Why lymphatic system absent in brain?

The lymphatic system is generally absent in the brain because the central nervous system (CNS) has evolved a unique system for waste clearance and immune defense. Instead, the brain relies on the glymphatic system, which utilizes a network of perivascular spaces to facilitate the movement of cerebrospinal fluid (CSF) and interstitial fluid, aiding in the removal of waste products. This adaptation helps maintain the brain's microenvironment and protects it from immune responses that could disrupt neural function.