Meninges: benign postoperative enhancement on MR images. 5 Burke JW, Podrasky AE, Bradley WG Jr.Normal anatomic features and nonneoplastic disease. 4 Meltzer CC, Fukui MB, Kanal E, Smirniotopoulos JG.MRI of non-ischemic vascular disease: aneurysms and vascular malformations. 3 Wilms G, Demaerel P, Bosmans H, Marchal G.The role of blood-brain barrier permeability in brain tumor imaging and therapeutics. 2 Provenzale JM, Mukundan S, Dewhirst M.Contrast media and the brain: the basis of CT and MR imaging enhancement. Understanding the classic patterns of lesion enhancement-and the radiologic-pathologic mechanisms that produce them-can improve image assessment and differential diagnosis. Thin enhancement of the ventricular margin occurs with infectious ependymitis. Thick and irregular periventricular enhancement is typical for primary central nervous system lymphoma. Demyelinating lesions, including both classic multiple sclerosis and tumefactive demyelination, may also create an open ring or incomplete ring sign. Some low-grade neoplasms are “fluid-secreting,” and they may form heterogeneously enhancing lesions with an incomplete ring sign as well as the classic “cyst-with-nodule” morphology. Ring enhancement that is smooth and thin is typical of an organizing abscess, whereas thick irregular rings suggest a necrotic neoplasm. Deeper lesions may form rings or affect the ventricular margins. Nodular subcortical lesions are typical for hematogenous dissemination and may be neoplastic (metastases) or infectious (septic emboli). Superficial gyral enhancement is seen after reperfusion in cerebral ischemia, during the healing phase of cerebral infarction, and with encephalitis. Leptomeningeal (pia-arachnoid) enhancement is present in meningitis and meningoencephalitis. Linear pachymeningeal (dura-arachnoid) enhancement occurs after surgery and with spontaneous intracranial hypotension. Extraaxial enhancing lesions include primary neoplasms (meningioma), granulomatous disease (sarcoid), and metastases (which often manifest as mass lesions). Brain and spinal cord enhancement is related to both intravascular and extravascular contrast material. Knowledge of the patterns and mechanisms of contrast enhancement facilitate radiologic differential diagnosis. Contrast material enhancement for cross-sectional imaging has been used since the mid 1970s for computed tomography and the mid 1980s for magnetic resonance imaging.
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