Cerebrospinal Fluid Leak and Idiopathic Intracranial Hypertension in a Transgender Male: Is Intracranial Hypertension Hormonally Mediated?

Introduction: The pathophysiology of idiopathic intracranial hypertension (IIH) is not fully characterized, and less is known about its development in transgender patients. Several cases of IIH in transgender patients have been reported, but fewer cases have been published that identify a cerebrospinal fluid (CSF) leak as a complication of IIH in this population. These patients can serve as an important study population, as an association between exogenous testosterone use in karyotypical females and development of IIH may support a hormonally mediated mechanism of development of this disease. Case Presentation: We describe the case of a 33-year-old obese (BMI: 30.58 kg/m2) female-to-male transgender patient on exogenous testosterone for 15 years who presented with 1 month of acute or chronic headache with profuse rhinorrhea. Fundoscopic exam revealed disk pallor and edema consistent with a Frisen grade 3 papilledema. Nasal secretion was positive for beta-2 transferrin, consistent with CSF. Computed tomography head demonstrated a 5-mm defect in the medial left middle cranial fossa, bilateral optic nerve prominence and tortuosity, and abnormal arachnoid granulations concerning for IIH. After a successful endoscopic endonasal repair of the left lateral sphenoid recess leak, our patient continued to report headaches, was started on acetazolamide, and noted improvement in symptoms. Conclusion: The case described herein further supports the growing body of evidence that implicates a hormonal mechanism of action in the development of IIH. Importantly, it also addresses the need for increased study and conversation about rare neurologic diseases in transgender patients.

Neuroimaging of Vermiform Giant Arachnoid Granulations in Children.

Arachnoid granulations (AGs) are generally benign structures within the subarachnoid space that extend into the dural sinuses and calvarial bone. They can present in a variety of sizes but are termed 'giant' arachnoid granulations (GAGs) when they are larger than 1 cm in diameter or take up a significant portion of the dural sinus' lumen. Vermiform giant arachnoid granulations are a specific type of GAG that are known for their worm-like appearance. Specifically, these vermiform GAGs can be challenging to diagnose as they can mimic other pathologies like dural sinus thrombosis, sinus cavernomas, or brain tumors. In this case series, we present two cases of vermiform giant arachnoid granulations, discuss their imaging characteristics and highlight the diagnostic challenges to improve identification and prevent misdiagnoses.

Arachnoid granulations in idiopathic intracranial hypertension: Do they have an influence?

OBJECTIVE: The aim of this study was to investigate whether the relative narrowing of the dural venous sinuses by arachnoid granulations (AGs) is more pronounced in patients with idiopathic intracranial hypertension (IIH) compared to healthy controls. BACKGROUND: IIH is characterized by increased intracranial pressure, which is associated with symptoms such as headache and visual disturbances. The role of cerebral venous drainage obstruction in IIH is the subject of ongoing research. MATERIALS AND METHODS: In this retrospective case-control study, 3D contrast-enhanced magnetic resonance images of a cohort of 43 patients with IIH were evaluated for (1) the number of AGs per venous sinus and (2) the diameters of the dural venous sinuses at the site of an AG and at standardized measurement points. In addition, the minimum width of the transverse/sigmoid sinus was measured. All data were compared to the same data from a cohort of 43 control participants. RESULTS: Patients with IIH showed less relative sinus narrowing by AG compared to controls (median: 7%, interquartile range [IQR] 10% vs. 11%, IQR 9% in controls; p = 0.009). In patients with IIH, sinus diameter was larger at the site of an AG (70 ± 25 mm2) compared to its diameter at the standardized measurement point (48 ± 23 mm2; p = 0.010). In the superior sagittal sinus (SSS), patients with IIH had smaller AGs (median: 3 mm2, IQR 2 mm2 vs. 5 mm2, IQR 3 mm2 in controls; p = 0.023) while the respective sinus segment was larger (median: 69 mm2; IQR 21 mm2 vs. 52 mm2, IQR 26 mm2 in controls; p = 0.002). The right transverse sinus was narrower in patients with IIH (41 ± 21 mm vs. 57 ± 20 mm in controls; p < 0.001). CONCLUSIONS: In contrast to our hypothesis, patients with IIH showed less pronounced relative sinus narrowing by AG compared to controls, especially within the SSS, where AGs were smaller and the corresponding sinus segment wider. Smaller AGs could result in lower cerebrospinal fluid resorption, favoring the development of IIH. Conversely, the smaller AGs could also be a consequence of IIH due to backpressure in the SSS because of the narrower transverse/sigmoid sinus, which widens the SSS and compresses the AG.

