I Already have Ankylosing Spondylitis. Now I Have Another Rare Condition?

The day I learned all about the Mullerian Cyst Of Hattori.

When you go to the emergency room, you expect to leave with answers, not more questions.

I live with ankylosing spondylitis (AS), a rare form of inflammatory arthritis that primarily affects the spine and sacroiliac joints. It causes chronic back pain, stiffness, and reduced mobility, and in some cases, the vertebrae can fuse together over time. But AS isn’t limited to the spine. It’s a systemic disease, which means it can affect other organs and systems throughout the body.

Globally, ankylosing spondylitis affects about 0.1% to 0.5% of the population. It usually begins in the late teens to early thirties, but diagnosis is often delayed for years. Historically, men were thought to be affected far more often than women, with a male-to-female ratio of 2–3:1, but awareness is growing, and more women are now being correctly diagnosed.

AS rarely exists in isolation. Many people develop comorbidities, or related health conditions, because of long-term inflammation. Hypertension is one of the most common, affecting around half of patients. Depression and mood disorders are also widespread, impacting roughly one in four. Pulmonary issues such as asthma or COPD, along with diabetes, thyroid disorders, and cardiovascular disease, are all more frequent in people with AS compared to the general population.

There are also well-known extra-articular complications—problems that occur outside the joints. Up to 30% of patients experience uveitis, a painful eye inflammation. Others develop inflammatory bowel disease, with rates far higher than average. Osteoporosis and increased fracture risk are also concerns, since spinal stiffness and inflammation reduce bone density. Some patients face breathing limitations when the rib joints are affected, restricting chest expansion. Personally, I also struggle with tendon inflammation, frozen joints, and even tendon tears.

Living with AS is difficult, and the treatments have often caused me more harm than good. I am currently in stage 2 chronic kidney disease (CKD), and I personally believe it’s from years of my kidneys struggling under the weight of so many medications.

A few weeks ago, I woke up at 4 a.m. on a Saturday in excruciating back pain. This was much worse than my usual AS pain, so I went to the ER. They didn’t do much for me, but they did order an MRI. That scan revealed something I had suspected for a few months from what I thought I saw on a previous CT scan: a mass behind my heart.

“1.4 cm left paracentral posterior mediastinal nonenhancing cyst possibly representing an esophageal duplication cyst or cyst of Hattori.”

No one mentioned it to me in the ER. I was simply told to follow up with my spine doctor and “take it easy.” It was only after I carefully read the report that I realized the finding was there at all. I brought it to my primary doctor, who is wonderful, but even she had never heard of a cyst of Hattori and couldn’t identify it clearly on the scans. Still, she referred me for a CT scan, which gave us more clarity. “Well circumscribed nonenhancing lesion in the posterior mediastinum at the level of the aortic arch measuring up to 1.7 cm. This lesion is attenuating higher than simple fluid and appears separate from the esophagus. Given the lesion location, and patient's gender this is favored to represent a Mullerian cyst of Hattori.”

In the meantime, I dove headfirst into research. I wanted to understand what this mysterious cyst meant for me, especially on top of everything I already manage with AS.

The more I read, the more I realized just how rare this finding was. The cyst of Hattori, also known as a Müllerian cyst of the mediastinum, was first described in the medical literature in 2005. Since then, only a few dozen cases have been documented worldwide. That means most doctors will go their entire careers without ever seeing one.

The cyst itself is considered benign, meaning noncancerous, but its location makes it unique. Mine sits in the posterior mediastinum, near the aortic arch and adjacent to the esophagus. Because it’s surrounded by such critical structures like the heart, lungs, and major vessels, it’s not something you can just ignore, even if it isn’t cancer. Because of the amount of autonomic symptoms I have struggled with for over a year, I am also very curious about the impacts of the cyst on the Vagus nerve, but we will get into that later.

What struck me most is that there’s very little information for patients. Most of what I found were dense pathology reports and surgical case studies. I could barely find a single plain-English explanation, let alone another patient’s story. My primary doctor, who is amazing and thorough, had never encountered this condition either. It was clear I had entered very uncharted territory.

For me, this discovery was more than just another line in a radiology report. It was another reminder that sometimes our bodies don’t follow the rules, and sometimes rare things really do happen. It also made me realize how important it is to share my experience. If I felt this lost and overwhelmed, what about the next person who reads “cyst of Hattori” on their scan? Who would they turn to?

That’s why I decided to start documenting everything here with not not just the medical facts, but the emotional side of facing a diagnosis so rare that most people, including doctors, have never even heard of it.

Living with ankylosing spondylitis is already a heavy burden, and now I’ve added a rare mediastinal cyst to the mix. At first, it felt overwhelming. How could something so unusual happen on top of everything else? But as strange as it sounds, this diagnosis has also given me a new purpose.

I want to use my experience to make sure that no one else feels as lost as I did when I first saw the words “cyst of Hattori” on a radiology report. If you’ve stumbled across this blog because you or someone you love has been diagnosed with one, I want you to know: you are not alone.

This condition may be rare, but that doesn’t mean your questions, or your fears, aren’t valid. My goal here is to share what I learn, break down the medical jargon into something understandable, and provide a place where patients can see their own experience reflected.

I don’t know exactly where this journey will lead. Maybe monitoring, maybe surgery, maybe more research as new case reports are published. But I do know this: I’ll keep telling my story, because rare doesn’t have to mean invisible.

If you’ve been diagnosed with a cyst of Hattori, or if you’re living with ankylosing spondylitis, I’d love to connect. Share your story, ask your questions, or just know that there’s someone else out here navigating the same uncertainty.

You are seen. You are heard. And together, we can shine a little light into the dark corners of rare disease.