Three sets of conjoined twins recently diagnosed by us in the antenatal period are presented. From these cases and a review of the literature we present the ...
1985, The British Journal oj Radiology, 58, 1053-1056
NOVEMBER
1985
Conjoined twins. Antenatal ultrasound diagnosis and a review of the literature By *E. J . Fitzgerald, M.B., M.R.C.P.I., F.R.C.R., A. Toi, M.D., F.R.C.P.(C) and t * D . L Cochlin, M.B., B.Ch., F.R.C.R. Department of Diagnostic Radiology, Me Master University Medical Centre, Hamilton, Ontario, Canada, and tDepartment of Radiology, East Glamorgan General Hospital, Church Village, Pontypridd
{Received December 1984 and in revised form April 1985)
ABSTRACT
Three sets of conjoined twins recently diagnosed by us in the antenatal period are presented. From these cases and a review of the literature we present the ultrasound diagnostic features of the various forms of this rare condition. We discuss the importance of associated anomalies and shared organs with their relevance to subsequent antenatal management and delivery. The importance of excluding this condition whenever twins are diagnosed on ultrasound is stressed.
strual dVta. The heads lay close together and the individual bodies could not be seen separately, apparently joined at thoracic and abdominal levels. Two spines were seen lying parallel to each other. On the basis of the above findings a diagnosis of conjoined twins was suggested. As this was the first time we had seen this condition, a further scan was performed a week later to confirm our findings. The fetal heads lay in the same relationship to each other as before. This time only two sets of limbs were found and again the babies were inseparable. On the basis of these
Prior to the advent of diagnostic ultrasound conjoined twins were rarely diagnosed prenatally, 6% in Harper's series of 36 cases (Harper et al, 1980) and 10 of 47 cases in Tan's review (Tan et al, 1971). The condition often presented initially with dystocia in the second stage of labour. Such a presentation involved emergency caesarian section, with its attendant risks to both mother and babies. Occasionally fetal destructive manoeuvres were necessary to allow delivery. Thus, diagnosis prior to labour is of vital importance to help reduce such morbidity and mortality (Vaughn & Powell, 1979). Conjoined twins can be diagnosed on plain abdominal radiographs. Several radiographic criteria have been suggested for such a diagnosis (Gray et al, 1950; Borden et al, 1974). These could prove useful when noted, but frequently invasive and potentially dangerous confirmatory tests such as amniography and fetography were necessary. With real-time ultrasound, the connecting tissues can be demonstrated (on a radiograph, this is apparent only if conjunction is bony), as can the presence of shared vital organs and the occurrence of anomalies, which are a frequent complication of the commoner types of twins. Our cases clearly illustrate several of the problems of initial diagnosis and of the presence of several of these anomalies.
•
CASE REPORTS
Case 1 A 25-year-old woman was scanned 16 weeks after her last menstrual period, with a SKI Echolife 3.5 MHz linear array probe. Twins were shown, with BPDs consistent with men*Present address: Department of Radiology, University Hospital of Wales, Heath Park, Cardiff CF4 4XW
V
FIG. 1.
Post-mortem radiograph of Case 1 showing parallel spines as noted on ultrasound.
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FIG. 2. Case 2. Sector scan showing the joined twins with a large shared heart (h). The two spines are marked S. Patient's bladder towards left. Hydramnios is also present. findings the diagnosis of conjoined twins (thoracopagus type) was felt to be confirmed. The patient and her husband were informed of the diagnosis and decided to continue with the pregnancy. The patient was delivered by caesarian section after spontaneous onset of labour at 32 weeks. The twins (Fig. 1) had an apgar score of 2 at one and five minutes. One died some hours after birth and the other at 48 hours. Autopsy showed a shared heart with only one ventricle; the liver was shared as was the bowel below the oesophagus. Case 2 This 31-year-old woman had two normal pregnancies previously. Her latest pregnancy proceeded apparently normally until 29 weeks gestational age when polyhydramnios occurred. On admission to her local hospital a clinical diagnosis of twins was made. An ultrasound scan confirmed this but the
-
FIG. 3. Case 2. Two stomachs (S). There is a single umbilical vein (arrow) which enters the single shared liver.
