Author: Vanessa Mora
Editor: Nicholas Jo
Conjoined twins, also known as Siamese twins, is a rare condition where genetically identical monoamniotic and monochorionic twins fuse during fertilization in the uterus (Mian et al., 2017). This rare condition occurs in 1 out of 50,000-100,000 live births, with a range of 40-60% being stillborn, 35% surviving for 24 hours, and an overall survival rate of 18% (Kapoor et al., 2012). Conjoined twins are classified based on physical attachment after birth (Mian et al., 2017).
The first ever successful conjoined twin separation was in 1953 with pygopagus twins (Carlson et al., 2018). Since then, conjoined twin separation has become more common, with a survival rate of 64% among 167 cases (Carlson et al., 2018). The classifications with the highest mortality are seen in thoracopagus and craniopagus twins with around 51% mortality, while pygopagus and ischiopagus have the lowest mortality rate of around 23% and 19% (Carlson et al., 2018).
Conjoined Twins, Siamese Twins, Identical Twins, Monozygotic Fission, Monozygotic Fusion, Monochorionic, Monoamniotic
The classification system of conjoined twins is based upon the point of attachment after birth. The possible attachments points are:
- Omphalopagus: Attachment is located on the abdomen, starting from the lower chest towards the groin (Mian et al., 2017). Gastrointestinal organs are mutually shared, excluding the heart (Mathew et al., 2017).
- Thoracopagus: Attachment is located on the upper chest and joined facing each other (Mian et al., 2017). Any cardiovascular body part may be shared, including the heart (Mathew et al., 2017).
- Cephalopagus: Attachment is located on the head towards the navel (Mathew et al., 2017). Gastrointestinal organs and two hearts are mutually shared (Mian et al., 2017).
- Ischiopagus: Attachment is predominantly located on the lower abdomen. However, sometimes attachment may begin from the head (Mian et al., 2017). Pelvic bones and genitalia are mutually shared (Mathew et al., 2017).
- Parapagus: Attachment is located on the sides. Some have separated torsos but remain attached, some share a torso but have two heads, and others may share one torso, one head but have two faces (Mathew et al., 2017).
- Pyopagus: Attachment is located in the lower back and coccyx. The spinal cord and anus are mutually shared (Mian et al., 2017).
Conjoined twins arise during a twin pregnancy, when the embryo’s separation on the 13th-15th day of fertilization is incomplete, or when the embryo fuses in early development (Kaufman, 2004).
Conjoined twin pregnancy symptoms are the same as a regular twin pregnancy (Mitsuda et al., 2019). Symptoms that indicate a twin pregnancy compared to a single child pregnancy are:
- Higher maternal hormone concentrations (androgens, estrogens, insulin-like growth factor (IGF)-1, IGF binding protein (BP)-3, and prolactin) (Houghton et al., 2019)
- Higher levels of Human chorionic gonadotropin (hCG) (Korevaar et al., 2015)
- Elevated levels of nausea and vomiting (Mitsuda et al., 2019).
Consumption of griseofulvin, an antifungal medication, during pregnancy has been linked to two cases of conjoined twins, as well as potential congenital disabilities (Mutchinick et al., 2011). Griseofulvin has the ability to cross the placental barrier and is classified as a teratogen that could potentially cause birth defects (Mutchinick et al., 2011). However, prescription of griseofulvin is uncommon as population-based studies conducted on 22,853 pregnancy outcomes with birth defects reported only 0.06% of cases had griseofulvin exposure (Mutchinick et al., 2011).
Consuming substances such as tobacco, alcohol and drugs during pregnancy have not been related to conjoined twin pregnancy (Sharma et al., 2010). Additionally, 5 cases of conjoined twins have been reported after exposure to chronic radiation doses during pregnancy (Mutchinick et al.,2011). Ethnicity may also increase the chance of producing conjoined twins, where India has 29%, and South Africa has 16% of conjoined twin cases (Sharma et al., 2010).
As early as 12 weeks of pregnancy until the end of the first trimester, an ultrasound is performed to diagnose conjoined twin pregnancy (Mian et al., 2017). Ultrasound scanning allows physicians to detect the position of shared organs, attachment location and areas of body/skin contact between fetuses (Mian et al., 2017). It can also determine the presence of significant complications, such as polyhydramnios, which is found in half of all conjoined twin cases. (Mian et al., 2017). Additionally, fetal echocardiography and 3D-MRI scans help define tissue characterization and provide a more accurate view of fetal abnormalities (Mathew et al., 2017).
Non-Pharmacological Treatment Protocol
Following diagnosis, a decision about surgical procedures can be made after birth. All conjoined births are advised to be done as Caesarian sections (Mian et al., 2017).
- Immediate separation surgery: Required if the location of attachment and sharing of organs is life-threatening to either twin. This procedure has the potential to save one or both twins (Mian et al., 2017).
- Delayed separation surgery: Performed if both twin vitals are stable. This can be done after birth, at three months of age (Mian et al., 2017).
An example of a successful operation involved an ischiopagus twin, where they shared a single terminal ileum and a colon (Carlson et al., 2018). The rest of the anatomical features of the twins are as follows: 4 kidneys, 2 bladdres where 1 ureter form each twin emptying to the bladder of the opposite twin (Carlson et al., 2018). The twins then shared a single anus with 4 ovaries and 2 uteri (Carlson et al., 2018). The most complex problem with separation is insufficient soft tissue coverage post operation which can be caused by tissue edema (Carlson et al., 2018).
The use of 3-D modelling as well as tissue expansion has been useful especially with this case study, and closure may not have been possible post surgery without these tools (Carlson et al., 2018). Negative pressure therapy and using allograft material can help solve small areas of exposure persistent after surgery but come with their own individual risks and complications (Carlson et al., 2018). Overall, the ischiopagus twins made a full recovery but their lower extremity function still continues to be monitored, with pelvic reconstructive surgery a possibility in the future (Carlson et al., 2018).
Articles on Misdiagnosis
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