|Year : 2016 | Volume
| Issue : 2 | Page : 130-132
Parasitic twins: Report of two cases
Ibrahim Aliyu1, Mohammad Aminu Mohammad2, Anyanwu Lofty-John Chukwuemeka2
1 Department of Paediatrics, Paediatric Surgery Unit, Aminu Kano Teaching Hospital, Bayero University, Kano, Kano State, Nigeria
2 Department of Surgery, Paediatric Surgery Unit, Aminu Kano Teaching Hospital, Bayero University, Kano, Kano State, Nigeria
|Date of Web Publication||31-Aug-2016|
Department of Paediatrics, Aminu Kano Teaching Hospital, Bayero University, Kano, Kano State
Source of Support: None, Conflict of Interest: None
Parasitic twin is a rare malformation, which involves two fetuses attached to each other, whereby one of the pair is viable and develops into a mature embryo (the host twin) called the autosite, while the second twin (parasite) is usually nonviable, but survives on the host twin; the site and extend of their attachment are varied and may be associated with other congenital malformations. Its exact cause is not completely understood. Though, it has been reported in many countries, there is dearth of information on its occurrence in Nigeria. Therefore, we report two cases of parasitic twins seen in our institution. The first case had an extra-limb, scrotal mass projecting from the anterior abdominal wall, which also had an anterior abdominal wall defect below the extra-limb, while the second case had a sacroccoygeal mass which was a duplicate gluteal mass with malformed lower limb, digit with a toe nail projecting from it and an atrophic scrotal skin attached. Both cases had chest, spinal X-rays and abdominal ultrasounds, which excluded any other malformation. They had successful surgical excision of parasites and are being followed-up in the surgical clinic both having appropriate developmental milestones.
Keywords: Autosite, congenital malformations, fetus in fetu, host twin, parasitic twins
|How to cite this article:|
Aliyu I, Mohammad MA, Chukwuemeka AL. Parasitic twins: Report of two cases. J Mahatma Gandhi Inst Med Sci 2016;21:130-2
| Introduction|| |
Parasitic twinning is a rare malformation characterized by a twin living in or on another host twin called the autosite. It is a product of monozygotic diamniotic twinning process whereby the parasitic twin stops developing, but still remains attached and survives on the host twin; it is essentially due to an incomplete and an unequal division of a fertilized ovum or blastocyst with one of the pair developing into a mature embryo while the parasite remains attached and underdeveloped. Why this occurs is not completely understood; however, two reasons namely the teratoma and the parasitic twin hypotheses have been proposed. It has a wide spectrum of clinical presentations with the parasite twin varying from vestigial primitive tissue to well-formed organs. Common sites of attachment are the retroperitonum in about 80% of cases while other sites such as the gastrointestinal tract, the limbs, and anterior abdominal wall had been reported; however, involvement of the back is a rare occurrence., So far, there is no report of this malformation from Nigeria to the best of the authors' knowledge. Therefore, we report two cases of parasitic twins successfully managed in Aminu Kano Teaching Hospital, Kano, Nigeria.
| Case Reports|| |
The first case was a male child seen on the 1st day of life with an extra-limb, scrotal mass projecting from the anterior abdominal wall, which also had an anterior abdominal wall defect below the extra-limb. The child was delivered at term to a 33-year-old mother of five children in a nonconsanguineous marriage setting. There was no family history of similar malformation or twin pregnancy. She never had any antenatal care and the delivery was spontaneous vertex delivery; the extra-limb was a lower limb with well-formed foot and five toes with nails, but it was nonfunctional and the anterior abdominal wall defect was partly covered with skin and a thickened membrane [Figure 1]. Radiograph of the limb showed calcified bones; abdominal ultrasound, chest and spinal X-rays, did not reveal any other abnormality. The diagnosis of parasitic twin with omphalocele major was made. The patient had surgical excision of the extra-limb which was also attached to the lower anterior thoracic wall; furthermore, the scrotal skin and redundant skin were also excised and the margin of the omphalocele was approximated.
The second case was also a male child first seen at the age of 3 months with the complaint of a mass at the lower back which was noticed since birth. The mass had been increasing in size. He was born to a monogamous family of three in a nonconsangiounous family setting; there was no family history of similar malformation. The mass which was a duplicate gluteal mass [Figure 2] was located at the sacroccygeal area, with a malformed lower limb, digit, and a nail projecting from it; it also had an atrophic scrotal skin attached. Abdominal ultrasound, chest, and spinal X-rays were normal. The mass was also successfully excised.
Both cases were being followed-up in the pediatric surgical unit for the past 2 and 1 year, respectively and they have appropriate developmental milestones for age.
| Discussion|| |
Parasitic twinning is a rare event with an estimated incidence of 1 in 500,000 live births. Common sites of attachment include the anterior abdomen, as was seen in our first case; the chest wall as well as the back may be involved, our second case involved the sacroccygeal region.
The controversy and confusion in distinguishing parasitic twin from a highly organized (differentiated) teratoma, especially when it affects the sacroccygeal region still rages on. Though, it may be difficult distinguishing highly organized teratoma from a parasitic twin some authors believe that both are the outcome of the same mechanism; while some may result in normal twinning, others result in conjoined symmetrical twins, asymmetrical twins, parasitic twins, fetus in fetu or teratomas. However, others authors have a different opinion and believe that a teratoma is a true neoplasm therefore have the risk of malignant spread if not properly managed. Furthermore, when spinal column or somatic distribution of human parts are present, teratoma is unlikely, but rather considered an amorphous fetus; and they believe parasitic twins and teratomas are unrelated. Though, there are reports of parasitic twins with absent spinal column; most authors agree that cases with highly developed organs are likely parasitic twins than highly differentiated teratomas. Furthermore, teratomas are commonly associated with spinal dysrraphism, but Peng and Li  had reported a case of spinal dysrraphism associated with parasitic twin, this makes the debate unending. However, our cases lacked spinal column, but they both had well-organized limbs with digits and nails indicative of high level of organogenesis which is not often associated with teratoma therefore, this made them parasitic twins.
Confusion still prevails on the use of terminologies associated with this malformation. While some authors still use parasitic twins and fetus in fetu interchangeably some restrict the use of the term to “ectoparasites” while fetus in fetu to those parasitic twins enclosed within the body of the autosite. Therefore, there is a need for a consensus stating a clear definition of terms, which will foster better understanding and reporting of this anomaly.
Though magnetic resonance imaging and computer tomography scan were not done, no other associated defect were observed and they improved remarkably after successful surgical resection of the parasites with normal neurodevelopment milestones.
| Conclusion|| |
Parasitic twins are rare, their sites and extent of attachment to the host twins varies. We have reported two cases who improved remarkably following successful excision of the “ectoparasitic” twins.
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[Figure 1], [Figure 2]