Neuroimaging: Idiopathic intracranial hypertension
Idiopathic intracranial hypertension, also known as the pseudotumor cerebri syndrome, is characterized by elevated intracranial pressure with clinical features of headaches, vision impairment, and occasionally cranial nerve palsies in the absence of a structural lesion on neuroimaging. But that doesn’t mean the neuroimaging has to be normal. This week, I chat with Dr. Anita Kholi about the radiographic correlates of IIH, their relevance and their prognostic utility. Check it out!
No imaging feature associated with IIH is perfect. But there are 4 major features to be on the lookout for:
- Empty sella
- Optic nerve sheath distension
- Flattening of the orbital globe
- Transverse sinus stenosis
Each feature occurs independently, and it’s thought that the likelihood of diagnosing IIH is greater with each additional imaging characteristic. While an empty sella may be telling, you need 3 out of 4 selected extra-parenchymal imaging features are a diagnostic requirement for IIH in patients without papilledema according to recent guidelines published in Neurology. And some features are more helpful than others in either ruling in IIH, or ruling it out. For example the most sensitive imaging marker, optic nerve sheath distension, is poorly specific. Optic nerve sheath distension occurs when the pressure inside the skull builds up so much that CSF is literally forced into any neighboring compartment–like the optic nerve sheath–causing local swelling. So a distended sheath simply indicate the presence of elevated intracranial pressure (ICP), but not necessarily an idiopathic elevation in ICP as you would see in pseudotumor cerebri. In contrast, markers like flattening of the posterior globe and empty sella are the most specific, but poorly sensitive. So if you see an empty sella, that’s highly reassuring that your patient has IIH and not something else that could potentially raise ICP. But the absence of an empty sella won’t rule out pseudotumor cerebri.
Some of these imaging features are reversible with treatment, whereas others may not be. And this kind of information can give you insight when you see a patient with an alleged history of IIH or someone with optic nerve atrophy or other abnormality on visual field exam or MRI. So I really recommend you take a listen to Dr. Kholi on this one. She can help you see the bigger picture.
Friedman DI, Liu GT and Digre KB. Revised diagnostic criteria for the pseudotumor cerebri syndrome in adults and children. Neurology. 2013;81:1159-65.
Bidot S and Bruce BB. Update on the Diagnosis and Treatment of Idiopathic Intracranial Hypertension. Semin Neurol. 2015;35:527-38.
Agid R, Farb RI, Willinsky RA, Mikulis DJ and Tomlinson G. Idiopathic intracranial hypertension: the validity of cross-sectional neuroimaging signs. Neuroradiology. 2006;48:521-7.
Bidot S, Saindane AM, Peragallo JH, Bruce BB, Newman NJ and Biousse V. Brain Imaging in Idiopathic Intracranial Hypertension. J Neuroophthalmol. 2015;35:400-11.
Bidot S, Clough L, Saindane AM, Newman NJ, Biousse V and Bruce BB. The Optic Canal Size Is Associated With the Severity of Papilledema and Poor Visual Function in Idiopathic Intracranial Hypertension. J Neuroophthalmol. 2016;36:120-5.
Zagardo MT, Cail WS, Kelman SE and Rothman MI. Reversible empty sella in idiopathic intracranial hypertension: an indicator of successful therapy? AJNR American journal of neuroradiology. 1996;17:1953-6.