Idiopathic intracranial hypertension: Imaging and clinical fundamentals

Table 1 Frisén Scale - papilledema grading system

Frisén Scale - papilledema grading system
Stage 0: Normal optic disc	Retinal NFL prominence at the nasal, superior, and inferior poles in an inverted proportion to disc diameter
	Radial NFL striations - no tortuosity
	Rarely obscuration of a major blood vessel, usually on the upper pole
Stage 1: Very early papilledema - minimal degree of edema	No elevation of the disc borders
	Obscuration of the nasal border of the disc
	Normal temporal disc margin
	Disruption of the normal radial NFL arrangement striations
	Subtle and grayish halo (C-shaped) with temporal gap; underlying retinal details obscured
	Concentric or radial choroidal folds
Stage 2: Early papilledema - low degree of edema	Obscuration of all borders
	Circumferential halo
	Elevation of the nasal border
	No obscuration of any major vessel
Stage 3: Moderate papilledema - moderate degree of edema	Obscurations of all borders
	Circumferential halo
	Obscuration of one or more segments of major blood vessels leaving the disc
	Elevation of all borders
	Peripapillary halo-irregular outer fringe with finger-like extensions
Stage 4: Marked papilledema - marked degree of edema	Total obscuration of a segment of a major blood vessel on the disc
	Elevation of the entire nerve head, including the cup
	Obscuration of all borders
	Complete peripapillary halo
Stage 5: Severe papilledema - severe degree of edema	Dome-shaped protrusions representing anterior expansion of the optic nerve head
	Peripapillary halo is narrow and smoothly demarcated
	Partial obscuration of all vessels and total obscuration of at least one major blood vessel on optic disc
	Obliteration of the optic cup

Adapted from Scott et al[59]. NFL: Nerve fiber layer.

Table 2 Diagnostic criteria for idiopathic intracranial hypertension

	Diagnostic criteria for idiopathic intracranial hypertension1
I	Papilledema
II	Normal neurologic examination excepting abnormalities of the cranial nerves (VIth or VIIth nerve dysfunction)
III	Neuroimaging: Normal brain parenchyma without signs of hydrocephalus, mass, structural lesions, or abnormal meningeal enhancement on MRI (performed with and without gadolinium) for typical patients (female and obese), and on MRI (performed with and without gadolinium) along with MRV for other patients; if MRI is unavailable or contraindicated, a contrast-enhanced CT may serve as an alternative
IV	Normal CSF composition
V	Increase LP opening pressure [≥ 250 mm CSF in adults and ≥ 280 mm CSF in children (250 mm CSF if the child is not sedated and not obese)] in an appropriately performed LP
Neuroimaging criteria	A: Empty sella
	B: Posterior globe flattening
	C: Optic nerve sheath distention (with or without optic nerve tortuosity)
	D: Transverse venous sinus stenosis

¹Criteria: (1) An idiopathic intracranial hypertension (IIH) diagnosis is confirmed if criteria I-V are met; (2) If only criteria I-IV are met, then IIH diagnosis is probable; (3) If criteria I (papilledema) is not met, an IIH diagnosis can be made if criteria II–V are met, and the patient demonstrates a unilateral or bilateral abducens nerve palsy; and (4) If criteria I (papilledema) is not met and there is no abducens nerve palsy, an IIH diagnosis can be suggested (but not made) if criteria II-V are met, and also at least 3 of the 4 neuroimaging criteria (A-D) are met.

Adapted from Friedman et al[1]. MRI: Magnetic resonance imaging; MRV: Magnetic resonance venography; CT: Computed tomography; LP: Lumbar puncture; CSF: Cerebrospinal fluid.

Table 3 Magnetic resonance imaging signs for the diagnosis of idiopathic intracranial hypertension

MRI finding	Sensitivity	Specificity	Ref.
Empty sella turcica	53.9%	94.3%	[104]
	26.7%	94.6%	[67]
	70%	95%	[97]
Partially empty sella	92%	74%	[68]
	43%	100%	[69]
	65.1%	95.3%	[70]
	53.3%	75%	[67]
	80%	92%	[76]
Posterior displacement of pituitary stalk	39.5%	90.7%	[70]
	42.7%	97.9%	[76]
Meningoceles	11%	100%	[79]
Meckel’s cave enlargement	60%	59%	[89]
	75%	86%	[68]
	9%	100%	[79]
Optic nerve tortuosity	60%	95%	[69]
	34.9%	86%	[70]
	40%	91.1%	[67]
	40%	95%	[97]
Optic nerve sheath distension	77%	85%	[89]
	84%	84%	[68]
	46%	100%	[69]
	66.7%	82.1%	[67]
	45%	95%	[97]
Optic nerve head enhancement	6.7%	98.2%	[67]
	50%	100%	[97]
Posterior globe flattening	55%	100%	[68]
	64%	100%	[69]
	43.3%	100%	[67]
	80%	95%	[97]
Optic nerve head protrusion	32%	100%	[69]
	37.2%	100%	[70]
	3.3%	100%	[67]
	30%	95%	[97]
DWI bright spot at fundus	9.5%	99%	[104]
	26.3%	100%	[103] (reader 1)
	42.1%	100%	[103] (reader 1)
Transverse sinus stenosis	73%	92%	[68]
	93%	93%	[107]
	94%	97%	[104]
	62.8%	100%	[70] (combined stenosis score)
Slit-like ventricles	3%	100%	[69]
	3.3%	100%	[67]
	39.5%	79.1%	[70]
Tight subarachnoid spaces	3%	100%	[69]
	0%	0%	[67]
Inferior position of cerebellar tonsils	16%1	95%1	[78]

¹Pooled data.

