Dilation Of Optic Nerve Sheath Research Articles

Dilated Optic Nerve Sheath in Mucopolysaccharidosis I: Common and Not Necessarily High Intracranial Pressure.

Hydrocephalus is one of the earliest manifestations of mucopolysaccharidosis I-Hurler syndrome, and delayed treatment of hydrocephalus can lead to neurocognitive delay or even death. Optic nerve sheath diameter has been established as a noninvasive measurement to detect elevated intracranial pressure. This study aimed to establish correlations between optic nerve sheath diameter and opening pressure. Forty-nine MR images and opening pressures in patients with mucopolysaccharidosis I-Hurler syndrome were retrospectively reviewed from 2008 to 2020. The optic nerve sheath diameter was measured 3 mm posterior to the posterior margin of the globe (retrobulbar) and 10 mm anterior to the optic foramen (midpoint segment), and the average was taken between the 2 eyes. Opening pressure was measured with the patient in the lateral decubitus position with controlled end-tidal CO2 on the same day as the MR imaging. The average retrobulbar optic nerve sheath diameter was 5.33 mm, higher than the previously reported measurement in healthy controls, in patients with idiopathic intracranial hypertension, and there was a positive correlation between age and the optic nerve sheath diameter measured at the retrobulbar or midpoint segment (retrobulbar segment, R 2 = 0.27, P < .01; midpoint segment, R 2 = 0.20, P < .01). However, there was no correlation between retrobulbar or midpoint segment optic nerve sheath diameter and opening pressure (retrobulbar segment, R 2 = 0.02, P = .17; midpoint segment, R 2 = 0.03, P < .12). This study shows a higher average optic nerve sheath diameter in patients with mucopolysaccharidosis I-Hurler syndrome than in healthy controls regardless of the location of the measurement. However, the degree of optic nerve sheath dilation does not correlate with opening pressure, suggesting that increased optic nerve sheath diameter is an ocular manifestation of mucopolysaccharidosis I-Hurler syndrome itself rather than a marker of elevated intracranial pressure.

Time course of optic nerve sheath dilation: In vitro response characteristics to controlled pressure elevations

BackgroundOptic nerve sheath (ONS) dilation indicates intracranial pressure elevation under clinical conditions but limited data exist with regard to the dynamics of sheath expansion. ObjectiveTo assess the time course of ONS widening and its stability under controlled pressure conditions in vitro. MethodsPre-defined pressure steps up to 65 mmHg were applied to the perineural space of ex-vivo human optic nerves (n = 16). Using ultrasound, the optic nerve sheath diameter (ONSD) was monitored over 500 s. Re-tests at low-pressure levels concluded each experimental series. ResultsIn most cases, 50% of the total diameter-change were achieved within 50 s after pressure onset and 95% of the maximal diameter after 200 s. The diametric gains in each experiment were strongly correlated with the applied pressure levels (coefficient of variance 0,96) within preparations with variability of the transfer function across preparations. The time course of the dilation was found to follow an approximate natural logarithmic function (R2 = 0.93–0.99). The re-test condition revealed unchanged time course properties (5% significance level) despite starting regularly from a higher baseline-diameter after preceding exposures. ConclusionsONS dilation commences rapidly after pressure exposure with a predictable time course over 3–4 min. Elasticity changes presumably affecting trabecular structures cause upward shifts of the optic nerve sheath pressure response. Clinically, ONSD shifts should be considered in serial measurements for increasing intracranial pressure monitoring, but relevant response delays are absent for lower or higher changes of intracranial pressure.

Intracranial pressure and visual acuity: The final frontier?

Intracranial pressure and visual acuity: The final frontier?

Bedside Optic Nerve Ultrasonography for Diagnosing Increased Intracranial Pressure: A Systematic Review and Meta-analysis.

