Review the pathophysiology of Intracranial Hypotension Syndrome (IHS) and understand its etiology as spontaneous or acquired. Understand the spectrum of imaging findings of the syndrome in the different imaging modalities such as brain and spine CT, MRI and scintigraphy. Discuss the natural history of the disease through MRI findings and how they evolve in response to a number of treatment options. Analyze the possible differential diagnoses and summarize the key points useful to give an accurate diagnosis.

CONTENTS 1. General aspects: causes and clinical presentation 2. Diagnostic workup 3. Imaging findings 3.1 General imaging aspects 3.2 Brain MRI 3.3 Spine imaging 3.4 Brain CT 4. Treatment and outcome 5. Differential diagnoses 6. Diagnostic pearls 7. Conclusion 8. References 1. GENERAL ASPECTS: CAUSES AND CLINICAL PRESENTATION The ample diagnostic umbrella of IHS includes multiple processes that cause a theoretical decrease in cerebrospinal fluid (CSF) pressure. IHS may be spontaneous or acquired. Both instances, however have in common a decrease in CSF pressure and/or...

2. DIAGNOSTIC WORKUP The diagnosis of spontaneous intracranial hypotension is made in the clinical context of orthostatic headache, by demonstrating CSF hypotension (either by lumbar puncture, imaging techniques, or by improvement of symptoms after epidural patching), and after excluding other causes that could justify the symptoms, such as dural puncture or other disorders(see table in Fig. 1 for diagnostic criteria) [4,5]. 3. IMAGING FINDINGS 3.1 General imaging aspects Head MRI with and without contrast is the most appropriate test to work up the diagnosis of...

6. DIAGNOSTIC PEARLS TO TAKE HOME Ultimate cause is low CSF volume/pressure, usually associated to CSF leakage which may be spontaneous or secondary Clinical presentation: Intense orthostatic headache Diagnosis is based on clinical presentation and proof of low CSF pressure (be it by lumbar puncture or imaging techniques) Cranial MRI best diagnostic tool. Typical imaging signs: “Sagging” descended central brain and brainstem, amygdala herniation, distended veins, diffuse pachymeningeal enhancement, and large hypophysis Sagittal midline T1 best demonstrates brain sagging. Contrast enhanced images useful for dural...

P.N.B.; D.E.N.V.; M.H.N.; and J.V.J. from the Department of Radiology, Hospital Universitari de Bellvitge, L'Hospitalet de Llobregat,Barcelona, Spain. J.J.S.F.; C.M.; and C.A.G. from the Department of Radiology, Institut de Diagnòstic per la Imatge-IDI, Hospital Universitari de Bellvitge, L'Hospitalet de Llobregat, Barcelona, Spain. P.P.dP. from the Department of Radiology,Hospital Universitari Germans Trias i Pujol, Badalona, Barcelona, Spain .

8. REFERENCES [1] Kranz PG, Tanpitukpongse TP, Choudhury KR, Amrhein TJ, Gray L. Imaging Signs in Spontaneous Intracranial Hypotension: Prevalence and Relationship to CSF Pressure. AJNR Am J Neuroradiol 2016;37:1374–8. [2] Kranz PG, Luetmer PH, Diehn FE, Amrhein TJ, Tanpitukpongse TP, Gray L. Myelographic Techniques for the Detection of Spinal CSF Leaks in Spontaneous Intracranial Hypotension. AJR Am J Roentgenol 2016;206:8–19. [3] Paldino M, Mogilner AY, Tenner MS. Intracranial hypotension syndrome: a comprehensive review. Neurosurg Focus 2003;15:ECP2. [4] Headache Classification Committee of the International Headache...