A14 Brain tumors (mass effect, edema)

Topic

The brain tumor grows according to Gompertzian kinetics; that is, it grows rapidly at first, but the growth rate becomes self-limiting as the tumor volume approaches the maximum volume sustainable by the surrounding tissue. The closer the tumor volume gets to this maximum sustainable volume, the slower the tumor grows, until growth effectively plateaus near that limit.

As the brain tumor grows, it damages the surrounding blood-brain barrier; this compromised barrier allows fluid to leak into nearby tissue, creating peritumoral edema around the tumor. The increase in tumor volume, combined with this peritumoral edema, raises intracranial pressure—following the volume-pressure relationship within the skull known as the Monro-Kellie doctrine, a concept already used to describe increased intracranial pressure in cases of traumatic brain injury.

This rise in intracranial pressure compresses the surrounding vasculature, thereby reducing local blood flow to the brain tissue near the tumor. Simultaneously, the increased intracranial pressure displaces brain structures from their normal positions—causing what is known as midline shift—and disrupts the effective functional connectivity of cortical networks adjacent to the tumor.

When intracranial pressure exceeds a critical threshold, a risk of herniation arises—that is, the risk that a portion of brain tissue will be forced out of its normal compartment within the skull. Herniation is the most serious acute complication caused by a brain tumor; it is the final outcome of a sequence that begins with tumor growth, proceeds through peritumoral edema and increased intracranial pressure, and culminates in the compromise of blood flow, positioning, and connectivity of the brain tissue surrounding the tumor.

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