The Optic Canal Size Is Associated With the Severity of Papilledema and Poor Visual Function in Idiopathic Intracranial Hypertension

Normal-Tension Glaucoma and Potential Clinical Links to Alzheimer's Disease

Glaucoma is a group of optic neuropathies and the world's leading cause of irreversible blindness. Normal-tension glaucoma (NTG) is a subtype of glaucoma that is characterized by a typical pattern of peripheral retinal loss, in which the patient's intraocular pressure (IOP) is considered within the normal range (<21 mmHg). Currently, the only targetable risk factor for glaucoma is lowering IOP, and patients with NTG continue to experience visual field loss after IOP-lowering treatments. This demonstrates the need for a better understanding of the pathogenesis of NTG and underlying mechanisms leading to neurodegeneration. Recent studies have found significant connections between NTG and cerebral manifestations, suggesting NTG as a neurodegenerative disease beyond the eye. Gaining a better understanding of NTG can potentially provide new Alzheimer's Disease diagnostics capabilities. This review identifies the epidemiology, current biomarkers, altered fluid dynamics, and cerebral and ocular manifestations to examine connections and discrepancies between the mechanisms of NTG and Alzheimer's Disease.

Expanding the clinical spectrum of idiopathic intracranial hypertension

PURPOSE OF REVIEW

Idiopathic intracranial hypertension (IIH) is a disorder of raised intracranial pressure (ICP). Although the majority of patients with IIH present classically with headache and papilledema, some patients may have unusual presentations or manifestations. Recent advancements in neuroimaging have facilitated the identification of other presentations associated with IIH. This review provides an overview of the expanding clinical spectrum of IIH.

RECENT FINDINGS

Presentations of IIH that are considered unusual include highly asymmetric or unilateral papilledema, IIH without papilledema, and IIH associated with cranial nerve involvement. These presentations likely reflect differences in the way cerebrospinal fluid (CSF) pressure is transmitted intracranially. Radiological signs of intracranial hypertension are increasingly recognized in patients with IIH and provide further insights into the effects of raised ICP on intracranial structures. Osseous changes in the skull base leading to formation of meningoceles and encephaloceles have been identified in patients with IIH, spontaneous skull base CSF leak, and drug-resistant temporal lobe epilepsy, suggesting a possible association.

SUMMARY

Clinicians should be familiar with the expanding clinical spectrum of IIH and the implications for the management of these presentations.

A-Scan Ultrasonographic Evaluation of Patients with Idiopathic Intracranial Hypertension: Comparison of Optic Nerves

Background: To evaluate the interocular optic nerve diameter (ONDs) asymmetry in patients with idiopathic intracranial hypertension (IIH) utilizing the A-scan ultrasound technique. Methods: Thirty-seven patients diagnosed with IIH were recruited from outpatients referred to the University Eye Unit between June 2014 and December 2021. Patients with optic disc pseudoedema or edema caused by other conditions were excluded. All patients with negative neuroimaging for intracranial space-occupying masses underwent standardized A-scan measurement of the OND in the primary gaze and lateral position (30 degrees test). Results: Mean, median, standard deviation, the minimum and maximum value of the two eyes at 0 degrees and the difference between the left and right thicker and thinner ONDs were measured. The two-tailed paired student t-test between the two eyes was performed using SPSS software. A statistically significant difference (p-value <0.001) between the two eyes, without a side prevalence, was found. Conclusions: Due to the differences between the ONDs of both eyes, we propose to use the mean of the ONDs between the left and right eyes at 0 degrees with the standardized A-scan diagnostic technique for a better follow-up of patients with IIH.

Case Report: Cerebrospinal Fluid Dynamics in the Optic Nerve Subarachnoid Space and the Brain Applying Diffusion Weighted MRI in Patients With Idiopathic Intracranial Hypertension—A Pilot Study

Purpose

The aim of this study was to examine the cerebrospinal fluid (CSF) flow rates in the subarachnoid space (SAS) of the optic nerve (ON) and the brain in patients with idiopathic intracranial hypertension (IIH) and papilledema (PE) compared to healthy controls by applying non-invasive diffusion-weighted MRI.

Methods

A retrospective analysis of diffusion-weighted MR images of 5 patients with IIH (10 ONs), mean age: 31 ± 10 years (5 women), and 11 healthy controls (22 ONs, mean age: 60 ± 13 years, 5 women) was performed. The flow velocity flow-range ratio (FRR) between the intracranial cavity and the SAS of the ON was calculated in both groups and then compared.

Results

The mean FRR was 0.55 ± 0.08 in patients with IIH and 0.63 ± 0.05 in healthy controls. The difference between patients with IIH and healthy controls was statistically significant (p < 0.05).

Conclusions

The CSF flow velocity was decreased in patients with IIH with PE compared to healthy controls. The reduced CSF flow dynamics might be involved in the pathophysiology of PE in IIH and diffusion-weighted MRI can be a useful non-invasive tool to study the CSF flow dynamics within the SAS ON.

