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ORIGINAL ARTICLE Table of Contents   
Year : 2022  |  Volume : 19  |  Issue : 4  |  Page : 223-227
External and internal parasitic conjoined twinning: Diverse presentation and different surgical challenges

1 Department of Pediatric Surgery, PGIMER, Chandigarh, India
2 Department of Pathology, PGIMER, Chandigarh, India
3 Department of Radiodiagnosis, PGIMER, Chandigarh, India
4 Department of Pathology, St. John's Medical College, Bengaluru, Karnataka, India

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Date of Submission21-May-2021
Date of Decision25-Jul-2021
Date of Acceptance08-Oct-2021
Date of Web Publication19-Aug-2022


Background: Parasitic conjoined twin is a rare but well-known entity with unclear embryopathogenesis. Abnormal conjoined twinning can result in an externally attached parasitic twin (PT), an enclosed foetus in foetu, or a mature teratoma. The treatment requires complete excision and reconstruction of local anatomy which is not always straightforward. Materials and Methods: PT cases presenting over 12 years were analysed. Patients with complete data, histopathological diagnosis and follow-up were included in the study. During follow-up, specific complications and related investigations were considered. Results: A total of five patients at four different sites were identified: two retroperitoneal foetus in foetu and three externally attached PTs which were located in the lumbar region, sacrococcygeal area and on the lower anterior abdominal wall. All patients underwent complete surgical excision. In foetus in foetu cases, the blood supply was directly from the aorta with a short stump while the three externally located ones required meticulous and careful dissection with the reconstruction of local anatomy. Conclusion: Parasitic conjoined twinning can present at different sites and surgical challenges vary accordingly. For surface lesions, reconstruction may be as complicated as excision. Prognosis can be affected by the excellence of anatomical restoration. Long-term follow-up is essential to address problems specific to the site of lesion and method of surgical reconstruction.

Keywords: Embryogenesis, foetus in foetu, mature teratoma, parasitic twin, surgical challenges

How to cite this article:
Menon P, Solanki S, Samujh R, Kakkar N, Bhatia A, Mohanty S, N. Rao K L. External and internal parasitic conjoined twinning: Diverse presentation and different surgical challenges. Afr J Paediatr Surg 2022;19:223-7

How to cite this URL:
Menon P, Solanki S, Samujh R, Kakkar N, Bhatia A, Mohanty S, N. Rao K L. External and internal parasitic conjoined twinning: Diverse presentation and different surgical challenges. Afr J Paediatr Surg [serial online] 2022 [cited 2023 Jan 27];19:223-7. Available from:

   Introduction Top

Parasitic twin (PT) is an extremely rare condition, with an estimated incidence of <0.1 in 100,000 births.[1] Historically, the terminology used in reports of PT has been inconsistent. Spencer defined PT as twins conjoined in one of the same anatomical locations as the more common 'complete' conjoined twins, one twin of the pair is severely defective (the 'parasite') and its counterpart ('autosite') must be mostly intact. The PT spectrum includes the externally attached parasite twin, foetus-in-foetu (FIF) or endo PT and mature teratoma.[2] PT can be detected during antenatal ultrasound (USG) screening. Postnatally, they may have varied presentations: asymptomatic, incidentally detected, symptomatic or obvious visible mass lesion.[3] Although treatment of choice is complete excision, as the site varies, the challenges met during surgeries are different. Here, we are describing PT at four different sites along with their management, surgical challenges, outcome and follow-up.

   Materials and Methods Top

This study was conducted in the department of paediatric surgery of a tertiary care centre. Patients were included from March 2008 to January 2020, and data were collected from record registers maintained by the department. Ethical clearance was obtained from the institute ethics committee (IEC/2020/SPL-821). All patients of PT (external and internal, i.e. FIF) who presented during this time duration were included in the study. Patients with complete clinical details including presentation, pre-operative investigations, histopathological diagnosis and follow-up were included in the study. Patients up to the age of 12 years were included irrespective of gender. Demographic data, clinical presentation, pre-operative investigations including imaging and tumour markers, operative details, post-operative complications, outcome and follow-up were analysed. Patients presenting in the emergency room or routine outpatient department were examined thoroughly and assessed for any immediate intervention. They underwent routine blood investigations such as complete blood count, renal function test and liver function test along with tumour markers including alpha-fetoprotein and human chorionic gonadotropin (βHCG). Radiological investigations were done according to the site of the mass lesion and clinical presentation. In general, plain radiographs were done for all the children as per the location. For intra-abdominal masses, USG was performed initially. Either contrast-enhanced computed tomography (CECT) scan or magnetic resonance imaging (MRI) was done for all the children before undergoing surgery. All patients were kept under routine follow-up, and along with clinical examination, timely radiological investigations and tumour markers were also assessed.

