Spinal cord involvement in pygopagus conjoined twins: case report and review of the literature

The role of intraoperative neuromonitoring in pygopagus separation: two-institution experience in Indonesia

INTRODUCTION

Pygopagus comprises 17% of all conjoined twin cases. Survival rate is higher compared to other variations of conjoined twins, but separation is a great challenge due to multiorgan involvement. Intraoperative neuromonitoring (IONM) used aims to aid operator in preserving as much function as possible.

CASE PRESENTATIONS

The authors reported 2 pairs of pygopagus separation. Intraoperatively, motor-evoked potential (MEP) and sensory-evoked potential (SEP) were used in all patients. Three patients survived in which all had transient motor deficits. Urinary retention was reported in one patient. One patient died 2 weeks after separation as twins only had one kidney which was spared for the healthier twin.

DISCUSSION

IONM was used to guide operator in dissecting, identify the ownership of the neural structures, and determine the safest point to separate in pygopagus separation. Despite the normal MEP and SEP recordings, transient motor weakness may still occur transiently. The motor tract development of children is achieved in adolescence, making MEP less accurate. However, the reliability of MEP increases when it is combined with SEP. Autonomic function monitoring such as bulbocavernosus reflex (BCR) could not be assessed due to the unavailability of the probe.

CONCLUSION

IONM can aid operator in pygopagus separation during determining the origins of the structure, dissecting, and cutting the neural structures. Normal MEP interpretations are still possible to correlate with transient deficits, but reliability can be improved with the use of SEP. In surgeries involving the lower spine level, BCR monitoring is recommended to avoid autonomic deficits.

Successful neurosurgical separation of conjoined spinal cords in pygopagus twins: illustrative cases

BACKGROUND

Conjoined twins represent a rare congenital malformation. Pygopagus twins are fused at the sacrum and perineum, with union of the spine. The authors report a successful separation of a unique case of pygopagus twins sharing a U-shaped spinal cord, which the authors identified through aberrant nerves by intraoperative physiological spinal root examination.

OBSERVATIONS

The 6-month-old male pygopagus conjoined twins, who were diagnosed in the prenatal period, underwent separation. They had a single dural sac containing a U-shaped continuous spinal cord; their filum terminale appeared completely fused and the anatomical border of the spinal cord was not distinguishable. A triggered electromyogram (tEMG) was used on each nerve root to determine which belonged to one twin versus the other, to detect nerve cross, and to identify functional midline cleavage. Finally, the twins were separated after spinal division. Both twins recovered uneventfully with no lower limb neurological deficits or walking impairment for 16 months.

LESSONS

Pygopagus twins with a conjoined spinal cord are very rare, but a good long-term functional prognosis can be expected with successful separation. Intraoperative tEMG is useful in spinal separation surgery for twins with a conjoined spinal cord.

Two is a Crowd: Two is a Crowd: On the Enigmatic Etiopathogenesis of Conjoined Twinning

In this article, we provide a comprehensive overview of multiple facets in the puzzling genesis of symmetrical conjoined twins. The etiopathogenesis of conjoined twins remains matter for ongoing debate and is currently cited-in virtually every paper on conjoined twins-as partial fission or secondary fusion. Both theories could potentially be extrapolated from embryological adjustments exclusively seen in conjoined twins. Adoption of these, seemingly factual, theoretical proposals has (unconsciously) resulted in crystallized patterns of verbal and graphic representations concerning the enigmatic genesis of conjoined twins. Critical evaluation on their plausibility and solidity remains however largely absent. As it appears, both the fission and fusion theories cannot be applied to the full range of conjunction possibilities and thus remain matter for persistent inconclusiveness. We propose that initial duplication of axially located morphogenetic potent primordia could be the initiating factor in the genesis of ventrally, laterally, and caudally conjoined twins. The mutual position of two primordia results in neo-axial orientation and/or interaction aplasia. Both these embryological adjustments result in conjunction patterns that may seemingly appear as being caused by fission or fusion. However, as we will substantiate, neither fission nor fusion are the cause of most conjoined twinning types; rather what is interpreted as fission or fusion is actually the result of the twinning process itself. Furthermore, we will discuss the currently held views on the origin of conjoined twins and its commonly assumed etiological correlation with monozygotic twinning. Finally, considerations are presented which indicate that the dorsal conjunction group is etiologically and pathogenetically different from other symmetric conjoined twins. This leads us to propose that dorsally united twins could actually be caused by secondary fusion of two initially separate monozygotic twins. An additional reason for the ongoing etiopathogenetic debate on the genesis of conjoined twins is because different types of conjoined twins are classically placed in one overarching receptacle, which has hindered the quest for answers. Clin. Anat. 32:722-741, 2019. © 2019 Wiley Periodicals, Inc.

