(Radiographics. 1999;19:260-263.)
© RSNA, 1999
US Case of the Day
Teresita L. Angtuaco, MD1,2,
Edgardo J. Angtuaco, MD1 and
J. Gerald Quirk, Jr, MD, PhD2
1 Departments of Radiology (T.L.A., E.J.A.)
2 Obstetrics and Gynecology (T.L.A., J.G.Q.), University of Arkansas for Medical Sciences, 4301 W Markham, Little Rock, AR 72205.
Index Terms: Fetus, abnormalities, 856.879 • Fetus, US, 856.1298 • Twins, abnormalities, 856.879
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HISTORY
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A 20-year-old gravida 4, para 2, aborta 1 woman was referred for management because of premature rupture of membranes and polyhydramnios. The patient had received no prior prenatal care, and her menstrual history was unreliable. A fetal gestational age of 30 weeks was estimated on the basis of an initial ultrasound (US) examination performed at the obstetrician's office. The referring obstetrician indicated that the fetal brain appeared abnormal but that he could not definitely delineate the extent of the abnormality.
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FINDINGS
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Repeat US was performed at the time of admission. Fetal visualization with the patient in the supine position was compromised by severe polyhydramnios. Adequate US images of the fetal head were optimally obtained only with the patient in a semiprone position with the knees flexed. The fetus had one head with two completely separate brains, each with its own set of cerebral vessels. The brains were united at the posterior fossa, where a large cystic structure was identified (Fig 1a). Two sets of cerebellar hemispheres were present but appeared to be hypoplastic. No cerebellar vermis was identified. Two faces and four eyes were seen, each eye within its own orbit (Fig 1b, 1c). Repeat cesarean section was planned because of ruptured membranes and a combined biparietal diameter of 14 cm. The fetus had an Apgar score of 2/2 at 1 and 5 minutes after delivery and died a few hours later.
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Figure 1a. (a) Coronal US image of the fetal brain shows complete duplication of normal-appearing cerebral structures. The cerebellar hemispheres are not well visualized, and there appears to be fusion at the posterior fossa. A large cystic structure is seen at the level of fusion (arrow). (b) Transverse US image through the fetal orbits demonstrates the two medial orbits (arrows) separated by a very thin septum of bone. (c) Transverse US image of the fetal face obtained just inferior to b shows two noses (arrows) projecting laterally from a shared medial cheek.
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Figure 1b. (a) Coronal US image of the fetal brain shows complete duplication of normal-appearing cerebral structures. The cerebellar hemispheres are not well visualized, and there appears to be fusion at the posterior fossa. A large cystic structure is seen at the level of fusion (arrow). (b) Transverse US image through the fetal orbits demonstrates the two medial orbits (arrows) separated by a very thin septum of bone. (c) Transverse US image of the fetal face obtained just inferior to b shows two noses (arrows) projecting laterally from a shared medial cheek.
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Figure 1c. (a) Coronal US image of the fetal brain shows complete duplication of normal-appearing cerebral structures. The cerebellar hemispheres are not well visualized, and there appears to be fusion at the posterior fossa. A large cystic structure is seen at the level of fusion (arrow). (b) Transverse US image through the fetal orbits demonstrates the two medial orbits (arrows) separated by a very thin septum of bone. (c) Transverse US image of the fetal face obtained just inferior to b shows two noses (arrows) projecting laterally from a shared medial cheek.
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DIAGNOSIS: Complete brain duplication with fusion at the posterior fossa (diprosopus tetraophthalmos).
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DISCUSSION
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The body appeared normal externally (Fig 2). The fetus had two faces that shared a medial cheek and ear, and normal-appearing ears were seen bilaterally (Fig 3). The term tetraophthalmos is used to describe a fetus with four eyes. In such cases, the two medial eyes may be completely separated or (as in this case) partially fused (1–3). Radiographs showed duplication of the cervical spine with multiple anomalies involving the cervical and thoracic vertebrae (Fig 4). Postmortem magnetic resonance (MR) imaging and examination of a gross autopsy specimen helped confirm the prenatal diagnosis of complete brain duplication with fusion at the posterior fossa (Figs 5, 6). MR imaging also demonstrated the presence of a left-sided diaphragmatic hernia (Fig 7).
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Figure 3. Postmortem photograph of the neonate demonstrates typical features of diprosopus tetraophthalmos with characteristic duplication of facial structures. The two faces share a medial cheek and ear, and normal-appearing ears are seen bilaterally.