Optic nerve ultrasonography (optic nerve sheath diameter sonography) has been proposed as a noninvasive, quick method for diagnosing increased intracranial pressure. To examine the accuracy of optic nerve ultrasonography for diagnosing increased intracranial pressure in children and adults. 13 databases from inception through May 2019, reference lists, and meeting proceedings. Prospective optic nerve ultrasonography diagnostic accuracy studies, published in any language, involving any age group or reference standard. 3 reviewers independently abstracted data and performed quality assessment. Of 71 eligible studies involving 4551 patients, 61 included adults, and 35 were rated as having low risk of bias. The pooled sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of optic nerve ultrasonography in patients with traumatic brain injury were 97% (95% CI, 92% to 99%), 86% (CI, 74% to 93%), 6.93 (CI, 3.55 to 13.54), and 0.04 (CI, 0.02 to 0.10), respectively. Respective estimates in patients with nontraumatic brain injury were 92% (CI, 86% to 96%), 86% (CI, 77% to 92%), 6.39 (CI, 3.77 to 10.84), and 0.09 (CI, 0.05 to 0.17). Accuracy estimates were similar among studies stratified by patient age, operator specialty and training level, reference standard, sonographer blinding status, and cutoff value. The optimal cutoff for optic nerve sheath dilatation on ultrasonography was 5.0 mm. Small studies, imprecise summary estimates, possible publication bias, and no evaluation of effect on clinical outcomes. Optic nerve ultrasonography can help diagnose increased intracranial pressure. A normal sheath diameter measurement has high sensitivity and a low negative likelihood ratio that may rule out increased intracranial pressure, whereas an elevated measurement, characterized by a high specificity and positive likelihood ratio, may indicate increased intracranial pressure and the need for additional confirmatory tests. None. (PROSPERO: CRD42017055485).

Observational Cohort Confirms Optic Nerve Sheath Dilation Post Valsalva in those with Prior mTBI

ObjectiveThe aim of this study was to prospectively assess the effect of mTBI on optic nerve sheath (ONS) dilation post transient increase in ICP.BackgroundOur cross-sectional study demonstrated that those with a history of mild traumatic brain injury (mTBI) at least one year following their injury have significant ONS dilation after Valsalva as measured by ultrasound compared to those without a history of mTBI. This showed that ONS dilation after Valsalva could be a potential non-invasive method of identifying individuals with a history of mTBI but needed prospective confirmation.Design/MethodsMixed martial arts competitors that did not have ONS dilation of more than 0.5 mm on Valsalva, a value set based on cross-sectional study results, were enrolled in this prospective observational cohort study. Baseline pre and post-Valsalva optic nerve sheath diameter (ONSD) measurements were obtained for screening purposes. Additional ONSD measurements were collected after 1, 6, and 12 months of enrollment. Participants were monitored for suspected mTBI via self-report and monthly calls. Within two weeks following a physician-confirmed mTBI, the participant was scanned.ResultsTwenty-one participants were enrolled and 16 (76.2%) were followed up with for one year. Three participants experienced a mTBI. Scans conducted within two weeks of the mTBI showed no significant ONS dilation post-Valsalva, which was most likely due to an elevated pre-Valsalva value compared to the participant’s baseline and one-year pre-Valsalva ONSD. At the one-year testing, individuals in the mTBI group had a significantly larger post than pre-Valsalva ONSD and a significant ONS dilation post-Valsalva (n = 3, mean = 1.01mm) when compared those who did not experience a mTBI (n = 13, mean = −0.12mm; p = 0.0032).ConclusionsThis study confirms the cross-sectional study results that following a mTBI, the ONS dilates significantly following Valsalva. Further exploration is needed into exactly when this dilation is seen during a patient’s recovery and why it seems delayed.

Increased Intracranial Pressure Damages Optic Nerve Structural Support.

