Cerebrospinal fluid and optic nerve sheath compartment syndrome: A common pathophysiological mechanism in five different cases?

Age related cerebrospinal fluid flow dynamics in the subarachnoid space of the optic nerve in patients with normal tension glaucoma, measured by diffusion weighted MRI

BACKGROUND/OBJECTIVES

We aimed to measure cerebrospinal fluid (CSF) flow rates in the subarachnoid space (SAS) of the optic nerve (ON) by applying non-invasive diffusion-weighted MRI in patients with normal tension glaucoma (NTG) compared to age-matched controls.

SUBJECTS/METHODS

In this prospective study, an analysis of diffusion-weighted images of 26 patients with NTG (49ONs) and age-matched volunteers (52ONs) was conducted. Subjects were classified into 4 groups: group I (50-59 y., n = 12 eyes), group II (60-69 y., n = 16 eyes), group III (70-79 y., n = 18 eyes) and group IV ( > 80 y., n = 6 eyes) for NTGs and healthy volunteers, respectively. The flow-range ratio (FRR) between the frontal lobe SAS and the SAS of the ON was calculated for each age category group and then compared between age-categories as well as between NTGs and controls.

RESULTS

The mean FRR for age groups were (I) 0.54 ± 0.06 and 0.62 ± 0.03 (p < 0.05), (II) 0.56 ± 0.08 and 0.63 ± 0.03 (p < 0.05), (III) 0.54 ± 0.06 and 0.62 ± 0.02 (p < 0.001) as well as (IV) 0.61 ± 0.03 and 0.61 ± 0.04, for NTGs and controls, respectively. Using pooled data, the difference between the FRR in NTGs and controls was statistically significant (p < 0.0001). There were no statistically significant differences within the age categories of the control group. When comparing the FRR of NTGs by age categories, no statistically significant difference was found between the subgroups.

CONCLUSIONS

FRR was significantly reduced in NTGs compared to age-matched controls without any significant differences within the age groups themselves. Given the physiological importance of CSF for the integrity of neurons, axons and glial cells, reduced CSF flow dynamics might be part of the underlying neurodegenerative process of NTG.

Novel Approaches to the Treatment of Idiopathic Intracranial Hypertension

PURPOSE OF REVIEW

Idiopathic intracranial hypertension (IIH) typically affects women of childbearing age, is associated with recent weight gain, and can result in debilitating headache as well as papilledema that can cause vision loss. There have been advances in the medical and surgical treatment of affected patients with IIH that can improve outcomes and tolerability of therapy.

RECENT FINDINGS

Medical treatment with agents that lower intracranial pressure through pathways other than carbonic anhydrase inhibition are being developed, and medically-directed weight loss as well as bariatric surgery now may be considered as primary therapy. New surgical options including venous sinus stenting have shown efficacy even with cases of severe vision loss. Our treatment options for IIH patients are becoming more diverse, and individualized treatment decisions are now possible to address specific components of the patient's disease manifestations and to lead to IIH remission.

Large-scale morphometry of the subarachnoid space of the optic nerve

BACKGROUND

The meninges, formed by dura, arachnoid and pia mater, cover the central nervous system and provide important barrier functions. Located between arachnoid and pia mater, the cerebrospinal fluid (CSF)-filled subarachnoid space (SAS) features a variety of trabeculae, septae and pillars. Like the arachnoid and the pia mater, these structures are covered with leptomeningeal or meningothelial cells (MECs) that form a barrier between CSF and the parenchyma of the optic nerve (ON). MECs contribute to the CSF proteome through extensive protein secretion. In vitro, they were shown to phagocytose potentially toxic proteins, such as α-synuclein and amyloid beta, as well as apoptotic cell bodies. They therefore may contribute to CSF homeostasis in the SAS as a functional exchange surface. Determining the total area of the SAS covered by these cells that are in direct contact with CSF is thus important for estimating their potential contribution to CSF homeostasis.

METHODS

Using synchrotron radiation-based micro-computed tomography (SRµCT), two 0.75 mm-thick sections of a human optic nerve were acquired at a resolution of 0.325 µm/pixel, producing images of multiple terabytes capturing the geometrical details of the CSF space. Special-purpose supercomputing techniques were employed to obtain a pixel-accurate morphometric description of the trabeculae and estimate internal volume and surface area of the ON SAS.

