Idiopathic intracranial hypertension (IIH), also referred to as pseudotumor cerebri, is a well known but poorly understood disease entity that presents neuroradiologists with both diagnostic and treatment challenges. The classic clinical presentation is that of an obese young woman, frequently African American, with headaches, nausea, vomiting, visual impairment, and possibly cranial nerve VI palsy. The pathophysiology of IIH is thought to be related to decreased CSF absorption at the arachnoid villi and/or venous outflow obstruction, which results in raised intracranial pressure. We as neuroradiologists typically play a vital role through our direction and interpretation of the pertinent imaging as well as by the performance of lumbar puncture, in order to measure opening pressure for diagnosis and to remove CSF for treatment. The interventional neuroradiologists among us may decide to take it a step further through cerebral venography, manography, and potential transverse sinus angioplasty and stenting, a controversial procedure that has been shown to help alleviate symptoms in some patients. Imaging findings in IIH can be subtle, and many patients with IIH have a normal scan. Findings to look for include reversed cupping of the optic disc (which corresponds to papilledema and visual loss), dilation and tortuosity of the optic nerve sheaths, empty sella, and transverse sinus stenosis. Interestingly, the ventricles are typically normal or slightly small in size.

In this issue of the AJNR News Digest, we focus on the work of authors who shed light on the pathophysiology, imaging patterns, and treatment of IIH. Excellent review articles on IIH are provided to us by authors Degnan, Passi, and Levy.^1,2 Alperin et al³ brilliantly use an automated method to transform the complex, 3D globe geometry into a 2D distance map, allowing for quantitative measurements of posterior sclera flattening and optic nerve protrusion. The authors demonstrate the advantage of this automated method over subjective assessment, and show that optic nerve protrusion has the strongest predictive value for papilledema grade as well as the highest sensitivity for assessment of treatment efficacy in patients with IIH. Another article by Alperin et al⁴ demonstrates the use of advanced MRI techniques to measure CSF volumes and cerebral venous drainage in patients with IIH. The authors elegantly show that patients with IIH have significantly increased extraventricular CSF volume, increased gray matter volume, and increased resistance to cerebral venous drainage, implicating both an impairment in CSF homeostasis as well as cerebral venous drainage in the pathophysiology of IIH. Hoffmann et al⁵ teach us that volumetric measurements of the optic nerve sheath and hypophysis can be used to accurately diagnose patients with IIH. Aiken et al⁶ explore the overlap in pathophysiology, clinical, and imaging findings between IIH and Chiari I malformation, with the emphasis that cerebellar tonsillar ectopia >5 mm, even with characteristic “peglike” morphology, may be seen in 20%

of patients with IIH. Interestingly, most of those patients responded to treatment of the IIH alone, without surgical decompression. The distinction between IIH and Chiari I is critical, given the vast difference in treatment approaches. We as neuroradiologists must be aware of this overlap so that we can seek out clinical and imaging findings that may suggest IIH, and avoid a misdiagnosis. Shofty et al⁷ focus their work on IIH in the pediatric population, as they discuss the role of optic nerve sheath diameter (ONSD) for diagnosis of IIH in pediatric patients. The authors establish age-correlated norms for ONSD in pediatric patients while demonstrating that the ONSD is larger in pediatric patients with IIH compared with controls. Finally, Ahmed et al⁸ and Bussière et al⁹ review their vast experience with transverse sinus stenting for IIH.

I sincerely hope that the increases in knowledge provided within these articles spur some interesting discussions in the reading room while also allowing us to better diagnose and treat patients with IIH.

References

1. Degnan AJ, Levy LM. Pseudotumor cerebri: brief review of clinical syndrome and imaging findings. AJNR Am J Neuroradiol 2011;32:1986–93, 10.3174/ajnr.A2404
2. Passi N, Degnan AJ, Levy LM. MR imaging of papilledema and visual pathways: effects of increased intracranial pressure and pathophysiologic mechanisms. AJNR Am J Neuroradiol 2013;34:919–24, 10.3174/ajnr.A3022
3. Alperin N, Bagci AM, Lam BL, et al. Automated quantitation of the posterior scleral flattening and optic nerve protrusion by MRI in idiopathic intracranial hypertension. AJNR Am J Neuroradiol 2013;34:2354–59, 10.30174/ajnr.A3600
4. Alperin N, Ranganathan S, Bagci AM, et al. MRI evidence of impaired CSF homeostasis in obesity-associated idiopathic intracranial hypertension. AJNR Am J Neuroradiol 2013;34:29–34, 10.3174/ajnr.A3171
5. Hoffmann J, Schmidt C, Kunte H, et al. Volumetric assessment of optic nerve sheath and hypophysis in idiopathic intracranial hypertension. AJNR Am J Neuroradiol 2013;35:513–18, 10.3174/ajnr.A3694
6. Aiken AH, Hoots JA, Saindane AM, et al. Incidence of cerebellar tonsillar ectopia in idiopathic intracranial hypertension: a mimic of the Chiari I malformation. AJNR Am J Neuroradiol 2012;33:1901–06, 10.3174/ajnr.A3068
7. Shofty B, Ben-Sira L, Constantini S, et al. 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;33:366–69, 10.3174/ajnr.A2779
8. Ahmed RM, Wilkinson M, Parker GD, et al. Transverse sinus stenting for idiopathic intracranial hypertension: a review of 52 patients and of model predictions. AJNR Am J Neuroradiol 2011;32:1408–14, 10.3174/ajnr.A2575
9. Bussière M, Falero R, Nicolle D, et al. Unilateral transverse sinus stenting of patients with idiopathic intracranial hypertension. AJNR Am J Neuroradiol 2010;31:645–50, 10.3174/ajnr.A1890

 

Image modified from: Alperin N, Ranganathan S, Bagci AM, et al. MRI Evidence of Impaired CSF Homeostasis in Obesity-Associated Idiopathic Intracranial Hypertension.