Welcome back to Fact Friday. Most weeks, we cover research based on large groups of patients. This week is different. We are looking at a single, carefully documented case report, published in the Journal of Clinical Medicine in September 2026, because it is a striking illustration of just how far endometriosis may reach beyond the pelvis, and because it may be useful information for anyone who has unexplained, cycle-linked symptoms that do not fit the usual picture.

A case report describes one patient in detail, rather than comparing large groups, so it cannot prove a cause and effect relationship the way a bigger study can. What it can do is highlight a pattern doctors should be alert to, and that is exactly what this paper sets out to do.

The report, by Tirnovanu and colleagues, describes a 48 year old woman who developed epilepsy at the age of 41. Her seizures involved episodes of impaired awareness, staring, confusion afterwards, and short term memory lapses. Over six months, she and her clinical team kept a detailed seizure and menstrual diary, and a clear pattern emerged: her seizures happened only during menstrual bleeding. This pattern is known medically as catamenial epilepsy, a term for epilepsy in which seizures cluster around specific points in the menstrual cycle. “Catamenial” simply means related to menstruation.

Notably, she had none of the classic pelvic symptoms usually associated with endometriosis. She did not have painful periods, pain during sex, or cyclical pelvic pain, and an earlier pelvic scan had found nothing unusual. Her condition was identified entirely through what was happening in her brain, not her pelvis.

Brain MRI scans taken in 2019 and 2020 showed a small lesion in the hippocampus, a seahorse shaped structure deep in the brain that plays a central role in memory and is also a common site for the type of brain activity that causes seizures. The lesion had features that were hard to pin down. Additional scanning using a technique called magnetic resonance spectroscopy, which looks at the chemical makeup of tissue rather than just its shape, did not clearly point to a tumour, but it was not fully conclusive either.

In other words, on imaging alone, this lesion could have been several different things: a low grade tumour, scarring, an old bleed, an infection, or a rare deposit of endometriosis-like tissue in the brain. The medical team could not safely take a biopsy, because of the risks of operating in that part of the brain, so they could not confirm the diagnosis under a microscope. For that reason, the authors describe this throughout as “presumed” cerebral endometriosis, a careful and honest way of saying this is their best explanation, not a proven fact.

She was first treated with standard anti-seizure medications, which did not fully control her seizures. Her care team then tried a hormonal approach instead, using progestin medications (dienogest and desogestrel, both types of progestogen hormone often used to manage endometriosis) over several years, in alternating six month courses. Anti-seizure medication was then stopped entirely after just three months of combined treatment.

The results were striking. Her neurological symptoms resolved completely. A follow-up MRI scan in March 2026 showed that the abnormal signal in her hippocampus had either disappeared or markedly reduced, while the overall shape of the hippocampus was preserved.

The authors also reviewed the existing medical literature and found only eight previously published cases of suspected endometriosis affecting the brain. This case adds a ninth, and the authors note that the hippocampus specifically had not been clearly documented as a site before. In short, this remains an extremely rare presentation, even among the already rare possibility of endometriosis-like tissue appearing outside the pelvis.

This fits into a wider, growing body of evidence, including research we have covered in previous Fact Fridays, that endometriosis can behave as a condition that reaches well beyond the reproductive system, rather than one that stays confined to a single part of the body. This case is a particularly vivid example of that idea, since it describes tissue behaving in a hormone-sensitive way in the brain itself.

To be clear from the outset, this does not mean endometriosis commonly affects the brain, or that seizures are a typical symptom of the condition. This is one of only nine documented cases worldwide. For the overwhelming majority of people living with endometriosis or adenomyosis, this case report has no direct bearing on their own health.

What it may be useful for is a different group: people who experience seizures or other unexplained neurological symptoms, such as memory lapses or confusion, that seem to track closely with their menstrual cycle, particularly where no clear cause has been found. This case is a reminder that a hormonal link to the menstrual cycle is worth mentioning to a doctor, even when symptoms are neurological rather than pelvic, and even when there is no history of a prior endometriosis diagnosis. The authors specifically suggest that clinicians consider this possibility in women of reproductive or perimenopausal age who have catamenial seizures or unexplained brain lesions, even without any pelvic symptoms at all.

It is also, more broadly, a reminder that endometriosis related processes appear to be capable of affecting tissue well outside the pelvis, and that hormonal treatment aimed at that process, rather than treatment aimed only at symptoms, can sometimes make a real difference.

This case report comes with substantial caveats, and the authors themselves are careful about this.

First, and most importantly, there was no tissue biopsy, so the diagnosis of cerebral endometriosis was never confirmed. It remains “presumed” rather than proven, because a biopsy in that part of the brain carried too much risk to justify.

Second, this is a single patient. A single case, however well documented, cannot establish how common this is, what causes it, or how reliably hormonal treatment would work for someone else with similar symptoms. Other explanations for her lesion and its improvement, including a slow growing low grade tumour, scar tissue, an old small bleed, or an unrelated inflammatory process, could not be fully ruled out.

Third, no ictal EEG or video-EEG monitoring was carried out during a live seizure, so the classification of her seizures relied partly on the reported pattern of symptoms and the seizure diary, rather than on a recording of brain activity during an actual event.

Finally, this is one case report in a specialist medical journal, not medical advice, and certainly not a reason for people with endometriosis to worry about their brain health without cause. If anything in this article resonates with symptoms you or someone you know is experiencing, the right step is a conversation with your own doctor or neurologist, who can consider your full individual history.

• A new case report describes a woman whose seizures occurred only during her menstrual period, a pattern known as catamenial epilepsy, linked to a brain lesion that improved after hormonal treatment typically used for endometriosis.
• She had no pelvic symptoms of endometriosis at all, and her condition was identified entirely through neurological symptoms and brain imaging.
• Because a biopsy was too risky to perform, the diagnosis remains “presumed” cerebral endometriosis rather than a confirmed one.
• This is only the ninth such case ever documented worldwide, and the first clearly involving the hippocampus, so it remains extremely rare.
• The case adds to growing evidence that endometriosis-related processes can affect tissue well beyond the pelvis, and it may be useful for clinicians assessing unexplained, cycle-linked neurological symptoms.
• This is one case, not proof of a common pattern, and it is not medical advice.

Cases like this one are rare, but they matter because they push the edges of what we understand about where and how endometriosis can show up in the body. For the vast majority of people living with endometriosis, this case changes nothing about their day to day experience. But for anyone whose unexplained neurological symptoms have always seemed to track their cycle, and who have never quite gotten an answer, this case is a useful piece of evidence to bring into that conversation with a doctor.

This article summarises one published case report for general information and awareness only. It is not medical advice. If any of this resonates with your own health or that of someone you care for, please speak with your GP, gynaecologist, or neurologist, who can take your full individual circumstances into account.