A 37-year-old G4P2A2 Hispanic female presents for her initial obstetrical visit at a gestational age of 12 weeks and four days. She has a history of one therapeutic abortion and one spontaneous abortion (third pregnancy). The patient is blood type O-positive, has an equivocal rubella titer and tests positive for tuberculosis (QuantiFERON).
Appl Radiol. 2018;47(5):29-32. © 2018 Anderson Publishing, Ltd.
| Type of Conjoined Twins (Incidence)2–4,6 | Illustration3 (inspired by the original artwork of Dr. Rowena Spenoer) | Site of Embryologic Disc Involvement3 | Degree of Union3 |
|---|---|---|---|
| Craniopagus (2.7%-5.0%) |
 |
Dorsal | - union of the calvarium |
| Rachipagus (1.4%-2.0%) |
 |
Dorsal | - union of the vertebral column (typically thoracic or lumbar; rarely with cervical involvement) |
| Pygopagus (1.4%-6.0%) |
 |
Dorsal | - union of the sacrum and coccyx |
| Parapagus Dicephalus (13.5%-24.2%) |
 |
Ventral (Lateral) | - two distinct heads and faces - variable union of thoraces - shared lower abdomen and pelvis - 4–7 extremities |
| Parapagus Diprosopus (0.4%-3.8%) |
 |
Ventral (Lateral) | - two faces on a single head - shared thorax - shared abdomen and pelvis - 4 extremities |
| Omphalopagus (7.3–37.8%) |
 |
Ventral (Rostral) | - union at umbilicus extendingsuperiority to include upperabdomen - may include part of the thorax(limited or no sternal involvement) |
| Thoracopagus (19.0%-56.3%) |
 |
Ventral (Rostral) | - union of the thoraces and upper abdomen |
| Cephalopagus (7.3–11.0%) |
 |
Ventral (Rostral) | - union of the entire head with a single face, extending caudal to the umbilicus |
| Ischiopagus (2.4%-11.0%) |
 |
Ventral (Caudal) | - union of the lower abdomen and pelvis (including urogenital structures) |
| Parapagus Dicephalus Subtype3 | Illustration3 (inspired by the original artwork of Dr. Rowena Spencer) |
Shared and Duplicated Anatomy3 |
|---|---|---|
| Parapagus dicephalus dibrachius dipus |
 |
- typically share a single heart (often with congenital defects) - two esophagi emptying into a single stomach - partial to complete spinal duplication |
| Parapagus dicephalus dibrachius tripus |
 |
- typically share a single heart (often with congenitaldefects) - greater likelihood of duplication of the perineal structures - partial to complete spinal duplication |
| Parapagus dicephalus tribrachius dipus |
 |
- partial to complete cardiac duplication - two esophagi - (+/-) duplication of the stomach and intestinal tract - (+/-) duplication of trachea and lungs - partial to complete spinal duplication |
| Parapagus dicephalus tribrachius tripus |
 |
- partial to complete cardiac duplication - two esophagi - (+/-) duplication of the stomach and intestinal tract - (+/-) duplication of trachea and lungs - greater likelihood of duplication of the perinealstructures - partial to complete spinal duplication |
| Parapagus dicephalus tetrabrachius dipus |
 |
- partial to complete cardiac duplication - two esophagi - (+/-) duplication of the stomach and intestinal tract - (+/-) duplication of trachea and lungs - partial to complete spinal duplication |
| Parapagus dicephalus tetrabrachius tripus |
 |
- partial to complete cardiac duplication - two esophagi - (+/-) duplication of the stomach and intestinal tract - (+/-) duplication of trachea and lungs - greater likelihood of duplication of the perinealstructures - partial to complete spinal duplication |
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