Summary

Idiopathic intracranial hypertension is a neurological disease, where vision loss is the most feared complication of this disorder. The pathophysiology of IIH is not fully understood but is strongly linked to a reduced uptake of CSF into the central dural sinus veins. In this study, we examined the CSF flow rates in the SAS ON and the brain in patients with IIH and PE compared to healthy controls by applying non-invasive diffusion-weighted MRI. Knowing about the flow ratio of CSF may be of clinical relevance for the treatment decisions of IIH. If medical treatment fails, surgical options for lowering the ICP pressure need to be taken into consideration. As the primary goal of treatment is to prevent the loss of vision and visual field, it is important to know whether the communication of CSF between the intracranial CSF and the CSF in the perioptic space is intact. We showed that the CSF flow velocity was decreased in IIH patients with PE compared to healthy controls. The reduced CSF flow might be involved in the pathophysiology of PE in IIH, and diffusion-weighted MRI can be a useful non-invasive tool to study the CSF flow dynamics within the SAS ON.

The odyssey of the ocular and cerebrospinal fluids during a mission to Mars: the "ocular glymphatic system" under pressure

A significant proportion of the astronauts who spend extended periods in microgravity develop ophthalmic abnormalities including optic disc edema, globe flattening, chorioretinal folds, and hyperopic refractive error shifts. A constellation of these neuro-ophthalmic findings has been termed "spaceflight-associated neuro-ocular syndrome". Understanding this syndrome is currently a top priority for NASA, especially in view of future long-duration missions (e.g., Mars missions). The recent discovery of an "ocular glymphatic system" can potentially help to unlock mechanisms underlying microgravity-induced optic disc edema. Indeed, a major paradigm shift is currently occurring in our understanding of transport of fluids and solutes through the optic nerve following the recent discovery of an optic nerve glymphatic pathway for influx of cerebrospinal fluid. In addition, the recent identification of an entirely new glymphatic pathway for efflux of ocular fluid may have profound implications for fluid dynamics in the eye. Observations pertaining to this ocular glymphatic pathway provide critical new insights into how intracranial pressure can alter basic fluid transport in the eye. We believe that these novel findings have the potential to be game changers in our understanding of the pathogenesis of optic disc edema in astronauts. In the present review, we integrate these new insights with findings on the intracranial and neuro-ophthalmologic effects of microgravity in one coherent conceptual framework. Further studies in this area of investigation could not only provide exciting new insights into the mechanisms underlying microgravity-induced optic disc edema but also offer opportunities to develop countermeasure strategies.

Cerebrospinal fluid and ophthalmic disease

PURPOSE OF REVIEW

The purpose of this review is to discuss the contemporary body of literature examining the relationship between cerebrospinal fluid (CSF) and ophthalmic disease. This review focuses on diseases that have a pathogenesis related to the translaminar pressure difference, defined as the pressure difference between the orbital subarachnoid space (OSAS) and the intraocular pressure. The diseases discussed include glaucoma, idiopathic intracranial hypertension, and spaceflight associated neuro-ocular syndrome.

RECENT FINDINGS

The relationship between cerebrospinal and ophthalmic disease has been investigated for over 100 years. Recent research provides insight into the mechanisms that dictate CSF circulation in the OSAS and how alterations in these mechanism lead to disease. This review discusses these recent findings and their relationship to major ophthalmic diseases.

SUMMARY

The recent findings provide insight into diseases that have pathogenic mechanisms that are not fully understood. This information will help physicians gain a clearer understanding of the relationship between CSF and ophthalmic disease and guide future research.

The use of OCT to detect signs of intracranial hypertension in patients with sagittal suture synostosis: Reference values and correlations

PURPOSE

To obtain pediatric normative reference values and determine whether optical coherence tomography (OCT) corresponds better with clinical signs of intracranial hypertension (ICH) compared to the traditional screening method fundoscopy in a large cohort of one type of single suture craniosynostosis.

METHODS

Control subjects without optic nerve diseases and isolated sagittal synostosis patients aged 3-10 years who underwent fundoscopy and OCT were included in this prospective cohort study. Normative reference values were obtained through bootstrap analysis. Main outcome was the association between peripapillary total retinal thickness (TRT) and total retinal volume (TRV) and appearance on fundoscopy. Signs and symptoms suggestive of ICH, including skull growth arrest, fingerprinting, and headache, were scored.

RESULTS

Sixty-four healthy controls and 93 isolated sagittal synostosis patients were included. Normative cut-off values for mean TRT are < 256 μm and > 504 μm and for mean TRV < 0.21 mm³ and > 0.39 mm³. TRT was increased in 16 (17%) and TRV in 15 (16%) of 93 patients, compared to only 4 patients with papilledema on fundoscopy (4%). Both parameters were associated with papilledema on fundoscopy (OR = 16.7, p = 0.02, and OR = 18.2, p = 0.01). Skull growth arrest was significantly associated with abnormal OCT parameters (OR = 13.65, p < 0.01).