RESULTS

In the bulbar segment, the ON SAS microstructure is shown to amplify the MECs surface area up to 4.85-fold compared to an "empty" ON SAS, while just occupying 35% of the volume. In the intraorbital segment, the microstructure occupies 35% of the volume and amplifies the ON SAS area 3.24-fold.

CONCLUSIONS

We provided for the first time an estimation of the interface area between CSF and MECs. This area is of importance for estimating a potential contribution of MECs on CSF homeostasis.

Optic nerve sheath fenestration for treating papilloedema in the era of cerebral venous sinus stenting

BACKGROUND

Pseudotumour cerebri (PTC) is the syndrome of intracranial hypertension without intracranial mass or hydrocephalus and is the commonest cause of papilloedema seen in many eye clinics. In the last 10 years, we have increasingly used TSS in patients whose papilloedema was not well controlled with medical treatment and have done fewer ONSFs. Here, we review our experience at Royal Prince Alfred Hospital Sydney with ONSF in 35 patients over the period 2002-2021.

METHODS

Retrospective case series of 35 patients, 30 of whom had primary PTC [i.e., idiopathic intracranial hypertension (IIH)] and 5 with secondary PTC.

RESULTS

Eighteen patients had bilateral ONSF and 17 patients unilateral ONSF, in each case of the worse eye. Thirteen patients then underwent transverse sinus stenting (TSS), in each case following ONSF. The primary outcome measures were visual acuity (VA) and mean deviation (MD) on visual field (VF) testing. MD improved by 5 dB or more in 34 of 70 total eyes (48.6%); VA improved by 0.2 logMAR (two lines on Snellen chart) or more in 21 eyes (30%), and by both in 15 eyes (21.4%). Final MD was -10 dB or better in 38 eyes (54.3%); final VA was 0.3 (6/12) or better in 54 eyes (77.1%), and both in 39 eyes (55.7%).

CONCLUSIONS

The results confirm that ONSF can relieve papilloedoema in both eyes and improve both VF and VA, even in cases of fulminant PTC with severe acute visual impairment.

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.

Cerebrospinal fluid dynamics along the optic nerve in patients with spontaneous cerebrospinal fluid rhinorrhea: a retrospective computed tomographic cisternography study

PURPOSE

Spontaneous cerebrospinal fluid (CSF) rhinorrhea is related to intracranial pressure (ICP) and dynamic changes. This study investigated CSF dynamics along the optic nerve (ON) in patients with spontaneous CSF rhinorrhea.

METHODS

The computed tomographic (CT) cisternographies of 66 patients (132 eyes) with spontaneous CSF rhinorrhea were analysed. The contrast-loaded CSF (CLCSF) density was measured in Hounsfield units (HU) at three regions of interest (ROIs) along the ON and adjusted by the basal cistern density. The CLCSF density and ON sheath diameter (ONSD) were analysed between both sides in the different ICP groups.

RESULTS

When comparing the density of CLCSF along the ON, no significant differences were found between the ipsilateral and contralateral sides of the leakage. The distribution of CLCSF along the ON showed a highly significant density reduction from the canalicular segment to the bulbar segment on both sides. The CLCSF density significantly decreased on the ipsilateral ON in the canalicular segment and tended to decrease on the ipsilateral ON in the bulbar and canal segments compared with that on the contralateral ON in the low-ICP group. The ONSD tended to decrease on the ipsilateral side of leakage.

CONCLUSIONS

According to the CLCSF density on CT cisternography, CSF dynamics along the ON may bilaterally decrease from the optic canal to the retrobulbar segment. Cerebrospinal fluid (CSF) dynamics are possibly influenced by differences in ICP, and a lower ICP may cause more obvious differences or impairments in CSF dynamics along the ipsilateral ON.

