Management and Delivery of Conjoined Twins
Alireza A. Shamshirsaz
Amy R. Mehollin-Ray
Michael A. Belfort
GENERAL PRINCIPLES
1.5/100,000 to 1/500,000 live births (1)
Each set of twins poses distinctive anatomical challenges.
Diagnostic imaging is essential. This provides excellent data for prenatal counseling and prenatal planning by the medical team for immediate postnatal management.
Postnatal imaging including high-quality ultrasound (US), computed tomography (CT), and/or magnetic resonance imaging (MRI) is often required to further define the anatomy (2).
IMAGING AND OTHER DIAGNOSTICS
Identify the appropriate anatomy in as much detail as possible.
Can be detected as early as the first-trimester scan (11-14 weeks). Signs in the scan: Fixed fetal position, scoliosis and neck hyperextension, atypical limb positioning, and umbilical cord with more than three vessels (3)
Conjoined twins have an increased incidence of associated anomalies.
Second-trimester US and MRI should be done in an expert fetal center to optimize diagnosis and management.
Ultrasound
Use a standardized approach (worksheet or checklist) for each twin’s anatomy.
Maintain twin labeling from the first trimester, being careful to label every image with the correct twin.
Note site of fusion, affected organs, and additional anomalies.
Utilize Doppler US to assess shared vasculature.
Transvaginal approach can be used for improved visualization of structures near the cervix.
Detailed fetal echocardiography should be performed for cardiac anatomy and sharing.
MRI
Care should be taken to ensure the naming convention from US is continued on MRI.
Planes may need to be added and adjusted to image each twin in anatomic planes as well as to image the area of fusion in standard planes.
Multiple pulse sequences should be utilized, including single-shot fast spin-echo (SSFSE) T2, balanced steady-state free precession (bSSFP) T2 for the vasculature, and T1 for the bowel.
Anatomical fusion can be categorized according to the following convention:
Dorsal union: May occur at the skull (craniopagus, Figure 6.6.1), at the coccyx (pygopagus), and at spine (rachipagus).
Lateral union twins, known as parapagus twins (Figure 6.6.2A,B), have side-to-side fusion at the level of the abdomen and pelvis. They can be fused for part, or all, of their spine and pelvis. They may have two or three legs between them (bipedus and tripedus, respectively) and two, three, or four arms (di-, tri-, and tetrabrachius, respectively). They may have one common trunk but two faces (diprosopic parapagus), or even separate heads (dicephalic) or thoraxes (dithoracic).
Ventral union may occur at the level of the pelvis (ischiopagus ˜5% of cases), abdomen (omphalopagus—Figure 6.6.3), chest wall (thoracopagus—commonest ˜70%), or at the face (cephalopagus). In cases of thoracopagus twins, they may or may not share a single heart or have parts of each heart fused (thoracopagus, Figure 6.6.4 A,B).
Thoracopagus variants are the most common of all, being noted in 40% to 60% of conjoined twins (4). The cardiac
defects found range from pericardial fusion (which does not pose a significant technical challenge) to fused hearts with single ventricle physiology (a likely inseparable condition) (5). In addition to help guide the counseling with regard to attempted separation, preoperative cardiac assessment is crucial to determining the need for perioperative cardiopulmonary support in those surgical candidates. It is unusual for thoracopagus twins to have fused lungs, but there may be differential lung growth and pulmonary hypoplasia more prominent in one twin than the other.
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