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|Year : 2020 | Volume
| Issue : 6 | Page : 1453-1455
Heteropagus Twins: A Tale of Two
Akash B Pati1, Santosh K Mahalik1, Suprava Naik2, Kanishka Das1
1 Department of Pediatric Surgery, All India Institute of Medical Sciences, Bhubaneswar, Odisha, India
2 Department of Radiodiagnosis, All India Institute of Medical Sciences, Bhubaneswar, Odisha, India
|Date of Web Publication||19-Dec-2020|
Dr. Kanishka Das
Department of Pediatric Surgery, All India Institute of Medical Sciences, Bhubaneswar, Odisha
Source of Support: None, Conflict of Interest: None
Parasitic twin is a rare occurrence, with rachispagus being the rarest. The surgical approach and timing are not standardized. We describe the management of two cases of rachispagus and review the sparse literature on this entity. Both cases were operated early because of the social burden on the family as well as difficulty in nursing care. The first patient had associated major systemic malformations in the autosite (cerebral, spinal and cardiac), and succumbed in the postoperative period. The entity was isolated in the second who is doing well.
Keywords: Abortive twinning, accessory limbs, heteropagus twins, parasitic twins, rachispagus
Key Messages: The outcome of the management of heteropagus twins depends upon the associated malformations in the autosite.
The vascular pedicle to parasitic twins should be imaged preoperatively and controlled during surgery.
|How to cite this article:|
Pati AB, Mahalik SK, Naik S, Das K. Heteropagus Twins: A Tale of Two. Neurol India 2020;68:1453-5
Monozygotic twins represent a spectrum from two separate twins having single amnion, chorion, or placenta to conjoined twins. The latter may be a diplopagus (symmetrically developed, classified according to the site of fusion) or heteropagus (asymmetrically developed, underdeveloped twin being parasitic on the developed twin or autosite). The term heteropagus twin was coined by Potter and Craig, whereas Willis described it as parasitic twins. The acardiac fetus (parasite) thrives on the normal fetus (autosite) through a vascular isthmus. We detail the management of two heteropagus twins where the parasite was attached to the dorsum of the autosite.
| » Case Details|| |
Case no 1
A 3 kg, term, female neonate of a fourth gravida mother with two first trimester miscarriage had accessory limbs behind the neck [Figure 1]a. She had tachypnoea, a left sternal systolic murmur, and cardiomegaly [Figure 1]b. Echocardiography revealed mesocardia, atrial and ventricular septal defects, left to right shunting, and normal biventricular function. Two accessory limbs articulated at the upper cervical vertebrae. Other features included posterior cranial fossa malformation and cervical spinal dysraphism [Figure 1]c, right pulmonary hypoplasia, and dextrocardia. The respiratory embarrassment necessitated mechanical ventilation. Besides the cardiac anomaly, an increased circulatory load because of the parasitic limb was suspected. Disarticulation of the accessory limbs and repair of dorsal meningomyelocele was performed. The superficial soft tissue reconstruction was curtailed because of excessive hemorrhage. She remained ventilator-dependent for weeks and developed chronic lung disease, pulmonary hypertension, progressive cerebral edema, and pericardial effusion before her demise on postoperative day 35.
|Figure 1: (a) Accessory limbs articulated behind the neck. (b) Chest skiagram showing cardiomegaly and the soft tissue shadow of the longer accessory limb (arrow) (c) Sagittal T1W magnetic resonance imaging of the brain and cervical spine shows a large defect in the occipital and upper cervical region with stretching and posterior displacement of the medulla (arrowhead) and herniation of neural elements through the defect. Accessory limb embedded in a fatty mass is seen in the upper cervical region posteriorly (arrow)|
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Case no. 2
A 6-month, female, born at term by normal delivery presented with an extra limb attached to the lower back since birth. A 10 Õ 10 cm midline, lumbosacral fatty mass had a limb protruding from its left half. There were patches of vascular malformation and a rudimentary phallic structure on the mass [Figure 2]a. The accessory limb was leg. There were no neurological deficits of the limb, bowel, or bladder in the autosite. Magnetic resonance imaging (MRI) showed a lipomyelomenigocele at L4–L5 and the adjacent accessory limb [Figure 2]b. The spinal cord buckled into the fatty mass and was tethered. The posterior cranial fossa and the rest of the spinal cord were normal. The limb was disarticulated after ligation of a stout, axial feeding iliofemoral vessel [Figure 2]c on a flat bone at the base of the parasite mimicking the iliac bone. The cord was detethered, reposited into the spinal canal, and the spinal dysraphism repaired. Transient postoperative neurogenic bladder and bowel features were managed with clean intermittent catheterization and daily enemas, respectively, till recovery for 3 months. At a 10-month follow-up, she is asymptomatic and thriving well.
