The pilocitic astrocytoma is more common in children, is infratentorial, and represents a cyst (an asterisk in Fig.29) with a parietal node (the head of the arrow in Fig. 1). Less common in adults, mainly in the form of solid formation and is located supratentorial (head arrow in Fig. 2).
0.6-5.1% of all tumors of the central nervous system, 6% of tumors of the central nervous system of childhood, 80% of all cerebellar astrocytomas, a peak occurrence of 5-15 years.
There are three different types of morphological structure:
- a cyst with a parietal node (the most common form), this form is most typical for infratentorial localization and is found mainly in children
- solid formation
- cystic and solid formation.
On the MRI cyst ↑ T2 and ↑ Flair ↓ T1, and a solid component → in T2 and T1 of the brain substance.
The cyst wall usually consists of a healthy cerebellar tissue, much less often of a tumor tissue.
Calcinates are found in 11% of cases, and vasogenic edema - in 5%.
On the CT scan, the contents of the cyst → cerebrospinal fluid, and the structure of the solid part → cerebral.
Hemorrhages and necrosis are not characteristic.
Tumor cyst in the left hemisphere of the cerebellum (arrowheads in Fig. 3), the contents of the cyst have ↑ MR-signal by Flair in comparison with the unchanged cerebrospinal liquor (asterisk in Fig. 3). The parietal node on the inner side of the cyst wall (arrow in Fig. 3).