Optical Coherence Tomography to Monitor Rebound Intracranial Hypertension with Increased Papilledema after Lumbar Puncture

Objective: We report that lumbar puncture (LP) with removal of cerebrospinal fluid (CSF) induced rebound intracranial hypertension with increased papilledema as monitored by optical coherence tomography (OCT). Background: Severe papilledema causes visual field loss and central vision damage if untreated. Fundoscopy is a key to diagnose papilledema, but is not sensitive enough to monitor therapeutic effects. Methods: OCT was applied to follow a 24-year-old woman with headache, visual dysfunction, severe bilateral papilledema, and elevated CSF opening pressure. She was first treated with serial LP, which led to symptom deterioration, increased CSF pressure, and increased the retinal nerve fiber layer (RNFL) thickness. She was then successfully treated with acetazolamide and furosemide. Results: OCT showed reduction of RNFL thickness directly after LP with CSF removal, accompanied with reduced CSF pressure. Increased RNFL thickness accompanied with worsened headache, visual dysfunction, and increased CSF pressure was observed on the next day after LP. Less than 24 h after start of medication, the symptoms had reversed and RNFL thickness was reduced. The patient was symptom-free 2 weeks after starting on medical treatment. Papilledema had vanished on fundoscopy 6 weeks after the therapy, and RNFL thickness was normalized at 3 months of follow-up. Conclusion: This case provides evidence that OCT is an objective and sensitive tool to monitor papilledema and its response to therapy, and thereby important to help in correct clinical decision-making.

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.

Head-Down Tilt Bed Rest Studies as a Terrestrial Analog for Spaceflight Associated Neuro-Ocular Syndrome

Astronauts who undergo prolonged periods of spaceflight may develop a unique constellation of neuro-ocular findings termed Spaceflight Associated Neuro-Ocular Syndrome (SANS). SANS is a disorder that is unique to spaceflight and has no terrestrial equivalent. The prevalence of SANS increases with increasing spaceflight duration and although there have been residual, structural, ocular changes noted, no irreversible or permanent visual loss has occurred after SANS, with the longest spaceflight to date being 14 months. These microgravity-induced findings are being actively investigated by the United States' National Aeronautics Space Administration (NASA) and SANS is a potential obstacle to future longer duration, manned, deep space flight missions. The pathophysiology of SANS remains incompletely understood but continues to be a subject of intense study by NASA and others. The study of SANS is of course partially limited by the small sample size of humans undergoing spaceflight. Therefore, identifying a terrestrial experimental model of SANS is imperative to facilitate its study and for testing of preventative measures and treatments. Head-down tilt bed rest (HDTBR) on Earth has emerged as one promising possibility. In this paper, we review the HDTBR as an analog for SANS pathogenesis; the clinical and imaging overlap between SANS and HDTBR studies; and potential SANS countermeasures that have been or could be tested with HDTBR.

Primary and Secondary Optic Nerve Sheath Meningioma

Objective  This study was aimed to review issues relating to the recognition, radiographic diagnosis, monitoring, and management of primary and secondary optic nerve sheath meningioma (ONSM). Design  This study is a review of peer-reviewed literature combined with illustrative case studies. Participants and Methods  A literature search was conducted via the PubMed database using pertinent search terms. Selected articles were limited to those written or translated into English. Additional works cited within articles were also included. Individual cases were drawn from the experience of a tertiary academic neuroophthalmic and orbital practice. Tables summarize radiotherapeutic and surgical studies, excluding single case reports and studies focusing on meningioma of intracranial origin. Main Outcome Measurements  Review of reported surgical and radiotherapeutic series is the primary measurement. Results  The natural history of optic nerve sheath meningiomas is primarily characterized by progressive ipsilateral vision loss. Diagnosis is typically based on radiographic imaging findings, with biopsy remaining indicated in some patients. Management strategies may include observation, radiation, and/or surgical intervention, or a combination of these approaches. The role of surgery, especially with respect to primary ONSM (pONSM), remains controversial. Advancement of radiotherapy techniques has shifted modern treatment paradigms in pONSM toward radiation as primary treatment, as surgical outcomes are inferior in major studies. Although radiation remains the treatment of choice in many cases, selected patients may benefit from surgery, especially in the setting of secondary ONSM (sONSM). Conclusion  A wide variety of radiotherapeutic and surgical treatment modalities for ONSM exist. The specific indications for each management strategy continue to be redefined.

