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Clinical Letters
Anencephalic Monocephalic Conjoined Twins Detected by Sonography Videos online at www.jultrasoundmed.org
A 26-year-old woman, gravida 1, para 0, aborta 1, was referred to our hospital in her 22nd week of pregnancy. She had an upper respiratory infection during pregnancy without any medical treatment. She had been taking folic acid for 4 months before pregnancy. She has been using an electric blanket as heating equipment while sleeping at night during pregnancy. She was a farmer. She did not use prescribed medications, tobacco, alcohol, or illicit drugs. Her pregnancy was spontaneous, and her medical and family histories were unremarkable. Neither she nor her husband had a family member with a history of twinning or congenital anomalies. Prenatal sonography was not performed until she was referred to our hospital. Her sonographic results (LOGIQ E9; GE Healthcare, Milwaukee, WI) revealed anencephalic monocephalic conjoined twins (anencephaly monocephalus cephalothoracoventropagus tetrabrachius) without clear ossification of the skull and tetrabrachius with a femur length of 1.4 cm (Figure 1, A and B). Moreover, sonography showed that the twins shared a single heart and liver (Videos 1 and 2). After diagnosis, the parents decided on termination of the pregnancy. Postmortem physical examination revealed anencephalic monocephalic conjoined twins with a facial appearance characterized by a single nose and mouth and double eyes and ears with a short and wide neck (Figure 1C). The upper lip was intact without unilateral or bilateral cleft lip and palate. The thorax and abdomen were fused, with 2 sets of upper limbs in the normal spatial orientation (making 4 total), and one hand was
J Ultrasound Med 2014; 33:547–551
valgus. Two opposite intact spines without spinal bifida, 2 sets of rib cages, 2 pelvises, and 4 legs were observed (Figure 1D). An anatomic examination of the internal organs was not performed, according to the parents’ request. The sex was not clear. The twins shared a single placenta. Conjoined twins are rare, and they are thoracopagus in most cases. This condition occurs in about 1% of monochorionic twin pregnancies1 and only arises when the twinning event occurs at about the primitive streak stage of development, about 13 to 14 days after fertilization. It is exclusively associated with the monoamniotic monochorionic type of placentation. Conjoined twins have 9 types2: (1) craniopagus: occipital fusion; (2) craniopagus: parietal fusion; (3) ischiopagus; (4) pygopagus; (5) parapagus; (6) dicephalus; (7) syncephalus; (8) cephalothoracopagus; and (9) thoracopagus (Figure 2). Our case was cephalothoracopagus, but it cannot be described as the cephalothoracopagus type. This type usually presents 2 faces on either side of the head, with each face a composite of that of both individuals. In this particularly rare variant of conjoined twins, a relatively normal face exists on one side of the head, but it is complemented by an otocephalic “face” on the other side. Ekinci et al3 reported a case of anencephalic monocephalus diprosopus, which is characterized by a single body, a single unusual head, and 2 faces in a spectrum of duplication of the craniofacial structures. Our case had only a single head and face. Even a rudimentary face was not observed on the other twin. Whether conjoined twinning is a result of fission or fusion is still much debated.2 However, the fertilized ovum generally undergoes fission to produce monovular twins, dividing before the notochord develops and separating sufficiently to prevent reunion of the embryos. The embryologic process can be distorted to cause fission of the notochord by teratogens. Although incomplete splitting of the embryonic axis is the commonly held view, Spencer4 speculated that conjoined twinning could not possibly result from a fission event and could only result from the fusion of monoamniotic twins. According to embryology, the cranial end of the embryonic axis cannot split as it elongates because it is the caudal end that proliferates, and the “anchoring” of the caudal extremity at the primitive pit probably prevents bifurcation. Twins resulting from such caudal duplication will be united laterally at the cranial end and separated caudally. This type of union has never been reported. Spencer4 postulated that conjoined twins result from the development of 2 independent notochords initially destined to become separate twins but too close to develop independently. However, our case is exactly the type mentioned. Therefore, we support the fission theory.