CONCLUSIONS

The established cut-off points can be applied to screen for ICH in pediatrics. The present study detected abnormalities with OCT more frequent than with fundoscopy, which were associated with skull growth arrest. Therefore, a combination of OCT, fundoscopy, and skull growth arrest can improve clinical decision-making in craniosynostosis.

Optic Nerve Angle in Idiopathic Intracranial Hypertension

BACKGROUND

The tortuosity of the optic nerve can be quantified radiologically by measuring the angle of optic nerve deformation (the "optic nerve angle" [ONA]). In patients with idiopathic intracranial hypertension (IIH), lowering the intracranial pressure (ICP) to a normal range by lumbar puncture leads to straightening of the optic nerve and an increase in the measured sagittal ONA on MRI. It is uncertain whether there is any correlation between ONA and cerebrospinal fluid (CSF) opening pressure or visual function.

METHODS

Retrospective study of patients with and without IIH who had MRI of the brain followed by lumbar puncture with CSF opening pressure within 24 hours of MRI. Before LP and within 24 hours of MRI of the brain, all patients with IIH had neuro-ophthalmologic assessment including visual acuity, Humphrey Visual Field (HVF), and fundus photography. Sagittal ONA was measured on multiplanar T2-SPACE images on a DICOM viewer. Papilledema on the fundus photographs was graded using the Frisén scale.

RESULTS

Fifty-four patients with IIH and 30 unmatched controls were included. The IIH group was 6.3 years younger (95% CI 2.4-10.3, P = 0.002), had 8.7 kg/m2 higher body mass index (4.9-12.5, P < 0.001), and 26.3% more women (P = 0.011) compared with controls. In both eyes, the ONA was significantly smaller in patients with IIH by 12° compared with controls (7°-17°, P < 0.00001). In the IIH group, no correlation between ONA and the CSF opening pressure was present in either eye (right eye r = 0.19, P = 0.15; left eye r = 0.18, P = 0.19) The ONA did not correlate with logarithm of the minimum angle of resolution visual acuity (right eye r = 0.26, P = 0.063; left eye r = 0.15, P = 0.27), HVF mean deviation (right eye r = 0.0059, P = 0.97; left eye r = -0.069, P = 0.63), or Frisén grade (Spearman's rho right eye 0.058, P = 0.67; left eye 0.14, P = 0.30).

CONCLUSIONS

The ONA is significantly smaller in patients with IIH compared to controls, but does not correlate with CSF opening pressure, severity of papilledema, or visual function. The ONA may be useful in identifying patients with raised ICP, but not necessarily those with a poor visual prognosis.

Absence of papilledema in large intracranial tumours

Papilledema refers to optic disc edema occurring secondary to raised intracranial pressure. In patients with intracranial tumours, tumour size might be the expected predictor of whether or not papilledema will develop, however, this is not the case in clinical practice. We report a series of 5 patients with large intracranial tumours and no evidence of papilledema and discuss the potential factors which may contribute to the lack of optic disc edema in these cases. Development of papilledema depends on both the presence of elevated intracranial pressure and transmission of elevated pressure to the subarachnoid space within the optic nerve sheath and to the optic nerve itself. We discuss how intracranial tumours may influence the physiology of the surrounding tissues, cerebrospinal fluid dynamics and cerebral venous outflow and how individual anatomic variations, particularly within the optic nerve sheath and optic canal, likely play a role in development of papilledema.

Three-Layered Optic Disc Hemorrhages in Idiopathic Intracranial Hypertension

Papilledema related to idiopathic intracranial hypertension (IIH) may present with optic disc hemorrhaging. The significance and characteristics of these hemorrhages still remains to be clarified. Here, we present 2 unique cases with severe unilateral optic disc hemorrhaging in all 3 retinal layers (preretinal, intraretinal, and subretinal) and a good visual outcome. A 42- and a 44-year-old woman presented with signs and symptoms of raised intracranial pressure. Visual acuity was normal and Humphrey visual field testing showed only mild vision loss with enlarged blind spots. Dilated fundus examination revealed moderate papilledema in both eyes with severe optic disc hemorrhaging in the left eye in the first patient and the right eye in the second patient. The optic disc hemorrhaging occurred in all 3 retinal layers (preretinal, intraretinal, and subretinal), and the fellow eyes had only minimal hemorrhage. All patients had normal magnetic resonance imaging/magnetic resonance venography, and lumbar punctures revealed elevated opening pressures and normal cerebrospinal fluid contents. The papilledema resolved after 4 months in both cases with medical therapy. Optic disc hemorrhaging may be severe in patients with IIH, but this does not necessarily confer a poor visual outcome. The differential diagnosis of hemorrhages in all 3 retinal layers may be expanded to include IIH.

