**Question:** All of the following are true about brain metastasis except:

A. Brain tumor cells originate from a primary site outside the central nervous system (CNS).
B. Brain tumor cells have crossed the blood-brain barrier (BBB).
C. Symptoms related to brain tumor are usually due to increased intracranial pressure.
D. Brain tumor cells are more likely to cause seizures.

**Core Concept:** Brain Metastasis is a condition where cancer cells from a primary tumor outside the brain disseminate to the brain through the bloodstream or lymphatic system. These cells can cause symptoms and signs due to the effects of mass effect, inflammation, or direct invasion into surrounding tissues. One of the key challenges in managing brain tumors is understanding the complex mechanisms of cancer cell invasion into the CNS.

**Why the Correct Answer is Right:**

D. Brain tumor cells are more likely to cause seizures (Option D) is incorrect because seizures in brain tumors are typically due to structural changes in the brain and not solely caused by tumor cells themselves. Seizures may occur when tumor cells invade and disrupt the normal neural pathways, leading to excitatory neural discharges. However, the presence of brain tumor does not inherently increase the likelihood of seizures.

**Why Each Wrong Option is Incorrect:**

A. Brain tumor cells originate from a primary site outside the CNS (Option A):
- Brain tumors can arise from various cell types within the brain, including astrocytes, oligodendrocytes, and ependymal cells. These are primary brain tumors.
- Secondary brain tumors, also known as brain metastases, originate from cancer cells that have spread to the brain from a primary tumor elsewhere in the body (e.g., lung, breast, or melanoma). However, the statement "Brain tumor cells originate from a primary site outside the CNS" is incorrect as it does not differentiate between primary and secondary brain tumors.

B. Brain tumor cells have not crossed the blood-brain barrier (BBB) (Option B):
- The blood-brain barrier (BBB) is a semipermeable barrier that protects the brain from harmful substances in the bloodstream and maintains the brain's unique environment. It prevents many drugs, toxins, and immune cells from entering the brain.
- Brain tumors, especially secondary ones, often cross the BBB due to disrupted tight junctions, inflammation, or other factors that weaken the barrier.

C. Symptoms related to brain tumors are usually caused by increased intracranial pressure (Option C):
- Brain tumors can lead to symptoms due to mass effect (increased intracranial pressure) and compression of surrounding brain structures (e.g., hydrocephalus, herniation).
- However, secondary brain tumors (metastatic brain tumors) can also cause symptoms and signs due to the presence of cancer cells, inflammation, and mass effect.

**Core Concept:** Secondary brain tumors (metastatic brain tumors) are more likely to cause symptoms due to the presence of cancer cells, inflammation, and mass effect within the brain parenchyma.

**Why Each Wrong Option is Incorrect:**

A. **