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Figure 1. Anencephalic monocephalic conjoined twins. A, Sonography revealed the twins’ head without clear ossification of the skull. B, Sonography revealed that the twins had 2 opposite intact spines. SP1 indicates spine 1; and SP2, spine 2. C, Postmortem physical examination revealed that the twins’ head was anencephalic, with a facial appearance characterized by a single nose and mouth and double eyes. The neck was short and wide, and the thorax and abdomen were fused. There were 2 sets of rib cages, 2 pelvises, and 4 legs. D, Postmortem physical examination revealed that the twins had 2 opposite intact spines without spinal bifida.
Figure 2. Types of conjoined twins: a, craniopagus, occipital fusion; b, craniopagus, parietal fusion; c, ischiopagus; d, pygopagus; e, parapagus; f, dicephalus; g, syncephalus; h, cephalothoracopagus; i, thoracopagus.
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Clinical Letters
In our case, the use of an electric blanket as heating equipment may have somehow affected the embryo. In a number of studies,5–9 hyperthermia as a teratogen has been considered to induce malformation. Hyperthermia may result from a temporary cessation of cell proliferation and partial necrosis of the embryonic neuroepithelium. Proliferating cells are particularly sensitive to temperature elevations, resulting in the arrest of mitotic activity and the immediate death of cells in mitosis, with threshold elevations and delayed death of cells probably in the synthesis phase with higher temperatures. This condition is particularly damaging to the central nervous system. When a threshold exposure occurs at the appropriate stages of embryonic development, exencephaly, anencephaly, encephalocoele, micrencephaly, microphthalmia, neurogenic talipes, and arthrogryposis can occur in a high proportion of exposed embryos. A study by Duong et al10 suggests that women who use hot tubs more than once during early pregnancy and for long periods have an increased risk of certain birth defect phenotypes, particularly anencephaly and gastroschisis. In conclusion, to the best of our knowledge, a case of anencephalic monocephalic conjoined twins in humans has not been reported previously. Prenatal sonography is important for discovering and identifying fetal malformations.
7.
Shiota K. Induction of neural tube defects and skeletal malformations in mice following brief hyperthermia in utero. Biol Neonate 1988; 53:86–97. 8. Edwards MJ. Hyperthermia as a teratogen: a review of experimental studies and their clinical significance. Teratog Carcinog Mutagen 1986; 6:563– 582. 9. Edwards MJ. Congenital malformations in the rat following induced hyperthermia during gestation. Teratology 1968; 1:173–177. 10. Duong HT, Shahrukh Hashmi S, Ramadhani T, Canfield MA, Scheuerle A, Kim Waller D; National Birth Defects Prevention Study. Maternal use of hot tub and major structural birth defects. Birth Defects Res A Clin Mol Teratol 2011; 91:836–841.
Haixian Zhang, BS, Zhi Yang, MD, BS, Guanghe Cui, MS Department of Ultrasonography Affiliated Hospital of Binzhou Medical University Binzhou, China doi:10.7863/ultra.33.3.549
References 1. 2. 3.
4. 5.
6.
Fitzgerald EJ, Toi A, Cochlin DL. Conjoined twins: antenatal ultrasound diagnosis and review of the literature. Br J Radiol 1985; 58:1053–1056. Kaufman MH. The embryology of conjoined twins. Childs Nerv Syst2004; 20:508–525. Ekinci G, Balci S, Erzen C. An anencephalic monocephalus diprosopus “headed twin”: postmortem and CT findings with emphasis on the cranial bones. Turk J Pediatr 2005; 47:195–198. Spencer R. Conjoined twins: theoretical embryologic basis. Teratology1992; 45:591–602. de la Rosa Morales V, Guzmán Juárez L, Guarneros Cortés CA. Maternal risk factors associated with anencephaly [in Spanish]. Ginecol Obstet Mex 2000; 68:476–481. Sandford MK, Kissling GE, Joubert PE. Neural tube defect etiology: new evidence concerning maternal hyperthermia, health and diet. Dev Med Child Neurol 1992; 34:661–675.