FIG. 4. Case 3. The sector scan taken transversely through the head shows a single large conjoined head (arrow at joining).
possibility of conjoined twins was raised. Because of this suspicion the patient was transferred to McMaster Medical Centre. On admission to our centre the patient's cervix was 3 cm dilated and fully effaced. Our ultrasound scan confirmed the diagnosis of conjoined twins, joined from the mid-sternum to the pelvis. Only a single shared heart was present (Fig. 2): a single liver but two distinct stomachs were present (Fig. 3). As only a single heart with shared ventricles was present it was felt that the twins were not separable surgically (Izukawa et al, 1978; Miller et al, 1983). Twins with shared atrial tissue have been successfully separated (Synhurst et al, 1979). Because of her clinical state she underwent a lower segment caesarian section at 32 weeks gestational age. Conjoined twins of total weight 3,230 g were delivered but both died on the first day. Autopsy confirmed the presence of a single heart with one ventricle and two aortas, a single shared liver, two stomachs and one bowel. Case 3 On the basis of an ultrasound scan performed elsewhere at 23 weeks gestation, this 33-year-old primigravida was said to have a single normal fetus, BPD being compatible with dates. Acute polyhydramnios was noted at 28 weeks' gestation and a further ultrasound study at the initial centre one week later was reported as showing a single fetus with a possible cardiac anomaly, type unspecified. Because of this possibility the patient was transferred to our centre and scanned upon admission. Severe polyhydramnios was present which interferred with visualisation of the fetal parts, but a twin pregnancy joined at the head (Fig. 4) with an abnormal cervical spine was seen. The thorax was inseparable anteriorly and only one active fetal heart was noted. A diagnosis was made of conjoined twins of cephalothoracopagus type. Spontaneous labour with rupture of membranes and loss of a large amount of liquor occurred that night. Because of the ultrasound findings a lower segment caesarian section was performed and conjoined twins weighing 1,910 g were delivered, dying shortly after birth. They were joined at the head and face anteriorly and at the thorax. Multiple severe neurological and cardiac anomalies, incompatible with life were found at autopsy.
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Conjoined twins. Antenatal ultrasound diagnosis TABLE I COMMONER TYPES OF FUSION
Types of fusion
Particular features
Prognosis
Thoracopagus
Common liver: 100% Common pericardium: 90% Hearts joined: 75% Common alimentary tract: 50%
Depends on the degree of union. With fused hearts, death generally occurs by three months
Xiphopagus
Common liver: 81 % GIT anomalies: 33% (omphalocele, common distal ileum or MeckeFs) Congenital heart disease: 25% after Fallot's.
Outcome more hopeful than for thoracopagous twins, because of lesser incidence of cardiac lesion.
Pygopagus
Common sacrum and Fairly good as no coccyx: 100% major organ system Single common shared. rectum, single bladder & urethra. Angiography necessary as frequently pelvic vessels anastomose freely.
Ischiopagus
Lower spine frequently abnormal. Legs opposite fusion frequently rudimentary.
Craniopagus
Depends on degree of Brains usually fusion of intracranial separate or not intimately connected structures.
