Tara George. Uterine (decidual) Casts, Don't Forget the Bubbles, 2021. Available at:
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 am I?”
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 address the upset and the fear head on.
The “thing” looks like this:
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 in shape 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 though there are case reports in association with Ectopic Pregnancy and 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 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.”