Actress Busy Philipps recently revealed that she underwent two surgeries this year after doctors found a rare brain tumour. They discovered it unexpectedly during a full-body MRI despite her not having obvious symptoms.The Dawson's Creek and Cougar Town actor, 47, told PEOPLE that the tumour was discovered in February after she underwent a Prenuvo full-body scan. The scan showed a 2.6-cm mass in her brain, which was later diagnosed as a grade 2 oligodendroglioma. She underwent surgery on March 2 to remove the tumour. She then needed a second operation after developing a staphylococcal infection at the surgical site. She has since returned to work and said she is now undergoing regular monitoring, without chemotherapy or radiation.What Is An Oligodendroglioma?An oligodendroglioma is a rare type of glioma, a tumour that develops from cells in the brain or spinal cord.These tumours arise from oligodendrocytes, cells that help produce myelin, the protective coating surrounding nerve fibres.Grade 2 oligodendrogliomas are generally slow-growing, although they are classified as malignant because they can grow back or become more aggressive over time.Dr Alexandra Miller, Philipps' neuro-oncologist at NYU Langone, told PEOPLE that the tumour is considered malignant because of its ability to regrow. She also said oligodendroglioma affects approximately 1,100 to 1,300 people in the US each year. “It is considered malignant, but it has the best prognosis of all of the malignant gliomas,” says Miller. “It’s sort of defined as a cancerous tumor based on the ability of the tumor to regrow over time, rather than it looking very malignant under the microscope.”Philipps’s early detection, before she had any symptoms, was beneficial, Dr. John Golfinos of NYU Langone said. He said that If she had waited until having symptoms like seizures, the tumor — which was a grade 2 on a scale of 2 to 4 — “would have been two or three times the size. It might have been much harder to take the whole thing out."Also read: Daraxonrasib: US FDA Approves Once-Daily Pill for Metastatic Pancreatic CancerBrain Tumours Can Remain Hidden For YearsOne striking part of Philipps' story is that she did not have obvious neurological symptoms. Oligodendrogliomas can sometimes grow slowly enough that people do not immediately notice anything is wrong. Symptoms depend heavily on where the tumour develops and can include seizures, headaches, changes in behaviour or personality, problems with speech or vision, weakness and difficulties with memory or thinking.Philipps has said that, in retrospect, she had noticed some changes in her emotions and behaviour, including episodes of irritability and crying, but did not know they could be due to a brain tumour.Also read: Dolly Parton Dies At 80 After ‘Brief Battle With Cancer’: What We Know So Far?After Surgery, Why She Didn't Need Chemotherapy Or RadiationSurgery is often the first treatment for oligodendroglioma. Doctors aim to remove as much of the tumour as possible while protecting healthy brain tissue, particularly parts responsible for speech, movement, memory and other essential functions.Her doctor, Orrin Devinsky of NYU Langone, was the physician who reviewed her MRI and told her that the mass was a genuine tumour and needed to be removed.In Philipps' case, surgeons successfully removed the 2.6-cm mass. The tissue was then examined to determine exactly what type of tumour she had.They found that it wasn't the brain tumour type that requires immediate chemotherapy or radiation. Because Philipps had a grade 2 oligodendroglioma that was surgically removed, her medical team has opted for regular monitoring rather than additional treatment at this stage.