Hyperintense areas in the intraorbital optic nerve evaluated by T2-weighted magnetic resonance imaging: a glymphatic pathway?

PURPOSE

The present study aimed to explore the glymphatic pathway in the intraorbital optic nerve (ON) using magnetic resonance imaging (MRI).

METHODS

Following conventional MRI examination, a total of 89 outpatients underwent T2-weighted imaging in thin-sliced coronal and sagittal sections. Moreover, three injected cadaver heads were dissected.

RESULTS

In the cadaver specimens, differences in appearance between the central and peripheral parts of the ON were not observed. On the axial T2-weighted MRI performed in the initial examination, the central part of the intraorbital ONs was delineated as a well-demarcated, linear hyperintense area in 19% of patients. On the thin-sliced serial coronal images, the hyperintense areas were identified on both sides in 91% of patients. They were delineated as continuous hyperintense areas in the ONs with an inconsistent appearance even in the same nerve. In 12.4% of patients, the areas were divided into the upper and lower parts by a horizontal septum, while others showed variable morphologies, lacking a septum. On thin-sliced sagittal images, hyperintense areas were identified in 46% of patients.

CONCLUSION

Hyperintense areas in the intraorbital ON detected on T2-weighted sequences may involve a glymphatic pathway with perivascular spaces of the ON and central retinal artery. These may be collapsed and difficult to identify on surgical and cadaver specimens.

Opto-chiasmatic apoplexy as a compartment syndrome? Anatomical and surgical considerations on two bleeding cavernous malformations

OBJECTIVE

Opto-chiasmatic (OC) cavernous malformations are sporadic lesions that are often misdiagnosed clinically and radiologically. Presenting symptoms range from incidental findings to the more frequent and dramatic "chiasmal apoplexy." The present study aims to evaluate the potential role of arachnoidal membranes of the basal cisterns in the onset of OC apoplexy. A possible mechanism resembling a compartment syndrome is discussed through the description of two cases of bleeding cavernomas.

METHODS

We describe clinical, radiological, intraoperative findings in two cases of young patients presenting with OC apoplexy from bleeding cavernoma. The first was a 38-year-old man diagnosed with optic neuritis at the first episode of visual acuity deterioration. The second patient was a 22 -year-old woman who suffered two OC apoplexy episodes from a recurrence, which also presented with bleeding.

RESULTS

Both patients were operated on via pterional craniotomy and presented a postoperative improvement of visual symptoms. The second patient experienced deterioration 30 months after surgical resection due to rebleeding from a recurrence and required a second operation. Follow-up revealed a good recovery of visual disturbances; MRI at 6 and 3 years showed in both patients an apparent complete removal of the cavernous malformations.

CONCLUSION

The cisternal environment where OC cavernous malformations develop and the paradigm of a compartment syndrome could explain the clinical presentation variability. This very rare subset of cavernomas would benefit from a classification system using ad hoc neuroimaging protocols and consistent indications.

Review: Optikussonografie – ein update 2020

Die Optikus-Sonografie bildet Papille, Sehnerv sowie dessen perineuralenLiquorraum ab und eröffnet damit u. a. einen diagnostischen Zugang zumintrakraniellen Liquorsystem und dessen Druck(ICP). Auf diese Weise lässt sich eine relevante ICP-Erhöhung über 20 mmHg nicht-invasiv und bettseitig belegen. Mit Einzelmessungen und Verlaufskontrollen hilft die Methode u. a. vor und nach der Etablierung eines invasiven ICP-Monitorings in der Intensiv- und Notfallmedizin sowie bei der Beurteilung chronischer Dysregulationen des ICP.

Is stagnant cerebrospinal fluid involved in the pathophysiology of normal tension glaucoma

Current concepts of the pathophysiology of normal tension glaucoma (NTG) include intraocular pressure, vascular dysregulation and the concept of a translaminar pressure gradient. Studies on NTG performed with cisternography demonstrated an impaired cerebrospinal fluid (CSF) dynamics in the subarachnoid space of the optic nerve sheath, most pronounced behind the lamina cribrosa. Stagnant CSF might be another risk factor for NTG.