|Figure 2: (a) Limb protruding from the lumbosacral fatty mass with rudimentary phallus (arrowhead). (b) Axial T2W magnetic resonance imaging at the level of the lumbar spine shows a defect in the posterior element of the L5 vertebra (arrow) with herniation of neural elements and fat through the defect. There is also a rudimentary limb in fatty mass in this region (short arrow). (c) Stout axial feeding vessel (arrow) supplying the accessory limb|
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| » Discussion|| |
Inconsistent terminology and reporting limit the accuracy of epidemiologic data in heteropagus twins. The incidence varies across the Atlantic from 0.05 to 0.1 per 1,00,000 live births in the United States to 0.02 per 1,00,000 live births in Europe. The embryo pathology of heteropagus twins is attributed to the failure of a complete division of the embryonic disc after day 13 of fertilization in monozygotic twin pregnancy, and an ischemic insult causes selective somatic atrophy of the dependent parasite. Hypoplastic vascular pedicles traversing from the autosite into the parasite are identified during surgical separation. Antenatal ultrasonography detects the twinning and associated autosite malformations; these determine the prognosis and dictate physician counseling, neither case described here was diagnosed antenatally.
A review of 39 cases of heteropagus twinning over a decade cites omphalopagus as the most common (59%) and rachispagus as the least common (10%) forms of the anomaly.In a series of 1200 conjoined twins, of 21 rachispagus, 20 were parasitic and 1 was complete with the dorsal union of 2 fully developed infants. Both our cases were rachispagus and, like most earlier cases, of the female gender. Limbs, partial or complete, are the most common structure duplicated on a rachispagus parasite, the cervicothoracic parasites feature upper limb—shoulder girdle—while the lumbosacral parasites bear the lower limb—pelvic girdle. The second parasite had an iliac-like bone that articulated with the autosite at its base. Vascular cutaneous lesions like the present case have been described earlier; however, the phallus-like structure did not have erectile tissue.
The limbs (15%) may have muscles,, some even with contractility. Both parasite limbs had skeletal muscle but no perceptible movement, presumably because of a lack of innervation. Spinal defects at the site of attachment are common in rachispagus twinning, but associated diastematomyelia and tethered cord syndrome are occasionally present. Besides a lipoma and an adjacent neural tube defect in both cases, the second had a tethering of the cord too.
Compared with conjoined twins, sharing of organs and vascularity with the autosite is less extensive in heteropagus twins and, hence, separation is technically easier. Combinations of imaging modalities (ultrasound, computed tomography, MRI, and echocardiography) are used to detect associated major systemic (cardiac, pulmonary, and central nervous) malformations and plan surgical separation with the conservation of autosite tissues to limit functional deficits. Unlike the second case, with a manageable tethered cord, the autosite in the first twin had systemic malformations that precluded survival. Preoperative localization of origin and course of the parasitic vascular pedicle from the autosite has been attempted with doppler ultrasound/MR angiography (MRA). Although the MRA did not identify the exact origin in our cases, a stout axial feeding vessel from the paravertebral perforators nourished the parasitic limb in the second case; we did not find such a feeder in the first.
Standard indications for separation of parasitic twins include respiratory distress, growth failure, and cardiac failure in the autosite; others are cosmetic and psychosocial reasons. An early definitive procedure after detailed imaging is advisable. Although parasitic twins can live into adolescence and beyond, most separations had been carried out in infancy in a single stage or multiple stages. In the first case, we staged the procedure because of the failure to identify a definite feeding vessel and intraoperative hemorrhage. The defect created by the removal of the parasite may require an additional procedure for closure.
Besides technical factors, the outcome of heteropagus twins depends upon the autosite malformations, especially cardiovascular and pulmonary. The morbidity can be limited by meticulous preservation of the autosite tissues; the neuropraxia after the cord detethering in the second case gradually resolved over weeks postoperatively. Long-term follow-up detects regrowth at the site of attachment, inclusion tumors (teratoma), and incisional hernias.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]