Optic nerve sheath diameter (ONSD) is used clinically as a noninvasive measure for elevated intracranial pressure (ICP). This study had two purposes: to investigate the immediate effects optic nerve sheath (ONS) dilation post-ICP increase on trabecular fibers connecting the optic nerve to the ONS and to document any changes in these fibers 30 days post-increased ICP. In a swine model, ICP was increased by inflating a Foley catheter balloon in the epidural space. Three control pigs received the catheter insertion without inflation (no increase in ICP) and four experimental pigs received the catheter with inflation (increased ICP). The control and two randomly selected pigs with increased ICP were euthanized immediately after the procedure. The two other pigs were euthanized 30 days post-catheter inflation. For all pigs, the ONS was removed and imaged using a scanning electron microscope, calculating percent porosity values. Porosity values for the experimental groups (Immediately measured [IM] μ = 0.5749; Delayed measured [DM] μ = 0.5714) were larger than the control group (μ = 0.4336) and statistically significant (IM vs. Control, p = 0.0018; DM vs. Control, p = 0.0092). There was no significant difference (p = 0.9485) in porosity of the DM group when compared with the IM group. This study demonstrated that the trabecular fibers immediately post-increased ICP (ONS dilation) were more porous than the control and remained statistically different (more porous) after 30 days. These results suggest a structural change that occurs in the ONS with elevations in ICP.

113 Ultrasound of the Optic Nerve Sheath as an Indicator of Mild Traumatic Brain Injury: Animal Model Provides Anatomical Basis

With no definitive method for diagnosis, many cases of mild traumatic brain injury (mTBI) receive suboptimal clinical management. Since emergency physicians and emergency medical services personnel are on the front lines with regard to mTBI, a tool for more accurate and timely indication of mTBI could improve diagnosis and management of mTBI in acute settings. Clinically, we have begun to validate that ultrasound measurements of optic nerve sheath dilation can be used to indicate mTBI. The objective of this study was to investigate the anatomical mechanism behind what has been observed clinically. More specifically, we evaluated the effect of increased intracranial pressure (ICP) on the fiber bundles connecting the optic nerve to the optic sheath in a swine model. Four experimental, 2 sham, and 4 normal swine were used in this study. In the experimental swine models, increased ICP was induced by passing a Foley catheter through a drilled opening into the epidural space and inflating a balloon. ICP was monitored continuously. For all animals, a section of optic nerve sheath with the intact nerve was removed after euthanasia and enucleation. The tissue was fixed overnight in paraformaldehyde and glutaraldehyde in a sodium cacodylate buffer, postfixed in osmium tetroxide in a sodium cacodylate buffer, dehydrated with a graded ethanol series, and critical point dried with carbon dioxide. The dried control and experimental model sections were mounted and imaged using a scanning electron microscope (SEM). Images of the trabecular meshwork were taken radially around the optic nerve at several magnifications. The images were segmented and analyzed using the ImageJ plug-in DiameterJ. Segmentation quality was confirmed using image subtraction of the original image from the segmented image and vice versa. All images had false positive and false negative total percentages of less than 5% of all pixels. Image overlays of the segmented and original images confirmed this qualitatively. This is an ongoing study. Image processing and analysis is still in progress. For a normal and an experimental animal, mean and median fiber bundle diameters were recorded for a total of 61 images. Thirty (49.1%) of the images analyzed were from the control sample and 31 (50.9%) were from the experimental sample. An analysis of variance found that both the mean (.52 μm) and median (.62 μm) fibrous bundle diameters were significantly different (ie, smaller) for the experimental model as compared to the mean (.73 μm) and median (.85 μm) fibrous bundle diameters for the control (p<.0001). The relationship between mean and median fibrous bundle diameters and sample (control or experimental) was not significantly correlated to radial location (relative to the optic nerve) or magnification of the image based on analyses of covariance. Thus far, this research demonstrates that in a swine model the fibrous bundles of the optic sheath’s connections to the optic nerve are statistically different (smaller) after exposure to increased ICP. We anticipate similar results from the other samples. Future research will evaluate if the thinning of fibrous bundles between optic sheath and optic nerve is caused by increased ICP. This will be accomplished by increasing the sample size and using other methods to induce increased ICP.