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Figure 5. Figures 5, 6. (5) Coronal T1-weighted spin-echo postmortem MR image of the conjoined brains (repetition time msec/echo time msec = 650/16) shows complete separation of the cerebral hemispheres. The cerebella (arrows) are markedly hypoplastic. A large fluid collection is seen inferior to the cerebellar hemispheres and is common to both brains. (6) Photograph of the conjoined brains (posterior view) helps confirm the findings at prenatal US and postmortem MR imaging (cf Figs 1, 5).
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Figure 6. Figures 5, 6. (5) Coronal T1-weighted spin-echo postmortem MR image of the conjoined brains (repetition time msec/echo time msec = 650/16) shows complete separation of the cerebral hemispheres. The cerebella (arrows) are markedly hypoplastic. A large fluid collection is seen inferior to the cerebellar hemispheres and is common to both brains. (6) Photograph of the conjoined brains (posterior view) helps confirm the findings at prenatal US and postmortem MR imaging (cf Figs 1, 5).
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Figure 7. Coronal T1-weighted (400/16) postmortem MR image of the chest and abdomen helps confirm the presence of a left-sided diaphragmatic hernia. The heart (arrow) is displaced within the right hemithorax.
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Monozygotic twins can develop into one of three types depending on the timing of zygotic division. In approximately one-third of cases, division occurs within the first 4 days of gestation, resulting in dichorionic diamniotic twins. In about two-thirds of cases, division occurs toward the end of the first week, resulting in monochorionic, diamniotic twins. In about 1%–3% of cases, the blastocyst does not separate until the second week, resulting in monochorionic, monoamniotic twins (4).
Conjoined twinning results from the incomplete division of a monozygotic twin 13 days after fertilization but before the third week of gestation. The incidence of conjoined twinning has been reported to be as low as one in every 58,000 deliveries in the Caucasian population and as high as one in every 6,454 deliveries in some Asian populations (4). In 6% of cases, conjoined twins are part of triplets. There is a striking preponderance of females, which has been reported to be as high as 95% (4).
Conjoined twins have been classified in a variety of ways on the basis of the site of fusion. The more fused twins are usually joined laterally, whereas the more separate twins are joined anteriorly, posteriorly, cranially, or caudally. In 1967, Guttmacher and Nichols (5) proposed a system of classification with a broad scheme into which most cases could be placed (6). Subcategories within that scheme, together with their relative frequencies, are shown in the Table (7).
Diprosopus twinning is an extremely rare, symmetric type of conjoined twinning that is seen in less than 1% of cases. Diprosopus twinning is characterized by a single body and a spectrum of duplication of craniofacial structures. It is this characteristic duplication that makes the diagnosis specific for diprosopus twinning. In the most extreme form of diprosopus twinning, two complete faces are seen, whereas the mildest form may demonstrate only an isolated duplication of the nose.
The fetus should also be meticulously examined for anomalies that are known to occur with higher frequency in twins. In this case, the presence of a diaphragmatic hernia was confirmed at autopsy.
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Footnotes
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Address reprint requests to T.L.A.
From the 1998 RSNA scientific assembly.
Received for publication August 28, 1998.
Revision received September 23, 1998. October 23, 1998.
Accepted for publication October 23, 1998.
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References
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Strauss S, Tamarkin M, Engelberg S, et al. Prenatal sonographic appearance of diprosopus. J Ultrasound Med 1987; 6:93-95.[Medline]
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Okazaki JR, Wilson JL, Holmes SM, et al. Diprosopus: diagnosis in utero. AJR 1987; 149:147-148.[Free Full Text]
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Chervenak FA, Pinto MM, Heller CI, et al. Obstetric significance of fetal craniofacial duplication: a case report. J Reprod Med 1985; 30:74-76.[Medline]
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Baldwin VJ. Pathology of multiple pregnancy. In: Wigglesworth JS, Singer DB, eds. Textbook of fetal and perinatal pathology. Boston, Mass: Blackwell, 1991; 306-343.
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Guttmacher AF, Nichols BL. Teratology of conjoined twins. Birth Def 1967; 3:3-9.
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Potter EJ, Craig JM. Pathology of the fetus and infant 3rd ed. Chicago, Ill: Year–Book Medical, 1975; 307-321.
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Pretorius DH, Mahony BS. Twin gestations. In: Nyberg DA, Mahony BS, Pretorius DH, eds. Diagnostic ultrasound of fetal anomalies. Chicago, Ill: Year–Book Medical, 1990; 609-622.
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HISTORY
FINDINGS