Successful separation of the conjoined thecal sac with an epidermal cyst in pygopagus twins

Pygopagus conjoined twins are very rare, and half of all pygopagus twins have other anomalies. This report describes the successful surgical separation of pygopagus twins who had a conjoined thecal sac and an epidermal cyst. Meticulous preoperative planning, development of a model simulator, multispecialty teamwork, and a staged surgery contributed to a successful outcome.

Successful separation of pygopagus conjoined twins and primary skin closure using V-shaped flaps

Pygopagus conjoined twins were born by caesarean section at 34 weeks of gestation. Initial evaluation revealed no other abnormalities apart from their attachment at lower back, buttocks and perineum. They had two separate anal and urogenital openings. Their investigations included roentgenograms, ultrasound, barium enema, cystourethrogram, CT scan and MRI. There were two separate spinal columns fused distally at the lower sacral level. Lower gastrointestinal studies showed two separate rectums and cystourethrogram showed normal and separate urinary tracts. MRI showed a single dural sac between two fused sacral bones with no other vertebral anomalies. They were successfully separated with primary skin closure using V-shaped flaps.

Separation of pyopagus conjoined twins: a New Zealand neurosurgical experience

Conjoined twins represent a rare form of incomplete embryonic separation. They are classified into eight different subtypes, with 18% representing pyopagus conjoints. History is scattered with accounts of the various types of conjoints and it is only recently that strategies have been devised to enable surgical separation of such twins. It is estimated that approximately 20 cases of separation of pyopagus twins have been performed. We provide a historical look at pyopagus conjoint twins and report our neurosurgical experience of Australasia's first separation of pyopagus twin girls.

Successful separation of pygopagus conjoined twins

Conjoined pygopagus twins are very rare. They represent about 17% of all conjoined twins and commonly share the gluteal region, terminal spine, and lower gastrointestinal, urological, and reproductive tracts. Meticulous preoperative investigations and planning as well as a multispecialty team approach contribute to the success of surgical separation. We report a case of successful surgical separation of pygopagus conjoined twins.

Ischiopagus and pygopagus conjoined twins: neurosurgical considerations

BACKGROUND

Neurosurgeons are familiar with the challenges presented by craniopagus twins, but other types of conjoined twins may also have neurosurgical implications. We report our experience in the management of ischiopagus and pygopagus conjoined twins.

METHODS

This is a retrospective review of the management of conjoined twins at Red Cross Children's Hospital in Cape Town, South Africa.

RESULTS

Twenty-three pairs of symmetrical conjoined twins were managed over a 40-year period (1964-2003), of which 16 (70%) were separated. Of these cases, 6 are the focus of this study, namely 4 pairs of ischiopagus twins and 2 pairs of pygopagus twins seen between 1993 and 2003. In 2 cases, there was direct involvement of the nervous system at the site of union, with 1 pair of ischiopagi manifesting end-to-end union of their spinal cords, while a pair of pygopagi had back-to-back fusion of the conus. Another pair of ischiopagi had a fused dural sac without joined neural elements, but one of these children developed syringomyelia 2 years after separation. Neuroimaging was invaluable in detecting these abnormalities. The one pair of ischiopagi who died before separation were HIV positive and had severe brain atrophy and cystic encephalmalacia at autopsy. Nine of the 12 children (75%) had bony abnormalities of the spine remote from the area of conjunction. The most common finding was the presence of hemivertebrae, usually in the thoracic spine. Six children manifested scoliosis, which has already progressed in the oldest two. Technical aspects such as timing and sequence of separation, the division of neural tissues and reconstruction are discussed, as are the long-term complications of their spinal abnormalities.

CONCLUSIONS

Ischiopagus and pygopagus conjoined twins manifest an interesting array of spinal abnormalities, which present challenges, not only at the time of separation, but also in their long-term management.