Detecting optic nerve head swelling on ultrasound and optical coherence tomography in children and young people: an observational study

BackgroundFollowing high-profile cases, referrals for evaluation of ‘suspicious optic discs’ to eye clinics in the UK have sharply increased, asking ophthalmologists to reliably distinguish between true and pseudopapilloedema. Optic nerve...

Spontaneous Cerebrospinal Fluid Rhinorrhea: Association with Body Weight and Imaging Data.

Objective Spontaneous cerebrospinal fluid rhinorrhea (SCSFR) might be the only clinical manifestation of idiopathic intracranial hypertension (IIH), which has been historically related to overweight. Our goal was to search for an association between SCSFR and increased body weight on the one hand and SCSFR and imaging findings suggestive of IIH on the other hand. Materials and Methods We retrospectively collected clinical and radiological data of patients operated on endoscopically for SCSFR in our institution from 1993 to 2013. Analyzed factors were body mass index (BMI), extended sphenoid sinus pneumatization on computed tomography, and empty sella and distention of the optic nerve sheath on magnetic resonance imaging. Results There were 15 patients: 8 females/7 males; mean age 50 years. Primary surgical success rate was 86.7%. Regarding body weight, 80% were overweight (BMI ≥ 25) versus 32% in the French general population ( p < 0.001). Among patients with SCSFR, 20% were obese (BMI ≥ 30) versus 15% in French individuals without SCSFR ( p = 0.483). Increased pneumatization of sphenoid sinuses was observed in 92.9 versus 27.5% in the general population ( p < 0.0001). Empty sella was found in 46.2 versus 3% in the general population ( p < 0.00001). Dilation of the optic nerve sheath was observed in 46.2 versus 15% in the general population ( p < 0.01). Conclusion We found statistically significant associations between SCSFR and overweight, increased pneumatization of sphenoid sinuses, empty sella, and dilation of optic nerve sheath, but not with obesity, which did not have any additional impact of CSF leak than did overweight.

Morphometric MRI changes in intracranial hypertension due to cerebral venous thrombosis: a retrospective imaging study

To evaluate whether some magnetic resonance imaging (MRI) signs suggesting idiopathic intracranial hypertension (IIH) could also be found in intracranial hypertension (IH) due to cerebral venous thrombosis (CVT) and to assess their possible contribution to diagnosing this disorder. Thirty-one patients with IH due to CVT were evaluated prospectively using MRI. A group of 33 age- and sex-matched healthy volunteers served as controls. The optic nerve and sheath, pituitary gland, and ventricles were assessed. The prevalence of each imaging feature was compared between the two groups. Optic nerve sheath (ONS) dilatation and decreased pituitary gland height were the most valid signs suggesting IH in CVT patients: sensitivity 70.97% and 87.1%, respectively; specificity 96.97% and 72.73%, respectively; area under the curve 0.840 and 0.809, respectively. The MRI finding that showed the strongest association with IH in CVT patients was ONS dilatation (odds ratio 78.5). The combination of T1-weighted volumetric MRI and magnetic resonance venography could be helpful for diagnosing IH with CVT. Abnormalities of the ONS and the pituitary gland were reliable diagnostic signs for IH due to CVT.

Optic nerve sonography in the diagnostic evaluation of pseudopapilledema and raised intracranial pressure: a cross-sectional study.

Introduction. Differentiating pseudopapilledema from papilledema which is optic disk edema and a result of increased ICP (intracranial pressure) is important and can be done with noninvasive methods like orbital ultrasound examination. Method. This was a cross-sectional study in which patients with optic nerve head swelling were referred for LP exam after optic nerve head swelling diagnosis confirmation and having normal brain imaging (CT scan). Before LP (lumbar puncture) exam the patients were referred for optic nerve ultrasound test of both eyes. Results. Considering 5.7 mm as the upper limit for normal ONSD (optic nerve sheath diameter), sensitivity and negative predictive value of optic sonography in diagnosis of pseudopapilledema are 100% for both eyes. Calculated accuracy validity of ONSD measurement in detecting pseudopapilledema is 90% for the right eye and 87% for the left eye. Conclusion. Our study demonstrated a close correlation between optic nerve sheath dilation on ocular ultrasound and evidence of elevated ICP with optic disk swelling. With the aid of noninvasive diagnostic tests we can avoid unnecessary concerns along with expensive and invasive neurological investigations while targeting the correct diagnosis in bilateral optic disk swelling. Our study showed optic nerve sonography as a reliable diagnostic method for further usage.