J Ultrasound Med 2014; 33:547–551
551
Clinical Letters
Anencephalic Monocephalic Conjoined Twins Detected by Sonography Videos online at www.jultrasoundmed.org
A 26-year-old woman, gravida 1, para 0, aborta 1, was referred to our hospital in her 22nd week of pregnancy. She had an upper respiratory infection during pregnancy without any medical treatment. She had been taking folic acid for 4 months before pregnancy. She has been using an electric blanket as heating equipment while sleeping at night during pregnancy. She was a farmer. She did not use prescribed medications, tobacco, alcohol, or illicit drugs. Her pregnancy was spontaneous, and her medical and family histories were unremarkable. Neither she nor her husband had a family member with a history of twinning or congenital anomalies. Prenatal sonography was not performed until she was referred to our hospital. Her sonographic results (LOGIQ E9; GE Healthcare, Milwaukee, WI) revealed anencephalic monocephalic conjoined twins (anencephaly monocephalus cephalothoracoventropagus tetrabrachius) without clear ossification of the skull and tetrabrachius with a femur length of 1.4 cm (Figure 1, A and B). Moreover, sonography showed that the twins shared a single heart and liver (Videos 1 and 2). After diagnosis, the parents decided on termination of the pregnancy. Postmortem physical examination revealed anencephalic monocephalic conjoined twins with a facial appearance characterized by a single nose and mouth and double eyes and ears with a short and wide neck (Figure 1C). The upper lip was intact without unilateral or bilateral cleft lip and palate. The thorax and abdomen were fused, with 2 sets of upper limbs in the normal spatial orientation (making 4 total), and one hand was
J Ultrasound Med 2014; 33:547–551
valgus. Two opposite intact spines without spinal bifida, 2 sets of rib cages, 2 pelvises, and 4 legs were observed (Figure 1D). An anatomic examination of the internal organs was not performed, according to the parents’ request. The sex was not clear. The twins shared a single placenta. Conjoined twins are rare, and they are thoracopagus in most cases. This condition occurs in about 1% of monochorionic twin pregnancies1 and only arises when the twinning event occurs at about the primitive streak stage of development, about 13 to 14 days after fertilization. It is exclusively associated with the monoamniotic monochorionic type of placentation. Conjoined twins have 9 types2: (1) craniopagus: occipital fusion; (2) craniopagus: parietal fusion; (3) ischiopagus; (4) pygopagus; (5) parapagus; (6) dicephalus; (7) syncephalus; (8) cephalothoracopagus; and (9) thoracopagus (Figure 2). Our case was cephalothoracopagus, but it cannot be described as the cephalothoracopagus type. This type usually presents 2 faces on either side of the head, with each face a composite of that of both individuals. In this particularly rare variant of conjoined twins, a relatively normal face exists on one side of the head, but it is complemented by an otocephalic “face” on the other side. Ekinci et al3 reported a case of anencephalic monocephalus diprosopus, which is characterized by a single body, a single unusual head, and 2 faces in a spectrum of duplication of the craniofacial structures. Our case had only a single head and face. Even a rudimentary face was not observed on the other twin. Whether conjoined twinning is a result of fission or fusion is still much debated.2 However, the fertilized ovum generally undergoes fission to produce monovular twins, dividing before the notochord develops and separating sufficiently to prevent reunion of the embryos. The embryologic process can be distorted to cause fission of the notochord by teratogens. Although incomplete splitting of the embryonic axis is the commonly held view, Spencer4 speculated that conjoined twinning could not possibly result from a fission event and could only result from the fusion of monoamniotic twins. According to embryology, the cranial end of the embryonic axis cannot split as it elongates because it is the caudal end that proliferates, and the “anchoring” of the caudal extremity at the primitive pit probably prevents bifurcation. Twins resulting from such caudal duplication will be united laterally at the cranial end and separated caudally. This type of union has never been reported. Spencer4 postulated that conjoined twins result from the development of 2 independent notochords initially destined to become separate twins but too close to develop independently. However, our case is exactly the type mentioned. Therefore, we support the fission theory.
