Idiopathic intracranial hypertension: Imaging and clinical fundamentals

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.