Spontaneous Cerebrospinal Fluid Rhinorrhea: Correlation with Body Weight and Radiological Data

Objectives: Search for correlations between spontaneous cerebrospinal fluid rhinorrhea (SCSFR) and overweight/obesity and imaging data. Methods: Retrospective study of patients with SCSFR operated in a tertiary center (1993-2013). A 2-sided test was used for statistics. Results: There were 17 patients with SCSFR: 9 females/8 males; mean age 45 years (range, 3-84 years). Abnormalities on computed tomography (CT) were: bone defect (12), sinus opacity (11). Abnormalities on magnetic resonance imaging (MRI): continuity with meninges (7), meningocele (6), empty sella (6), dilation of optic nerve sheath (6), pneumocephalus (1). Patients underwent endoscopic closure of osteo-meningeal defect with fat. Primary success rate was 13 out of 17 (76.5%). Regarding body mass index (BMI), 12 patients out of 17 (70.6%) were overweight (BMI ≥25) versus 32% in the French general population ( P = .001). Among patients with SCSFR and overweight, 3 out of 12 (25%) were obese (BMI ≥30) versus 15% in overweight individuals ( P = .483). Increased pneumatization of sinuses was observed in 15 out of 17 (88%) versus 35% in the general population ( P = .00009). Empty sella was found in 6 out of 17 (35.3%) versus 5.5% in the general population ( P = .0002). Dilation of optic nerve sheath was observed in 6 out of 17 (35.3%) versus 10% in the general population ( P = .0047). Conclusions: We found statistically significant correlations between SCSFR and overweight individuals, increased pneumatization of sinuses, empty sella, and dilation of optic nerve sheath, but not with obesity. This could be due to the small number of patients in this study and a weak statistical power for obesity. The 2-sided test is ideal for small samples of patients, but a greater number is needed in the future to confirm these preliminary results.

83 Time Correlation of Optic Nerve Sheath Diameter to Increasing Intracranial Pressure in a Cadaveric Model

Ultrasound (US) evaluation of the optic nerve sheath width (diameter) has been shown to correlate with intracranial pressure. Normal optic nerve sheath diameter as measured 3 mm distal to the posterior globe is less than 5 mm. As intracranial pressure increases, the optic nerve sheath dilates. However, the speed at which the optic nerve sheath dilation occurs is unknown. Our objective was to determine the speed and the extent of dilation of the optic nerve sheath using a cadaveric model with increasing intracranial pressure. This was a prospective observational cadaveric trial comparing 2D US measurements of the optic nerve sheath to invasive intracranial monitoring of the intracranial space. Using an intracranial monitoring device, 5 ml of saline was instilled in the intracranial space while simultaneous measurements of the optic nerve sheath diameter were made using a SonoSite Micromaxx US system and a L38 (10 - 5 MHz) linear transducer. Measurements of the intracranial pressure were noted as changes from the baseline intracranial pressure. US measurements of the optic nerve sheath were taken in a single plane 3 mm distal to the posterior globe. US measurements were made every 5 minutes after fluid instillation until no further changes in the optic nerve sheath were detected. Three measurements of the optic nerve sheath were averaged for each measurement trial. The intracranial pressure increased immediately after fluid instillation into the intracranial space. However, as the fluid redistributed within the intracranial space, the pressure would decrease and would reach a steady-state baseline within the first 5 minutes. The optic nerve sheath diameter changed immediately with instillation of fluid into the intracranial space. There was little change in the optic nerve sheath diameter as the fluid redistributed within the intracranial space. However, the amount of change in the optic nerve sheath diameter was not proportional to the amount of fluid instilled into the intracranial space or to the intracranial space measurements. Figure 1 demonstrates the change in optic nerve sheath diameter and intracranial pressure values for 1 hour duration of the experiment. Although the change in optic nerve sheath dilation is simultaneous with intracranial pressure increase, the behavior of optic nerve sheath dilation (varies from 4.2 mm to 5.3 mm) is less dynamic than change in intracranial pressure levels (4 cm/H¬2O to 34 cm/ H¬2O). The change in the optic nerve sheath diameter is simultaneous with the increase in the intracranial pressure. However, the optic nerve sheath dilation is less dynamic compared to change in the intracranial pressure level.