No reliable statistics
DISCUSSION
Conjoined twins are rare. The exact incidence is not known but is about 1 per 50,000 births (Hanson 1975; Potter & Craig, 1975). The incidence appears remarkably similar throughout the world although an incidence as high as 1 per 20,000 births has been reported from Atlanta (Compton, 1971; Hanson, 1975). The defect is said to occur early in monoamniotic monochorionic pregnancies; its cause is not known and it does not tend to recur (Harper et al, 1980). Females predominate in the order of 2 or 3 to 1. Polyhydramnios is frequent, occurring in 50% of cases, as opposed to 10% of normal twins and 2% of normal single pregnancies (Chan, 1976). Classification is according to site of fusion. Other anomalies are frequently associated with some types of fusion (Table I). The anomalies are commonest and most severe with thoracopagus twins. Awareness of these lesions is important once the actual diagnosis of conjoining has been made as ultrasound can then be used to search for
and assess the severity of these lesions, which greatly influence the survival rate. The prenatal diagnosis of this condition is thus important for several reasons. It allows correct planning of the site and type of delivery, referral to a centre where appropriate obstetric and paediatric surgical facilities are available should separation be contemplated (Vaughn & Powell, 1979; Fagan, 1977). The most important first step in making the diagnosis is awareness of its possibility. All sets of twins when examined with ultrasound should be shown to be separated from each other. If separation is suspected but cannot be confirmed, careful examination with realtime ultrasound allows full assessment of the site and type of joining, it being the only method which shows the soft tissue conjunction. It also allows shared organs to be seen, and both babies can be carefully screened for other system abnormalities. It is important to remember that thoracopagus twins are not mirror images of each other (Edwards et al, 1977). If there is doubt about the diagnosis on the initial scan, several helpful features (which we found useful in our first case) have been described. These include fetal heads and body parts at the same level, constant relative fetal positions over a considerable length of time and over several examinations, as well as en face fetal positions, hyperextension of one or both cervical spines and a single umbilical cord with more than three vessels (Austin et al, 1980). If doubt remains, X-ray examination may follow (Gore et al, 1982). The ultrasound diagnosis makes previously-used invasive procedures such as amniography and fetography unnecessary. Although ultrasound is very informative, other tests may be necessary after birth both to visualise shared organs and assess the possibility of successful separation. These twins can be difficult to manipulate to obtain good radiographic visualisation (Schnyder et al, 1979). Separate and independent QRS complexes on standard echocardiography do not preclude cardiac union at the atrial level. Miller et al (1983) suggest that 2D echocardiography is indicated. Radionuclide scanning helps to show whether the gallbladder and biliary trees are separated. Contrast radiography allows demonstration of the degree of sharing of the gastrointestinal tract. CT and ultrasound scans show the presence of kidneys and contrast medium, given during the CT scan, can show if renal function is present. Once the condition has been diagnosed on ultrasound, preparation for delivery can be made. Caesarian section is the preferred method of delivery (Vaughn & Powell, 1979), especially if the pregnancy goes to term, as it gives the best chance of fetal survival with least maternal morbidity. If the twins are not at-term, but premature labour has begun, abdominal delivery should also be considered, as dystocia may still occur and require intra-uterine surgical separation. Such a procedure greatly threatens fetal survival and may harm the mother.
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CONCLUSION
C.
M.,
N I X , W.
G.
& WALLACE,
A.
J.,
1950.
Thoracopagus: Prenatal diagnosis. Radiology, 54, 398-400. Real-time ultrasound is the best method of diagnosis and initial assessment of conjoined twins. The possi- HANSON, J. W., 1975. Incidence of conjoined twins. Lancet, ii, 1257. bility of this diagnosis should be considered with all HARPER, R. G., KENIGSBERG, K., SIA, C. G., HORN, D., STERN, twins, and separation should be actively sought in all D. & BONGIOVI, V., 1980. Xiphopagus conjoined twins: A normal twin pregnancies. 300-year review of the obstetric, morphopathologic, neonatal and surgical parameters. American Journal of Obstetrics & Gynecology, 137, 617-629.
ACKNOWLEDGMENTS
We would like to thank Dr. R. Brice, Department of Obstetrics and Gynaecology, McMaster University Medical Centre, for all his help and advice.
IZUKAWA, T., KIDD, B. S. L., MOES, C. A. F., TYRRELL, M. J., IVES, E. J., SIMPSON, J. S. & SHANDLING, B., 1978.
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