Brain Imaging in Idiopathic Intracranial Hypertension

Weakness of the sixth cranial nerve is the most common cause of an ocular motor cranial nerve palsy. It is often difficult to identify a corresponding abnormality on neuroimaging to correlate with the clinical examination.; ; High-resolution 3D skull base magnetic resonance imaging (MRI) allows for visualization of the sixth nerve along much of its course and may increase sensitivity for abnormalities in regions that previously were challenging to evaluate. In this review, the authors share their experience with high-resolution imaging of the sixth nerve.; ; For each segment, anatomic features visible on high-resolution imaging are described along with relevant pathologic entities.; ; We present a segmental approach to high-resolution 3D MRI for evaluation of the sixth nerve from the nuclear to the orbital segment.

State-of-the-Art Review Section Editors: Valérie Biousse, MD Steven Galetta, MD Brain Imaging in Idiopathic Intracranial Hypertension Samuel Bidot, MD, Amit M. Saindane, MD, Jason H. Peragallo, MD, Beau B. Bruce, MD, PhD, Nancy J. Newman, MD, Valérie Biousse, MD Background: The primary role of brain imaging in idiopathic intracranial hypertension (IIH) is to exclude other pathologies causing intracranial hypertension. However, subtle radiologic findings suggestive of IIH have emerged with modern neuroimaging. This review provides a detailed description of the imaging findings reported in IIH and discusses their possible roles in the pathophysiology and the diagnosis of IIH. Evidence Acquisition: References were identified by searches of PubMed from 1955 to January 2015, with the terms "idiopathic intracranial hypertension," "pseudotumor cerebri," "intracranial hypertension," "benign intracranial hypertension," "magnetic resonance imaging," "magnetic resonance venography," "computed tomography (CT)," "CT venography," "imaging," and "cerebrospinal fluid (CSF) leak." Additional references were identified by hand search of relevant articles. When possible, we extracted the number of patients and control subjects from each study for each radiological finding. When at least 2 studies used the same criteria to define a radiological finding, all patients from these studies were pooled to obtain a mean sensitivity and specificity with 95% confidence interval. Results: Specific neuroimaging findings may suggest longstanding IIH, including empty sella, flattening of the posterior globes, optic nerve head protrusion, distention of the optic nerve sheaths, tortuosity of the optic nerve, cerebellar tonsillar herniation, meningoceles, CSF leaks, and transverse venous sinus stenosis. Departments of Ophthalmology (SB, JHP, BBB, NJN, VB), Radiology and Imaging Sciences (AMS), Pediatrics (JHP), and Neurology (BBB, NJN, VB), Emory University School of Medicine, Atlanta, Georgia; Department of Epidemiology (BBB), Rollins School of Public Health, Emory University, Atlanta, Georgia; and Department of Neurological Surgery (NJN), Emory University School of Medicine, Atlanta, Georgia. Supported in part by an unrestricted departmental Grant (Department of Ophthalmology) from Research to Prevent Blindness, Inc, New York, and by NIH/NEI core Grant P30-EY06360 (Department of Ophthalmology). Dr. Bidot receives research support from Berthe Fouassier Foundation (Paris, France) and the Philippe Foundation (New York, NY). Dr. Bruce receives research support from the NIH/ NEI (K23-EY019341). Dr. Newman received the Research to Prevent Blindness Lew R. Wasserman Merit Award. The authors report no conflicts of interest. Address correspondence to Valérie Biousse, MD, NeuroOphthalmology Unit, Emory Eye Center, The Emory Clinic, 1365-B Clifton Road NE, Atlanta, GA 30322; E-mail: [e-mail] 400 Conclusion: Although IIH remains a diagnosis of exclusion, the most recently proposed diagnostic criteria have included neuroimaging findings to suggest IIH when major diagnostic criteria are not fulfilled. However, these findings are not diagnostic of IIH, and their presence is not required for the diagnosis of definite IIH. Their incidental discovery on brain imaging should not prompt invasive procedures, unless other signs of IIH, such as papilledema, are present. Journal of Neuro-Ophthalmology 2015;35:400-411 doi: 10.1097/WNO.0000000000000303 © 2015 by North American Neuro-Ophthalmology Society A ccording to the modified Dandy criteria (1), the primary role of brain imaging in idiopathic intracranial hypertension (IIH) is to exclude other pathologies causing increased cerebrospinal fluid (CSF) pressure. However, since the earliest reports showing demineralization of the pituitary fossa on plain skull radiographs and small size of the ventricles on ventriculography in so-called "benign intracranial hypertension" (2), a constellation of more subtle findings suggestive of longstanding IIH gradually has emerged with modern neuroimaging. Their introduction in the most recent, albeit controversial (3,4), diagnostic criteria for the diagnosis of "possible IIH" (5) reflects the growing interest in the primary diagnosis of IIH rather than excluding an alternative condition (Table 1). Magnetic resonance imaging (MRI) is the imaging of choice in IIH (5), in excluding other causes of increased intracranial pressure (ICP). MRI findings of raised ICP include empty sella flattening of the posterior globes, distention of the optic nerve sheaths, cerebellar tonsillar herniation, meningoceles, and transverse venous sinus stenosis (Table 2). Whether these findings truly assist clinicians in establishing the diagnosis of IIH or generate a number of overdiagnoses remains unclear. This review provides a detailed description of the neuroimaging findings reported in IIH (Methods) and discusses their possible roles in the pathophysiology and diagnosis of this disorder. Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review TABLE 1. Most recently proposed diagnostic criteria for idiopathic intracranial hypertension (IIH) (5) 1. Required for the diagnosis of IIH A diagnosis of IIH is definite if the patient fulfills criteria A-E. The diagnosis is considered probable if criteria A-D are met but the measured CSF pressure is lower than specified for a definite diagnosis A. Papilledema B. Normal neurologic examination except for cranial nerve abnormalities C. Neuroimaging: normal brain parenchyma without evidence of hydrocephalus, mass, or structural lesion and no abnormal meningeal enhancement on MRI, with and without gadolinium, for typical patients (obese women), and MRI, with and without contrast, and MRV for others; if MRI is unavailable or contraindicated, contrast-enhanced CT may be used D. Normal CSF composition E. Elevated lumbar puncture CSF opening pressure ($250 mm water in adults and $280 mm water in children [250 mm water if the child is not sedated and not obese]) in a properly performed lumbar puncture 2. Diagnosis of IIH without papilledema In the absence of papilledema, a diagnosis of IIH can be made if B-E from above are satisfied, and in addition, the patient has a unilateral or bilateral abducens nerve palsy In the absence of papilledema or sixth nerve palsy, a diagnosis of IIH can be suggested, but not made, if B-E from above are satisfied, and in addition, at least 3 of the following neuroimaging criteria are satisfied Empty sella Flattening of the posterior aspect of the globe Distention of the perioptic subarachnoid space with or without a tortuous optic nerve Transverse venous sinus stenosis CSF: cerebrospinal fluid; CT: computed tomography; MRI: magnetic resonance imaging; MRV: magnetic resonance venography. METHODS Search Strategy and Selection Criteria References for this review were identified by searches of PubMed from 1955 to January 2015, with the terms "idiopathic intracranial hypertension," "pseudotumor cerebri," "intracranial hypertension," "benign intracranial hypertension," "MRI," "magnetic resonance venography (MRV)," "computed tomography (CT)," "CT venography (CTV)," "imaging," and "CSF leak." Additional references were identified by hand search of journals and relevant articles. Only articles published in English and in French were reviewed. The final reference list was generated on the basis of originality and relevance to the topics covered in the review. Priority was given to the most recent references. Statistical Analysis When possible, we extracted the number of patients and, if available, the number of control subjects from each study for each radiological finding. When at least 2 studies used the same criteria to define a radiological finding, all patients from these studies were pooled to obtain a mean sensitivity with its 95% confidence interval (CI) by normal approximation to the binomial. When control subjects were available, the same method was used to obtain the mean TABLE 2. Neuroimaging findings described in idiopathic intracranial hypertension (IIH) Presumed Mechanism Findings Bony erosion from IIH Empty sella CSF leak Meningocele/meningoencephalocele Foramen ovale widening Mechanical Posterior flattening of the posterior deformation from IIH poles Optic nerve head protrusion Distention of the optic nerve sheath Vertical tortuosity of the optic nerve Transverse sinus venous stenosis Papilledema Enhancement of the optic nerve head Uncertain Tonsillar herniation $5 mm Pooled Sensitivity [95% CI] Pooled Specificity [95% CI] 80% [71-89] (11,12) NA 11% [4-18]* (39) 50% [36-64]* (20) 66% [60-72] (8-10,12,19,20) 83% [76-90] (8-10) NA 0% [NA]* (39) 80% [69-91]* (20) 98% [96-100] (8-10,20) 36% 58% 43% 97% 17% 16% 99% 89% 90% 93% 99% 95% [28-44] (8-10,12,19,20) [48-68] (9,10,12) [37-50] (8-10,12,19,20) [93-100] (55,64,66) [11-23] (8-10,19) [10-22] (9,34,37) [98-100] (8-10,20) [85-95] (9,10) [85-95] (8-10,20) [84-97]* (55) [97-100] (8-10) [91-100] (9,34) Pooled sensitivity and specificity were obtained from at least 2 studies using the same criteria to define the findings. *Obtained from one single study (provided by the authors or recalculated). CSF, cerebrospinal fluid; NA, not available. Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 401 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review specificity with its 95% CI. Our intention is to provide useful information to clinicians regarding the sensitivity and specificity, including their CI, of each radiologic finding by pooling several similar studies. However, differences among centers of MRI brand, protocol, data postprocessing, and, to a lesser extend, IIH criteria might reduce the scope of these results. EMPTY SELLA Empty sella is the most commonly reported imaging finding in patients with IIH, but it is also quite common in the general population. The term "empty sella" refers to complete or partial CSF filling of the sella turcica associated with lack of visible pituitary gland on mid-sagittal T1 MRI FIG. 1. Precontrast mid-sagittal T1 magnetic resonance imaging (MRI) of empty sella based on the classification of Yuh et al (11). A. Category I, normal. The anterior aspect of the pituitary gland appears isointense with brain and fills the sella turcica. B. Category II, mild superior concavity, less than 1/3 height of the sella turcica. C. Category III, moderate concavity, between 1/3 and 2/3 height of the sella turcica. D. Category IV, severe concavity, more than 2/3 height of the sella turcica. E. Category V, no pituitary tissue visible. A partially empty sella is defined by Grade III and IV and an empty sella by Grade V. 402 Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review (Fig. 1) (6). Unlike secondary empty sella, in which the size of the pituitary gland is decreased with respect to the sella turcica (7), primary empty sella is believed to be related to an intrasellar herniation of arachnoid mater and CSF, which flattens the pituitary gland and remodels the sella turcica (7). The sensitivity of empty sella in IIH ranges from 65% to 80%, depending on the definition used (8-12). With the commonly used system developed by Yuh et al (11) (Fig. 1), the pooled sensitivity is estimated to be 80% (95% CI: 71- 89) (11,12). Severe empty sella (Category V) with lack of visible pituitary gland is uncommon, found in less than 10% of cases (11,12). However, an empty sella is not specific to IIH and has been found in various causes of chronic intracranial hypertension such as cerebral venous sinus thrombosis and intracranial space-occupying lesions (11-13). In addition, it has been reported as an incidental radiologic finding in normal subjects (14), in whom it has the same appearance as in IIH patients (15). The specificity of empty sella in IIH ranges broadly across studies from 70% (10) to 100% (11). When using the definition based on the cross-sectional area of the sella (Fig. 1) (8-10), the pooled specificity is estimated at 83% (95% CI: 76-90). Few morphometric studies of the sellar region in patients with IIH have been performed (6,12,16,17). Taken together, they suggest that enlargement and remodeling of the sella turcica is the main contributor to the empty sella appearance. Yet, some degree of compression of the pituitary gland