This is the second and final volume of the American Journal of Neuroradiology Special Collection on Brain Tumor Imaging, which focuses on articles related to imaging of tumors after therapy. I would like to thank Mauricio Castillo, Editor-in-Chief of AJNR , for inviting me to be a Guest Editor and

Brain tumors are a heterogeneous group of neoplasm with a diverse histological, molecular, and genetic spectrum and a widely variable clinical course and prognosis. Although most brain tumors, especially the malignant variety, remain difficult to cure, there are promising novel therapies and drug delivery systems that are under active investigation. One of the greatest challenges in developing effective therapy for brain tumors is the lack of specific markers to directly and accurately assess antitumor effect early and noninvasively. Further challenge lies in the fact that early treatment response can be transient and may not necessarily translate into long-term response or a favorable clinical outcome. In addition, there may be a small window of opportunity to assess therapeutic efficacy so that ineffective toxic therapy can be switched over to more effective therapy before there is widespread damage to the normal brain. The search for reliable and accurate predictors of treatment outcome that can be used to guide therapy and to improve survival in patients in malignant brain tumor has continued over several decades with modest success. This article will provide a general overview and current status of using quantitative maps derived from physiology-based magnetic resonance imaging to assess therapy response and to predict clinical outcome early during the course of therapy.

Imaging technology continues to advance and simplify the diagnosis of neurotologic pathology. Namely, high-resolution magnetic resonance imaging has provided detailed evaluation of the internal auditory canal and membranous labyrinth. Conversely, the role of high-resolution magnetic resonance imaging as a screening tool remains controversial. Functional imaging studies, such as functional magnetic resonance imaging and single photon emission computed tomography are beginning to find significant roles in the evaluation of patients with cochlear implants. General imaging principles and imaging strategies for specific pathologic conditions of the temporal bone are also discussed.

BACKGROUND AND PURPOSE: MR imaging characteristics of gliomatosis cerebri reiterate the diffuse nature of this tumor but are nonspecific and thus may pose a diagnostic challenge. Because perfusion MR imaging can provide a physiologic map of the microcirculation, we compared the measured relative cerebral blood volume (rCBV) at perfusion imaging with histopathologic findings in gliomatosis cerebri. MR spectroscopic findings were also reviewed.METHODS: Retrospective analysis was performed of conventional and perfusion MR images from seven patients with proved gliomatosis cerebri. The conventional MR images were evaluated for the presence or absence of contrast enhancement, necrosis, and extent of T2-weighted signal intensity abnormality. Dynamic contrast-enhanced T2*-weighted gradient-echo echo-planar images were acquired during the first pass of a bolus injection of gadopentetate dimeglumine. The rCBV was calculated by using nondiffusible tracer kinetics and expressed relative to normal-appearing white matter. Pathologic findings were reviewed in all patients and compared with the MR perfusion data. Multivoxel 2D chemical shift imaging proton MR spectroscopic data were available for three patients and single-voxel data for one patient.RESULTS: Conventional MR images showed diffuse abnormality in all cases and absence of contrast enhancement in all but one case. Average rCBV range was 0.75-1.26 (mean, 1.02 +/- 0.42 [SD]). MR spectroscopic data revealed spectra consistent with presence of tumoral disease. Histopathologic review showed absence of vascular hyperplasia in all specimens.CONCLUSION: The low MR rCBV measurements of gliomatosis cerebri are in concordance with the lack of vascular hyperplasia found at histopathologic examination; thus, perfusion MR imaging provides useful adjunctive information that is not available from conventional MR imaging techniques.