Non-neoplastic tumour associated cysts (TACs) are benign fluid-containing cysts adjacent to, but not within, a neoplasm.
TACs are most likely represent trapped encysted pools of CSF adjacent to large extra-axial neoplasms when a tumour grows it traps the CSF between it and the adjacent brain. It is considered a tumour "epiphenomenon".
- smooth well-demarcated cyst
- extra-axial TACs are more common than intra-axial, e.g. meningioma, craniopharyngioma, vestibular schwannoma
- can be single or multiple
- it abuts the tumour directly
- vary from small to very large size
- enhancement: absent or minimal
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