appears likely with IIH as partial (6), and even complete (18) resolution of the "empty sella" appearance has been reported after treatment of IIH. Few studies mention how long it takes for empty sella to develop in a patient with IIH. Saindane et al (15), using cross-sectional data, demonstrated that the sellar width on average enlarges 1 mm per decade in patients with IIH, suggesting that the bony findings take years to develop. ORBITAL FINDINGS The orbital findings in IIH mirror the mechanical deformations of the optic nerve sheath, lamina cribrosa, and posterior sclera secondary to elevated CSF pressure transmitted along the intraorbital optic nerve. Studies (8- 10,12,19,20) have most often reported these findings based on subjective radiologic interpretation, likely explaining suboptimal reader agreement (21) and the wide range of sensitivity reported. Posterior Globe flattening and Optic Nerve Head Protrusion Posterior globe flattening and, in more severe cases, optic nerve head protrusion correspond to loss of normal curvature of the posterior sclera seen on axial MRI at the bulbar insertion of the optic nerve (Fig. 2) (10). On funduscopic examination, IIH patients with posterior globe flattening may have macular choroidal folds. In some patients, flattening of the posterior globes and choroidal folds may precede papilledema, emphasizing the importance of including intracranial hypertension, and especially IIH, in the differential diagnosis of "flat globe syndrome" (22). The sensitivity of posterior globe flattening in IIH ranges from 43% to 85% and from 3% to 59% for optic nerve head protrusion and a pooled sensitivity of 66% (95% CI: 60-72) and 36% (95% CI: 26-44), respectively (8-10,12,19,20), and a pooled specificity of 98% (95% CI: 96-100) and 99% (95% CI: 98-100), respectively (8-10,20). Posterior globe flattening likely reflects the gradient between the perioptic CSF and the intraocular pressures. It is not specific for IIH, as ocular hypotony displays a similar appearance on MRI (23). Enhancement of the Optic Disc Enhancement of the optic disc on postcontrast axial T1 orbital MRI (Fig. 3) is one of the less sensitive findings in IIH, likely because of the small size of the region of FIG. 2. A. Axial T2 fat-saturated scan shows flattening of the posterior globes (arrows) around the insertion of the optic nerve. B. There is protrusion of the optic nerve head into the vitreous cavity (arrows) on axial fluid-attenuated inversion recovery (FLAIR) image. Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 403 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review at 58% (95% CI: 48-68) (9,10,12), and pooled specificity is estimated at 89% (95% CI: 85-95) (9,10). Vertical Tortuosity of the Optic Nerve The "kinked" appearance of the intraorbital portion of the optic nerve is visualized best on oblique sagittal views (Fig. 5). It is believed to be secondary to the distention of the sheath between the 2 ends of its intraorbital optic nerve, which are fixed at the scleral insertion and orbital apex (8). Based only on subjective impression and not quantifiable characteristics, its sensitivity ranges from 21% to 55%, with a pooled sensitivity of 43% (95% CI: 37-50) (8-10,12,19,20) and a pooled specificity of 90% (95% CI: 85-95) (9-10,20). FIG. 3. Postcontrast axial T1 magnetic resonance imaging (MRI) with fat suppression reveals enhancement of the optic nerve head (arrow). Flattening of the posterior globes is seen bilaterally. interest (24). Its sensitivity ranges from 2% to 50%, with a pooled sensitivity of 17% (95% CI: 11-23) (8-10,19). It is not specific for papilledema, and it has been reported in other causes of optic disc edema (25-27). Its specificity is very high, close to 100%, as it has so rarely been reported in normal controls (8-10). Distention of the Optic Nerve Sheaths Radiologic distension of the optic nerve sheaths ["optic nerve unfoldment" in anatomic studies (27)] results from increased ICP in the perioptic subarachnoid space (Fig. 4). It is typically seen in IIH patients (28), with a wide ranging sensitivity from 45% to 89% (8-10,12,19,20), likely related to the use of inconsistent definitions. Applying the definition based on the absolute width of the perioptic CSF (CSF ring .2 mm), its pooled sensitivity is estimated FIG. 4. Coronal T2 orbital magnetic resonance imaging (MRI). Distention of the optic nerve sheath (described as "optic nerve unfoldment" anatomically (27)) appears as an enlarged cerebrospinal fluid (CSF) ring surrounding the optic nerve (arrow). 404 Optic Canal Size The size of the optic canal rarely is measured with MRI in patients with IIH, and more easily performed on orbital CT. It has been suggested that optic canal may be larger on the side of the worse papilledema in selected patients with very asymmetric papilledema from IIH (29). It is unclear, however, whether a larger canal is congenital (and therefore may contribute to asymmetric papilledema by facilitating the transmission of CSF pressure to the lamina cribrosa, leading to worse papilledema) or may develop over time in patients with chronic untreated IIH because of bony erosion. This finding might shed light on some of the factors contributing to papilledema but requires further study. CEREBELLAR TONSILLAR HERNIATION Tonsillar herniation is the caudal displacement of the cerebellar tonsils $5 mm into the upper cervical spinal canal through the foramen magnum and is best visualized on mid-sagittal T1 MRI (Fig. 6) (30). Although tonsillar herniation is the hallmark of Chiari malformation Type I (CM1) (31) (Fig. 6B), these 2 conditions are not synonymous. Up to 15% of the normal population have a small degree herniation of the tonsils ($2 mm and ,5 mm) below the foramen magnum (tonsillar ectopia) (32). Cerebellar tonsillar herniation also has been reported after lumbar puncture and placement of a lumbar-peritoneal shunt. More recently, confusion has arisen with studies reporting patients with typical CM1 displaying radiologic findings of chronically increased ICP (33) and typical IIH patients with herniation of the cerebellar tonsils (some of whom met the criteria for CM1) (Fig. 6C, D) (34). It is unclear whether these patients have primary CM1 complicated by increased ICP, or IIH complicated by CM1-like tonsillar herniation, or both conditions. The distinction is very challenging in clinical practice and makes treatment more difficult (33). The sensitivity of cerebellar tonsillar herniation in IIH ranges between 6% and 21% (9,34-36) with a pooled sensitivity of 16% (95% CI: 10-22) (9,34,36) and a pooled specificity of 95% (95% CI: 91-100) (9,34). Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review believe that the tonsillar descent often observed in IIH is related to the increased ICP. This association between tonsillar herniation and IIH is emerging, and the prevalence of IIH in tonsillar herniation and the direction of the causation, if any, between these 2 entities are still controversial. MENINGOCELES AND MENINGOENCEPHALOCELES Bony remodeling associated with IIH may lead to herniation of meninges (meningocele) or brain tissue (meningoencephalocele) through skull base foramina or areas of thin bone of the skull base. Meningoceles and meningoencephaloceles are best demonstrated on MRI with contrast (Fig. 7A, B) (39) and have been strongly associated with CSF leaks. In one study, 9/79 patients with IIH (11% [95% CI: 4-18]) had asymptomatic meningoceles, nearly all located in Meckel cave and in the petrous apex (Fig. 7C), vs. none in controls (40). FORAMEN OVALE WIDENING Widening of the foramen ovale, visualized best on axial high-resolution CT scan, likely is related to herniation of the contents of Meckel cave through the foramen ovale leading to bony remodeling. Its sensitivity and specificity are 50% and 80%, respectively, using a cutoff value of 30 mm2 (20). The utility of this finding on routine imaging for patients with presumed IIH remains unclear. FIG. 5. A. Postcontrast T1 magnetic resonance imaging (MRI) reformatted in a sagittal oblique plane shows vertical tortuosity of the right optic nerve following the shape of the letter "S" in its vertical component (arrow). B. Noncontrast axial T1 scan reveals that the left optic nerve cannot be entirely displayed along a single plane because the signal of orbital fat obscures the mid-portion of the nerve (arrow) ["smear sign" (8)]. Although there is growing evidence of an association between IIH and cerebellar herniation, their relationship remains poorly understood. Progressive enlargement of the foramen magnum with secondary caudal descent of the tonsils might be hypothesized, as previously seen in thin bones of the skull base (37). However, one study (38) looking at the posterior fossa size in patients with IIH, patients with Chiari 1, and controls showed that the foramen magnum size was not different between IIH patients and controls. This finding would argue that the bony foramen magnum is not expanded in IIH. Some authors have referred to a lower than usual position of the cerebellar tonsils in IIH as "tonsillar descent," implying a dynamic process pushing the tonsils down, either because of low pressure below (such as in spontaneous intracranial hypotension) or high pressure above (such as in IIH). We Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 SPONTANEOUS CEREBROSPINAL FLUID LEAKS IIH is an increasingly recognized etiology of spontaneous skull base CSF leaks in the otolaryngology and neurosurgery literature (37,41-48). Otolaryngologists have emphasized that spontaneous skull base CSF leaks might represent a variant of IIH in patients who do not develop typical symptoms and signs of IIH because the leak acts as a "natural" CSF diversion (43). Noncontrast high-resolution CT scanning with thin sections allowing multiplanar reconstruction is the firstline imaging technique to localize bone defects at the skull base with a sensitivity up to 92% and a specificity of 100% (Fig. 8) (39). In difficult cases, such as those with multiple defects or a negative CT scan despite an active CSF leak, CT or MR cisternography (39,49) may help identify the site of the CSF leak (39). CSF leaks are associated with meningoceles and meningoencephaloceles in 50%-100% of cases (39,45). When a CSF leak is diagnosed, brain MRI is recommended to help differentiate herniated intracranial contents from sequestered secretions within the paranasal sinuses (Fig. 7B). In addition, brain MRI allows screening for findings consistent with long405 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review FIG. 6. Noncontrast T1 mid-sagittal magnetic resonance imaging (MRI) with dashed line (McRae line) from the basion to the opisthion, defining the foramen magnum. A. Normal position of the cerebellar tonsils with respect to the foramen magnum in an IIH patient. The inferior pole of the cerebellar tonsils normally lies at the level of or just above the foramen magnum. B. Chiari I malformation (CM1). CM1 is generally believed to be congenital and diagnosed on strict radiologic criteria, including downward extension of peg-shaped cerebellar tonsils at least 5 mm below the foramen magnum without mass or other cause of acquired tonsillar herniation. For borderline cases (tonsillar herniation $3 mm but ,5 mm), the association with other radiologic findings commonly seen in CM1, such as syringomyelia or kinking of the cervico-medullary junction, help establish the diagnosis. C. Cerebellar tonsillar ectopia refers to the low-lying configuration of the tonsils, up to 2 or 3 mm below the foramen magnum. A partially empty sella (Category IV) is also present (arrow). D. CM1-like configuration of the cerebellar tonsils in a patient with IIH. Cerebellar tonsils extend to 10 mm below the foramen magnum. In addition, there is a partially empty sella, (Category III) (arrow). standing IIH, such as a partial or complete empty sella, reported in 66%-100% of cases with spontaneous CSF leaks (41,45,50). Interestingly, unlike in patients with spontaneous spinal CSF leaks, pachymeningeal enhancement and sagging of the brain are uncommon in patients with CSF leaks presumed to be secondary to IIH (51). This may be explained by the relative lack of low CSF pressure in these patients. SLITLIKE VENTRICLES Early descriptions of patients with IIH emphasized the radiologic finding of "slit-like" ventricles as opposed to the dilated ventricles of patients with obstructive hydrocephalus. This was mostly reported before the era of modern neuroimaging when patients with suspected increased ICP were evaluated with plain skull radiographs, ventriculography, and pneumoencephalography (52). Although slitlike 406 ventricles were reported in studies using older generation CT scan imaging (53), this finding has not been corroborated on more recent MRI studies (9,10,17,20). CEREBRAL VENOUS SINUS IMAGING The primary role of intracranial vascular imaging in patients suspected of IIH is to exclude cerebral venous sinus thrombosis (54) and, more rarely, dural fistulas. Improvement in MRI techniques has allowed reliable visualization of the