MRI: Magnetic resonance imaging; DWI: Diffusion-weighted imaging.

Table 4 A step-by-step checklist for the radiologist to enable the systematic assessment of suspected idiopathic intracranial hypertension cases

Step-by-step checklist
Step 1: Exclude the presence of an alternative and obvious cause of increased intracranial pressure. Note: This is a vital step required for IIH diagnosis, according to the revised criteria[1]	Normal brain parenchyma without findings suggesting the presence of: (1) Hydrocephalus; (2) Masses or structural lesions; (3) Abnormal meningeal enhancement (caution should be exercised as diffuse dural enhancement may be encountered following a lumbar puncture); and (4) Venous sinus thrombosis
Step 2: Assess the presence of neuroimaging findings commonly encountered in IIH patients. Note: These findings demonstrate varying sensitivities and specificities. Various combinations of the related neuroimaging findings may be encountered, although their absence does not rule out the diagnosis. The radiologists should be aware of these signs to assist in the proper and timely diagnosis of the condition and/or to advocate for equivocal cases	Primary neuroimaging signs1. Note: These signs are very important to be assessed and mentioned in the report, as the presence of 3 out of 4 of them may suggest (but not verify) the probability of IIH diagnosis in specific clinical scenarios according to the revised IIH criteria[1]: (1) Empty sella turcica (Figure 3) (CSF-filled sella turcica, compressing the pituitary gland housed within it); (2) Posterior globe flattening (Figure 10) (loss of the normal posterior sclera curvature at the optic nerve insertion point); (3) Optic nerve sheath distension (Figure 8) (increased diameter of the optic nerve sheath with CSF filling of the subarachnoid space between the nerve and its expanded sheath; typically measured at 3 mm from the posterior globe margin; whether optic nerve tortuosity is synchronously present will not alter the evaluation of the presence of this sign as positive or negative); and (4) Transverse venous sinus stenosis (Figure 12) [most commonly occurs at the lateral aspect (transverse-sigmoid sinus junction) and may be caused by intrinsic or extrinsic processes. Assess using the combined venous conduit score or the index of transverse sinus stenosis]
	Other neuroimaging signs. Note: Although not part of the revised criteria for the diagnosis of IIH[1], these are signs useful to assess and mention in the report as, nonetheless, they may be encountered in IIH cases: (1) Optic nerve tortuosity (Figure 7) (optic nerve tortuosity depicted in the horizontal, or preferably, the vertical planes); (2) Optic nerve head protrusion (Figure 10) (the imaging representation of papilledema; usually evaluated as hypointense relative to the vitreous fluid of the globe in T2-weighted images); (3) Optic nerve head enhancement (Figure 9) (contrast-enhanced optic nerve head within the posterior aspect of the globe); (4) Posterior displacement of the pituitary stalk (Figure 4) (besides pituitary gland compression, the pituitary stalk is posteriorly displaced); (5) Meningoceles (Figure 5) (meningeal protrusions through weak or defective points, usually in the skull base, usually in sphenoid bone wings); (6) Meckel’s cave enlargement (Figure 6) (CSF-filled enlargement of Meckel’s caves); (7) DWI bright spot at fundus (Figure 11) (abnormal hyperintensity at the optic nerve head encountered on DWI; recently reported as a marker of papilledema); (8) Slit-like ventricles (Figure 13) (narrowing/collapse of the lateral ventricle walls); (9) Tight subarachnoid spaces (Figure 13) (very small sulci and cisterns not typically expected in the normal adult population); and (10) Inferior position of cerebellar tonsils (Figure 14) (cerebellar tonsillar displacement through the foramen magnum into the upper portion of the spinal canal)
Step 3: Correlate with the clinical presentation and clinical findings. Note: Close communication and collaboration with referring physicians are important both for patient care and for the advancement of medical knowledge. Correlating the various findings encountered on imaging studies by the radiologist with the level of clinical suspicion and the other IIH diagnostic criteria, as communicated by the referring physicians, enables the radiologist to acknowledge which of them are usually most relevant and to what extent

¹These neuroimaging signs are included in the “STOP” acronym for idiopathic intracranial hypertension, which will be explained below in the manuscript.

IIH: Idiopathic intracranial hypertension; CSF: Cerebrospinal fluid; DWI: Diffusion-weighted imaging.