Endovascular Shunting for Communicating Hydrocephalus Using a Biologically Inspired Transdural Cerebrospinal Fluid Valved eShunt® Implant.

Cerebrospinal fluid (CSF) bathing the central nervous system is produced by brain and choroid plexus within the ventricles for re-absorption into the venous circulation through arachnoid granulations (AG). Communicating hydrocephalus results from disruption of the absorptive process, necessitating surgical catheter-based shunt placement to relieve excess pressure from CSF buildup. Adjustable valve designs and antibiotic impregnation have minimally impacted persistent failure rates and postoperative complications. To confront this challenge, we have developed an innovative endovascular shunt implant biologically inspired from AG function to restore the natural dynamics of CSF drainage while concurrently addressing the predominant factors contributing to conventional shunt malfunction.

The role of arachnoid granulations in idiopathic intracranial hypertension.

OBJECTIVES: Idiopathic intracranial hypertension (IIH) is a disease defined by elevated intracranial pressure (ICP) without an established etiology. Arachnoid granulations (AG) are conduits for CSF resorption from the subarachnoid space to the venous system. AG have been implicated to play a central role in maintaining CSF homeostasis. We tested the hypothesis that patients with fewer visible AG on MRI are more likely to present with IIH. METHODS: In this institutional review board (Institutional Review Board)-approved retrospective chart review study, 65 patients with a clinical diagnosis of idiopathic intracranial hypertension were compared to 144 control patients who met inclusion/exclusion criteria. Patients' signs and symptoms pertaining to IIH were obtained through the electronic medical record Brain MR images were reviewed for the number and distribution of AGs indenting the dural venous sinuses. The presence of imaging and clinical findings associated with long standing increased ICP was noted. Propensity score method (with inverse probability weighting technique) was used to compare case and control groups. RESULTS: In the control group, the number of AG indenting the dural venous sinuses on MRI (NAG) was lower in women compared to men when matched for age (20-45 yo) and BMI (>30 kg/m2). The NAG was lower in 20-45 yo females in the IIH group as compared to the 20-45 yo females in the control group. This statistically significant difference persists when controlled for BMI. In contrast, the NAG in >45 yo females in the IIH group trended higher compared to the >45 yo females in the control group. CONCLUSION: Our results suggest that alterations in arachnoid granulations could play a role in the development of IIH.

Microanatomical study of arachnoid granulations and meningeal architecture around Meckel's cave.

Although the microanatomy of Meckel's cave (MC) has been well studied, there are still controversies regarding the meningeal architecture of the space. Moreover, there are only general mentions of the arachnoid granulations near MC in just a few sources. This study is aimed at determining the frequency, location, and anatomical variability of the main clusters of arachnoid granulations around MC. The dissection involved 26 isolated specimens of MC fixed in formalin (neutral buffered, 10%). This number included five freshly harvested specimens examined histologically. Additional paraffin block with MC horizontal section was taken from our neuroanatomical collection. Carefully selected anatomical and histological techniques were applied to assess the complex relationships between the arachnoid granulations and adjacent structures. Arachnoid granulations were found around MC in all specimens with different anatomical variations. The main clusters of arachnoid granulations were close to the trigeminal ganglion and its divisions. The dorsolateral wall of MC was a thick layer formed by interweaving bundles of collagen fibers arranged in various directions. The entire MC was surrounded by a dural sleeve (envelope). This sleeve separated MC from the lateral sellar compartment. At its anterior (rostral) end, it formed a cribriform area pierced by individual fascicles of the trigeminal nerve's primary divisions. The connective tissue forming the sleeve was not only continuous with the epineurium but also shifted to the perineuria surrounding individual nerve fascicles. The meningeal architecture around MC has a complex and multilayer arrangement with a collagenous sleeve closely related to the trigeminal ganglion. Arachnoid granulations are typically found around MC.