549
A 4 C J 4 J 4 S 4 C
4 u J 4 o J 4
G 4 n J 4 e 4 C C Z 4 a J 5 S A 5 S 5
C 5 5
5 S C C 5 V
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Clinical Letters
A
B
C
D
Figure 1. Anencephalic monocephalic conjoined twins. A, Sonography revealed the twins’ head without clear ossification of the skull. B, Sonography revealed that the twins had 2 opposite intact spines. SP1 indicates spine 1; and SP2, spine 2. C, Postmortem physical examination revealed that the twins’ head was anencephalic, with a facial appearance characterized by a single nose and mouth and double eyes. The neck was short and wide, and the thorax and abdomen were fused. There were 2 sets of rib cages, 2 pelvises, and 4 legs. D, Postmortem physical examination revealed that the twins had 2 opposite intact spines without spinal bifida.
Figure 2. Types of conjoined twins: a, craniopagus, occipital fusion; b, craniopagus, parietal fusion; c, ischiopagus; d, pygopagus; e, parapagus; f, dicephalus; g, syncephalus; h, cephalothoracopagus; i, thoracopagus.
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Clinical Letters
In our case, the use of an electric blanket as heating equipment may have somehow affected the embryo. In a number of studies,5–9 hyperthermia as a teratogen has been considered to induce malformation. Hyperthermia may result from a temporary cessation of cell proliferation and partial necrosis of the embryonic neuroepithelium. Proliferating cells are particularly sensitive to temperature elevations, resulting in the arrest of mitotic activity and the immediate death of cells in mitosis, with threshold elevations and delayed death of cells probably in the synthesis phase with higher temperatures. This condition is particularly damaging to the central nervous system. When a threshold exposure occurs at the appropriate stages of embryonic development, exencephaly, anencephaly, encephalocoele, micrencephaly, microphthalmia, neurogenic talipes, and arthrogryposis can occur in a high proportion of exposed embryos. A study by Duong et al10 suggests that women who use hot tubs more than once during early pregnancy and for long periods have an increased risk of certain birth defect phenotypes, particularly anencephaly and gastroschisis. In conclusion, to the best of our knowledge, a case of anencephalic monocephalic conjoined twins in humans has not been reported previously. Prenatal sonography is important for discovering and identifying fetal malformations.
7.
Shiota K. Induction of neural tube defects and skeletal malformations in mice following brief hyperthermia in utero. Biol Neonate 1988; 53:86–97. 8. Edwards MJ. Hyperthermia as a teratogen: a review of experimental studies and their clinical significance. Teratog Carcinog Mutagen 1986; 6:563– 582. 9. Edwards MJ. Congenital malformations in the rat following induced hyperthermia during gestation. Teratology 1968; 1:173–177. 10. Duong HT, Shahrukh Hashmi S, Ramadhani T, Canfield MA, Scheuerle A, Kim Waller D; National Birth Defects Prevention Study. Maternal use of hot tub and major structural birth defects. Birth Defects Res A Clin Mol Teratol 2011; 91:836–841.
Haixian Zhang, BS, Zhi Yang, MD, BS, Guanghe Cui, MS Department of Ultrasonography Affiliated Hospital of Binzhou Medical University Binzhou, China doi:10.7863/ultra.33.3.549
References 1. 2. 3.
4. 5.
6.
Fitzgerald EJ, Toi A, Cochlin DL. Conjoined twins: antenatal ultrasound diagnosis and review of the literature. Br J Radiol 1985; 58:1053–1056. Kaufman MH. The embryology of conjoined twins. Childs Nerv Syst2004; 20:508–525. Ekinci G, Balci S, Erzen C. An anencephalic monocephalus diprosopus “headed twin”: postmortem and CT findings with emphasis on the cranial bones. Turk J Pediatr 2005; 47:195–198. Spencer R. Conjoined twins: theoretical embryologic basis. Teratology1992; 45:591–602. de la Rosa Morales V, Guzmán Juárez L, Guarneros Cortés CA. Maternal risk factors associated with anencephaly [in Spanish]. Ginecol Obstet Mex 2000; 68:476–481. Sandford MK, Kissling GE, Joubert PE. Neural tube defect etiology: new evidence concerning maternal hyperthermia, health and diet. Dev Med Child Neurol 1992; 34:661–675.
J Ultrasound Med 2014; 33:547–551
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