   Results Top

A total of five patients were enrolled in the study. The patients' details and their management are mentioned in [Table 1]. Preoperatively, AFP and βHCG levels were in the normal range in all the cases. In all patients, complete surgical excision of the mass could be achieved without injuring the neighbouring structures. All excised specimens were sent for histopathological examination which was suggestive of PT with the presence of different mature organs. In the last follow-up, none of the patients had any major issues related to the primary lesion or surgery.
Table 1: Patients' detail and their management

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In our first case [S. no. 1, [Table 1] and [Figure 1]], during surgery, the mass was meticulously separated from the neural structures and required a lengthy dissection as it was not easy to distinguish between normal structures and abnormal tumour elements. After complete excision of the large mass in the presence of an open neural canal, closure of the defect was also a challenge. The dura was initially closed followed by reinforcement with lumbosacral fascia. The skin and subcutaneous tissues were also extensively mobilised and closure was achieved. The child is under regular follow-up and doing well.
Figure 1: (a) Pre-operative photograph showing a skin-covered mass lesion with limb formation at the back. The magnetic resonance imaging (b) showing solid (red arrow) and cystic component (black arrow) of the mass lesion and open spinal canal (blue arrow) with the adhesion of nerves with mass. Intraoperative image (c) showing open spinal canal and nerve fibres with mass lesion and excised specimen (d) containing limb, bowel, and mesentery along with soft tissue

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Two patients had retroperitoneal (RP) FIF [S. no. 2 and 3, [Table 1] and [Figure 2]]; in both cases, the mass was very close to the major vessels and was receiving its blood supply directly from the aorta. The supplying vessels were also very short and dissection had to be done close to the aorta.
Figure 2: The contrast-enhanced computed tomography (a) shows solid and cystic mass (black arrow) in the right retroperitoneum, reaching up to midline (red arrow) and displacing major vessels. Excised specimen of the left retroperitoneal foetus in foetu (b) shows the budding limb-like structure (black arrow) and bowel with mesentery

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Our fourth case [S. no. 4, [Table 1] and [Figure 3]] was a pygopagus PT and the mass lesion was at the sacrococcygeal region, close to the anal verge and obstructing the anal opening. The muscle complex was stretched out due to the pedicle of the tumour, which was coursing through it. The anal canal had a common wall with the tumour base and had to be carefully dissected from it. After the excision of the mass, the remaining anal opening was found to be very narrow, the surrounding muscles were very thin and abnormally oriented. The patient required anorectoplasty and muscular reconstruction in the presence of flabby, stretched and imprecise anatomy. Our patient had frequent stools during the 1st year of his life but at present is fully continent at 5 years of age.
Figure 3: Pre-operative image (a) shows an attached mass lesion at the sacrococcygeal region. The contrast-enhanced computed tomography (b) shows attached pedunculated mass from the anal canal region containing long bones. Intraoperative image (c) showing close adherence with the anal canal and stenotic anal opening (black arrow showing feeding tube in the anal opening). Follow-up image (d) of the patient showing healed wound

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The last case [S. no. 5, [Table 1] and [Figure 4]] had very complex anatomy (omphalopagus PT) because of the presence of a large omphalocoele along with the mass and distorted perineal structure. Hence here, the main challenge was the closure of the abdominal muscle defect as well as reconstruction of perineal anatomy. For abdominal wall closure, both rectus muscles were mobilised from the pubic bone and closed in the midline under tension. For genital reconstruction, labial folds were created from the remaining surrounding tissue, maintaining the appropriate position of the urethral and vaginal orifices.
Figure 4: Pre-operative image (a) showing exomphalos (black arrow) and distorted perineum (b) and abnormal vestibule (black arrow). Intraoperative image (c) after the closure of rectus sheath and immediate post-operative image (d) after local reconstruction

