Brain and Its Coverings
Technological advances in radiology during the past 30 years have vastly improved our ability to diagnose neurologic diseases. Prior to the introduction of computed tomography (CT) in 1974, neuroradiologic examinations of the brain consisted primarily of plain films of the skull, cerebral arteri-ography, pneumoencephalography, and conventional nuclear medicine studies. Unfortunately, these techniques, for the most part, provided only indirect information about sus-pected intracranial processes, were insensitive in detecting subtle or early brain lesions, or were potentially harmful to the patient. Computed tomography revolutionized the radio-logic workup of central nervous system (CNS) abnormalities because for the first time normal and abnormal structures could be directly visualized with minimal risk to the patient.
In the late 1980s, it became apparent that magnetic reso-nance (MR) imaging would become the procedure of choicefor evaluating many neurologic disorders, as well as for demonstrating vascular flow phenomena. Since then, there have been many technological advances associated with this modality. These include improvements in magnet and coil design, decrease in imaging time, and the development of new pulse sequences. In addition to advances in conventional anatomic imaging, there has also been substantial growth of “physiologic” MR imaging including MR spectroscopy (MRS), diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging, and functional MR imaging (fMRI), among others. These imaging modalities provide functional information about the brain and have the potential to greatly extend our understanding of neuropathology beyond struc-ture alone.
Revolutionary breakthroughs in CT scanning technology during the 1990s facilitated the development of advanced CT applications, namely, dynamic contrast-enhanced CT angiog-raphy (CTA) and CT perfusion (CTP). These techniques, which allow high spatial resolution imaging of the cervical and intracranial vasculature, are currently being used in the evaluation of the acute stroke patient in many medical cen-ters. Furthermore, recent technologic advances in CT imag-ing have markedly decreased scan times and have allowed evaluation of very tiny anatomic structures because of im-provement in spatial resolution.
Recent advances in nuclear medicine functional imaging techniques, including single photon emission computed to-mography (SPECT) and positron emission tomography (PET), improvements in conventional angiographic meth-ods, and expansion of catheter-based therapeutic procedures have provided the neuroradiologist today with an even greater variety of strategies for diagnosing and treating neu-rologic abnormalities.
The strengths and weaknesses of these techniques are discussed. Imaging anatomy of the brain and its coverings is briefly reviewed. Basic guidelines pertaining to technique selection for evaluating common neurologic conditions are provided. Finally, examples of common brain abnormalities are presented. It is assumed that readers have a basic understanding of neuroanatomy and neuropathology.
Although this may give some insight into neuro-radiologic study interpretation, that is not its primary goal. Rather, readers should expect to become reasonably familiar with the various techniques employed to examine the brain and should gain some idea about the appropriate ordering of examinations in specific clinical situations.