transverse venous sinuses where focal stenosis was previously often overlooked in patients with IIH (55-57). More than a decade ago, Farb et al (55) used a new MRV technique (auto-triggered elliptic-centricordered three-dimensional gadolinium-enhanced MRV [ATECO MRV]) to demonstrate bilateral distal transverse sinus stenoses in IIH patients (Fig. 9) with a sensitivity Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review dients across transverse venous sinus stenoses in patients with IIH (58,59). It has since been proposed that bilateral transverse sinus stenosis, or stenosis of a dominant transverse venous sinus, might lead to the following series of events: decreased venous outflow drainage, cerebral venous hypertension, CSF passive resorption impairment, further raising CSF pressure resulting in external compression of the distal portion of the transverse venous sinuses, leading to worsening of the venous stenosis and perpetuation of this vicious cycle (60,61). Such bilateral transverse venous sinus stenosis also is often found in patients with intracranial hypertension not due to IIH (13,33). Assessing the sensitivity of bilateral transverse venous sinus stenosis is challenging because of inconsistent definitions across studies (55,62-65) and the use of various venous imaging techniques, including flow-sensitive MRV (9,62,65), contrast-enhanced MRV (55,64,66), and CTV (63,67). Using contrast-enhanced MRV, the pooled sensitivity of bilateral transverse venous sinus stenosis is estimated to be 97% (95% CI: 93-100) (55,64,66). However, transverse venous sinus stenosis can be found incidentally in normal subjects (68). It has been pointed out that, depending on the definition of transverse venous sinus stenosis, 100% of patients with IIH have bilateral stenosis on MRV (64). Furthermore, in the absence of bilateral venous stenosis on MRV of patients with presumed IIH, clinicians should reconsider the diagnosis of IIH. This point also was emphasized in the most recently proposed modified Dandy criteria (Table 1) (5), in which bilateral transverse venous sinus stenosis was introduced as a minor diagnostic criterion of IIH. BRAIN IMAGING IN PEDIATRIC INTRACRANIAL HYPERTENSION FIG. 7. A. Coronal thin section computed tomography (CT) demonstrates a bony defect (arrow) in the skull base. Meningocele/meningoencephalocele and sequestered secretions in the sphenoid sinus have the same appearance. B. Coronal T2 magnetic resonance image of same patient as in A shows that sphenoid sinus abnormality is composed of brain tissue. C. Axial T2 scan reveals meningoceles involving both of Meckel caves (arrows). and a specificity of 93%. This finding supported a role of venous hypertension in patients with IIH, as suggested by previous manometric studies which found pressure graBidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 There are few reports of the imaging findings of pediatric IIH patients and little is known regarding the potential pitfalls of applying the findings reported in adults with IIH to children. A study evaluating the optic nerve sheaths of pediatric IIH patients on MRI found larger diameters in comparison with normal children (69). One cross-sectional study conducted in pediatric IIH (70) demonstrated that no single finding other than vertical tortuosity of the optic nerves was found to be statistically different from controls, whereas a subsequent cross-sectional study (71) showed that many neuroimaging findings (empty sella, flattening of posterior globe, intraocular protrusion of the optic nerve head, optic nerve sheath distension, and tortuosity of the optic nerve) were more prevalent in pediatric patients with IIH than in controls. The use of general anesthesia in 50% of patients in the former study (70), vs. 14% in the latter study (71), may have elevated the PCO2, and thereby transiently raised the CSF pressure in the control group, possibly explaining the lack of difference reported in the former study. One study 407 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review FIG. 8. A. Coronal thin section computed tomography (CT) shows a bony defect of the right anterior ethmoid roof (arrow) in an untreated IIH patient with opacification of the ipsilateral ethmoid air cells. B. 3D reconstruction, endocranial view of same patient as (A), demonstrates the bony defect (arrow). (72) found that the prevalence of empty sella in children without increased ICP was lower than that in adults (1.2%, 95% CI: 0.1-2.3). However, no adults were recruited into a control group. All 4 children with IIH in that study had an empty sella. To our knowledge, no studies have directly compared the prevalence of neuroimaging findings in adults with IIH to children with IIH. However, we identified 2 IIH studies using the same imaging criteria; one included 16 adults (8) and the other 23 children (70). We analyzed the data of each (Fisher exact test) and found that the neuroimaging findings were not statistically different in adult and pediatric IIH, except for empty sella, which was less prevalent in children (26% vs. 69%, P = 0.01). FIG. 9. A. Posterior view of maximum intensity projection (MIP) of contrast-enhanced magnetic resonance venogram reveals bilateral transverse sinus stenosis. Most often, stenoses appear as smooth narrowing of the transverse sinus ("extraluminal" type, 80%, arrowhead) but may display an abrupt filling defect ("intraluminal" type, 20%, arrow). The significance of these 2 types of stenosis is uncertain. The extraluminal type is likely secondary to extrinsic compression by raised cerebrospinal fluid (CSF) pressure and likely to resolve after increased intracranial pressure (ICP) reduction. The intraluminal type is more likely a primary stenosis, usually related to giant arachnoid granulations. B. Unilateral stenosis of the dominant right transverse sinus (arrow). Asymmetry in the transverses sinuses is common in normal individuals, with the right typically dominant and the left hypoplastic (arrowhead) or aplastic. 