Arachnoid granulations may be protective against the development of shunt dependent chronic hydrocephalus after aneurysm subarachnoid hemorrhage*.

BACKGROUND AND PURPOSE: Chronic hydrocephalus may develop as a sequela of aneurysmal subarachnoid hemorrhage, requiring long-term cerebrospinal fluid shunting. Several clinical predictors of chronic hydrocephalus and shunt dependence have been proposed. However, no anatomical predictors have been identified. MATERIALS AND METHODS: A retrospective cohort study was performed including 61 patients with aneurysmal subarachnoid hemorrhage. Clinical characteristics were noted for each patient including presentation World Federation of Neurosurgical Societies grade, modified Fischer grade, aneurysm characteristics, requirement for acute and chronic cerebrospinal fluid diversion, and 3-month modified Rankin scale. CT images were evaluated to determine the Evans' index and to enumerate the number of arachnoid granulations. Association between the clinical characteristics with ventriculoperitoneal shunt insertion and the 3-month modified Rankin scale were assessed. RESULTS: The initial Evans' index was positively associated with mFisher grade and age, but not the number of arachnoid granulations. 16.4% patients required insertion of a ventriculoperitoneal shunt. The number of arachnoid granulations were a significant negative predictor of ventriculoperitoneal shunt insertion [OR: 0.251 (95% CI:0.073-0.862; p = 0.028)]. There was significant difference in the number of arachnoid granulations between those with and without ventriculoperitoneal shunt (p = 0.002). No patient with greater than 4 arachnoid granulations required a ventriculoperitoneal shunt, irrespective of severity of initial grade. CONCLUSION: Arachnoid granulations may be protective against the development of shunt dependent chronic hydrocephalus after aneurysmal subarachnoid hemorrhage. This is irrespective of presenting hemorrhage severity. This is a potentially novel radiologic biomarker and anatomic predictor of shunt dependence.

Evaluation of anterior and middle cranial fossa intraosseous arachnoid granulations with 3D T2-SPACE sequence.

OBJECTIVES: Arachnoid granulations (AG) can be located anywhere outside the dural sinuses. Their presence is thought to be associated with idiopathic intracranial hypertension (IIH) and cerebrospinal fluid (CSF) leaks. It was aimed to evaluate the intraosseous AGs located in the middle and anterior cranial fosses in detail with three-dimensional T2-SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolution-Siemens) imaging and to investigate their clinical significance. MATERIALS AND METHODS: Sixty-five intraosseous AG of 46 patients were included in this retrospective study. The highest diameter, bone indentation degree (in the inner tabula, diploe distance, reaching and exceeding the outer tabula), content (CSF/+parenchyma) of each AG were evaluated by 2 experienced radiologists. In addition, the presence of other MRI findings supporting IIH was examined. RESULTS: Additional signs of IIH were detected in 25 patients, and they were statistically significantly more common in the middle cranial fossa. Parenchymal herniation (in four patients) was more common in the young population. CONCLUSIONS: Intraosseous AGs can be evaluated in detail with T2-SPACE imaging. Determining intraosseous AG is very important both as an indicator of IIH and in terms of its content. T2-SPACE imaging is superior to CT and conventional sequences in this regard.

