A brain tumor is an abnormal growth of tissue in the brain. The most common surgical treatments are removal via craniotomy or transsphenoidal surgery. Other common surgical treatments include radiosurgery and laser interstitial ablation therapy. In some cases, a tumor may not be amenable to surgical removal, but a surgical biopsy may still be necessary to definitively diagnose the tumor before proceeding with medical treatments.

Depending on a brain tumor’s origin, it is classified as either primary or secondary, and depending on a brain tumor’s behavior, it is classified as either benign or malignant.

Benign Tumors

A benign tumor does not contain cancer cells and usually, once removed, does not recur. Most benign brain tumors do not invade surrounding tissue and therefore have clear borders; however, these tumors can cause symptoms similar to malignant tumors because of their size and location in the brain. Often, benign tumors can be cured with resection.

Malignant Tumors

Malignant brain tumors contain cancer cells, are usually fast growing and invade surrounding tissue. Malignant brain tumors very rarely metastasize outside of the brain, but they often spread beyond the margins of the resection and thus, may recur after treatment.

Tumor Classification

The World Health Organization grades tumors on a scale of one to four on the basis of tumor cell appearance and tumor behavior. The higher the grade, the more aggressive and abnormal the tumor.

  • Grade 1 tumors are slow-growing and benign, and they do not spread in the brain
  • Grade 2 tumors are slow-growing but the cells have an abnormal appearance and can progress to higher grades over time
  • Grade 3 tumors are fast-growing and malignant
  • Grade 4, the most malignant and aggressive tumors, are fast-growing with highly abnormal cellular appearance.

There are also some molecular features that have a great influence on the prognosis for brain tumors, the most important of which is the mutation of a gene called IDH1.

There are many different types of brain tumors, and they are usually categorized by the type of cell from which the tumor originates. Some tumors are also categorized by the area of the brain where they occur.