Urological problems in conjoined twins


Mr Wilcox Department of Urology, Great Ormond Street Children’s Hospital NHS Trust, Great Ormond Street, London WC1N 3JH, UK.



 To review the urological abnormalities in conjoined twins, a rare congenital abnormality arising from an incomplete separation of a pair of monozygotic twins, and who can be joined from the head to the pelvis with varying degrees of union.

Patients and methods

 The records and urological anomalies of conjoined twins presenting from 1985 to 1995 were reviewed retrospectively and the management and surgical reconstruction described.


 Seven of 11 sets of conjoined twins underwent surgical exploration. Complex urological problems occurred in all twins with omphalo-ischiopagus. The urological anomalies were: Set 1; both twins had one lateral crossed fused renal ectopia with uncrossed ureters draining into a single bladder with one urethra. They had one set of genitalia. Each twin received one crossed fused ectopic kidney, half the bladder and genitalia, with one retaining the urethra and one a vesicostomy. Set 2; these twins had four kidneys (two lateral and two central that were fused), four ureters (two of which crossed) and these drained into two sagittal bladders that emptied by one urethra associated with a single set of external genitalia containing three corpora cavernosa. At separation, the crossed ureters were re-routed, each received a bladder and the genitalia were split. Set 3; there were four kidneys with two crossed ureters draining into two collateral bladders, there was a partial duplication of the urethra and a single hypospadiac penis. After separation, each had kidneys draining into a bladder, one received the urethra and external genitalia, and one a urostomy.


 Complex urological problems occur in conjoined twins, although restricted to those with pelvic fusion (ischiopagus). Assessment and treatment needs to be individualised and overseen by a surgeon with experience in complex urology.


Conjoined twins are rare, with an estimated incidence of 1 in 50 000 live births [ 1], with most being female [ 2]. Conjoined twins are monozygotic, monochorionic twins, in whom there is incomplete separation of the inner cell mass at around 13–15 days of gestation [ 3]. The classification of conjoined twins depends on where they are joined: thoracopagus (thorax), omphalopagus (umbilicus), pyopagus (buttocks), ischiopagus (ischium), and craniopagus (cranium). In addition, the twins can be further classified according to the number of lower limbs present, i.e. tetrapus (four), tripus (three) and bipus (two). We report our experience with urological anomalies in conjoined twins treated between 1985 and 1995.

Patients and methods

Between 1985 and 1995, seven sets of conjoined twins were surgically separated at Great Ormond Street Children’s Hospital. Their notes were reviewed and urological anomalies were encountered in three sets of twins. All three were joined at the pelvis (ischiopagus). This report describes the urological anomalies and the specific features relevant to the management of their urological problems.

 All three sets of twins were delivered by Caesarean section at an outside hospital and referred for separation. All the twins were extensively investigated before the operation. Investigation of the genitourinary tract included ultrasonography, micturating cysto-urethrography, isotope renography, IVU, CT, MRI and cysto-urethroscopy.

 Planning for the separation requires almost military precision and a multidisciplinary approach. At the planning meetings, anaesthetists and surgeons from cardiothoracic, general paediatric, plastic and urology departments were present. In addition, ward and theatre nurses, as well as therapists and managers, were involved in the organization. The operation required two operating theatres and two sets of theatre personnel. Both twins were anaesthetized simultaneously and individually monitored. Individual surgeons performed their specific tasks co-ordinated by a general paediatric surgeon. After separation, each twin was moved to their own operating suite and concurrent reconstruction was continued. The specific urological problems of each set of twins will be reported.

Twin pair 1

A female set, brachio-thoraco-omphalo-ischiopagus bipus twins, were separated at 3 years of age [ 4] (Fig. 1a). The urological anomalies were that twin 1 had a lateral pelvic crossed fused ectopic kidney and twin 2 had a single lateral normally placed kidney. These kidneys drained in to a single shared bladder, which emptied via a single urethra (Fig. 1b). The twins shared a single vagina and uterus, and each twin had a fallopian tube associated with one ovary. Twin 2 had an additional pelvic ovary. At separation twin 1 received most of the bladder and the urethra, twin 2 had the remaining bladder tubularized and exteriorized as a vesicostomy (Fig. 1c). The internal and external genitalia were bisected in a sagittal plane and repaired. Despite the use of pre-operative tissue expanders, skin closure was only possible using prolene mesh (Fig. 1d1 a, Conjoined twin pair 1). Post-operatively twin 2 died on the third day, probably secondary to cardiac insufficiency. Twin 1 is currently 8 years old and mobile with an artificial limb. She has urinary control, with normal renal function.

Figure 1 a, Conjoined twin pair 1.

Figure 1 a, Conjoined twin pair 1.

before separation. A schematic diagram illustrates b, the urological anomalies before and c, the urological situation after separation; d, a conjoined twin immediately after separation, with the prolene mesh allowing closure visible.

