Finding a spot or lesion on the brain can be concerning for patients and doctors alike. However, many incidental findings turn out to be benign. This article will explore the different types of benign brain lesions and when further testing may be warranted. Quick answers to common questions about brain lesions will be provided in the opening paragraphs.
What is a brain lesion? A brain lesion is any abnormal tissue found in the brain. This can include tumors, cysts, scars, or other anomalies.
What causes benign brain lesions? There are many potential causes including congenital disorders, infection, trauma, and normal aging. Many benign lesions are incidental findings that don’t cause symptoms.
How common are benign brain lesions? Very common. As many as 90% of healthy adults have at least one benign brain lesion that went undetected. Improvements in neuroimaging have led to more incidental findings.
Can a benign brain lesion become cancerous? Extremely rare. The vast majority of benign lesions remain stable over time and do not become cancerous. Certain types like low grade gliomas can transform but this is uncommon.
Types of Benign Brain Lesions
There are many types of non-cancerous brain lesions. Some of the most common include:
Cavernous Malformations
Also called cavernous angiomas, these are clusters of abnormal blood vessels that can leak blood into the surrounding brain tissue. They occur in up to 0.5% of the population. Cavernous malformations may be single or multiple lesions. Most cases are asymptomatic but seizures can occur in 30% of patients, especially if the lesion is near the brain’s cortex. Hemorrhage is the most serious complication but is still rare. No treatment is required for asymptomatic cavernous malformations. Anti-seizure medications can control seizures. Surgery may be an option for lesions causing repeated bleeding or seizures.
Developmental Venous Anomalies
These are veins that fail to develop normally and have an abnormal, widened appearance. Developmental venous anomalies (DVAs) are thought to occur in up to 2.6% of the population. They rarely cause symptoms and have a very low risk of hemorrhage (0.22-1.8%). DVAs are often found incidentally on CT or MRI scans. No treatment is required since they are benign vascular malformations. Rarely, DVAs may co-occur with cavernous malformations.
Capillary Telangiectasias
Capillary telangiectasias are abnormal dilations of very small blood vessels called capillaries. They are sometimes likened to “mini AVMs” but have a very low risk of bleeding (0.15%/year). Capillary telangiectasias often do not cause any symptoms and are found incidentally. No treatment is required unless they become symptomatic. The lesions can calcify and stabilize over time.
Lipomas
Lipomas are benign fatty tumors composed of mature fat cells. They can occur anywhere in the body including the brain, although brain lipomas are rare. Most cases are asymptomatic incidental findings. Symptoms may include seizures or headaches. Treatment is not required for asymptomatic cases. Symptomatic brain lipomas may be surgically removed depending on the location.
Epidermoid and Dermoid Cysts
Epidermoid and dermoid cysts both arise from ectoderm tissue that gets trapped during embryonic development. Epidermoid cysts contain keratin while dermoids contain skin, hair follicles, and glandular material. Both types of cysts are initially benign lesions. Very rarely, malignant transformation into squamous cell carcinoma can occur but this usually takes decades. Small cysts that don’t cause symptoms can simply be monitored. Large or symptomatic cysts may require surgical removal.
Pineal Cysts
The pineal gland is a small structure located deep in the center of the brain. Pineal cysts are fluid-filled sacs that commonly form in the pineal gland during aging. The prevalence ranges from 10-40% in adults but is likely higher with advanced neuroimaging. Pineal cysts smaller than 1 cm almost never cause problems. Larger ones can occasionally cause headaches, vertigo, or eye movement disorders if they compress surrounding structures. Treatment is not typically needed.
Arachnoid Cysts
Arachnoid cysts are cysts that form between layers of the meninges known as the arachnoid mater. They contain cerebrospinal fluid (CSF). Most cases are congenital. Arachnoid cysts usually do not cause symptoms unless they are large or expand. Headache, seizures and neurologic deficits may result from compression of adjacent brain structures. Small asymptomatic cysts can simply be monitored. Larger symptomatic cysts may require drainage or surgical removal.
Rathke’s Cleft Cysts
Rathke’s cleft cysts arise from remnants of the Rathke pouch which forms the anterior pituitary gland during embryonic development. These cysts are filled with fluid and are located between the anterior and posterior pituitary glands. Most remain small and asymptomatic. When enlarged, they can compress surrounding structures causing headaches, hormone dysfunction, and vision changes. Treatment options range from watchful waiting to surgical drainage or removal via the nasal passage.
When to Investigate Further
Most benign brain lesions are simply monitored over time without requiring active treatment. However, there are some scenarios when further investigation with additional testing should be considered:
– New onset of neurologic symptoms that correlate with the lesion location
– Lesion shows evidence of growth or change on subsequent imaging
– Lesion has characteristics suspicious for cancer (e.g. irregular borders, enhancement, edema)
– Patient is immunocompromised
– Patient has a history of cancer
– Lesion is accompanied by additional abnormalities (e.g. microhemorrhages)
An expanding lesion or one causing symptoms warrants closer follow up with MRI scans every 3-6 months. Contrast-enhanced MRI provides additional detail about lesion morphology and potential growth when the initial findings are ambiguous.
