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1、Etiology and Diagnosis of Intracranial Hypertension: Using MRI to Narrow an Index Patients Differential Michael A. DyerHarvard Medical School, July 2009Beth Israel Deaconess Medical Center Department of RadiologyDr. Gillian LiebermanObjectivesUsing an index case of a patient with intracranial hypert
2、ension (IH), this presentation will provide the skills and knowledge necessary to:?Recognize the signs of IH on MRI?Understand the logical basis for the differential diagnosis of IH?Develop a foundation for systematically approaching MR scans in patients with IHOur Index Patient: Chief Complaint, Hi
3、story, and Physical?34 year-old woman with chronic headache (recently worsened) and blurred vision referred to an ophthalmologist ?Complicated medical history, Papilledema including 50 lb weight gain in the past 1-2 years?Physical exam: optic disc swelling, i.e. papilledema (see figure)?Referred by
4、the ophthalmologist for an MRI to look for the potential cause of the patients signs and symptoms(Bienfang, DC; UpToDate)Before looking at our patients MRI, well review (1) a few points about CTsand MRIs; and (2) a few points about different MRI sequencesMenu of Tests: CT vs. MRI in Patients with Pa
5、pilledema?Depending on the suspected cause of a patients papilledema, physicians may choose to order a CT and/or an MRI?For example, as we will explore later in the presentation, subarachnoid hemorrhage is one potential cause of papilledema; in a patient with acute subarachnoid hemorrhage, CT is usu
6、ally the test of choice?MRI, on the other hand, is preferable to CT for diagnosis of many other causes of papilledema, e.g. soft tissue lesions?This presentation concentrates only on diagnosis using MRIDistinguishing MRI Sequences?“T1” = T1 weighted image (fluid is dark, i.e. low intensity)?“T2” = T
7、2 weighted image (fluid is bright, i.e. high intensity)?“C+” = Image enhanced with gadolinium (i.e. IV contrast was administered)?“FLAIR” = Fluid attenuated inversion recovery (a sequence that nulls signals from fluids to allow visualization of lesions whose signals are normally obscured by the sign
8、al from cerebrospinal fluid)?“MP-RAGE” = Magnetization prepared rapid acquisition gradient echo; designed for rapid image acquisition (a T1 weighted scan)Now lets look at our patients MRIOur Patient: Evidence of Intracranial Hypertension on MRIFindings?Increased fluid in optic nerve sheath bilateral
9、ly (bright signal)?Mild flattening of posterior globes?Tortuous optic nervesOur PatientNormalAxial T2 MRI (PACS BIDMC)Axial T2 MRI (PACS BIDMC)What fluid could be responsible for the high intensity signal surrounding the optic nerve within the optic sheath?Review of CSF Flow?CSF can track along pote
10、ntial space surrounding optic nerveCSF Production and FlowCSF in Optic Nerve Sheath (Cummings, B; IUPUCAnatomy)(CorkreyOHara, JK website)CSF and Intracranial Hypertension?Increased pressure within the intracranial compartment is necessary for CSF to track along the optic sheath?Sometimes intracrania
11、l hypertension causes other findings, such as hydrocephalusNow lets review some basic principles of intracranial pressure to understand what couldunderlie our patients MRI findings that are suggestive of intracranial hypertensionCompliance and Intracranial Pressure?Compliance is equal to change in v
12、olume divided by change in pressure (C = V / P) The cranial compartment is incompressible (i.e. it has a low compliance) If compliance is low, then for a given increase in volume, there will be a large increase in pressure (P = V / C)?Therefore, any change in volume of the structures or fluids withi
13、n the cranium will produce large changes in pressureAs a result, to generate a differential diagnosis for intracranial hypertension (and therefore, to find a cause for the patients papilledemaand orbital MRI findings), lets consider what inside the intracranial compartment could be increased in volu
14、meMajor Physical Components of the Intracranial Compartment1. Blood2. Brain3. CSFCauses of Intracranial Hypertension: Differential Diagnosis1. Increased blood volume2. Increased brain volume3. Increased CSF volumeCauses of Intracranial Hypertension: Differential Diagnosis1. Increased blood volumea.
15、occlusion (e.g. venous thrombosis) b. blood outside vessels (i.e. hemorrhagic stroke)2. Increased brain volume3. Increased CSF volumeCauses of Intracranial Hypertension: Differential Diagnosis1. Increased blood volumea. occlusion (e.g. venous thrombosis) b. blood outside vessels (i.e. hemorrhagic stroke)2. Increased brain volumea. intracranial mass (e.g. tumor) b. cerebral edema 3. Increased CSF volumeCauses of Intracranial Hypertension: Differential Diagnosis1. Increased blood volumea. occlusion (e.g.
