Meningiomas can shrink on their own, but true spontaneous disappearance is exceptionally rare. In the largest volumetric tracking study of untreated meningiomas, about 2.5% showed measurable regression over a follow-up period of roughly two and a half years, while roughly a third stayed the same size and the majority grew slowly.1Journal of Neurosurgery. Natural history of meningiomas: a serial volumetric analysis of 240 tumors A separate study found a higher shrinkage rate of around 14%, though not all of that qualifies as dramatic regression.2Neuro-Oncology Advances. Growth dynamics of untreated meningiomas Most documented cases involve partial shrinkage rather than complete vanishing, and the story behind why it happens is more interesting than a simple yes or no.
How Common Is Spontaneous Regression?
A literature review published in 2025 combed through the medical literature and found only 21 reported cases of meningiomas that spontaneously regressed.3PubMed Central. Spontaneous Regression of Meningiomas: Literature Review and Case Report That is a tiny number given how common meningiomas are (they account for roughly a third of all primary brain tumors). The low count partly reflects genuine rarity, but it also reflects reporting bias: if a tumor quietly shrinks on serial imaging and a patient never develops symptoms, the case may never make it into a journal. Doctors are more likely to write up a case when something dramatic or unexpected happens.
Among those 21 cases, none had been confirmed by biopsy. Every diagnosis was based on imaging alone, which is standard practice for suspected meningiomas managed with observation rather than surgery. That detail matters because it leaves open a small possibility that some of these “regressing meningiomas” were not actually meningiomas at all, a point we will return to below.
Looking at larger observational datasets paints a broader picture. When researchers tracked 240 meningiomas with precise volumetric software, six tumors (2.5%) regressed, with a median volume reduction of about 21% over roughly 29 months. The patients with regressing tumors tended to be older, with a mean age of about 73. Statistically, no clinical or imaging feature reliably predicted which tumors would shrink.1Journal of Neurosurgery. Natural history of meningiomas: a serial volumetric analysis of 240 tumors In another cohort of 235 untreated meningiomas, 33 tumors (14%) shrank, 64 (about 27%) were stable, and 138 (roughly 59%) grew during the observation period.2Neuro-Oncology Advances. Growth dynamics of untreated meningiomas The difference in shrinkage rates between studies likely reflects how “shrinkage” was defined and how precisely volume was measured. Even in the study reporting 14%, most of the shrinkage was modest, not the dramatic regression seen in case reports.
Hormones Are the Biggest Identifiable Trigger
If you dig into the cases where a meningioma clearly regressed, the single most common thread is a change in hormone exposure. Of the 21 cases identified in the literature review, 13 (about 62%) were linked to hormonal shifts or medication changes. Nine of those involved stopping a progesterone-type drug.3PubMed Central. Spontaneous Regression of Meningiomas: Literature Review and Case Report Meningiomas frequently express progesterone receptors, and gene expression research has found that progesterone receptor status is tied to distinct molecular profiles in these tumors, suggesting that the hormone does not just passively sit on the surface but actively influences how the tumor behaves at a genetic level.4PubMed Central. Specific genes expressed in association with progesterone receptors in meningioma
Cyproterone acetate (CPA), a progestin used in Europe for conditions ranging from severe acne to prostate cancer, has drawn the most attention. In one widely cited case, a patient who stopped taking CPA saw a frontal meningioma shrink from 16 cubic centimeters to just 1.9 cubic centimeters within six months, an 88% reduction in volume.5American Journal of Neuroradiology. Abrupt Regression of a Meningioma after Discontinuation of Cyproterone Treatment A larger French study tracked 137 meningiomas after CPA was stopped and found that about 88% of the tumors responded to some degree, with nearly half shrinking to a very small residual volume. Only around 12% of the meningiomas failed to respond at all.6PubMed Central. Prediction of meningioma shrinkage after cyproterone acetate cessation
CPA is not the only progestin implicated. Nomegestrol acetate, another progesterone-like drug, has produced similar patterns. In a series of three patients who stopped nomegestrol, all tumors began shrinking within the first month, and one shrank by 70% in the first year.7PubMed. Spontaneous regression of meningiomas after interruption of nomegestrol acetate: a series of three patients Megestrol acetate, sometimes prescribed for appetite stimulation or breast cancer, has also been linked to meningioma regression when stopped. In one case, multiple meningiomas shrank on follow-up imaging taken just four months after discontinuation.8PubMed Central. Regression of Multiple Meningiomas after Discontinuation of Chronic Hormone Therapy: A Case Report
Some of the most striking examples come from patients with large tumors who were already scheduled for surgery. In two such patients, simply stopping the progestin treatment caused tumors exceeding 60 cubic centimeters to drop to around 11 and 13 cubic centimeters, reductions of over 80%, during a single year. Imaging showed the tumors also lost their blood supply as they shrank.9World Neurosurgery. Dramatic Shrinkage with Reduced Vascularization of Large Meningiomas After Cessation of Progestin Treatment In other words, some patients avoided brain surgery entirely because the tumor collapsed once the hormonal fuel was removed.
