What Is a Decidual Cast?

A decidual cast, known medically as membranous dysmenorrhea, is a rare phenomenon in which the lining of the uterus is expelled from the body in one large piece instead of the typically small pieces passed during a menstrual period. The large collection of tissue, blood, and mucus remains the same shape as the uterus.

This article discusses the symptoms and causes associated with a decidual cast.

What Is the Structure of a Decidual Cast?

A decidual cast is made up of uterine lining tissue known as the endometrium, along with mucus and blood. Typically, people who have menstrual periods shed the uterus lining monthly.

The lining is expelled from the body in small bits with blood over two to seven days, which is the average length of a menstrual period. In the rare instance that a person develops a decidual cast, the lining does not break up correctly and is expelled through the vaginal canal in one large uterus-shaped piece.

The cast will be red or pink and shaped like an upside-down triangle, like the uterus. In terms of size, it's, on average, the same size as a person's palm, but that can vary according to the size of the individual. It may also have a fleshy appearance resembling red meat, or it may look like a larger version of blood clots typically passed during menstruation.

What Are the Symptoms of a Decidual Cast?

A person with a decidual cast may experience symptoms similar to those of a typical menstrual period, such as spotting or menstrual cramps. However, the cramps or abdominal pain associated with decidual casts is typically much more severe than in a typical menstrual period.

Other symptoms associated with a decidual cast include:

• Heavy bleeding
• Abdominal pain that is severe and worsens over time
• Possible nausea or dizziness

What Causes a Decidual Cast?

Medical researchers aren’t sure what causes a decidual cast, but there are some theories on why it develops, including progesterone-based hormonal birth control and ectopic pregnancies.

Hormonal Birth Control

Hormonal birth control works by stopping the ovulation process in the body by causing a decrease in cervical mucus. When that happens, it’s more difficult for sperm to make it to an egg and fertilize it. Decidual casts can occur in someone who has recently started or stopped using birth control with progesterone.

Ectopic Pregnancies

Ectopic pregnancies occur when a fertilized egg gets implanted outside of the uterus. While this typically occurs in the fallopian tubes, it can also implant in the ovaries, cervix, or abdomen. It is unclear why an ectopic pregnancy would lead to a decidual cast.

Other Documented Causes

Other possible documented causes include:

• Following postpartum hemorrhage
• Miscarriages
• Abortion
• Spontaneous/idiopathic (occurring without a known cause)

Medical researchers aren’t sure how birth control, ectopic pregnancies, and other possible causes lead to the adhesion of the uterine lining in a decidual cast. It could, however, have to do with how hormones affect cell-to-cell adhesion in the body.

What Is the Diagnostic Process for a Decidual Cast?

Diagnosing a decidual cast is often done by examining symptoms and gathering a person's health history. Medical providers will have to investigate several diagnostic options since it can be mistaken for other conditions, such as:

• Miscarriage
• Pregnancy
• Abortion
• Rhabdomyosarcoma (a rare soft tissue cancer)
• Fibroepithelial polyps
• Sarcoma botryoides (a subtype of a cancerous tumor
• Uterine masses

Pelvic ultrasounds, blood tests to check for pregnancy, and other imaging tests may also help determine what's causing the symptoms. If a person passes a decidual cast during the diagnostic process, that will likely be ruled as the cause of the symptoms if the tests do not find anything else worth pursuing.

Are There Long-Term Complications Associated With Decidual Casts?

The information available on decidual casts is scarce because of the low occurrence rates. That makes it hard to tell on a grander scale if any other health issues or long-term complications are associated with developing a decidual cast.

That said, current research has found that people who expel a decidual cast from their body are relieved of their symptoms immediately, and it usually doesn't occur again. Decidual casts are not associated with any long-term health consequences.

Summary

A decidual cast is the entire uterine lining shedding at once in the shape of the uterus. Medical providers are unsure of the cause. Its symptoms, such as severe cramps and abdominal pain, go away immediately following its passage out of the vaginal canal.

The occurrence rate of a decidual cast is so rare that there is very little documentation or research on what causes it or if it indicates another health issue. Some medical researchers have found that it is most likely to occur in people who have recently started or stopped progesterone-based birth control or are experiencing an ectopic pregnancy.

Research has found no connection between the mass and other severe health issues. However, if you experience severe abnormal cramping around your period or pass a decidual cast and are not relieved of the pain, you should go to the emergency room immediately. Ectopic pregnancies can lead to a decidual cast and are considered medical emergencies that could be life-threatening.