408 Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review DIAGNOSTIC VALUE OF THE COMBINATION OF VARIOUS IMAGING FINDINGS IN INTRACRANIAL HYPERTENSION None of the imaging findings discussed have shown, in isolation, both high sensitivity and specificity for IIH. Although many reports have addressed the diagnostic value of each finding separately on cross-sectional studies, only 2 have focused on the combination of some of these findings in adults with IIH (9,10). However, inconsistent results have emerged, as the methods were not comparable. One study (9) reported that any single finding, including a partially empty sella, flattening of the posterior globe, or bilateral transverse sinus stenosis, increased the sensitivity for IIH to z85% while maintaining a high specificity (z95%). However, any combination of 2 of these findings increased the specificity to 100%, but lowered the sensitivity between z35% and z55%, depending on the combination. Conversely, the other study (10) showed that the combination of a totally empty sella and/or flattening of the posterior globe added little value, but bilateral transverse venous sinus stenoses were not included, limiting the scope of these results. One study (70) addressed the combination of imaging findings in pediatric IIH and demonstrated that a combination of $3 imaging findings (flattening of posterior globe, optic nerve sheath distension, intraocular protrusion of the optic nerve head, tortuosity of the optic nerve, and empty sella) had a sensitivity of z45% and a specificity of 95% for the diagnosis of IIH in children. INCIDENTAL FINDING OF NEUROIMAGING SIGNS SUGGESTING INTRACRANIAL HYPERTENSION Because of the increasing prevalence of IIH paralleling the increasing prevalence of obesity, clinicians other than neuroophthalmologists are becoming more aware of IIH. Although this increased awareness is to be encouraged, it has had the unfortunate effect of overdiagnosis of IIH in young obese women with chronic headaches or anomalous optic nerves, many without clearly documented papilledema. Furthermore, no study has addressed the predictive value of the imaging findings of IIH, which have also been reported in healthy subjects, patients with secondary causes of increased ICP (13), and patients with primary headache syndromes (65,73). Clinicians must be aware that these imaging findings are not diagnostic of IIH and should not prompt invasive or costly investigations when discovered incidentally (74), unless the patient also has papilledema or other compelling symptoms or signs of elevated ICP. FUTURE DIRECTIONS While a variety of neuroimaging findings may be suggestive of chronically elevated ICP, none are indicative of whether Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 the ICP in a patient is normal or abnormal. In addition, it is unclear how long it takes for most neuroimaging signs of raised ICP to develop and how often reversibility of these signs is observed once ICP is normalized. Various approaches to noninvasively estimate ICP using imaging are currently under investigation (75). Transcranial Doppler ultrasound has been used to measure blood flow in major brain arteries, most commonly the middle cerebral artery. This technique can provide measurements of mean blood flow velocity and pulsatility index, a measure of relative vascular pulsatility (76). However, there is a complex relationship between pulsatility index and ICP that makes clinical application of this technique difficult. Phase contrast MRI gated to the cardiac cycle (77) enables quantitative measurement of CSF and blood flow and pulsatility. By varying the sensitivity of the technique, high velocity flow in arteries, or low velocity flow in veins and CSF, can be assessed (78). Estimates of intracranial compliance have been obtained based on relative distribution of arterial, venous, and CSF pulsatility at the craniocervical junction (79). This technique has been applied to patients with IIH (80) and has suggested reduced spinal canal compliance in patients with IIH compared with control individuals. Future studies using this technique and others under development correlating noninvasive measures directly to opening pressure measurements have the potential to validate an MRI-based method for estimating ICP in a clinically relevant fashion. CONCLUSION Emergent brain imaging (ideally brain MRI with and without contrast) and venous imaging with contrast (MRV or CTV) are the first-line tests in patients in whom IIH is suspected to exclude a space-occupying process, obstructive hydrocephalus, or cerebral venous sinus thrombosis. Although the diagnosis of IIH remains a diagnosis of exclusion, specific imaging findings on brain MRI and MRV may suggest IIH and prompt further investigations (Table 2). The most recently proposed modified diagnostic criteria for IIH (5) include these imaging findings in detail but do not require their presence to make a definite diagnosis of IIH. The description of such findings on routine MRI reports may result in overdiagnosis of IIH and must therefore be interpreted with caution. Because of the high sensitivity of some of these findings, we believe that their absence, rather than their presence, may be more important in establishing the diagnosis of IIH. If absent, the clinician should consider alternate diagnoses. However, it is likely that some of these findings such as empty sella and bony remodeling require some time to develop in patients with IIH and, therefore, may be absent initially. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design, S. Bidot, A. M. Saindane, J. H. Peragallo, B. B. Bruce, N. J. Newman, and V. Biousse. b. Acquisition of data, S. Bidot, A. M. Saindane, J. H. Peragallo, B. B. Bruce, N. J. 409 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review Newman, and V. Biousse. c. Analysis and interpretation of data, S. Bidot, A. M. Saindane, J. H. Peragallo, B. B. Bruce, N. J. Newman, and V. Biousse. Category 2: a. Drafting the manuscript, S. Bidot, A. M. Saindane, J. H. Peragallo, B. B. Bruce, N. J. Newman, and V. Biousse. b. Revising it for intellectual content, S. Bidot, A. M. Saindane, J. H. Peragallo, B. B. Bruce, N. J. Newman, and V. Biousse. Category 3: a. Final approval of the completed manuscript, S. Bidot, A. M. Saindane, J. H. Peragallo, B. B. Bruce, N. J. Newman, and V. Biousse. 19. 20. 21. REFERENCES 1. Friedman DI, Jacobson DM. Diagnostic criteria for idiopathic intracranial hypertension. Neurology. 2002;59:1492-1495. 2. Boddie HG, Banna M, Bradley WG. "Benign" intracranial hypertension. A survey of the clinical and radiological features, and long-term prognosis. Brain. 1974;97:313-326. 3. Wall M, Corbett JJ. Revised diagnostic criteria for the pseudotumor cerebri syndrome in adults and children. Neurology. 2014;83:198-199. 4. Dasheiff R, Friedman DI, Liu GT, Digre KB. Ducks in a row. Neurology. 2014;82:1012. 5. Friedman DI, Liu GT, Digre KB. Revised diagnostic criteria for the pseudotumor cerebri syndrome in adults and children. Neurology. 2013;81:1159-1165. 