First trimester diagnosis of dicephalic parapagus conjoined twins via transvaginal ultrasonography
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First Trimester Diagnosis of Dicephalic Parapagus Conjoined Twins via Transvaginal Ultrasonography Fisun Vural, MD,1 Birol Vural, MD2 1 The Specialists of Obstetrics and Gynecology, Go¨lcu ¨ k State Hospital, Obstetrics and Gynecology Clinic, Merkez mah, Turgut Sayın cad, 31, sokak No: 7/3, Kocaeli, Turkey 2 Kocaeli University School of Medicine, Obstetrics and Gynecology Department, Kocaeli, Turkey
Received 11 May 2004; accepted 31 January 2005
ABSTRACT: Conjoined twins are rare, and most cases are thoracopagus. Parapagus conjoined twins (one body with two heads) are extremely rare. We report a case of dicephalic parapagus twins that was diagnosed in the first trimester at 10 weeks via transvaginal ultrasonography. ª 2005 Wiley Periodicals, Inc. J Clin Ultrasound 33:364–366, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jcu.20141 Keywords: conjoined twins; parapagus twins; transvaginal ultrasonography
mong monochorionic twin pregnancies, 1.3% are conjoined twins.1 The exact frequency of conjoined twins is not established, and the estimated incidence varies in the literature; however, they occur in approximately 1 in 250,000 live births.2 Conjoined twins occur if twinning is initiated after the embryonic disc and rudimentary amniotic sac have been formed.2 In Greek, para means ‘‘side’’ and pagus means ‘‘fixed’’; thus parapagus means ‘‘fixed side by side.’’ Dicephalus parapagus refers to the union of the entire trunk but not the heads. Diprosopic parapagus is a malformation with one trunk and one head with two faces.3 We report a rare case of dicephalic parapagus that was diagnosed during the first trimester; the benefits of transvaginal ultrasonography at first trimester are emphasized.
Correspondence to: F. Vural 2005 Wiley Periodicals, Inc.
M.K. is a 24-year-old nulliparous woman who was admitted to our clinic with vaginal bleeding after a 10-week period of amenorrhea. The size of the uterus was 9 weeks’ gestational age at bimanual examination, and vaginal bleeding was minimal. Transabdominal ultrasonography (Toshiba, Tosbee, 3.5 MHz, Tokyo, Japan) revealed a 9-weekold fetus with no cardiac activity. The diameter of the gestational sac was 50.2 mm (10 wk ± 1 d) and crown rump lenght was 35.1 mm (9 wk ± 5 d). There was a suspicious mass lateral to the head of the fetus. The patient underwent transvaginal ultrasonography (Toshiba, Tosbee, 5 MHz), which revealed and ultrasonographic image of two fetal heads with one trunk, abdomen, and pelvis (Figure 1). There was a single umbilical cord and no amniotic membrane separating the gestational sac (Figure 2). The two trunks were joined (Figure 3). There were four arms and two legs (Figure 4). The diagnosis of dicephalus parapagus was made on the observation of two heads, one body, and one umbilical cord ultrasonographically. Because the case was a missed abortion, fetal hearts could not be detected. Theropeutic abortion via dilatation and curettage was performed. DISCUSSION
The benefits of sonography in early pregnancy includes the detection of fetal anomalies such as anencephaly, Potter syndrome, Meckel-Gruber syndrome, fetal exomphalos, and Siamese twins.4 Although the diagnosis of conjoined twins can frequently be made at midpregnancy using two JOURNAL OF CLINICAL ULTRASOUND
PARAPAGUS CONJOINED TWINS
FIGURE 1. Transvaginal sonogram of parapagus twins obtained at 10 weeks shows two fetal heads (arrows) with one trunk.
FIGURE 2. Transvaginal sonogram of parapagus twins shows a single umbilical cord (arrow) and no separating membrane.
FIGURE 3. Transverse transvaginal sonogram shows two joined trunks. VOL. 33, NO. 7, SEPTEMBER 2005
FIGURE 4. Transvaginal sonogram of parapagus twins shows four arms (stars), two legs (plus signs), and a single umbilical cord (UC, arrow).
