Rachipagus - Twins fused dorsally above the sacrum, involving different segments of the column. This type is extremely rare, and I have yet to find a set on any of my searches.
Rare forms of conjoined twins, having different patterns:
Parasitic twins: Asymmetrical conjoined twins, one twin being small, less formed, and dependent upon the other.
Fetus in fetu: Situation in which an imperfect fetus is contained completely within the body of its sibling.
An attempt to standardise and classify conjoined twins according to the external forms of conjunction has been proposed by Leacham (Table 1). (2)
|| Joined at chest
|| Joined at head and chest
|| Single trunk and two heads
|| Joined at head
|| Joined at abdomen
|| Dorsal union of head and trunk
|| Joined at chest and abdomen
Classification of dicephalus:
• dicephalus dipus dibrachius: a fetus with two heads but only two feet and two arms.
• dicephalus dipus tetrabrachius: conjoined twins with only two legs, but with varying degrees of fusion of the upper trunk, each component having a head and pair of arms.
• dicephalus dipus tribrachius: a fetus with two heads, two feet, but with a median third arm or arm rudiment.
• dicephalus dipygus, anakatadidymus.
• dicephalus parasiticus, desmiognathus.
• dicephalus tripus tribrachius: a fetus with a common trunk, but with two heads, three arms, and three legs, the third limbs being either rudimentary or complete.
Implications for targeted examinations: Antenatal diagnosis by ultrasound is possible in modern day obstetrics. Conjoined twins should be suspected in all monochorionic, monoamniotic twin pregnancies, and careful sonographic assessment should be performed to identify the presence of shared fetal organs. (6) Ultrasonographic identification of any of the following classical signs may suggest the diagnosis: lack of separating membrane, inability to separate fetal bodies, 3 or more vessels in cord, or alternatively 2-vessels cord (5), both fetal heads in the same plane, unusual backward flexion of the cervical spine, no change in the relative position after maternal movement and manual manipulations and inability to separate fetal bodies after careful observation. (7)
Differential diagnosis: The condition should be differentiated with following: multiple gestation, teratoma, cystic gyroma, neoplasm, parasitic twin.
Associated anomalies: Among the most frequent anomalies associated with conjoined twinning are duplication of visceral organs, omphalocele, facial clefts, meningomyelocele and imperforate anus (10). Cardiac defects are the frequently reported findings as well.
Prognosis: There are reliable reports of unseparated dicephali reaching maturity; 1 pair (the Tocci brothers) reached at least 34 years of age. In the absence of concomitant cardiac, pulmonary, and intestinal malformations, dicephalus conjoined twins may well attain adulthood. This appears to be unrelated to whether they have 4 (dicephalus tetrabrachius) or 3 (dicephalus tribrachius) arms at birth.(4) Prognosis, obstetric management, and treatment planning are determined by degree of fusion and extent of joining of fetal organs(9).
Recurrence risk: appears to be negligible.
Management: Prior to 24 weeks of gestation vaginal delivery is appropriate. Cesarean section is recommended in most third-trimester deliveries because of the high incidence of dystocia and resultant fetal damage and risk of maternal morbidity. (9)
1 - Conjoined Twins, by Rowena Spencer, published by Johns Hopkins Press, Baltimore, MD.
2- Gerlis LM, Seo JW, Ho SY, Chi JG. Morphology of the cardiovascular system in conjoined twins: spatial and sequential segmental arrangements in 36 cases. Teratology. 1993; 47:91- 108.
3- Finberg HJ. Ultrasound Evaluation In Multiple Gestation. In Callen"s Ultrasonography in Obstetrics and Gynecology:Harcourt Publishers 3rd edition,1994;Chapter 8:121-124.
4- Bondeson J. Kennedy Institute of Rheumatology, Hammersmith, London, England. Copyright 2001 by W.B. Saunders Company.
5-Koontz, WL, Herbert, WN, Seeds, JW, Cephalo, RC: Ultrasonography in the diagnosis of conjoined twins; A report of two cases. J Reprod Med 28:627, 1983.
6- Levi CS, Lyons EA, Martel MJ, Dashefsky SM, Holt SC. Sonography in the diagnosis and management of Multifetal Pregnancy. In Rumack"s Diagnostic Ultrasound: St. Louis, Mosby- Year Book Inc,1997;Chapter 35: 1062-1065.
7- Kalchbrenner M, Weiner S, Templeton J, Losure TA. Prenatal Ultrasound Diagnosis of Thoracophagus Conjoined Twins. J Clin Ultrasound 1987; 15: 59-63.
8- Y. Goldberg, I. Ben-Shlomo, E. Weiner and E. Shalev , First trimester diagnosis of conjoined twins in a triplet pregnancy after IVF and ICSI: Case report Human Reproduction, Vol. 15, No. 6, 1413-1415, June 2000
9- Tandon R, Sterns LP, Edwards JE. Thoracopagus Twins. Arch Pathol 1974; 98: 248-251.
10-Romero R, Pilu G, Jeanty P et al: Prenatal Diagnosis of Congenital Anomalies. Norwalk, CT, Appleton & Lange, 1988, pp 405-409.