6. Ranganathan S, Lee SH, Checkver A, Sklar E, Lam BL, Danton GH, Alperin NJ. Magnetic resonance imaging finding of empty sella in obesity related idiopathic intracranial hypertension is associated with enlarged sella turcica. Neuroradiology. 2013;55:955-961. 7. Sage MR, Blumbergs PC. Primary empty sella turcica: a radiological-anatomical correlation. Australas Radiol. 2000;44:341-348. 8. Brodsky MC, Vaphiades M. Magnetic resonance imaging in pseudotumor cerebri. Ophthalmology. 1998;105:1686- 1693. 9. Maralani PJ, Hassanlou M, Torres C, Chakraborty S, Kingstone M, Patel V, Zackon D, Bussiere M. Accuracy of brain imaging in the diagnosis of idiopathic intracranial hypertension. Clin Radiol. 2012;67:656-663. 10. Agid R, Farb RI, Willinsky RA, Mikulis DJ, Tomlinson G. Idiopathic intracranial hypertension: the validity of crosssectional neuroimaging signs. Neuroradiology. 2006;48:521- 527. 11. Yuh WT, Zhu M, Taoka T, Quets JP, Maley JE, Muhonen MG, Schuster ME, Kardon RH. MR imaging of pituitary morphology in idiopathic intracranial hypertension. J Magn Reson Imaging. 2000;12:808-813. 12. Ridha MA, Saindane AM, Bruce BB, Riggeal BD, Kelly LP, Newman NJ, Biousse V. MRI findings of elevated intracranial pressure in cerebral venous thrombosis versus idiopathic intracranial hypertension with transverse sinus stenosis. Neuroophthalmology. 2013;37:1-6. 13. Rohr AC, Riedel C, Fruehauf MC, van Baalen A, Bartsch T, Hedderich J, Alfke K, Doerner L, Jansen O. MR imaging findings in patients with secondary intracranial hypertension. AJNR Am J Neuroradiol. 2011;32:1021-1029. 14. Foresti M, Guidali A, Susanna P. Primary empty sella: incidence in 500 asymptomatic subjects examined with magnetic resonance [in Italian]. Radiol Med. 1991;81:803-807. 15. Saindane AM, Lim PP, Aiken AH, Chen Z, Hudgins PA. Factors determining the clinical significance of an "empty" sella turcica. AJR Am J Roentgenol. 2013;200:1125-1131. 16. Kyung SE, Botelho JV, Horton JC. Enlargement of the sella turcica in pseudotumor cerebri. J Neurosurg. 2014;120:538-542. 17. Hoffmann J, Huppertz HJ, Schmidt C, Kunte H, Harms L, Klingebiel R, Wiener E. Morphometric and volumetric MRI changes in idiopathic intracranial hypertension. Cephalalgia. 2013;33:1075-1084. 18. Zagardo MT, Cail WS, Kelman SE, Rothman MI. Reversible empty sella in idiopathic intracranial hypertension: an indicator 410 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. of successful therapy? AJNR Am J Neuroradiol. 1996;17:1953-1956. Saindane AM, Bruce BB, Riggeal BD, Newman NJ, Biousse V. Association of MRI findings and visual outcome in idiopathic intracranial hypertension. AJR Am J Roentgenol. 2013;201:412-418. Butros SR, Goncalves LF, Thompson D, Agarwal A, Lee HK. Imaging features of idiopathic intracranial hypertension, including a new finding: widening of the foramen ovale. Acta Radiol. 2012;53:682-688. Alperin NJ, Bagci AM, Lam BL, Sklar E. Automated quantitation of the posterior scleral flattening and optic nerve protrusion by MRI in idiopathic intracranial hypertension. AJNR Am J Neuroradiol. 2013;34:2354-2359. Jacobson DM. Intracranial hypertension and the syndrome of acquired hyperopia with choroidal folds. J Neuroophthalmol. 1995;15:178-185. Brodsky MC. Flattening of the posterior sclera: hypotony or elevated intracranial pressure? Am J Ophthalmol. 2004;138:511. Brodsky MC, Glasier CM. Magnetic resonance visualization of the swollen optic disc in papilledema. J Neuroophthalmol. 1995;15:122-124. Purvin VA, Sundaram S, Kawasaki A. Neuroretinitis: review of the literature and new observations. J Neuroophthalmol. 2011;31:58-68. Rizzo JF, Andreoli CM, Rabinov JD. Use of magnetic resonance imaging to differentiate optic neuritis and nonarteritic anterior ischemic optic neuropathy. Ophthalmology. 2002;109:1679- 1684. Hayreh SS. The sheath of the optic nerve. Ophthalmologica. 1984;189:54-63. Hoffmann J, Schmidt C, Kunte H, Klingebiel R, Harms L, Huppertz HJ, Ludemann L, Wiener E. Volumetric assessment of optic nerve sheath and hypophysis in idiopathic intracranial hypertension. AJNR Am J Neuroradiol. 2014;35:513-518. Bidot S, Bruce BB, Saindane AM, Newman NJ, Biousse V. Asymmetric papilledema in idiopathic intracranial hypertension. J Neuroophthalmol. 2015;35:31-36. Hadley DM. The chiari malformations. J Neurol Neurosurg Psychiatr. 2002;72(suppl 2):ii38-ii40. McVige JW, Leonardo J. Imaging of Chiari type I malformation and syringohydromyelia. Neurol Clin. 2014;32:95-126. Barkovich AJ, Wippold FJ, Sherman JL, Citrin CM. Significance of cerebellar tonsillar position on MR. AJNR Am J Neuroradiol. 1986;7:795-799. Saindane AM, Bruce BB, Desai NK, Roller LA, Newman NJ, Biousse V. Transverse sinus stenosis in adult patients with Chiari malformation type I. AJR Am J Roentgenol. 2014;203:890-896. Aiken AH, Hoots JA, Saindane AM, Hudgins PA. Incidence of cerebellar tonsillar ectopia in idiopathic intracranial hypertension: a mimic of the Chiari I malformation. AJNR Am J Neuroradiol. 2012;33:1901-1906. Johnston I, Jacobson E, Besser M. The acquired Chiari malformation and syringomyelia following spinal CSF drainage: a study of incidence and management. Acta Neurochir (Wien). 1998;140:417-427. Banik R, Lin D, Miller NR. Prevalence of Chiari I malformation and cerebellar ectopia in patients with pseudotumor cerebri. J Neurol Sci. 2006;247:71-75. Pérez MA, Bialer OY, Bruce BB, Newman NJ, Biousse V. Primary spontaneous cerebrospinal fluid leaks and idiopathic intracranial hypertension. J Neuroophthalmol. 2013;33:330-337. Roller LA, Bruce BB, Saindane AM. Demographic confounders in volumetric MRI analysis: is the posterior fossa really small in the adult Chiari 1 malformation? AJR Am J Roentgenol. 2015;204:835-841. Lloyd KM, DelGaudio JM, Hudgins PA. Imaging of skull base cerebrospinal fluid leaks in adults. Radiology. 2008;248:725- 736. Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. State-of-the-Art Review 40. Bialer OY, Rueda MP, Bruce BB, Newman NJ, Biousse V, Saindane AM. Meningoceles in idiopathic intracranial hypertension. AJR Am J Roentgenol. 2014;202:608-613. 41. Schlosser R. Significance of empty sella in cerebrospinal fluid leaks. Otolaryngol Head Neck Surg. 2003;128:32-38. 42. Schlosser R. Cerebrospinal fluid pressure monitoring after repair of cerebrospinal fluid leaks. Otolaryngol Head Neck Surg. 2004;130:443-448. 43. Schlosser RJ, Woodworth BA, Wilensky EM, Grady MS, Bolger WE. Spontaneous cerebrospinal fluid leaks: a variant of benign intracranial hypertension. Ann Otol Rhinol Laryngol. 2006;115:495-500. 44. Scurry WC, Ort SA, Peterson WM, Sheehan JM, Isaacson JE. Idiopathic temporal bone encephaloceles in the obese patient. Otolaryngol Head Neck Surg. 2007;136:961-965. 