Anatomy imaging and hemodynamics research on the cerebral vein and venous sinus among individuals without cranial sinus and jugular vein diseases.

In recent years, imaging technology has allowed the visualization of intracranial and extracranial vascular systems. However, compared with the cerebral arterial system, the relative lack of image information, individual differences in the anatomy of the cerebral veins and venous sinuses, and several unique structures often cause neurologists and radiologists to miss or over-diagnose. This increases the difficulty of the clinical diagnosis and treatment of cerebral venous system diseases. This review focuses on applying different imaging methods to the normal anatomical morphology of the cerebral venous system and special structural and physiological parameters, such as hemodynamics, in people without cranial sinus and jugular vein diseases and explores its clinical significance. We hope this study will reinforce the importance of studying the cerebral venous system anatomy and imaging data and will help diagnose and treat systemic diseases.

Anatomical Study of Arachnoid Granulation in Superior Sagittal Sinus Correlated to Growth Patterns of Meningiomas.

Meningiomas in the parasagittal region were formed by arachnoidal cells disseminated among arachnoid granulations. The purpose of this study was to characterize the morphology of chordae willisii, and AGs found in the superior sagittal sinus. This study used 20 anatomical specimens. Rigid endoscopes were introduced via torcula herophili into the sinus lumen. The morphological features of arachnoid granulation and chordae willisii were analyzed, and then arachnoid granulations and chordae willisii were assessed by elastic fiber stains, Masson's stains, and imaging analysis. Three types of arachnoid granulations were present in the examined sinuses. There were 365 counts of arachnoid granulations in examined sinuses by imaging analysis, averaging 1.36 ± 2.58 per sinus. Types I, II, and III made up 20.27, 45.20, and 34.52% of 268 patients, respectively. Microscopy of chordae willisii transverse sections indicated the existence of a single layer and a multiple-layered dura sinus wall. The dural sinus wall was the thickest one in the superior sagittal sinus. The thickness of longitudinal lamellae was significantly greater than trabeculae. This study reveals the anatomical differences between arachnoid granulations in the superior sagittal sinus. The arachnoid granulations classification enables surgeons to predict preoperatively growth patterns, followed by safely achieving the optimal range of parasagittal meningioma resection.

A subset of arachnoid granulations in humans drain to the venous circulation via intradural lymphatic vascular channels.

OBJECTIVE: The discovery of dural lymphatics has spurred interest in the mechanisms of drainage of interstitial fluid from the CNS, the anatomical components involved in clearance of macromolecules from the brain, mechanisms of entry and exit of immune components, and how these pathways may be involved in neurodegenerative diseases and cancer metastasis. In this study the authors describe connections between a subset of arachnoid granulations (AGs) and the venous circulation via intradural vascular channels (IVCs), which stain positively with established lymphatic markers. The authors postulate that the AGs may serve as a component of the human brain's lymphatic system. METHODS: AGs and IVCs were examined by high-resolution dissection under stereoscope bilaterally in 8 fresh and formalin-fixed human cadaveric heads. The superior sagittal sinus (SSS) and adjacent dura mater were immunostained with antibodies against Lyve-1 (lymphatic marker), podoplanin (lymphatic marker), CD45 (panhematopoietic marker), and DAPI (nuclear marker). RESULTS: AGs can be classified as intradural or interdural, depending on their location and site of drainage. Interdural AGs are distinct from the dura, adhere to arachnoid membranes, and occasionally open directly in the inferolateral wall or floor of the SSS, although some cross the infradural folds of the dura's inner layer to meet with intradural AGs and IVCs. Intradural AGs are located within the leaflets of the dura. The total number of openings from the AGs, lateral lacunae, and cortical veins into the SSS was 45 ± 5.62 per head. On average each cadaveric head contained 6 ± 1.30 intradural AGs. Some intradural AGs do not directly open into the SSS and use IVCs to connect to the venous circulation. Using immunostaining methods, the authors demonstrate that these tubular channels stain positively with vascular and lymphatic markers (Lyve-1, podoplanin). CONCLUSIONS: AGs consist of two subtypes with differing modes of drainage into the SSS. A subset of AGs located intradurally use tubular channels, which stain positively with vascular and lymphatic markers to connect to the venous lacunae and ultimately to the SSS. The present study suggests that AGs may function as a component of brain lymphatics. This finding has important clinical implications for cancer metastasis to and from the CNS and may shed light on mechanisms of altered clearance of macromolecules in the setting of neurodegenerative diseases.

