were calculated for 214 patients on axial and direct coronal CT images, and the effects of age and sex were analyzed. Normal range for the diameters as given by mean+/-2SDs of extraocular muscles were medial rectus, 2.2--5.4 mm; lateral rectus, 2.1--4.9 mm; inferior rectus, 2.5--5.7 mm; and superior complex group, 2.6--6.4 mm. The mean optic nerve-sheath complex was 4.1 mm and the values ranged from 2.9 mm to 5.3 mm. The mean length of the interzygomatic line was 103.8 mm. The normal posterior position of the globe as here designed was 11.2 mm behind the interzygomatic line (range, 6.4--15.3 mm). All parameters under study were a little larger in males than females. Statistically, however, there was no significant difference between males' and females' results, nor between the various age groups (p>0.05). Our CT results may help clinical ophthalmologists to accurately assess enlargement of the extraocular muscles and the optic nerve as well as aiding in the evaluation of exophthalmos.

Optic Neuritis in Herpes Zoster Ophthalmicus

Background: Optic neuritis in herpes zoster ophthalmicus (HZO) has been reported rarely. We report two cases of HZO optic neuritis with detailed magnetic resonance imaging study and treatment responses. Cases: One patient presented with anterior optic nerve involvement, and the second presented with retrobulbar optic neuritis. Contrast enhanced T 1-weighted images were obtained in these 2 patients. Intravenous acyclovir and oral prednisolone were given simultaneously. Observations: Magnetic resonance imaging revealed peripheral enhancement of the optic nerve sheath complex on T 1-weighted scan. Both patients recovered their vision within 3 months following the start of treatment. Conclusions: Magnetic resonance imaging is helpful for the diagnosis of HZO optic neuritis. Systemic acyclovir and steroid are effective in the treatment of HZO optic neuritis.

MR Imaging of the Orbital Apex: Anatomy and Pathology

The apex of the orbit is basically formed by the optic canal, the superior orbital fissure, and their contents. Space-occupying lesions in this area can result in clinical deficits caused by compression of the optic nerve or extraocular muscles. Evenvascular changes in the cavernous sinus can produce a direct mass effect and affect the orbit a p ex. When pathologic changes in this region is suspected, contrast-enhanced MR imaging with fat saturation is very useful. According to the anatomic regions from which the lesions arise, they can be classified as belonging to one of five groups; lesions of the optic nerve-sheath complex, of the conal and intraconal spaces, of the extraconal space and bony orbit, of the cavernous sinus or diffuse. The characteristic MR findings of various orbital lesions will be described in this paper.