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   Discussion Top

The embryopathogenesis of the PT spectrum forms a continuum and they are all variations of abnormal conjoined twinning, with the site of union and the extent of damage (or defect) of one embryo resulting in one of the pathologies.[2]

There are several theories on its origin, with the two major theories being labelled as 'fission' and 'fusion.'. Proponents of the former suggest that incomplete fission of the blastocyst inner cell mass during the primitive streak stage, which occurs 13–15 days post-fertilisation, results in two centres of axial growth that retain a connection at some point.[1] 'Fusion', in contrast, refers to two originally distinct inner cell masses that coalesce secondarily at a later stage.[1] The theory for the development of asymmetry between autosite and parasite after these events was first postulated by Donitz. who proposed that vascular compromise causes the tissue of the PT to become dependent on collaterals derived from the autosite and selective ischemic atrophy of the deprived portion of the parasite's body follows.[1],[4]

In a previous report of two similar cases, the authors have mentioned the attachments of the rachipagus PT to the spinal cord and highlighted the difficulty as well as the importance of untethering and proper dissection of neural elements.[5] Similarly, two cases of RP FIF were reported, wherein the blood supply was arising directly from the aorta as seen in our cases also.[6] One should therefore be very careful during dissection as injury to major vessels can be catastrophic. Second, before ligation of a vessel, one must ensure that it is supplying only the mass and not any nearby organ like the kidney. The latter problem is more likely if FIF is receiving its blood supply from the same area as normal aortic branches such as the celiac trunk, superior mesenteric artery and renal artery.

One report of PT at the sacrococcygeal region was reported in a very low birth weight baby, who was haemodynamically unstable due to the large mass and required emergency surgery as a life-saving procedure.[7] In another case, the mass was not apparent from the outside but presented with a lump over the buttock noticed by the mother. In both cases, a good outcome was reported during the follow-up.[8]

A case of omphalopagus PT in an 11-year-old female child has been reported. The patient had an abdominal mass that was noticed since birth. A computed tomography (CT) scan showed that there was no sharing of any organ with the parasite. The mass was excised completely, and primary closure was achieved. The mass was composed mainly of bowel along with skin, hair, skeletal muscle and cartilage.[9] Another reported case described in a newborn with omphalopagus PT had large omphalocoele and multiple cardiac anomalies, i.e., transposition of great arteries, coarctation of aorta and ventricular septal defect. The patient underwent multiple surgeries. Initially, the rudimentary limb was excised then cardiac surgery was performed followed by laparotomy for gastric perforation repair and at last excision of mass was done. The child had a stormy post-operative course with a long hospital stay (117 days) but eventually was discharged on nasojejunal feeds.[10] In large omphalocoeles, abdominal wall closure is always a challenge. In our case, it was under tension even after extensive mobilisation of muscles, and therefore, the child was kept on a ventilator along with deep sedation. In reported literature, staged closure, use of tissue expander (subcutaneous as well as intraperitoneal) and mesh have been described to overcome tissue deficiency.[11]

Due to overlapping embryopathogenesis, and common histopathological features, there have been many attempts to define external PT, FIF and mature teratoma separately. Spencer suggested that the external PT is a grossly defective foetus, or foetal parts, attached externally to a relatively normal twin in one of the same areas in which intact conjoined twins are united. In FIF, there is a mass enclosed within a distinct sac, covered by skin, recognisable anatomic features and attached to the host by a pedicle containing a few large blood vessels. A teratoma consists of a chaotic mixture of microscopically identifiable tissues, rarely with more differentiation than a well-formed tooth or a portion of the intestine. It is also found within the body of the autosite and is immediately adjacent to the original location of the neural tube or alimentary tract but enclosed in connective tissue with a broad attachment to the surrounding tissue. It is capable of independent growth and may become malignant.[2]

During clinical examination and investigations, often it is not possible to differentiate between teratoma and PT preoperatively. Therefore, in every patient, serum AFP and βHCG should be done. These tumour markers can be normal or high in cases of immature teratoma while cases of PT and mature teratoma always show a normal level. In our study, all five cases had normal tumour markers. As most cases present in the early neonatal period or infancy, it is easier and quicker to perform a CECT. However, as seen in our rachipagus PT [S. no. 1, [Table 1]] where there was the involvement of the spinal cord, MRI was preferred.