The evaluation of cerebral venous normal anatomy and variations by phase-contrast cranial magnetic resonance venography.

BACKGROUND: The aim of our study was to determine the ability of the phase-contrast-cranial magnetic resonance venography (PC-CMRV) technique to detect cranial anatomy, variations, thrombosis, to reveal the deficits of the technique and to discuss the reasons for these deficits on a physics basis. MATERIALS AND METHODS: Phase-contrast's detection rates of anatomic variations and physiological filling defects (FDs) were evaluated in 136 patients and compared with the time-of-flight technique magnetic resonance imaging (MRI) and cadaveric studies. RESULTS: The dominance correlation between the three evaluated sinuses (transverse sinus [TS], sigmoid sinus, jugular vein) which originated from different embryological buds was statistically significant and the right vessel chain was dominant. PC is inadequate to show some vessels like inferior sagittal sinus (anatomically, this vessel is approximately present in 100% of the cases, but it was only visualised in 41.2% of the patients in PC-MRI). Visualisation of major veins was sufficient. PC-MRI created physiological FDs in 27.2% (72.3% middle, 10.3% inner, 17% outer part) of the patients. The FDs were concentrated in the middle part and not observed in the dominant sinus. CONCLUSIONS: The defects of visualisation are present due to the PC's technique. It can be misdiagnosed as agenesis or thrombosis. PC creates a high incidence of physiologic FDs in TS. The results are not reliable, especially if FDs are in the middle part or non-dominant side.

[A case of spontaneous middle cranial fossa cerebrospinal fluid leak presenting as recurrent bacterial meningitis].

A 19-year-old man with a history of Chiari type I malformation was admitted to our hospital two times within a 2-month period because of bacterial meningitis. Cerebrospinal fluid (CSF) analysis showed neutrophilic pleocytosis and hypoglycorrhachia. During the second admission, we became aware of hearing loss on the right since age 15 years. High-resolution temporal bone CT showed soft tissue opacification of the right epitympanum and external auditory canal. Tissue biopsy resulted in CSF otorrhea and pneumocephalus. CT cisternography revealed a temporal bone CSF leak. Brain MRI showed a dural defect localized to the anterior petrous apex. Using a combined middle cranial fossa-transmastoid approach, the dural defect and associated arachnoid granulations were located along the superior side of the greater petrosal nerve and repaired. A CSF leak without underlying pathology, such as trauma, surgery, or congenital abnormality, is defined as spontaneous. Spontaneous CSF leak should be considered as a cause of recurrent bacterial meningitis even when CSF otorrhea and fluid behind the tympanic membrane are clinically absent.

No Arachnoid Granulations-No Problems: Number, Size, and Distribution of Arachnoid Granulations From Birth to 80 Years of Age.