45. Seth R, Rajasekaran K III, Luong A, Benninger MS, Batra PS. Spontaneous CSF leaks: factors predictive of additional interventions. Laryngoscope. 2010;120:2141-2146. 46. Brainard L, Chen DA, Aziz KM, Hillman TA. Association of benign intracranial hypertension and spontaneous encephalocele with cerebrospinal fluid leak. Otol Neurotol. 2012;33:1621-1624. 47. Aaron G, Doyle J, Vaphiades MS, Riley KO, Woodworth BA. Increased intracranial pressure in spontaneous CSF leak patients is not associated with papilledema. Otolaryngol Head Neck Surg. 2014;151:1061-1066. 48. Rosenfeld E, Dotan G, Kimchi TJ, Kesler A. Spontaneous cerebrospinal fluid otorrhea and rhinorrhea in idiopathic intracranial hypertension patients. J Neuroophthalmol. 2013;33:113-116. 49. Selcuk H, Albayram S, Ozer H, Ulus S, Sanus GZ, Kaynar MY, Kocer N, Islak C. Intrathecal gadolinium-enhanced MR cisternography in the evaluation of CSF leakage. AJNR Am J Neuroradiol. 2010;31:71-75. 50. Prichard CN, Isaacson B, Oghalai JS, Coker NJ, Vrabec JT. Adult spontaneous CSF otorrhea: correlation with radiographic empty sella. Otolaryngol Head Neck Surg. 2006;134:767-771. 51. Schievink WI. Spontaneous spinal cerebrospinal fluid leaks. Cephalalgia. 2008;28:1345-1356. 52. Jacobson HG, Shapiro JH. Pseudotumor cerebri. Radiology. 1964;82:202-210. 53. Weisberg LA. Computed tomography in benign intracranial hypertension. Neurology. 1985;35:1075-1078. 54. Biousse V, Ameri A, Bousser MG. Isolated intracranial hypertension as the only sign of cerebral venous thrombosis. Neurology. 1999;53:1537-1542. 55. Farb RI, Vanek I, Scott JN, Mikulis DJ, Willinsky RA, Tomlinson G, terBrugge KG. Idiopathic intracranial hypertension: the prevalence and morphology of sinovenous stenosis. Neurology. 2003;60:1418-1424. 56. Lee AG, Brazis PW. Magnetic resonance venography in idiopathic pseudotumor cerebri. J Neuroophthalmol. 2000;20:12-13. 57. Johnston I, Kollar C, Dunkley S, Assaad N, Parker G. Cranial venous outflow obstruction in the pseudotumour syndrome: incidence, nature and relevance. J Clin Neurosci. 2002;9:273- 278. 58. King JO, Mitchell PJ, Thomson KR, Tress BM. Cerebral venography and manometry in idiopathic intracranial hypertension. Neurology. 1995;45:2224-2228. 59. King JO, Mitchell PJ, Thomson KR, Tress BM. Manometry combined with cervical puncture in idiopathic intracranial hypertension. Neurology. 2002;58:26-30. 60. Biousse V, Bruce BB, Newman NJ. Update on the pathophysiology and management of idiopathic intracranial hypertension. J Neurol Neurosurg Psychiatr. 2012;83:488- 494. 61. McGeeney BE, Friedman DI. Pseudotumor cerebri pathophysiology. Headache. 2014;54:445-458. 62. Higgins JNP, Gillard JH, Owler BK, Harkness K, Pickard JD. MR venography in idiopathic intracranial hypertension: Bidot et al: J Neuro-Ophthalmol 2015; 35: 400-411 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. unappreciated and misunderstood. J Neurol Neurosurg Psychiatr. 2004;75:621-625. Connor SEJ, Siddiqui MA, Stewart VR, O'Flynn EAM. The relationship of transverse sinus stenosis to bony groove dimensions provides an insight into the aetiology of idiopathic intracranial hypertension. Neuroradiology. 2008;50:999- 1004. Riggeal BD, Bruce BB, Saindane AM, Ridha MA, Kelly LP, Newman NJ, Biousse V. Clinical course of idiopathic intracranial hypertension with transverse sinus stenosis. Neurology. 2013;80:289-295. Bono F, Messina D, Giliberto C, Cristiano D, Broussard G, D'Asero S, Condino F, Mangone L, Mastrandrea C, Fera F, Quattrone A. Bilateral transverse sinus stenosis and idiopathic intracranial hypertension without papilledema in chronic tension-type headache. J Neurol. 2008;255:807-812. Horev A, Hallevy H, Plakht Y, Shorer Z, Wirguin I, Shelef I. Changes in cerebral venous sinuses diameter after lumbar puncture in idiopathic intracranial hypertension: a prospective MRI study. J Neuroimaging. 2013;23:375-378. Higgins JNP, Tipper G, Varley M, Pickard JD. Transverse sinus stenoses in benign intracranial hypertension demonstrated on CT venography. Br J Neurosurg. 2005;19:137-140. Kelly LP, Saindane AM, Bruce BB, Ridha MA, Riggeal BD, Newman NJ, Biousse V. Does bilateral transverse cerebral venous sinus stenosis exist in patients without increased intracranial pressure? Clin Neurol Neurosurg. 2013;115:1215-1219. Shofty B, Ben-Sira L, Constantini S, Freedman S, Kesler A. Optic nerve sheath diameter on MR imaging: establishment of norms and comparison of pediatric patients with idiopathic intracranial hypertension with healthy controls. AJNR Am J Neuroradiol. 2012;33:366-369. Lim MJ, Pushparajah K, Jan W, Calver D, Lin JP. Magnetic resonance imaging changes in idiopathic intracranial hypertension in children. J Child Neurol. 2010;25:294-299. Görkem SB, Do ganay S, Canpolat M, Koc G, Dogan MS, Per H, Coşkun A. MR imaging findings in children with pseudotumor cerebri and comparison with healthy controls. Childs Nerv Syst. 2015;31:373-380. Takanashi J, Suzuki H, Nagasawa K, Kobayashi K, Saeki N, Kohno Y. Empty sella in children as a key for diagnosis. Brain Dev. 2001;23:422-423. Bono F, Messina D, Giliberto C, Cristiano D, Broussard G, Fera F, Condino F, Lavano A, Quattrone A. Bilateral transverse sinus stenosis predicts IIH without papilledema in patients with migraine. Neurology. 2006;67:419-423. Sadun AA, Chu ER, Boisvert CJ. Neuro-ophthalmology safer than MRI? Ophthalmology. 2013;120:879. Bruce BB. Noninvasive assessment of cerebrospinal fluid pressure. J Neuroophthalmol. 2014;34:288-294. Lindegaard KF, Bakke SJ, Grolimund P, Aaslid R, Huber P, Nornes H. Assessment of intracranial hemodynamics in carotid artery disease by transcranial Doppler ultrasound. J Neurosurg. 1985;63:890-898. Enzmann DR, Pelc NJ. Normal flow patterns of intracranial and spinal cerebrospinal fluid defined with phase-contrast cine MR imaging. Radiology. 1991;178:467-474. Enzmann DR, Pelc NJ. Cerebrospinal fluid flow measured by phase-contrast cine MR. AJNR Am J Neuroradiol. 1993;14:1301-1307. Alperin NJ, Lee SH, Loth F, Raksin PB, Lichtor T. MR-Intracranial pressure (ICP): a method to measure intracranial elastance and pressure noninvasively by means of MR imaging: baboon and human study. Radiology. 2000;217:877-885. Tain RW, Bagci AM, Lam BL, Sklar EM, Ertl-Wagner B, Alperin NJ. Determination of cranio-spinal canal compliance distribution by MRI: methodology and early application in idiopathic intracranial hypertension. J Magn Reson Imaging. 2011;34:1397-1404. 411 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.