Meningiomas are the most commonly diagnosed primary central nervous system tumors, originating from the meninges, the protective layers covering the brain and spinal cord. These slow-growing masses are typically discovered incidentally during imaging for other conditions, and the majority are classified as benign. While true spontaneous disappearance or regression is an extremely rare event in medical literature, stability, or stasis, is a common and highly relevant characteristic of their natural history.
Understanding Meningiomas
Meningiomas arise from the arachnoid cap cells, which are part of the meningeal layers surrounding the brain and spinal cord. They are generally considered slow-growing, accounting for approximately 38% of all primary intracranial tumors diagnosed in adults. Many people live with a meningioma for years without experiencing symptoms. Symptoms, which can include headaches, seizures, or subtle changes in vision or motor function, occur when the mass presses on adjacent brain tissue.
Healthcare providers categorize these tumors using the World Health Organization (WHO) grading system, based on how the cells appear under a microscope. The vast majority (over 80%) are classified as WHO Grade I meningiomas, meaning they are benign and have a low recurrence risk. Grade II (atypical) and Grade III (anaplastic) tumors are less common and exhibit progressively more aggressive growth patterns and a higher likelihood of recurrence. This grading is a primary factor in predicting the tumor’s behavior and guiding long-term management decisions.
The Possibility of Spontaneous Regression and Stasis
Spontaneous regression—the complete, unprompted shrinking and disappearance of a meningioma—is an exceptionally infrequent occurrence. When documented, it is typically reported as an isolated case study. For most patients, the far more likely scenario is stability (stasis), where the tumor remains unchanged in size over many years of observation.
The most common explanation for rare instances of regression is the tumor’s sensitivity to sex hormones. Approximately 70% of meningiomas express progesterone receptors, and a smaller percentage express estrogen receptors. The presence of these receptors suggests that the tumor’s growth can be influenced by fluctuations in the body’s hormone levels.
True regression has been observed in women following a decrease in hormone levels, such as after pregnancy or entering menopause. Shrinkage has also been documented when patients discontinue certain exogenous progestin medications. This change in the hormonal environment appears to halt the tumor’s growth stimulus, sometimes leading to a measurable reduction in volume.
Other, less common mechanisms linked to spontaneous regression involve events that cause tumor cell death. These include intratumoral hemorrhage (bleeding within the mass) or significant calcification, which can reduce the blood supply to the tumor cells. However, the primary expectation for an asymptomatic meningioma is that it will either maintain its size or grow very slowly over time.
Management When Regression Does Not Occur
For small, asymptomatic meningiomas, especially those classified as WHO Grade I, the preferred initial strategy is often “watchful waiting,” or active surveillance. This approach involves closely monitoring the tumor with periodic magnetic resonance imaging (MRI) scans, typically every six to twelve months. The goal is to track the tumor’s growth rate and ensure it does not begin to cause new or worsening symptoms.
Intervention becomes necessary when the tumor is growing rapidly, causing neurological symptoms, or posing a threat to surrounding structures. The two main forms of active treatment are surgical resection and radiation therapy. Surgical resection aims to remove the tumor completely, but this is sometimes limited by the tumor’s location, particularly if it is near sensitive areas like the optic nerve or major blood vessels.
Radiation Therapy Options
When complete surgical removal is not possible, or for patients who cannot undergo surgery, radiation therapy is used to stop the tumor’s growth. Stereotactic radiosurgery (SRS) is a non-invasive treatment delivering a high dose of targeted radiation in one or a few sessions, typically used for smaller tumors. For larger masses or those located next to highly sensitive brain structures, fractionated radiation therapy is delivered in smaller doses over several weeks to protect surrounding healthy tissue.
The decision to treat is highly individualized, depending on the tumor’s size, its specific location, the patient’s overall health, and the tumor’s grade.