Introduction: The study aims to quantify changes in the number, size, and distribution of arachnoid granulations during the human lifespan to elucidate their role in cerebrospinal fluid physiology. Material and Methods: 3T magnetic resonance imaging of the brain was performed in 120 subjects of different ages (neonate, 2 years, 10 years, 20 years, 40 years, 60 years, and 80 years) all with the normal findings of the cerebrospinal fluid system (CSF). At each age, 10 male and 10 female subjects were analyzed. Group scanned at neonatal age was re-scanned at the age of two, while all other groups were scanned once. Arachnoid granulations were analyzed on T2 coronal and axial sections. Each arachnoid granulation was described concerning size and position relative to the superior sagittal, transverse, and sigmoid sinuses and surrounding cranial bones. Results: Our study shows that 85% of neonates and 2-year-old children do not have visible arachnoid granulations in the dural sinuses and cranial bones on magnetic resonance imaging. With age, the percentage of patients with arachnoid granulations in the superior sagittal sinus increases significantly, but there is no increase in the sigmoid and transverse sinuses. However, numerous individuals in different age groups do not have arachnoid granulations in dural sinuses. Arachnoid granulations in the cranial bones are found only around the superior sagittal sinus, for the first time at the age of 10, and over time their number increases significantly. From the age of 60 onwards, arachnoid granulations were more numerous in the cranial bones than in the dural sinuses. Conclusion: The results show that the number, size, and distribution of arachnoid granulations in the superior sagittal sinus and surrounding cranial bones change significantly over a lifetime. However, numerous individuals with a completely normal CSF system do not have arachnoid granulations in the dural sinuses, which calls into question their role in CSF physiology. It can be assumed that arachnoid granulations do not play an essential role in CSF absorption as it is generally accepted. Therefore, the lack of arachnoid granulations does not appear to cause problems in intracranial fluid homeostasis.

Changes of arachnoid granulations after subarachnoid hemorrhage in cynomolgus monkeys.

This research explores ultrastructural changes of arachnoid granulations associated with hydrocephalus after subarachnoid hemorrhage in cynomolgus monkeys. It provides a theoretical basis for further study of the etiology and prevention of hydrocephalus. Female cynomolgus monkeys about one-year-old were selected. The position range of arachnoid granulations in superior sagittal sinus and transverse sinus was determined in a randomly selected control monkey. The morphology of normal arachnoid granulations in cynomolgus monkeys was observed under a transmission electron microscope. A primate model of subarachnoid hemorrhage was established by injecting autologous blood into cisterna magna. Vomiting, movement disorder, and reduced level of consciousness were gradually observed in monkeys. Computed tomography and magnetic resonance imaging scan results confirmed subarachnoid hemorrhage and hydrocephalus, and the morphology of arachnoid granulations in hydrocephalus was observed under a transmission electron microscope. Extensive fibrosis of arachnoid granulations was observed under a transmission electron microscope in cynomolgus monkeys with hydrocephalus after subarachnoid hemorrhage.

Arachnoid granulations bulging into the transverse sinus, sigmoid sinus, straight sinus, and confluens sinuum: a magnetic resonance imaging study.

PURPOSE: Few studies have explored arachnoid granulations (AGs) bulging into the cranial dural sinuses using contrast-enhanced magnetic resonance imaging (MRI). This study aimed to explore such AGs in the transverse (TS), sigmoid (SigS), and straight (StS) sinuses, and confluens sinuum (ConfS) using thin-sliced, contrast MRI. METHODS: A total of 102 patients with intact dural sinuses underwent thin-sliced, contrast MRI in the axial, coronal, and sagittal planes. RESULTS: In 88.2%, more than one AG was identified in the TS and SigS, StS, and ConfS. In the TS, AGs were identified in 40.2% on the right side and 37.3% on the left and were frequently located in the middle and lateral thirds. In the SigS, AGs were identified on the right in 17.6% and on the left in 18.6% in the distal region. In the StS, AGs were identified in 35.3% of cases, most frequently located in the proximal third, followed by the distal third. In the ConfS, AGs were identified in 20.6% of cases. Furthermore, in 23.5%, a collection of multiple AGs of varying sizes was found in the TS. A statistical difference was not shown between the mean age of 90 patients with AGs and that of 12 patients without identifiable AGs. CONCLUSIONS: Bulging AGs may more frequently found in the TS. Thin-sliced, contrast MRI is useful for delineating AGs.

Evaluation of fluid channels in the human dura and superior sagittal sinus in older patients.