Etiology, pathogenesis and management of idiopathic intracranial hypertension, and role of optic canal size in asymmetric papilledema: A review

Idiopathic intracranial hypertension (IIH) is characterized by raised intracranial pressure of unknown origin that primarily afflicts obese women of childbearing age. There are several treatment options, but currently there are none that are effective for the entire affected population. The lack of a universally effective treatment is related to an incomplete understanding of the etiology of the condition and the lack of a well-defined pathophysiological mechanism for the disease process. Classically, IIH has been thought of as a diagnosis of exclusion once radiographical imaging has ruled out all other causes of elevated intracranial pressure. Today, we know that imaging does capture subtle changes, and might provide keys to finally understand the pathogenesis of IIH so that a definitive treatment can be discovered or developed. Recently, advancements in radiography, optical coherence tomography, and electroretinography have shown promise for the future of IIH evaluation. A topic within IIH imaging that has recently sparked interest is the possibility that the severity of papilledema may have an association with the size of the optic canal. In this article, we also discuss the recent studies on the relationship between asymmetric papilledema and optic canal size.

Assessment of the Optic Foramen Shape and Size in Human Fetuses

OBJECTIVE

This study was aimed to obtain data on the dimensions of the optic foramen in human fetuses for early childhood surgeries.

METHODS

Twenty-five formalin-fixed fetuses (16 boys and 9 girls) with average age 21.68 ± 3.12 gestational weeks (range, 16-28 weeks) in the inventory of Anatomy Department, Faculty of Medicine were included in the study. The surface area, width, and height of the optic foramen were bilaterally measured using a digital image analysis software.

RESULTS

The forms of the optic foramen were described as oval shaped (72%, 36 foramina) and round shaped (28%, 14 foramina). The surface area, width, and height of the optic foramen were found as 2.40 ± 1.02 mm, 1.83 ± 0.59 mm, and 1.58 ± 0.36 mm, respectively. The measurements of the parameters related to the optic foramen were not statistically different in terms of sides and sexes (P > 0.05). Linear functions for the height, width and surface area of the optic foramen were calculated as: y = 0.711 + 0.040 × weeks, y = -0.019 + 0.086 × weeks, and y = -0.400 + 0.129 × weeks, respectively.

CONCLUSION

The linear functions in this study can be used to estimate the dimensions of the optic foramen. The calculated regression equations, representing the growth dynamic of the optic foramen showed that the surface area, width, and height were increasing according to gestational ages between 16 and 28 weeks. Microanatomical knowledge related to the optic foramen may be beneficial for surgeons to avoid iatrogenic injury in infants and for anatomists to understand the development of the fetal skull base.

Atypical presentations of idiopathic intracranial hypertension

Idiopathic intracranial hypertension (IIH) is a disorder of unknown etiology that results in isolated raised intracranial pressure. Classic symptoms and signs of IIH include headache, papilledema, diplopia from sixth nerve palsy and divergence insufficiency, and pulsatile tinnitus. Atypical presentations include: (1) highly asymmetric or even unilateral papilledema, and IIH without papilledema; (2) ocular motor disturbances from third nerve palsy, fourth nerve palsy, internuclear ophthalmoplegia, diffuse ophthalmoplegia, and skew deviation; (3) olfactory dysfunction; (4) trigeminal nerve dysfunction; (5) facial nerve dysfunction; (6) hearing loss and vestibular dysfunction; (7) lower cranial nerve dysfunction including deviated uvula, torticollis, and tongue weakness; (8) spontaneous skull base cerebrospinal fluid leak; and (9) seizures. Although atypical findings should raise a red flag and prompt further investigation for an alternative etiology, clinicians should be familiar with these unusual presentations.

Reviewing the Recent Developments in Idiopathic Intracranial Hypertension

There is increasing evidence and appreciation of idiopathic intracranial hypertension (IIH) in medicine. The pathological processes underlying raised intracranial pressure are being studied, with new insights found in both hormonal dysregulation and the metabolic neuroendocrine axis. These will potentially lead to novel therapeutic targets for IIH. The first consensus guidelines have been published on the investigation and management of adult IIH, and the International Headache Society criteria for headache attributable to IIH have been modified to reflect our evolving understanding of IIH. Randomized clinical trials have been published, and a number of studies in this disease area are ongoing.

Posterior Globe Flattening without Papilledema in Idiopathic Intracranial Hypertension

A 64-year-old woman had a one-year history of transient visual obscurations in the left eye and was found to have left optic disc oedema with preserved visual function. She was diagnosed with unilateral papilloedema related to idiopathic intracranial hypertension. Magnetic resonance imaging of the orbits showed flattening of the globe in the right eye, which did not have disc oedema. Flattening of the posterior globe without papilloedema suggests that the barrier to transmission of cerebrospinal fluid pressure to optic nerve head is at the level of the lamina cribrosa and may be due to connective tissue changes in this area.