Lesions with more concerning features may necessitate brain biopsy to examine cells under the microscope. Biopsy can diagnose cancer versus benign tumors. Other advanced imaging like MR spectroscopy can help characterize lesions by analyzing their chemical composition.
Benign vs. Cancerous Brain Lesions
Distinguishing benign lesions from brain cancer can be challenging. There are some characteristic differences:
| Features | Benign Lesions | Malignant Lesions |
|---|---|---|
| Borders | Well-defined, smooth | Poorly defined, irregular |
| Enhancement | No enhancement or mild peripheral enhancement with contrast | Marked enhancement, especially along margins |
| Surrounding edema | No edema | Often surrounded by vasogenic edema |
| Growth | Slow or no growth | Rapid progression on sequential imaging |
| Metabolism on PET | No increased metabolic activity | Hypermetabolic |
| Symptoms | Often asymptomatic | Progressive neurologic symptoms correlating to location |
These factors help differentiate likely benign lesions from more suspicious ones requiring expedited follow up. However, imaging cannot conclusively diagnose benignancy versus malignancy. Tissue biopsy and analysis under microscopy remains the gold standard.
When to Biopsy Brain Lesions
The decision of whether to biopsy a brain lesion depends on several factors:
– Likelihood of the lesion being malignant based on imaging characteristics and clinical presentation
– Risks associated with the biopsy procedure and potential complications
– Whether the results would significantly alter treatment recommendations
– Patient’s overall health status and life expectancy
Biopsy should be strongly considered for lesions with imaging features that are atypical for benign lesions, including:
– Areas of necrosis
– Irregular borders
– Heterogeneous enhancement pattern
– Significant edema
– Restricted diffusion on MRI
– Rapid interval growth
Biopsy is also more likely to be recommended if the lesion is accompanied by:
– New onset seizures
– Focal neurologic deficits corresponding to the lesion location
– Significant mass effect on surrounding brain
The risks associated with biopsy are relatively low at experienced centers, usually under 2%. However, biopsies in certain locations like the brainstem carry higher risk. The benefit of obtaining a diagnosis needs to be weighed against the small chance of complication.
For older patients or those with significant health issues, the results of biopsy are less likely to change management. On the other hand, biopsy can guide treatment in younger, healthy patients if cancer is confirmed.
MRI-guided needle biopsy performed through a small burr hole is the most common approach. Open biopsy with a larger craniotomy may be required for lesions in difficult to access regions. Stereotactic techniques help ensure accuracy.
Management of Benign Brain Lesions
Watchful Waiting
This is the typical approach for incidental lesions that are likely benign based on imaging characteristics. After the initial discovery, further growth or change is uncommon for benign lesions. Repeat MRI scans may be performed initially at 6 month intervals and then less frequently if there is no progression.
Medical Treatment
Medications to control seizure activity may be prescribed for patients whose lesions cause epilepsy. Occasionally steroids are used short-term to reduce edema and mass effect surrounding brain lesions.
Surgery
Surgery may be warranted if a lesion shows evidence of growth or causes refractory seizures, hemorrhage, or progressive neurologic deficits. The risks associated with surgery need to be weighed against potential benefits. Small asymptomatic lesions likely don’t warrant the risks of surgery in most cases.
Radiation Therapy
Standard external beam radiation is not used for benign lesions, since the risks outweigh the very limited benefits. However, radiosurgery techniques like Gamma Knife can sometimes be applied to AVMs, cavernomas, or benign tumors near critical structures when surgery would carry significant risks.
Serial Monitoring
Most benign lesions are simply monitored with interval imaging such as annual MRIs. More frequent monitoring every 3-6 months may be done initially if there are ambiguous features warranting closer follow up. Changes in size, characteristics, or symptoms would prompt MRI at shorter intervals.
Prognosis of Benign Brain Lesions
The long-term outlook for benign brain lesions is generally excellent. Asymptomatic lesions often remain stable and do not impact longevity or quality of life. Symptomatic lesions causing seizures, headaches, or focal deficits can often be managed successfully with medications if surgery is not appropriate. Malignant transformation of benign lesions is exceedingly rare.
Patients can often be reassured that incidental findings on brain imaging likely do not represent cancers or pose other threats if they have the typical characteristics of benign lesions. However, appropriate follow up and monitoring for any interval changes is prudent. With routine surveillance, outcomes for benign brain lesions are favorable.
Conclusion
While discovering a brain lesion can be unsettling for patients, the majority of incidental findings turn out to be benign processes that do not cause major symptoms or require intervention. Distinguishing worrisome lesions from benign ones relies on a combination of imaging features, clinical presentation, and risk factors. With a thorough evaluation and appropriate follow up, patients with benign brain lesions can be managed conservatively and have an excellent long-term prognosis in most cases.