Pregnancy, Menopause, and Natural Hormone Shifts
Exogenous drugs are not the only way hormone levels change. Pregnancy temporarily floods the body with progesterone, and meningiomas have been reported to grow during pregnancy and then regress after delivery.10PubMed Central. Postpartum Regression of a Presumed Cavernous Meningioma One case described a 32-year-old woman who developed severe headaches and vision problems near the end of her second pregnancy due to a large sphenoid wing mass. After she gave birth and her hormone levels normalized, repeat imaging two months later showed significant shrinkage of the tumor.11Journal of Neurosurgery. Hormone-dependent shrinkage of a sphenoid wing meningioma after pregnancy: case report
Menopause represents another natural drop in progesterone (and estrogen), and it has been noted in at least one of the reported regression cases. The practical takeaway here is that if you are a woman diagnosed with a meningioma during or shortly after pregnancy, your doctor should repeat imaging once hormone levels have settled. A tumor that looks alarming at 38 weeks of gestation may look very different a few months postpartum.
When There Is No Obvious Explanation
About a third of the documented regression cases have no identifiable trigger. No medication was stopped, no pregnancy ended, no hormonal shift was apparent. These are the cases that truly qualify as “spontaneous.”3PubMed Central. Spontaneous Regression of Meningiomas: Literature Review and Case Report What causes them remains unclear. Several hypotheses exist, but none is firmly established.
One documented pattern involves calcification. A case report described a falx meningioma that gradually shrank from 25.5 cubic centimeters to 9.9 cubic centimeters over seven years while simultaneously becoming more calcified on imaging. The surrounding brain swelling also faded.12PubMed Central. Spontaneous regression together with increased calcification of incidental meningioma Calcification in a meningioma is generally considered a sign of slow or inactive biology, and it is possible that some tumors essentially burn themselves out as they become increasingly calcified, cutting off their own blood supply in the process.
Another case involved a posterior fossa meningioma in a 55-year-old woman. The tumor held steady at about 1.6 centimeters for two years, then slowly shrank over the next decade, eventually reducing its volume from 2.3 cubic centimeters to 0.5 cubic centimeters without any identifiable cause.13PubMed Central. Spontaneous regression of a posterior fossa meningioma: A case report Cases like this suggest that whatever process drives regression can be extremely slow, unfolding over years or even a decade.
The immune system may play a role. Meningiomas are known to be infiltrated by immune cells, and the balance between the tumor’s ability to suppress the local immune response and the body’s ability to mount one may occasionally tip in favor of regression.14PubMed Central. Basis for Immunotherapy for Treatment of Meningiomas One case in the literature involved a tumor that regressed after it bled internally (intratumoral hemorrhage), which may have triggered an immune reaction against the exposed tumor tissue.3PubMed Central. Spontaneous Regression of Meningiomas: Literature Review and Case Report But this remains speculative.
Could It Have Been Something Else Entirely?
One underappreciated possibility is that the “meningioma” that disappeared was never a meningioma in the first place. The published regression cases are all based on imaging, and MRI is not infallible. A range of dural lesions can look strikingly similar to meningiomas on a scan, including solitary fibrous tumors, dural metastases from other cancers, inflammatory conditions like neurosarcoidosis, and even Rosai-Dorfman disease.15PubMed Central. Dural lesions mimicking meningiomas: A pictorial essay Some of these conditions can resolve on their own or respond to systemic treatment, which could create the illusion of a meningioma vanishing.
This does not mean every reported regression is a misdiagnosis. Many cases have imaging characteristics that are highly consistent with meningioma, and serial scans showing gradual, consistent shrinkage are harder to explain as a different entity that spontaneously resolved. But it is worth keeping in mind, especially if a “meningioma” behaves in a way that seems too good to be true. In some clinical settings, if a presumed meningioma shrinks rapidly and unexpectedly, doctors may actually recommend further investigation to rule out a different diagnosis.