dimensional and, more recently, three-dimensional sonography,5 cases have been reported in the literature that were diagnosed either by transvaginal ultrasonography or three-dimensional sonography in the first trimester.6,7 Parapagus twins represent an extremely rare type of conjoined twins, and there is little information in the literature. Knowledge of the classification of conjoined twins is important for correct diagnosis and management of the patient. In spite of much embryological research, the reports on classification of conjoined twins are limited.3 Some classifications are based on the sharing of heart and umbilicus,3 whereas others are based on the presence of ventral union (cephalopagus, thoracopagus, omphalopagus, ischiopagus), lateral union (parapagus), or dorsal union (craniopagus, pyopagus, rachipagus).8 Still others distinguish between divergent and convergent twins.9 Conjoined twins are mainly classified according to incomplete duplication (parasitic)10 or complete duplication. There are eight types of completely duplicated conjoined twins8 1. Cephalopagus: Fusing from the top of the head down to the umbilicus. There are two faces on opposite sides of the conjoined head, but one face may be quite rudimentary. The lower abdomen and pelvis are not united, and there are four arms and four legs. 2. Thoracopagus: United face to face from the upper thorax down to the umbilicus. The union always involves the heart. The pelvises are not conjoned, and there are four arms and legs. 3. Omphalopagus: Fetuses are joined face to face, primarily in the area of the umbilicus. The 365
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union often includes the inferior lower thorax but never the heart or single patent intercardiac vessel. The pelvises are not united, and there are four arms and four legs. Ischiopagus: United from umbilicus down to a large conjoined pelvis with two sacrums and two symphises pubis. There are four arms and four legs, and the external genitalia and anus are always involved. Craniopagus: United on any portion of the skull except the face and foramen magnum. The trunks are not united, and there are four arms and legs. Pyopagus: Share the sacrococcygeal and perineal regions, usually one anus with two rectums, four arms, and four legs. Rachipagus: Fused above the sacrum; the union may involve occiput as well as vertebral column. Parapagus conjoined twins
Parallel duplication of two notochords in close proximity will produce twins conjoined laterally, which has previously been known as diprosopus or dicephalus but is more properly called parapagus. They are always joined anterolaterally, pulled together ventrally by closure of the umbilicus, and are always single at the caudal end but double at the cranial end. This type of twinning is the type most likely to have missing parts as a result of close proximity of two notochords. The site of origin of the fusion of the embryos determines the extent of the union; the space separating the cranial ends determines which structures will be duplicated. Variability in the site of fusion accounts for the differences in this group of twins. The union always extends from the pelvis to the diaphragm, including the umbilicus, and may involve the chest, neck, or even the head. Most commonly they are joined up to the top of the chest with a fused heart, liver, and diaphragm but with duplicated respiratory and upper gastrointestinal tracts; two arms, two legs, and two complete spinal cords and vertebral columns; and a shared genitourinary system and lower gastrointestinal system. The number of extremities varies
with the extent of original embryonic fusion. All parapagus twins have one umbilicus and a conjoined diaphragm and liver.3 In this case, there was a single umbilical cord and a single shared pelvic region and abdomen, but two joined thoraxes, four arms, and two legs. Siamese or conjoined twins have intrigued physicians for centuries. They present complex and challenging ethical, medical, and legal issues to anyone involved in their care.2 Their management is often extremely complex, and experience with large numbers is restricted to a few centers worldwide. Early diagnosis allows the physician and parents to discuss the possibility of early termination. REFERENCES 1. Sebire NJ, Souka A, Skentou H, et al. First trimester diagnosis of monoamniotic twin pregnancies. Ultrasound Obstet Gynecol 2001;6:223. 2. Kohli N. Ethical issues surrounding seperation of conjoined twins. J La State Med Soc 2001;153:559. 3. Spencer R. Conjoined twins: theoretical embryologic basis. Teratology 1992;45:591. 4. Schmidt W, Kubli F. Early diagnosis of severe congenital malformations by ultrasonography. J Perinat Med 1982;10:233. 5. Bonilla-Musoles F, Machado LE, Osborne NG, et al. Two-dimensional and three-dimensional sonography of conjoined twins. J Clin Ultrasound 2002;30: 68. 6. Hill LM. The sonographic detection of early first trimester conjoined twins. Prenat Diagn 1997;17: 961. 7. Bega G, Wapner R, Lev-Toaff A, et al. Diagnosis of conjoined twins at 10 weeks using three-dimentional ultrasound: a case report. Ultrasound Obstet Gynecol 2000;16:388. 8. Spencer R. Anatomic description of conjoined twins: a plea for standardized terminology. J Paediat Sur 1996;31:941. 9. Kalchbrenner M, Weiner S, Templeton J, et al. Prenatal ultrasound diagnosis of thoracopagus conjoined twins. J Clin Ultrasound 1987;15:59. 10. Esenkaya S, Gurbuz B, Yalti S. Asymmetric parasitic dicephalus conjoined twins. J Clin Ultrasound 2004;32:102.
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