Ischiopagus parasitic twin

A rare case report

Abstract

Parasitic conjoined twinning is a rare clinical entity with a reported incidence of only 1/1 million births. The most common site of attachment of the parasite is epigastrium. The parasitic attachment at ischium is among the least common subtypes. Here, we report a case of ischiopagus parasitic twin with a favorable outcome. The host twin had no major anomaly, and the twins did not share any organ. Surgical separation of parasitic twin and primary closure of the defect of autosite was done without challenges. The aim of this communication is to add to the literature another rare case of parasitic twinning and to highlight the fact that ischiopagus parasitic twinning although, rare, has a good prognosis in the absence of associated anomalies.

INTRODUCTION

Conjoined twin, a subset of monozygotic twinning, is a rare entity with an estimated incidence varying from 1 in 50,000 to 1 in 100,000 live births.[¹] In asymmetric conjoined twins, also termed as heteropagus or parasitic conjoined twins, the parasite may be attached to the visible surface of the autosite or inside it. The asymmetrical conjoined twining is extremely rare with an incidence of about 1/million births.[²] Ischiopagus parasitic twins are among the rarest in the heteropagus twins.[³] Herein, we report a case of ischiopagus parasitic twins.

CASE REPORT

A full term male newborn baby weighing 3.4 kg was delivered per vaginam to a 21-year-old primigravida in a primary health center. The baby cried immediately after birth and required no resuscitation. Apgar scores at 1 and 5 min after birth were 8/10 and 9/10 respectively. There was a huge mass attached to the right hip of the baby. The newborn baby was referred to our center for further investigations and treatment. There was a history of epilepsy in mother since childhood, and she was on phenytoin, 300 mg daily, which was discontinued after confirmation of pregnancy. No seizure activity was noticed during pregnancy. There was a perinatal history of mild pregnancy-induced hypertension in the mother.

Examination revealed a full term neonate with no facial dysmorphism. A mass was found attached to the right hip of the neonate. The anal opening and genitals were normal. There was no urinary or anal incontinence. There was no neurological deficit in the lower limbs of the baby. The mass measured 15 cm × 15 cm in size and consisted of two rudimentary lower limbs and one upper limb bud [Figure 1]. It was firm in consistency. The systemic examination revealed no abnormality. Plain radiograph of this mass showed limb bones, few metatarsals and phalanges [Figure 2]. There was no intra-abdominal attachment. Ultrasonography of chest, skull, spine and abdomen was normal. Echocardiography of the neonate revealed no abnormality. Computed tomographic scan revealed a parasitic twin comprising lower limbs attached to the right hip of the autosite by muscular attachment behind the anal canal and below the sacrum [Figure 3]. No bony attachment was visualized between the autosite and parasite. Upper limb bud appeared as a soft tissue projection on computed tomography.

Figure 1: The separated parasite showing two rudimentary lower limbs and an upper limb bud

Figure 2: Radiograph of the conjoined twin revealing attachment of the parasite to right hip of autosite in lateral view

Figure 3: Computed tomography of the parasite showing metatarsals and phalanges

A diagnosis of ischiopagus parasitic twin was made. After an initial stabilization, the patient had complete surgical excision of the parasite under general anesthesia and there were no challenges with wound closure. Histopathological examination of the excised mass confirmed an ischiopagus parasitic twin. The postoperative recovery was uneventful, and the baby did well in the follow-up period.

DISCUSSION

Several classifications of embryonic duplications have been proposed. Most of them classified the duplications as free monozygotic twins, complete symmetric conjoined twins, incomplete symmetric conjoined twins and unequal asymmetric conjoined twins, commonly known as heteropagus.[⁴] A well-developed twin is termed as autosite, and its counterpart is known as the parasite in the heterozygous variety.

