Chapter 27 - Physiological imaging in infection, inflammation and demyelination

Summary

Introduction

This chapter will offer an overview of physiological imaging of infectious inflammatory and demyelinating diseases. It will describe routine imaging findings and the current and potential roles of a variety of techniques. Subsequent chapters will provide more detailed information of specific techniques as they apply to a variety of disease processes.

Magnetic resonance imaging (MRI) has had a profound effect on detection, management, and outcome of central nervous system (CNS) infectious, inflammatory, and demyelinating diseases. While this statement seems to apply uniformly to virtually all CNS disorders, there is a difference. Despite recent therapeutic advances, outcomes for many disorders (e.g., stroke, neoplasm, and neurodegenerative diseases) have improved only modestly because effective treatments are not yet available. In these disorders, the MRI tools discussed in this book will play an important role in developing and monitoring new therapies. In infectious and inflammatory diseases, effective treatments are available for many disorders but success is dependent upon early institution of the correct therapeutic regimen. Use of MRI has led to a dramatic improvement in outcome by allowing for early and accurate detection of many of these disorders. The presence of characteristic MRI features often allows for accurate diagnosis, at least in the hands of experienced neuroradiologists. In these disorders, physiological techniques such as diffusion-weighted imaging (DWI),[1] diffusion tensor imaging (DTI),[2] perfusion-weighted imaging (PWI), and MR spectroscopy (MRS) [3,4] are useful additions to “routine” MR since they may allow for earlier detection (e.g., DWI in herpes simplex type 1 [HSV-1] encephalitis [5]) or more accurate characterization of lesions (e.g., DWI [6] and MRS in brain abscesses [7,8]). There is a tendency to assume that these new tools will be used most often and prove most beneficial to experts but this is not the case. Experts typically recognize critical but subtle differences between different lesions while less-experienced readers may not always appreciate these differences. Findings on physiological techniques can, therefore, improve diagnostic accuracy by providing simple unambiguous information suggestive of the correct diagnosis.