Development of optic disc drusen in familial pseudopapilloedema: a paediatric case series

Sir, Optic disc swelling in a child, with no other features suggestive of raised intracranial pressure is a challenging clinical scenario. These children frequently undergo invasive investigations, such as neuroimaging and lumbar puncture, even though the clinical suspicion of serious pathology is low. In this study, we report a new clinical presentation of benign optic disc swelling in five siblings of two families, where optic disc drusen were not present at first presentation, but developed many months later as shown on serial B-scan ultrasonography. We have termed this unusual presentation ‘familial pseudopapilloedema'. Five children (two siblings from one family and three siblings from another family) underwent examination and B-scan ultrasonography at first presentation and at all subsequent examinations. Age range at first presentation was 18 months to 12 years with a mean of 6.5 years. The male to female ratio was 4 : 1. All five children had clinically apparent optic disc swelling without other ophthalmoscopic features of papilloedema (retinal nerve fibre layer swelling, surrounding disc haemorrhages, cotton wool spots, hyperemia, venous congestion, Patton's lines, or exudates1). None had any symptoms suggestive of raised intracranial pressure, other neurological disease, or systemic upset (Table 1). Table 1 Summary table showing each of the five children's age, reason for presentation, vision, refraction, and investigations Serial B-scan ultrasonography showed no drusen at the first visit. However, all children developed small linear drusen at the optic disc over time (Figure 1). The mean time for development of drusen detectable on B-scan was 2.7 years. At no point was there optic nerve sheath dilation on B-scan. In two children, CT scans were conducted and reported as normal. A CT scan was avoided in three children because of the absence of optic nerve sheath swelling on sonography, the absence of symptoms of raised intracranial pressure and normal visual function.2, 3 Figure 1 B-scan of small linear disc drusen (arrow) in one of the subjects.

Isolated facial palsy as a hallmark of CSF overdrainage in shunted intracranial arachnoid cyst

An 18-year-old man with an intracranial arachnoid cyst (Fig. 1) and existing cysto-peritoneal shunt for 10 years was admitted to our department because of orthostatic headache, nausea and vomiting. Neurological examination was inconspicuous. The shunt was ligated because of an assumed CSF overdrainage. Clinical symptoms persisted, so that magnetic resonance (MR) imaging as well as lumbar puncture were performed, without signs of an increasing intracranial pressure. Myelocisternography excluded CSF leakage. However, this investigation showed just a partial disabled shunt. In a second surgery the shunt was completely ligated. Intermittent diplopia occurred and neuro-ophthalmological examination revealed papilledema. MR imaging indicated an increasing arachnoid cyst and optic nerve sheath dilation, compared to the pre-operative MRI. The patient underwent a shunt revision and an adjustable valve with an opening pressure >140 mmH2O on the left side was implanted. Subsequently, diplopia, papilledema, and headaches disappeared. Two days postoperatively, the patient developed an isolated mild facial palsy on the right side (opposite to the site of the arachnoid cyst; House–Brackmann grade II) as well as headaches. Opening pressure of the valve was decreased to >120 mmH2O and the headaches disappeared. Nevertheless, the facial palsy on the right side aggravated (House–Brackmann grade III) and additionally appeared on the left side (House–Brackmann grade II). MR imaging showed a reduction of the arachnoid cyst and diminished optic nerve sheaths compared to the previous MRI. The opening pressure was readjusted again to >140 mmH2O. After readjusting the opening pressure, bilateral facial palsy was regressive and disappeared within a few days. The patient showed no clinical signs of increasing intracranial pressure and was discharged with no neurological deficits. Possible other causes of facial palsy (meningitis, viral, borreliosis, etc.) were excluded.

