1 The main differential consideration between peripherally enhancing parenchymal lesions is cystic/necrotic neoplasm (primary or metastatic) versus abscess. Neoplasms include high-grade necrotic gliomas such as glioblastomas and anaplastic astrocytomas, and lower-grade neoplasms such as hemangioblastoma, pilocytic astrocytoma, and ganglioglioma, as well as metastases. Occasionally, demyelinating lesions or evolving hematoma can have a similar appearance. Some of these lesions have distinguishing features such as a mural nodule (hemangioblastoma or pilocytic astrocytoma), but others may look similar on conventional imaging, with peripheral enhancement and surrounding reaction or edema (low density on computed tomography or hyperintensity on T2-weighted magnetic resonance (MR) imaging. A variety of differentiating features has been described based on characteristics of the wall, the enhancement found, and the surrounding reaction (Table 1.1). Recently, newer imaging techniques such as diffusion weighted imaging, MR perfusion imaging, and MR spectroscopy have also been shown to help in differentiating these lesions.
Peripherally Enhancing Cystic Brain Lesions
| Neoplasm | Abscess | |
|---|---|---|
| Enhancement of Wall | Nodular | Smooth |
| Surrounding Edema | Variable; may be less extensive for primary tumors, but more extensive for metastases |
