When a tumor is detected on a brain MRI, one of the first questions that generally comes to patients’ minds is:
“Do I need surgery?”
The short answer: No. Not every tumor seen in the brain needs to be operated on.
For some brain tumors, surgery is the most appropriate and sometimes the most important treatment option. However, some tumors can be monitored with regular MRI scans alone; some can be treated with radiosurgery methods such as Gamma Knife; and in some cases, performing only a small biopsy rather than completely removing the tumor may be sufficient.
The right decision is based on the tumor’s type, size, location in the brain, whether it is growing, the symptoms it causes in the patient, and the person’s overall health status [1–3].
First of all, a “brain tumor” is not a single disease
“Brain tumor” is a very broad term.
A meningioma, glioma, pituitary tumor, vestibular schwannoma, or brain metastasis originating from cancer in another part of the body are entirely different diseases.
Therefore, simply seeing the word “tumor” or “mass” in an MRI report is not sufficient to make a decision about surgery.
The important thing is first to understand what type of tumor we are dealing with.
In which situations is surgery more necessary?
Surgery comes to the forefront particularly in certain situations.
If the tumor is putting pressure on the brain
Large tumors can put pressure on surrounding brain tissue and cause brain edema.
As a result;
- -weakness in an arm or leg,
- -speech impairment,
- -balance problems,
- -epileptic seizures,
- -changes in consciousness
- -or symptoms related to increased intracranial pressure
may occur.
Especially in large tumors causing significant pressure, surgery may be important to rapidly reduce the tumor burden and relieve pressure on the brain. Current guidelines for brain metastases also state that, particularly in large lesions causing mass effect, surgery may provide greater benefit [3].
If we need to know exactly what the tumor is
MRI provides very important information about what a tumor may be, but it does not always establish a definitive diagnosis.
For a definitive diagnosis, it may sometimes be necessary to obtain tissue from the tumor and perform pathological examination of this tissue and, increasingly today, molecular analysis.
In this case, complete removal of the tumor or obtaining only a small biopsy may be necessary.
If the tumor is growing
Seeing that a tumor under observation is growing on serial MRI scans may also change the treatment decision.
For example, while some incidentally found meningiomas that cause no symptoms may initially be monitored only, treatment becomes a consideration when a meningioma begins to grow or causes symptoms [1].
So which brain tumors can be monitored without surgery?
One of the best examples is small, incidentally detected meningiomas.
A small meningioma may be seen on an MRI performed for another reason. The patient may have no symptoms, and the tumor may not be putting pressure on important brain structures.
In such a patient, immediate surgery is not always necessary.
The European Association of Neuro-Oncology (EANO) meningioma guideline also states that regular MRI surveillance is one of the first options for asymptomatic, incidentally detected meningiomas [1].
The important thing here is not “doing nothing,” but rather monitoring in a controlled manner.
MRI follow-up assesses whether the tumor is growing, and a treatment decision is made later if necessary.
Can Gamma Knife be used instead of surgery?
For some patients, yes.
Gamma Knife is a stereotactic radiosurgery method that treats a defined target with highly precise radiation beams without opening the skull.
Particularly for;
- -some small- or medium-sized meningiomas,
- -some brain metastases,
- -vestibular schwannomas,
- -some pituitary tumors
Gamma Knife may be an appropriate option.
For example, the EANO meningioma guideline states that radiosurgery may be an alternative to surgery for meningiomas of appropriate size and in certain locations [1].
Likewise, stereotactic radiosurgery is an important treatment option for brain metastases, especially for small lesions. Current guidelines state that even multiple brain metastases can be treated with stereotactic radiosurgery in appropriate patients [3].
However, Gamma Knife and open surgery are not two methods that completely replace one another.
For example, surgery may be the more appropriate option for a very large tumor that is putting serious pressure on the brain and needs to be relieved quickly. In contrast, radiosurgery may offer advantages for some tumors that are small, well-defined, and located in an area where surgery is risky.
The situation is different in gliomas
The approach may differ for gliomas that develop from the brain’s own cells.
Especially in glioblastoma and some diffuse gliomas, surgery is important not only to reduce the mass in the brain, but also to establish a definitive diagnosis and determine the tumor’s molecular characteristics.
The 2026 EANS–EANO guideline recommends the greatest possible extent of tumor removal in newly diagnosed glioblastomas, as long as it is safe. It also states that safe surgical resection in IDH-mutant gliomas may provide benefits in terms of survival and seizure control [2].
The important word here is **“safe.”**
The goal is not simply to make the tumor disappear completely on MRI. If attempting to remove the entire tumor creates a risk of damaging speech, movement, vision, or other important brain functions, the surgical strategy should be modified accordingly.
Is the idea that “the entire tumor must be removed” always correct?
No.
In brain surgery, the goal is not only to remove as much tumor as possible, but also to preserve the patient’s neurological functions.
Some tumors may encase critical structures such as important blood vessels, nerves, or the brainstem.
In this situation, it may not be appropriate to cause a serious neurological deficit in order to remove the tumor completely.
For example, in some skull base meningiomas, the safe portion of the tumor may be removed surgically, while a small portion in a high-risk area may be intentionally left behind. The remaining portion can later be monitored or treated with Gamma Knife. The EANO guideline also accepts this approach, in which planned subtotal surgery and radiosurgery can be used together [1].
In other words, the goal of a good brain tumor surgery is not always:
“Removing the tumor completely at all costs”
.
The main goal should be:
“Providing the greatest benefit to the patient with the least neurological risk”.
What is the decision based on?
When a brain tumor is seen, the treatment decision is not based solely on the tumor’s size.
The main factors that need to be assessed together are:
- -The likely type of tumor
- -Its location in the brain
- -Its size
- -Whether there is edema around it or pressure on the brain
- -Whether it has grown compared with previous MRIs
- -The patient’s age
- -The patient’s symptoms
- -Overall health status
- -Whether a definitive pathological diagnosis is needed
- -The neurological risk that surgery may pose
- -Whether Gamma Knife or other treatment options are feasible
Therefore, two tumors of the same size may be treated entirely differently in two different patients.
Conclusion
Seeing a tumor in the brain does not necessarily mean that surgery will be required.
Some tumors can be safely monitored. Some can be treated with radiosurgery methods such as Gamma Knife. Some require only a biopsy. For some tumors, surgery is the treatment that will provide the greatest benefit to the patient.
The important question is not only “Can this tumor be operated on?”.
The more appropriate question is:
“Which treatment is the safest and most effective for this patient?”
Sometimes the answer is observation, sometimes Gamma Knife, sometimes surgery, and sometimes a combination of these methods.
Therefore, in brain tumor treatment, it is important for the decision to be individualized by an experienced neurosurgery and multidisciplinary team that can assess the tumor’s imaging characteristics, the patient’s clinical condition, and all available treatment options together.
References
1. Goldbrunner R, Stavrinou P, Jenkinson MD, et al. EANO guideline on the diagnosis and management of meningiomas. Neuro Oncol. 2021;23(11):1821–1834. doi:10.1093/neuonc/noab150.
2. Goldbrunner R, Foroglou N, Grossman R, et al. EANS-EANO guidelines on the extent of resection in gliomas. Neuro Oncol. 2026;28(1):38–54. doi:10.1093/neuonc/noaf217.
3. Vogelbaum MA, Brown PD, Messersmith H, et al. Treatment for Brain Metastases: ASCO-SNO-ASTRO Guideline. Neuro Oncol. 2022;24(3):331–357. doi:10.1093/neuonc/noab205.