The role of intracranial pressure in glaucoma and therapeutic implications

Despite glaucoma being the second leading cause of blindness globally, its pathogenesis remains incompletely understood. Although intraocular pressure (IOP) contributes to glaucoma, and reducing IOP slows progress of the disease, some patients progress despite normal IOP (NTG). Glaucomatous damage causes characteristic cupping of the optic nerve where it passes through the lamina cribrosa. There is evidence that cerebrospinal fluid (CSF) within the optic nerve sheath has a different composition from CSF surrounding the brain. Furthermore, fluctuations in CSF flow into the optic nerve sheath may be reduced by trabeculae within the sheath, and on standing intracranial pressure (ICP) within the sheath is stabilised at around 3 mmHg due to orbital pressure. Blood pressure has been linked both to glaucoma and ICP. These facts have led some to conclude that ICP does not play a role in glaucoma. However, according to stress formulae and Laplace's Law, stress within the lamina cribrosa is dependent on the forces on either side of it, (IOP and ICP), and its thickness. On lying flat at night, ICP between the brain and optic nerve sheath should equalise. Most evidence suggests ICP is lower in glaucoma than in control groups, and that the lamina cribrosa is thinner and more posteriorly displaced in glaucoma. Subjects who have had ICP reduced have developed signs of glaucoma. This review finds most evidence supports a role for low ICP in the pathogenesis of glaucoma. Caffeine, theophylline and vitamin A may increase ICP, and could be new candidates for an oral treatment.

Optic nerve sheath diameter asymmetry in healthy subjects and patients with intracranial hypertension

BACKGROUND

Ultrasonography of the optic nerve sheath diameter (ONSD) is used for the non-invasive assessment of increased intracranial pressure (ICP). ONSD values are usually obtained by averaging the measurements of the two eyes, but asymmetric ONSD dilation is possible, leading to potentially inaccurate ICP estimation when using binocular averaging. In addition, few data are available about the asymmetry of the ONSD and the use of the maximum ONSD value between eyes for raised ICP detection. The aim of the study was to evaluate the interocular ONSD asymmetry in healthy subjects and patients with intracranial hypertension (IH) by ultrasonography and to investigate whether the maximum ONSD could be as useful as the binocular assessment.

METHODS

Forty healthy subjects and 40 patients with IH (20 with idiopathic intracranial hypertension and 20 with intracerebral hemorrhage) who underwent transorbital sonography were retrospectively enrolled. The prevalence and degree of ONSD asymmetry were compared among groups; ONSD median binocular and maximum values were compared.

RESULTS

Forty-two out of 80 subjects (52.5%) showed significant ONSD asymmetry, without significant differences in prevalence among groups (p = 0.28). The median asymmetry was higher in patients than in healthy subjects (0.45 mm vs 0.23 mm; p = 0.007), without significant differences between the two pathologies (p = 0.58). Both binocular and maximum ONSD measurements were significantly higher in patients with IH than in controls (p < 0.001).

CONCLUSIONS

Interocular ONSD asymmetry occurs both in healthy subjects and, more consistently, in patients with IH. Both binocular and maximum ONSD may be useful markers for increased ICP detection.

Methods for Quantifying Optic Disc Volume and Peripapillary Deflection Volume Using Radial Optical Coherence Tomography Scans and Association With Intracranial Pressure

Purpose: Papilledema and peripapillary deformation of Bruch's membrane (BM) are associated with elevated intracranial pressure (ICP). We have developed a novel methodology to measure these parameters using a radial optical coherence tomography (OCT) scan pattern and apply this to test the hypothesis that ICP is associated with volumetric features of ophthalmic structures.

Methods: 6-radial OCT B-scans centered over the optic nerve head were acquired in 17 subjects (30 eyes) before lumbar puncture with measurement of ICP (range: 10–55 cm H₂O). Internal limiting membrane (ILM) and BM were segmented. Three definitions of BM were studied to account for imaging artifact affecting peripapillary BM: connecting rater-identified BM margins(traditional), connecting rater-identified BM 1.6 mm on either side of the ONH(estimated), and excluding BM in the central 3.2 mm of the images(excluded). Optic nerve head volume (ONHV), BM displacement volume (BMDV) and cup volume (CV) were calculated by interpolating between B-scans. Ganglion cell complex volume (GCCV) was measured in the macula. Linear generalized estimating equations (GEE) modeled ONVH, BMDV, and CV as a function of ICP and GCCV.

Results: Increased ONHV was associated with elevated ICP for traditional (p = 0.006), estimated (p = 0.003) and excluded (p = 0.05) BM definitions. Decreased BMDV was associated with elevated ICP for traditional (p < 0.0005), estimated (p < 0.0005) and excluded (p = 0.001) definitions. Decreased ONHV was independently associated with decreased GCCV (p = 0.001) and decreased ICP (p = 0.031) in multivariable models. CV was neither associated with ICP nor GCCV in univariate or multivariable models.

Conclusions: Elevated ICP is associated with ONHV increase and BMDV decrease, calculated from OCT images accounting for image artifact. Ganglion cell atrophy affects the relationship between ICP and ONHV. OCT derived volumetric measures of the posterior eye may have application as biomarkers for elevated ICP.

Evaluation of optic canal anatomy and symmetry using CT

Objective

We aim to describe the anatomy and symmetry patterns of the optic canal in patients having undergone maxillofacial CT imaging.

Methods

In this retrospective chart review, we included all patients who received sinus and maxillofacial CT at the University of North Carolina hospitals between 2008 and 2016, without facial or cranial fractures or other medical conditions that would affect optic canal size. We measured the length of ≥75% enclosed canal, minimum cross-sectional area and minimum diameter bilaterally using iNtuition TeraRecon (Durham, North Carolina) and compared bilateral symmetry using a 20 % difference threshold. Each parameter above was compared among white, black, non-white and non-black patients.

