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Uterine (decidual) Casts


Lucy, 15, arrives in the ED sobbing hysterically, clutching a wad of toilet paper. “I thought it was my period… only I had the worst period pains ever. I went to bed with a hot water bottle, and it got worse, and then… this came out”. She sobs, opening the tissue to show you a fleshy, pale triangular thing. Approximately 5cm long.  “What is it? It’s disgusting. Have I got cancer? I’m not pregnant?”

Bodily secretions in tissues are rarely a source of delight but are common opening gambits. Vomit, faeces, sputum, vaginal discharge, worms, lice, blood clots and products of conception may be saved up and brought to the doctor to add colour to the history. They present a challenge as often we don’t want to look. We don’t trust ourselves not to recoil or be disturbed and being presented with a “sample” early on can catch us off guard. It plays havoc with the “history, examination, management plan” structure we like to impose on our consultations.  In presentation terms, though, this is a gem of a presentation. We have an “Idea”, a “Concern” and it won’t be long before we elicit an “Expectation”.  Avoiding the enormous cue as it is thrust into your orbit, whilst tempting, risks dismissing the concerns. This can destroy any fledgling rapport and make the whole encounter even harder.  It is going to be necessary to take a history, but right now we have a distressed teenager, an unidentified object in a tissue and a lot of emotion. It may well be easiest to address this gift up front and just take a look. This is the time to address the upset and the fear head-on.

The “thing” looks like this:

Decidual cast

A uterine or decidual cast occurs when the entire endometrial lining is shed in one piece. They are uncommon but frequently cause distress to the patient and can be extremely painful to pass.  A cast looks almost triangular, and if shed whole, you can see the contours of the uterine cavity in a sort of fleshy model if you look closely.

Lucy tells you she had a Nexplanon contraceptive implant fitted about 6 weeks ago. She is not currently sexually active.  Her last period started the day before she had her implant fitted. She’s well otherwise with no past medical history. She had some light PV spotting yesterday and this morning but it has been light.  Since she passed the mass her pain has settled completely. Her observations are normal. She is happy to do a pregnancy test which is negative.  She just wants to know what it was, why it happened and if she can go home now.

The vast majority of uterine casts have no identifiable precipitating causes. However, there are case reports associated with ectopic pregnancy. They may be slightly more common in users of hormonal contraception though having had a cast is not a contraindication for continued use, nor are recurrent casts likely with continued use. The pain associated with the passage of the cast is often severe – remember they are passing a 5cm mass through their cervix.

You reassure Lucy that this is not cancer, that she wasn’t pregnant and that this was a cast.  You explain what a cast is and that it is unlikely to recur.  She goes home much reassured and relieved.

You decide to send the cast to the lab for histology and a few days later a report lands in your in-tray which reads “extensively decidualized endometrial tissue with minimal glandular structures lined by low cuboidal epithelium, consistent with a uterine or decidual cast. No chorionic villi were identified.


Nunes, R.D. and Pissetti, V.C., 2015. Membranous Dysmenorrhea–Case Report. Obstet Gynecol Cases Rev2, p.042.

Strauss, L., 2018. Fleshy Mass Passed Vaginally by a Young Woman. American family physician98(7), pp.449-450.


  • Dr Tara George. MBChB (Hons) Sheffield 2002, FRCGP, DCH, DRCOG, DFSRH, PGCertMedEd Salaried GP and GP Trainer, Wingerworth Surgery, Wingerworth, Derbyshire. GP Training Programme Director, Chesterfield and the Derbyshire Dales GP Speciality Training Programme. Out of Hours GP and supervisor, Derbyshire Health United. Early Years Tutor, Phase 1, Sheffield University Medical School. Mentor, GP-s peer mentoring service and Derbyshire GPTF new to practice scheme. External Advisor RCGP. Host Bedside Reading podcast. Pronouns: she/her When she's not doing doctory things Tara loves to bake, to read novels, run and take out some of that pent up angst in Rockbox classes.

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5 thoughts on “Uterine (decidual) Casts”

  1. I am on Camrese birth control and have passed my second deciduous cast in the past 6 months. It was very painful, but instant relief when it passed. It’s hard finding info on this, and reading that it’s a very rare thing scared me since it happened twice already

  2. I’m 18,and I started the Depo shot in May.
    June 25th I started to bleed a little. Light and spotty, so I didn’t care much. Way better than my usual crampy angry heavy periods so I ignored it.

    By July 11th I started to worry a little bit. And then July 12th came with the actual worst pain I have ever been in in my life. Pain I couldn’t stand. I nearly puked it hurts so bad.
    And then I saw this when I wiped after peeing. And freaked tf out because “what the hell is this and why is it here and what the fuck???”
    So I did some research, laid down when I felt a little bit better. And then got even *worse cramps*. Bad enough I just curled up and sobbed for a couple hours in my bed with a stuffed dinasour.

    And then saw that I’d passed a second one. And now I’m concerned again because I’m still cramping horribly and I feel like maybe I have a third?? But there’s no physical way to have three uteruses? And they’re both big and roughly the same size and shape so I figured “each half” but..
    Three? In less than three hours?

    I’ll update whenever I figure more out. But rn I’m just scared and in pain and I hate that we don’t get taught even a fraction of this in school.

  3. I’ve been having this almost every month for the past 7 years. Not been on contraceptives for 3 years. Done a pregnancy test which was negative so not ectopic pregnancy. No endometriosis. When i mention to gp, they just say blood clot due to hormone imbalance and offer me the contraceptive pill! Underdiagnosed because it gets ignored.

  4. I just passed on this morning. The pain from it lasted a few days. It was like a stabbing ripping type of cramp center pelvic and lower abs area. I tried taking a couple baths with eased the pain and pressure a little bit just enough to get little naps in off and on. I also tried my Delta 8 that I use which helped as well. While I was in the tub I went to sit up and move a little and seen this huge thing laying at bottom of the tub. At first I didn’t know what it was. Then I remembered the size and shape of the uterus and went “my uterus fell out” lol. Texted my sister that’s a nurse she wasn’t sure and asked my manager I work with if she knew after I emailed my primary doctor. My manager sent me the link to this page when I texted her the photo I had taken. I am on the Depo birth control shot first dose so I figured some breakthrough bleeding would occur because I was warned it might and periods be very light which it was. But the pain of passing that entire lining of the uterus in one piece was painful as can be. Almost as painful as passing a kidney stone but it’s bigger and going through a more tight area which is the cervix. I didn’t even know about the cast part till my manager told me cuz I also have endometriosis as to why I been put on the Depo shot. If that cast happens again I’m digging it out instead of being in bad pain for nearly 3days.

  5. Hey thanks for publishing this. This is near EXACTLY what I’m going through. I’ve had my nexplanon implant for about 2.5 weeks now and this is my first period with this contraceptive. The cramps I’ve experienced yesterday and today are the worst I’ve ever experienced (not the worst pain ever but I’ve never had cramps this bad is all) and I just found exactly what was described as the uterine cast. Immediate panic and of course I turn to Google for an answer. Luckily this was the first link I clicked on. Much appreciated!