Twin pair 2

A male set, omphalo-ischiopagus bipus twins were separated at 10 months of age (Fig. 2a). Each twin had a normally placed lateral kidney, the medial kidneys had fused in the midline and the ureters draining the midline kidneys crossed to the contralateral bladder. There were two bladders, which were sagittally placed and drained by a partially duplicated urethra (Fig. 2b). There was one set of external genitalia containing three corpora cavernosa. Each twin had one intrascrotal and one intra-abdominal testicle. At separation each twin received two kidneys, the lateral one and the divided fused midline kidney; this ureter was re-routed into the ipsilateral bladder. The bladders were divided in a sagittal plane with each twin receiving one half of each bladder and a urethra (Fig. 2c2 a, Conjoined twin pair2). Twin 1 received one corpora cavernosa and has a ‘lateral’ epispadiac penis and two testicles, one intra-abdominal. Twin 2 received two corpora cavernosa and two testicles. Closure was only possible using prolene mesh. Twin 2 unfortunately died one year after separation from aspiration of a foreign body. At that time his midline kidney had VUR and contributed 12% of renal function. The bladder was poorly contractile but did empty. As he was less than 2 years of age, urinary continence could not be assessed. He had a good cosmetic result from the genital reconstruction. Twin 1 is now 4 years old and has recently been fitted with an artificial limb. His midline kidney contributes 37% of the renal function and he has bilateral VUR. He has recurrent UTIs which are partially controlled with continuous antibiotic prophylaxis. Recently he has been shown to have ureteric stones which will require surgical removal. At present he has no urinary control despite a good bladder neck on cystoscopy. He is awaiting stone removal and further genital reconstruction.

Figure 2 a, Conjoined twin pair2.

Figure 2 a, Conjoined twin pair2.

before separation. A schematic diagram illustrates b, the urological anomalies before and c, the urological situation after separation.

Twin pair 3

A male set, omphalo-ischiopagus tripus twins, were separated at 8 months of age (Fig. 3a). Each twin had two kidneys, with one of the ureters from each twin crossed and inserting into the contralateral bladder. Both kidneys in twin 2 were duplex. The bladders were collateral and each drained by its own urethra. The two urethrae joined, ending as a single hypospadiac urethra. Twin 1 also had a colo-urethral fistula (Fig. 3b). The twins shared one set of external genitalia. On separation, each twin received two kidneys and a bladder. In twin 1 the crossed ureter was disconnected and re-routed as a right-to-left transuretero-ureterostomy, the colo-urethral fistula was divided and this twin received the external genitalia. Twin 2 had the bladder neck divided and a urostomy formed from the crossed ureter was disconnected and re-implanted into the bladder; twin 2 had no external genitalia (Fig. 3c). Post-operatively both twins survived, are now mobile on artificial limbs and are currently 10 years old. Twin 1 has subsequently had Bioplastique injected into the bladder neck, but unfortunately is still incontinent of urine. Twin 2 has had a Casale tube created from the bladder and bladder emptying is currently controlled by suprapubic catheterization [ 5].

Figure 3 a,Conjoined twin pair 3.

Figure 3 a,Conjoined twin pair 3.

before separation. A schematic diagram b, the urological anomalies before and c, the urological situation after separation.


Conjoined twins are rare and with the increasing ability of prenatal ultrasonography to detect the anomaly, it is likely that the number of live newborns with this problem will further decrease. The extensive investigations and separation of a set of conjoined twins requires a meticulous and multidisciplinary approach, with one surgeon co-ordinating the management. Many investigations are necessary but need to be tailored to each set. MRI has been shown to provide excellent anatomical imaging [ 4, 6] and angiography has been helpful in defining specific vascular supply. Further investigation of the urinary tract has included ultrasonography, isotope renography, micturating cysto-urethrography and cystoscopy.

 Separation is rarely an urgent undertaking and needs to be carefully planned. The ideal time for separation is within the first year, as this enables the necessary investigations to be performed. Delaying separation into early childhood will inevitably result in both increased postural deformities and psychological problems [ 4], with no benefit. Planning is crucial for success; meetings are held in which all medical, nursing, therapy and administrative teams are present, so ensuring that the operation can run smoothly.

 Of the seven sets of twins treated in the last 10 years, only three had urological problems. These were all joined at the pelvis. In these cases they were all ischiopagus but other reports have shown urological abnormalities with pyopagus sets [ 7, 8]. These combined cases indicate that urological abnormalities are restricted only to those in whom the pelvis is joined, either ischiopagus or pyopagus twins.

 Most twins shared four kidneys and two bladders, with the consistent feature that one ureter crosses to the contralateral twin [ 7[8]–9]. In most cases the bladders are collateral, but in one of the present twins the bladders were sagittally placed, which presented a reconstructive challenge. This was solved by dividing the bladders in half and giving each twin one half of each bladder. The lower urinary tract shows considerable individual variation, but in most cases a bladder can be reconstructed [ 7]. Urinary continence has been achieved in one of the four children still alive; other centres have reported more success [ 7, 8] and further surgery is planned in the remaining three who are incontinent. Genital separation and reconstruction was possible in all but one of the present patients. There has been no pattern to these procedures, making comparison of results difficult; each requires an individual approach. This has previously been stressed by others with experience in this complex field [ 7]. When confronted with a set of conjoined twins, surgical separation appears often the only way to provide each child with a hope of some normality. With detailed investigations and an experienced multidisciplinary approach, most twins can now be separated.