Hypertension intracrânienne « bénigne » : imagerie et thérapeutiques endovasculaires

Neuroimaging is useful in benign intracranial hypertension (BIH), contributing to its diagnosis criteria and ruling out other causes of intracranial hypertension. CT and/or MR results may be normal or may show small ventricles, an empty sella, or more frequently optic nerve sheath dilatation. Diffusion as well as perfusion MR studies show conflicting results. Venous sinus imaging plays a growing role in BIH evaluation, because impaired cranial venous outflow is a common factor in the pathogenesis of BIH and venous sinus stenosis is frequently observed in this condition. Angiography is not the gold standard for this evaluation: angio-MR (with dynamic sequences) clearly demonstrates venous sinus stenosis (mostly located in the transverse sinus). We believe that this investigation must be carried out in every case of BIH. For medically refractory cases of BIH with associated sinus venous stenosis, sinus pressure recording may be necessary, sometimes leading to endovascular treatment of the stenosis (stenting). The results are promising, but long-term follow-up of these patients is needed.

The optic nerve sheath on MRI in acute optic neuritis

Optic nerve sheath dilatation or gadolinium-enhancement on magnetic resonance imaging in acute optic neuritis have been previously reported but have been thought to be rare occurrences. This study recruited 33 patients with acute unilateral optic neuritis. All had their optic nerves imaged with fat-saturated fast spin-echo (FSE) imaging, and 28 had imaging before and after triple-dose gadolinium-enhanced fat-saturated T(1)-weighted imaging. Follow-up imaging was performed on 20 patients (15 following gadolinium). A dilated subarachnoid space at the anterior end of the symptomatic optic nerve on FSE imaging was seen in 15/33 cases. In three of these cases, dilatation was visible on short-term follow-up. Optic nerve sheath enhancement was seen in 21/28 cases acutely: seven at the anterior end of the lesion only, five at the posterior end only and nine at both ends. Optic sheath enhancement was seen in 13 patients on follow-up. This study suggests that optic nerve sheath dilatation on FSE images and optic nerve sheath enhancement on triple-dose gadolinium-enhanced images are common findings in acute optic neuritis. Optic nerve sheath dilatation may be due to inflammation of the optic nerve, with its associated swelling, interrupting the communication between the subarachnoid space of the diseased optic nerve and the chiasmal cistern. Optic nerve sheath enhancement suggests that meningeal inflammation occurs in optic neuritis, in agreement with pathological studies of both optic neuritis and multiple sclerosis.

Intraocular and optic nerve sheath hemorrhage in cases of sudden intracranial hypertension.

✓ The eyes of 23 patients with sudden intracranial hypertension were studied at post-mortem. Intraocular hemorrhage had occurred in 37% and optic nerve sheath hemorrhage in 87%. Expansion of the optic nerve sheath, particularly the fusiform retrobulbar portion, was a consistent finding. The subdural space of the optic nerve sheath bore the brunt of the hemorrhage which sometimes communicated with perivascular intradural hemorrhages. Optic nerve sheath hemorrhage is shown to result from rupture of dural and bridging vessels of the optic nerve sheath; this we conclude is subsequent to optic nerve sheath dilatation caused by the transmission of intracranial pressure through the subarachnoid communication between the optic nerve sheath and the intracranial cavity. Intraocular hemorrhage is the result of retinal venous hypertension and rupture brought on by obstruction of both the central retinal vein and the retinochoroidal anastomosis.