In general, most cases have a good outcome after surgery. Few site-specific complications such as tracheostomy in the case of neck PT and ventriculoperitoneal shunt in two cases of intracranial PT have been reported.[12] Malignant transformation of PT has also been reported.[13] We have previously reported a case of partial FIF over the mandible region although that patient did not survive because of associated complex congenital heart anomalies.[14]

These children require long-term follow-up as problems can arise later in life. In our patients, during follow-up, along with clinical examination, radiological investigation in the form of USG was performed for the RP lesions. In both cases, USG was normal at the last follow-up. No CT/MRI was performed for surface lesions as there was no indication during the clinical examination. The problems that could appear related to anatomical reconstruction were also addressed during follow-up such as size of the anal opening and continence status in the case of anorectoplasty, signs of tethered cord in the case of spinal dissection and urethral/vaginal stenosis in the cases where perineal reconstruction was done.

   Conclusion Top

Parasitic conjoined twinning can present at different sites and surgical challenges vary accordingly. For surface lesions, reconstruction may be as complicated as excision. Prognosis can be affected by the excellence of anatomical restoration. Long-term follow-up is essential to address problems specific to the site of lesion and method of surgical reconstruction.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Sharma G, Mobin SS, Lypka M, Urata M. Heteropagus (parasitic) twins: A review. J Pediatr Surg 2010;45:2454-63.  Back to cited text no. 1
Spencer R. Parasitic conjoined twins: External, internal (fetuses in fetu and teratomas), and detached (acardiacs). Clin Anat 2001;14:428-44.  Back to cited text no. 2
Ji Y, Chen S, Zhong L, Jiang X, Jin S, Kong F, et al. Fetus in fetu: Two case reports and literature review. BMC Pediatr 2014;14:88.  Back to cited text no. 3
Anca FA, Negru A, Mihart AE, Grigoriu C, Bohîlțea RE. Special forms in twin pregnancy - asymmetric conjoined twins. J Med Life 2015;8:115-8.  Back to cited text no. 4
Navaei AA, Habibi Z, Moradi E, Nejat F. Parasitic rachipagus twins; report of two cases. Childs Nerv Syst 2015;31:1001-3.  Back to cited text no. 5
Goyal RB, Gupta R, Prabhakar G, Dagla R. Fetus in fetu: Report of two cases. APSP J Case Rep 2014;5:28.  Back to cited text no. 6
Trairongchitmoh C. Sacrococcygeal fetus in fetu. J Pediatr Surg Case Rep 2020;59:101501.  Back to cited text no. 7
Karaman I, Erdoğan D, Ozalevli S, Karaman A, Cavuşoğlu YH, Aslan MK, et al. Fetus in fetu: A report of two cases. J Indian Assoc Pediatr Surg 2008;13:30-2.  Back to cited text no. 8
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Satter E, Tomita S. A case report of an omphalopagus heteropagus (parasitic) twin. J Pediatr Surg 2008;43:E37-9.  Back to cited text no. 9
De Ugarte DA, Boechat MI, Shaw WW, Laks H, Williams H, Atkinson JB. Parasitic omphalopagus complicated by omphalocele and congenital heart disease. J Pediatr Surg 2002;37:1357-8.  Back to cited text no. 10
Shah RS, Parelkar SV, Sanghvi BV, Gupta RK, Mudkhedkar KP. Staged repair of giant exomphalos major using tissue expanders. J Pediatr Surg Case Rep 2016;13:13-7.  Back to cited text no. 11
Prescher LM, Butler WJ, Vachon TA, Henry MC, Latendresse T, Ignacio RC Jr. Fetus in fetu: Review of the literature over the past 15 years. J Pediatr Surg Case Rep 2015;3:554-62.  Back to cited text no. 12
Hopkins KL, Dickson PK, Ball TI, Ricketts RR, O'Shea PA, Abramowsky CR. Fetus-in-fetu with malignant recurrence. J Pediatr Surg 1997;32:1476-9.  Back to cited text no. 13
Madakshira MG, Kakkar N, Menon P. Partial “fetus in fetu”. Indian J Pathol Microbiol 2018;61:626-7.  Back to cited text no. 14
[PUBMED]  [Full text]  

Correspondence Address:
Dr. Shailesh Solanki
Block 5D, Room No. 5422, Advanced Pediatric Centre, PGIMER, Sector 12, Chandigarh - 160 012
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ajps.ajps_78_21

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