Imaging description

An expansile hyperintense T2 signal mass with symptoms of increased intracranial pressure and sometimes seizures is an imaging conundrum. It may represent a relatively low-grade glioma, or it may represent higher-grade neoplasms. Gliomas are classified into WHO grades I–IV according to histologic criteria. Low-grade gliomas (LGGs) affect both children and adults. The predominant histologic type of glioma found in children is a grade I tumor, juvenile pilocytic astrocytoma (JPA) (Fig. 24.1), which is often curable if completely resectable. However, LGGs in adults, known as WHO grade II gliomas, are infiltrative and may not be completely resected surgically [1].

The LGG accounts for about 20–30% of all gliomas in adults [2]. An LGG is a slow-growing, diffusely infiltrating astrocytic or oligodendrocytic neoplasm with a high degree of cellular differentiation. The recent discovery of isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) mutations in glioma has provided reproducible prognostic biomarkers and novel therapeutic targets [3]. More than 60% are associated with p53 mutation; they are also associated with a few chromosomal abnormalities. About two-thirds are supratentorial, predominantly involving the frontal and temporal lobes. About half of the infratentorial brainstem gliomas are low-grade astrocytomas. On non-contrast CT, they appear as ill-defined isodense to hypodense masses without significant enhancement (Fig. 24.2). About 20% exhibit areas of calcification, with rare cyst formation. On MRI, they appear as homogeneous hypointense T1 signal, predominantly white matter mass, which can be expansile and may appear well circumscribed (Fig. 24.3) but infiltrates the surrounding brain parenchyma. Hemorrhage and surrounding edema are rarely seen [4]. On FLAIR-weighted imaging, a homogeneous hyperintense mass is seen and no significant post-contrast enhancement is seen.