Results

Of 335 patients, the mean canal length was 5.61±2.22 mm. The mean minimum area was 11.84±3.11 mm². The mean minimum diameter was 3.28±0.55 mm. A total of 39.4% (132/335) of patients had asymmetric canal lengths, 18.8% (63/335) had asymmetric minimum areas, and 12.5% (42/335) had asymmetric minimum diameters. No differences were found between racial groups. The right optic canal was larger than the left (right: 12.12 mm vs left: 11.55 mm, p<0.0001).

Conclusion

Optic canal asymmetry is not uncommon. It may affect risk of papilloedema severity, explain cases of unilateral or asymmetric papilloedema and possibly asymmetric glaucoma.

Optic canal size in idiopathic intracranial hypertension and asymmetric papilledema

OBJECTIVE

Asymmetric papilledema (AP) is a rare condition in idiopathic intracranial hypertension (IIH). As the pathophysiology of papilledema developement in IIH remains unclear, the study of AP could clarify some etiologic aspects. We aimed to evaluate bony optic canal size in IIH patients with AP.

PATIENTS AND METHODS

All IIH patients based on modified Dandy criteria in our referral tertiary eye hospital underwent neuro-opthalmologic exams and grading of papilledema according to modified Frisén scale. Very asymmetric papilledema (VAP) defined as a ≥2 grade difference between the two eyes. Clinical features, cerebrospinal fluid opening pressure (CSF OP), best corrected visual acuity, Humphery visual field, and brain magnetic resonance imaging (MRI) and MR venography was performed for all patients. Spiral orbital computed tomography (CT) scan which is the choice method for details of bony structures with axial, coronal and sagittal planes was done in patients with VAP.

RESULT

59 patients with IIH were diagnosed that 18.6% of them (n = 11) had VAP. There was no IIH patient with strictly unilateral Papilledema. Presenting symptoms and CSF OP was not significantly different between patients with symmetric and asymmetric papilledema. In patients with VAP, bony optic canal size was not statistically significant different in axial, coronal and sagittal plane when comparing the eye with higher grade edema to the fellow eye.

CONCLUSION

Our study showed that bony optic canal size evaluated by orbital CT scan was not different in VAP in IIH patients. Finding the exact pathophysiology of AP need further studies.

Impaired cerebrospinal fluid dynamics along the entire optic nerve in normal-tension glaucoma

PURPOSE

To investigate the cerebrospinal fluid (CSF) dynamics along the entire optic nerve (ON) in patients with normal-tension glaucoma (NTG).

METHODS

Retrospective analysis of computed tomographic (CT) cisternographies in Caucasian patients with NTG. Fifty-six patients (99 of 112 eyes) fulfilled the diagnostic criteria of NTG and underwent CT-cisternography. Twelve subjects without NTG (24 eyes) served as controls. Contrast-loaded cerebrospinal fluid (CLCSF) density measurements in Hounsfield units (HU) were performed at four defined regions along the ON and in the basal cistern.

RESULTS

In NTG patients, the mean density CLCSF in the bulbar segment measured 76 ± 49 HU right and 88 ± 74 HU left, in the mid-orbital segment 117 ± 92 HU right and 119 ± 73 HU left, in the intracanalicular ON portion 209 ± 88 HU right and 216 ± 101 HU left, in the intracranial ON portion 290 ± 106 HU right and 286 ± 118 HU left and in the basal cistern 517 ± 213 HU. The distribution of CLCSF along the ON showed a statistically significant reduction in the intraorbital ON segments in NTG patients compared to controls without NTG with the far largest difference within the retrobulbar segment (-150 HU right and -117 HU left; right: p < 0.001, left: p < 0.001).

CONCLUSION

This study demonstrates a gradual reduction in CLCSF towards the retrobulbar segment in NTG, while in controls without NTG, no reduction in CLCSF was measured within the orbital segments. Impaired CSF dynamics along the ON may contribute to the pathophysiology of NTG.

