The cause of oligodendroglioma often isn't known. This tumor starts as a growth of cells in the brain or spinal cord. It forms in cells called oligodendrocytes. Oligodendrocytes help protect nerve cells and help with the flow of electrical signals in the brain.

Oligodendroglioma happens when oligodendrocytes develop changes in their DNA. A cell's DNA holds the instructions that tell the cell what to do. In healthy cells, the DNA gives instructions to grow and multiply at a set rate. The instructions tell the cells to die at a set time. In tumor cells, the DNA changes give different instructions. The changes tell the tumor cells to grow and multiply quickly. Tumor cells can keep living when healthy cells would die. This causes too many cells.

The tumor cells form a growth that may press on nearby parts of the brain or spinal cord as the growth gets bigger. Sometimes the DNA changes turn the tumor cells into cancer cells. Cancer cells can invade and destroy healthy body tissue.