When the story doesn’t seem to fit

3 minute read

A young girl presents an interesting diagnostic challenge for this GP

An exasperated mother presented with her 15-year-old daughter, an only child little known to the GP. She handed him a specimen container.

This contained a fresh fetal-like tan-coloured mass measuring 55x48x up to 9mm thick (about 20ml in volume) see figure 1.

Figure 1: The specimen appeared to be evidence of a miscarriage

Following eight hours of severe lower abdominal pain with associated vomiting, the girl had apparently passed this mass per vagina earlier that morning.

Her last menstrual period was two months prior.

She repeatedly declared before a doubting audience that she was “still a virgin”.

Her past history included, an attempted suicide by overdose and hanging a month previously following her parents’ separation. She was being treated with:

– fluoxetine 20mg daily

– Yaz (ethinyloestradiol 20mcg with drospirenone 3mg) for acne and dysmenorrhoea. However, she reported taking this only intermittently.

Menarche had occurred at age 11 and subsequent periods had been regular.


Serum ?HCG was negative.

FBC, ESR, CRP, U/LFTs were all normal. Urine MCS was clear.

Histology report:

The sections showed a patchily haemorrhagic and inflamed decidualised endometrial cast.

Scattered atrophic and somewhat degenerate glands were present in the decidualised stroma which also showed a mixed infiltrate of lymphocytes, histiocytes and neutrophils.

Chorionic villi and trophoblastic cells were not found.


The finding that the tissue was in fact a decidualised endometrial cast was believed to be keeping with the prolonged use of a progestrogen.

The differential diagnosis of a decidualised endometrium of a pregnancy was considered but thought less likely on histology and inconsistent with the girl’s history.

Three weeks later, a pelvic ultrasound revealed a normal midline uterus 81ml in volume albeit retroverted with an endometrium up to 0.7cm neither thickened nor hypovascular and with no mass within.


Decidual casts are unusual though well known to gynaecologists1. However, they are little recognised if at all in general practice.

Such casts can be elaborate, displaying the internal architecture of not only the uterus but also the fallopian tubes2. They are formed secondary to the influence of progesterone, and their expulsion is often painful3 as would be expected with their passage through a tight cervix.

Drospirenone is a potent synthetic progesterone with antimineralocorticoid and antiandrogenic properties. It is well absorbed orally4. Normally, progesterone maintains the “secretory” phase of the menstrual cycle, thus keeping the endometrial lining intact. Its administration may thus be helpful in delaying the onset of the menses or “deciduous” phase.

Drosperinone has a comparatively long excretion half-life of about 40 hours whereas that of the oestrogen, ethinyloestradiol is about 24 hours4.

The intermittent taking of Yaz would thus cause the progesterone effect to predominate, hence allowing the formation of a ‘cast’.

Dr George Turner FRACGP Trinity Beach, Qld


1. J.P.Maxwell (1929). On uterine casts. International Journal of Obstetrics and Gynaecology, 36,544

2. R Pingili, W Jackson. Decidual Cast. The Internet Journal of Gynecology and Obstetrics. 2007 Volume 9 Number 1

3. Singh V1, Talib N, Strickland J.Decidual cast in a girl receiving depot medroxyprogesterone acetate–a case report. J Pediatr Adolesc Gynecol. 2007 Jun;20(3):191-4.

4. MIMS Yaz Revision date 01/06/2016

Consent obtained from both patient and parent.

Paper read by and acceptable to patient and parent.

Conflicts of interest – Nil

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