External and internal parasitic conjoined twinning: Diverse presentation and different surgical challenges

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.