What Monitoring Looks Like in Practice
Most incidentally discovered meningiomas, meaning those found by accident during a scan done for another reason, are managed with observation rather than immediate treatment. The European Association of Neuro-Oncology (EANO) recommends annual MRI scans for suspected low-grade meningiomas for the first five years, with scan intervals widening after that.16Neuro-Oncology. EANO guideline on the diagnosis and management of meningiomas The rationale is that most growth occurs within the first five years after discovery, with a plateau afterward. But this is far from settled. Some rapid growth and symptom development have been reported at median follow-up times of two to three years, and guidelines differ considerably on how often to scan and when it is safe to stop.17PubMed Central. The management of incidental meningioma: An unresolved clinical conundrum
The UK’s NICE guidelines, for instance, recommend a scan at one year and then again at five years, or stopping follow-up altogether. That approach might miss a tumor that begins growing at year two or three. The variability across guidelines reflects genuine uncertainty: the evidence base for optimal surveillance of these tumors is thin, and clinicians have to weigh the cost and anxiety of repeated imaging against the risk of missing growth that requires intervention.
Volumetric measurement, where software calculates the three-dimensional volume of the tumor rather than relying on simple diameter measurements, is becoming more common and is more sensitive to subtle changes. One research group established that the smallest volume change reliably detectable on standard MRI is around 0.2 cubic centimeters, and another defined their threshold for meaningful growth at a relative volume increase exceeding about 14%, accounting for measurement error.18PubMed Central. Exploring the role of volumetric and radiological features in meningioma behaviour and follow-up strategies 1Journal of Neurosurgery. Natural history of meningiomas: a serial volumetric analysis of 240 tumors These thresholds matter because calling a tumor “stable” or “regressing” depends heavily on how precisely you measure it.
What About Children?
Meningiomas in children are uncommon, accounting for a very small fraction of pediatric brain tumors. Their biology differs from adult meningiomas in several ways, including a higher rate of atypical features and a different distribution across the brain. Spontaneous regression in children is even more rarely documented than in adults, though it has been reported. In one pediatric case, a relapsed parasagittal meningioma showed a downgrading in histological grade on recurrence, and the residual tumor then demonstrated spontaneous regression.19PubMed. Pediatric meningiomas: a report of 5 cases and review of literature Because the hormonal milieu is different in children, and because neurofibromatosis type 2 is a more common underlying cause of pediatric meningiomas, the mechanisms behind any regression in this age group may differ from those in adults.
Should You Count on Regression?
Given how rare spontaneous regression is in the absence of a clear trigger like stopping a progestin, planning around it would be unwise. Most untreated meningiomas grow, even if slowly. In the study of 235 tumors tracked over time, nearly 59% grew during the observation period.2Neuro-Oncology Advances. Growth dynamics of untreated meningiomas The odds favor growth over shrinkage for any individual tumor.
That said, the existence of regression, however uncommon, has practical value. It reinforces the rationale for a watch-and-wait approach to incidental meningiomas that are not causing symptoms. It also underscores the importance of reviewing a patient’s medication history. If someone is taking a progestin and develops a meningioma, stopping the medication (when medically appropriate) may be the single most effective intervention, sometimes shrinking the tumor more dramatically than surgery or radiation would. The French data showing that 88% of CPA-associated meningiomas respond to drug cessation is remarkable for a tumor type with no approved drug therapy.6PubMed Central. Prediction of meningioma shrinkage after cyproterone acetate cessation
The Progestin Connection Beyond CPA
The link between progestins and meningioma risk has gained increasing attention from regulatory agencies in recent years, particularly in France, where CPA was widely prescribed at doses much higher than those used in most other countries. But the issue extends beyond CPA. Any long-term progestin exposure may be relevant, including certain forms of hormone replacement therapy and some injectable contraceptives. The molecular relationship is real: gene expression patterns in meningiomas differ significantly depending on whether the tumor expresses progesterone receptors, and the receptor-positive tumors appear to have a distinct genetic profile involving the region of chromosome 22 near the NF2 gene, mutations in which are among the earliest events in meningioma development.4PubMed Central. Specific genes expressed in association with progesterone receptors in meningioma
What this means practically is that if you have a meningioma and are taking any progestin-containing medication, it is worth discussing with your doctor whether the medication could be contributing to tumor growth and whether alternatives exist. Not every meningioma is hormone-driven, and not every progestin carries the same risk profile, but the conversation is worth having because the potential payoff (significant tumor shrinkage without surgery) is substantial.
Researchers have not yet identified reliable ways to predict in advance which tumors will respond to hormonal withdrawal and which will not. The French CPA study attempted to find predictors by clustering tumors into response categories, but the responders and non-responders did not differ in easily measurable ways before drug cessation.6PubMed Central. Prediction of meningioma shrinkage after cyproterone acetate cessation Until better biomarkers emerge, the practical approach remains straightforward: stop the drug, repeat imaging over the following months, and let the tumor’s response guide further management. For the minority of tumors that do not respond, surgery and radiation remain effective fallback options.