In conjoined twinning, the site of fusion of the twins can be at the chest (thoracopagus), umbilicus (omphalopagus), rump (pyopagus), hip (ischiopagus), cranium (craniopagus), side (parapagus), head (cephalopagus) or spine (rachipagus).[⁵] Thoracopagus is the most common form accounting for 42% of cases and ischiopagus conjoined twinning accounts only for 1.8% of the cases.[¹] Only one-fifth of cases of ischiopagus conjoined twins present as parasitic twinning.[⁶]

A recent review of 39 cases of parasitic twins reported in 10-year interval described epigastric heteropagus as the most common anatomical type (59%). Ischiopagus parasitic twins accounted only for 5 of the 39 reports (13%).[³] Amuabunos etal. reviewed the literature of conjoined twins in Nigeria over the last 76 years (1935-2012) and found only 21 cases of conjoined twins. Another eight cases were found in Nigerian news reports. Out of these 28 cases, only two were of heteropagus variety.[⁷] Symmetric conjoined twins are monozygotic, monoamniotic, and monochorionic. They are always of the same gender, with a 3:1 female preponderance. The sex difference is less pronounced in heteropagus twins with a reported female preponderance of 51% to 54%.[³] The autosite in the reported case was of male gender.

The etiology of conjoined twins is complicated. Two major theories have been proposed - fission theory and the fusion theory. According to fission theory, incomplete division of the embryo occurs which is followed by 14-15 days after fertilization.[⁸] Whereas fusion theory states that two heterozygotic embryos fuse together at the end of 2 ^nd week of gestation to form a common embryonical structure containing two embryonic discs but a single yolk sac.[⁹] Long-term usage of contraceptive drugs, abnormal calcium metabolism and extremely underweight woman with ovulatory dysfunctions are suspected in etiology.[¹⁰] Studies analyzing both symmetric and asymmetric conjoined twins found no effect of maternal age, parity and consanguinity. In the index case, there is the history of prolonged antenatal exposure to phenytoin which is known to interfere with calcium metabolism.

Various congenital defects such as anencephaly, cleft lip, cleft palate, lumbosacral meningomyelocele, cardiac anomalies, gastrointestinal and urogenital anomalies may be associated with conjoined twins. Abdominal wall and spinal defects are commonly seen in omphalopagus and rachipagus twins, respectively.[¹¹] There was no such association in the index case.

Antenatal diagnosis of parasitic twinning plays an important role in the management so that the plan for mode of delivery can be decided as per the size and location of parasite. A severely affected or malformed autosite can be terminated at appropriate time if indicated. Na'aya etal. emphasized the need of antenatal ultrasonography for early diagnosis and management of parasitic twinning.[¹²] The diagnosis of heteropagus twins can be made during the antenatal period by ultrasonography or in the postnatal period by radiography, ultrasonography, computed tomography, magnetic resonance imaging or histopathology of the separated mass. The imaging studies in the preoperative period defines the extent of parasitic organs that may reside within the autosite. Echocardiography is often necessary in case of thoracopagus and omphalopagus as 25% to 39% of them have associated cardiac defects.[³] Abnormal vascular communications and previously unidentified anomalies may be seen during surgery. The complex nature of the presentation of parasitic twinning demand an integrated team approach for successful outcome. The inputs from pediatrician, pediatric surgeon, radiologist, anesthetist, cardiologist and thoracic vascular surgeon may be needed at various stages of management of this rare clinical entity.

The outcome is more favorable in cases of heteropagus twins as compared to symmetric conjoined twins because of less extensive vascular and visceral connections in the former. The ultimate survival, however, depends upon the associated anomalies especially the cardiac defects. The autosite, in the absence of a major cardiac defect, usually have a good prognosis following a successful separation surgery. The index patient did fairly well in follow-up.

CONCLUSION

Ischiopagus is among the rarest of the conjoined twins. A team approach is required in the management of parasitic conjoined twins and outcome is usually good in the absence of other associated anomalies.

Source of Support:

Nil

Conflict of Interest:

None declared.