Perioptic Cerebrospinal Fluid Dynamics in Idiopathic Intracranial Hypertension

Purpose: To examine the cerebrospinal fluid (CSF) dynamics along the entire optic nerve in patients with idiopathic intracranial hypertension (IIH) and papilledema by computed tomographic (CT) cisternography. Methods: Retrospective analysis of CT cisternographies in 16 patients with a history of IIH and papilledema (14 females and 2 males, mean age: 49 ± 16 years). Contrast loaded CSF (CLCSF) was measured in Hounsfield Units (HU) at three defined regions of interest (ROI) along the optic nerve (orbital optic nerve portion: bulbar and mid-orbital segment, intracranial optic nerve portion) and additionally in the basal cistern. The density measurements in ROI 1, ROI 2, and ROI 3 consist of measurements of the optic nerve complex: optic nerve sheath, CLCSF filled SAS and optic nerve tissue. As controls served a group of patients (mean age: 60 ± 19 years) without elevated intracranial pressure and without papilledema. Results: In IIH patients the mean CLCSF density in the bulbar segment measured 65 ± 53 HU on the right and 63 ± 35 HU on the left side, in the mid-orbital segment 68 ± 37 HU right and 60 ± 21 HU left. In the intracranial optic nerve portion 303 ± 137 HU right and 323 ± 169 HU left and in the basal cistern 623 ± 188 HU. Within the optic nerve the difference of CLCSF density showed a highly statistical difference (p < 0.001) between the intracranial optic nerve portion and the mid-orbital segment. CLCSF density was statistically significantly (p < 0.001) reduced in both intraorbital optic nerve segments in patients with IIH compared to controls. Conclusions: The current study demonstrates reduced CLCSF density within the orbital optic nerve segments in patients with IIH and papilledema compared to 12 controls without elevated intracranial pressure and without papilledema. Impaired CSF dynamics could be involved in the pathophysiology of optic nerve damage in PE in IIH.

Do Optic Canal Dimensions Measured on CT Influence the Degree of Papilloedema and Visual Dysfunction in Idiopathic Intracranial Hypertension?

A recent study found that increased optic canal area on magnetic resonance imaging was associated with worse papilloedema in idiopathic intracranial hypertension (IIH). We repeated this study using more accurate computerized tomography derived measurements. Optic canal dimensions were measured from 42 IIH patients and 24 controls.  These were compared with papilloedema grade.  There was no correlation between any of the optic canal measurements and papilloedema grade and no significant difference in optic canal measurements between patients and controls. Our results cast doubt on the existing literature regarding the association between optic canal size and the degree of papilloedema in IIH. CT delineates bony anatomy more accurately than MRI and our CT-derived optic canal measurements cast doubt on the existing literature regarding the association between optic canal size and the degree of Papilloedema in IIH.

Use of A-scan Ultrasound and Optical Coherence Tomography to Differentiate Papilledema From Pseudopapilledema

SIGNIFICANCE

Differentiating papilledema from pseudopapilledema reflecting tilted/crowded optic discs or disc drusen is critical but can be challenging. Our study suggests that spectral-domain optical coherence tomography (OCT) peripapillary retinal nerve fiber layer thickness and retrobulbar optic nerve sheath diameter (ONSD) measured by A-scan ultrasound provide useful information when differentiating the two conditions.

PURPOSE

To evaluate the use of A-scan ultrasound and spectral-domain OCT retinal nerve fiber layer thickness (RNFLT) in differentiating papilledema associated with idiopathic intracranial hypertension from pseudopapilledema.

METHODS

Retrospective cross-sectional analysis included 23 papilledema and 28 pseudopapilledema patients. Ultrasound-measured ONSD at primary gaze, percent change in ONSD at lateral gaze (30° test), and peripapillary RNFLT were analyzed. Receiver operating characteristic curves were constructed using one eye from each subject.

RESULTS

Compared with pseudopapilledema, papilledema eyes showed larger mean ONSD (5.4 ± 0.6 vs. 4.0 ± 0.3 mm, P < .0001), greater change of ONSD at lateral gaze (22.4 ± 8.4% vs. 2.8 ± 4.8%, P < .0001), and thicker retinal nerve fiber layer (219.1 ± 104.6 vs. 102.4 ± 20.1 μm, P < .0001). Optic nerve sheath diameter and 30° test had the greatest area under the receiver operating characteristic curve, 0.98 and 0.97, respectively; followed by inferior quadrant (0.90) and average RNFLT (0.87). All papilledema eyes with Frisén scale greater than grade II were accurately diagnosed by ONSD, 30° test, or OCT. In mild papilledema (Frisén scale grades I and II, n = 15), area under the receiver operating characteristic curve remained high for ONSD (0.95) and 30° test (0.93) but decreased to 0.61 to 0.71 for RNFLT. At 95% specificity, sensitivities for ONSD, 30° test, and RNFLT were 91.3%, 91.3%, and 56.5%, respectively, for the entire papilledema group and 80.0%, 86.7%, and 13.3% for the mild papilledema subgroup.

CONCLUSIONS

Retinal nerve fiber layer thickness can potentially be used to detect moderate to severe papilledema. A-scan may further assist differentiation of mild papilledema from pseudopapilledema.

Outcomes of endoscopic optic nerve decompression in patients with idiopathic intracranial hypertension

BACKGROUND

The conventional treatment for idiopathic intracranial hypertension involves weight loss, steroids, diuretics, and/or serial lumbar punctures; however, if the symptoms persist or worsen, surgical intervention is recommended. Surgical options include cerebrospinal fluid diversion procedures, such as ventriculoperitoneal and lumboperitoneal shunts, and optic nerve decompression with nerve sheath fenestration. The latter can be carried out using an endoscopic approach, but the outcomes of this technique have not been firmly established.

METHODS

This systematic review examined the outcomes of performing endoscopic optic nerve decompression (EOND) in patients with idiopathic intracranial hypertension (IIH). Six studies were included for a total of 34 patients.

