Clinical applications of susceptibility-weighted imaging in detecting and grading intracranial gliomas: a review

Abstract

Susceptibility-weighted imaging (SWI) is a technique that exploits the susceptibility difference between tissues to provide contrast for different regions of the brain. In essence, it uses the deoxygenated hemoglobin of veins, hemosiderin of hemorrhage, etc. as intrinsic contrast agents, allowing for much better visualization of blood and microvessels even without administration of an external contrast agent. It is a fast-evolving field that is being constantly improved and increasingly implemented with updates in relevant technology. Multiple studies have been done on the role of SWI in the management of various neurologic disorders and it is also being seen as a further step in the neuroradiologist's goal of being able to noninvasively grade tumors in order to influence therapy. This article briefly reviews the evolution of SWI since its conception and provides the reader with a comprehensive summary of various studies that have been done on its application for detecting and grading intraaxial brain tumors, specifically gliomas. Other useful magnetic resonance techniques that have shown promise in grading gliomas are also discussed.

Figure 1

Grade 1 astrocytoma. Nonspecific findings of a tumor mass on (A) T1- and (B) T2-weighted images. Comparison of hypointensity on SWI (C) and hyperintensity on phase image (D) is suggestive of calcification, which was confirmed on CT (E). The presence of calcification and lack of hemorrhage is also suggestive of a low-grade tumor.

Figure 2

Grade 2 astrocytoma as seen on (a) T1-weighted image, (b) T2-weighted image, (c) contrast-enhanced T1 and (d) SWI. Note the lack of susceptibility signals in the low-grade tumor on SWI.

Figure 3

High-grade astrocytoma (GBM) on (a) a T1-weighted image, (b) a T2-weighted image, (c) contrast-enhanced T1 and (d) SWI. The increased number of vessels and microhemorrhages on SWI suggested a high tumor grade, which was confirmed on pathology. Also note the high contrast with which surrounding edema is visible on SWI.

Figure 4

Histopathologically confirmed grade IV GBM. (a) T2-weighted Image shows extensive necrosis and edema with mid-line shift. (b) Contrast-enhanced T1-weighted Image shows fair enhancement of the lesion. (c) Low ADC values are seen in the diffusion-weighted image, and (d) extensive areas of hemorrhage are seen on the susceptibility-weighted image indicating a higher tumor grade.