Pilomyxoid astrocytomas are an uncommon and aggressive variant of pilocytic astrocytoma with unique clinical and histopathologic characteristics.

Epidemiology

Pilomyxoid astrocytomas are usually encountered in young children and infants (mean age of 10-18 months), however, adults cases have been described. As most of these tumors have been previously classified as pilocytic astrocytomas it is uncertain whether they have a distinctive epidemiology.

Although it has been suggested that pilomyxoid astrocytomas should be considered WHO grade II tumors (compared to pilocytic astrocytomas WHO grade I), in the 2016 update to the WHO classification of CNS tumors a formal grade has not been given. 

MRI features

T1: T1 shows an isointense signal

T2: usually shows hyperintense signal, reflecting its myxoid matrix

GRE/SWI: approximately 20% of pilomyxoid astrocytomas show intra-tumoral hemorrhage

T1 C+ (Gd): Contrast enhancement is common and is usually in the solid component but may be also peripheral

DWI/ADC: usually showshigh ADC values (facilitated diffusion), reflecting its myxoid matrix