RESULTS

The patients presented with visual field disturbances (32 of 32 [100%]), visual acuity disruptions (33 of 34 [97.1%]), papilledema (26 of 34 [76.5%]), and persistent headache (30 of 33 [90.1%]). The mean duration of symptoms ranged from 7 to 32 months. Overall, the patients showed post-EOND improvement in signs and symptoms associated with IIH, specifically visual field deficits (93.8%), visual acuity (85.3%), papilledema (81.4%), and headaches (81.8%). Interestingly, 11 cases showed postoperative improvement in their symptoms with bony decompression of the optic canal alone, without nerve sheath fenestration. There were no major adverse events or complications reported with this approach.

CONCLUSION

EOND appears to be a promising and safe surgical alternative for patients with IIH who fail to respond to medical treatment. Further studies are needed before we can attest to the clinical validity of this procedure.

Intracanalicular Optic Nerve Swelling and Signal Change in Fulminant Untreated Idiopathic Intracranial Hypertension

The role of the optic canal in the pathogenesis of papilloedema has been under scrutiny recently. Whether a larger canal precedes more severe papilloedema or is the result of bone remodelling from chronically raised pressure across a pressure gradient is not clear. The authors present the magnetic resonance imaging findings of a 29-year-old female with fulminant and untreated idiopathic intracranial hypertension. Imaging showed focal expansion and intrinsic signal changes of the intracanalicular optic nerve. The authors discuss the possibility of either fluid accumulation within the optic nerves from a water hammer effect across blocked optic canals resulting from the steep pressure gradient or opticomalacia (optic nerve softening) from chronic ischaemia.

Idiopathic intracranial hypertension: Contemporary review and implications for the otolaryngologist

OBJECTIVES

1) Review controversies pertaining to the pathophysiology, diagnosis, and treatment of idiopathic intracranial hypertension. 2) Discuss the evolving role of otolaryngologists in managing this disease and related disorders.

DATA SOURCES

Primary literature review, Centers for Disease Control and Prevention website, International Classification of Headache Disorders, Second Edition.

METHODS

A comprehensive review of the primary literature was performed from 1990 to 2016 utilizing keywords idiopathic intracranial hypertension, pseudotumor cerebri, benign intracranial hypertension, spontaneous cerebrospinal fluid leak, and encephalocele. Articles were included at the discretion of the authors based on novel and/or historical contributions to the literature.

RESULTS

The incidence of idiopathic intracranial hypertension is increasing along with the obesity epidemic. Undiagnosed patients may present to otolaryngologists with pulsatile tinnitus, dizziness, sleep apnea, and spontaneous cerebrospinal fluid leaks. Although diagnosis is predicated upon imaging findings and lumbar puncture, radiographic signs including empty sella, optic nerve dilation, and globe flattening may suggest the diagnosis. The most effective intervention is weight loss combined with acetazolamide. Surgery is reserved for severe or refractory symptoms and can be highly morbid. Otolaryngologists are increasingly responsible for managing a number of secondary disorders including cerebrospinal fluid rhinorrhea and otorrhea. Failure to manage intracranial hypertension may lead to adverse surgical outcomes.

CONCLUSIONS

The knowledge base for idiopathic intracranial hypertension has greatly expanded over the past 25 years. This disease is associated with a number of conditions directly relevant to otolaryngologists. A keen understanding of this disorder and its management may optimize outcomes in a growing number of patients. Laryngoscope, 128:248-256, 2018.

The Optic Canal: A Bottleneck for Cerebrospinal Fluid Dynamics in Normal-Tension Glaucoma?

Purpose

To report on the optic canal cross-sectional area (OCA) in Caucasian patients with normal-tension glaucoma (NTG) compared with Caucasian control subjects without known optic nerve (ON) diseases.

Methods

Retrospective analysis of computed tomographic images of the cranium and orbits in 56 NTG patients (30 females and 26 males; 99 of 112 eyes; mean age 67.7 ± 11.1 years). Fifty-six age- and gender-matched subjects (mean age: 68.0 ± 11.2 years) without known ON diseases served as controls. The OCA at the orbital opening was measured in square millimeters by using the tool “freehand.” Statistical analysis was performed by using the independent two-tailed t-test.

Results

The mean orbital opening OCA in NTGs measured 14.5 ± 3.5 mm² (right OCA: 14.4 ± 3.6 mm², left OCA: 14.5 ± 3.4 mm²) and in controls measured 18.3 ± 2.6 mm² (right OCA: 18.5 ± 2.7 mm², left OCA: 18.1 ± 2.5 mm²). The difference between NTG and controls was statistically significant (p < 0.000 for the right OCA, p < 0.000 for the left OCA).

Conclusion

This study demonstrates narrower OCAs in Caucasian NTG patients compared with Caucasian control subjects without known ON diseases. Narrower OCAs might contribute to a discontinuity of the cerebrospinal fluid flow between the intracranial and orbital subarachnoid space in NTG patients. This might have an influence onto the pathophysiology in NTG.