AIM: Recent studies suggest the leptomeninges may have a lymphatic drainage system connecting the subarachnoid space with dorsal cervical lymph nodes. The distribution and histologic features of any dural "lymphatics" has not been established or extensively studied. MATERIAL AND METHODS: Duras from 113 patients were evaluated including 96 formalin-fixed dural samples (mean age 62 years) collected from 2010 to 2015. An additional 17 samples were collected from Alzheimer's disease (AD) patients (mean age 81) autopsied between 1995 and 1997. Two, 2 cm length coronal sections were taken from mid-convexity dura, parallel to the middle meningeal artery, 3-5 cm below and perpendicular to the superior sagittal sinus (SSS). Sections of twenty-two cases were also taken of the SSS and peri-SSS dura. To screen for possible lymphatics, 52 dural and 22 SSS samples from these cases were evaluated with CD31 and podoplanin (D240) immunohistochemistry. RESULTS: Numerous unlined microscopic channels were found in 101 of 113 (89 %). In non-AD duras, 86 of 92 (93 %) had numerous channels. Duras with AD had significantly less channels i.e. 15 of 21(71 %, P = 0.048). None of the channels had lymphocytes, or neutrophils in their lumena. In the superior sagittal sinus, 9 of 9 non-AD and 12/13 AD SSS duras had fluid channels. Congo red stains revealed no amyloid-like material in the AD duras. Immunohistochemically, CD31 was not found in fluid channels but was in endothelium in 36 of 36 non-AD duras and in most blood vessels including 16 of 16 AD patients. Seven of 36 (19 %) with non-AD and 1 of 16 (6%) with AD had podoplanin in thin walled vessels suggestive of lymphatics but none showed staining in fluid channels. CONCLUSIONS: Unlined fluid channels are present in the dura but not clearly lymphatic.

The Regulation of Cerebral Spinal Fluid Flow and Its Relevance to the Glymphatic System.

PURPOSE OF REVIEW: The glymphatic system is a relatively new concept that has been associated with regulation of cerebrospinal fluid (CSF), as well as brain waste clearance. Novel techniques to study glymphatic dysfunction have in turn prompted a reassessment of brain physiology and underlying elements of neurological disease. This review incorporates a contemporary imaging perspective focused on understanding the regulation of CSF flow, thus expanding the putative clinical relevance of this system and the relationships between CSF flow and glymphatic function. RECENT FINDINGS: MR imaging studies, especially those that employ intrathecal gadolinium contrast, have identified potentially new pathways regulating CSF production, absorption, and clearance. These studies, when viewed in the context of more historical anatomic descriptors of CSF production and absorption, provide a more robust description of CSF physiology and waste clearance. CSF production and resorption are under-investigated and could be related to various pathophysiologic processes in neurodegeneration. Anatomically based clinical exemplars of CSF clearance are discussed. Future studies should focus on linking glymphatic functionality with neurological disease.

The Role of Arachnoid Granulations and the Glymphatic System in the Pathophysiology of Idiopathic Intracranial Hypertension.

PURPOSE OF REVIEW: Idiopathic intracranial hypertension (IIH) is a disorder characterized by long-standing elevated intracranial pressure (ICP). As the name applies, no uniform cause has been identified. IIH is typically characterized by headaches, pulsatile tinnitus, and visual deterioration. RECENT FINDINGS: Anomalies in cerebrospinal fluid (CSF) absorption are implicated in the pathophysiology of IIH. Non-invasive imaging of the brain parenchyma and the cerebral venous sinus has improved, and research has gained a better understanding of the role of cerebral venous sinus stenosis. Both have led to a better delineation of the role of arachnoid granulations (AG) and the glymphatic system in the development of IIH. IIH may occur as a result of restrictions of CSF absorption from the venous system, and or the congestion and overflow of the glymphatic system. Elucidating these mechanisms will lead to greater understanding of its underlying pathophysiologic mechanisms.