Pygomelia: A Rare Lower Limb Malformation and Surgical Management

Abstract

Introduction:

Pygomelia is a rare subtype of polymelia characterized by accessory lower limbs attached to the pelvic region. These anomalies often serve as markers for complex multisystem duplications or occult spinal dysraphism.

Case presentation:

A 3-month-old female infant from a twin pregnancy presented with a left iliosacral supernumerary limb featuring hip, knee, and ankle joints and an imperforate vulvar remnant. MRI identified an associated lipomeningocele with a low-lying tethered cord and a lumbar syringomyelia. Surgical resection was done at 5.5 months, prioritizing dural integrity and host neurologic preservation.

Discussion:

Embryogenesis remains debated between parasitic twinning and caudal duplication syndrome (CDS). Modern management emphasizes high-resolution imaging to identify “hidden” dysraphic anomalies.

Conclusion:

Early multidisciplinary resection and neurologic protection facilitate favorable long-term ambulation, although functional continence requires longitudinal monitoring.

Pygomelia is an extremely rare congenital malformation defined by the presence of accessory lower limb segments abnormally positioned in the pelvic or lumbar region. It is classified as a subtype of polymelia and is considered a focal axial patterning error.¹

The etiopathogenesis remains a subject of ongoing debate, with modern frameworks contrasting parasitic twinning (rachipagus conjoined twinning) with the caudal duplication syndrome (CDS) spectrum.^2,3 Historically, these rare cases were established as surgical landmarks in the orthopaedic literature by Norman (1964)⁴ and Hanley and Stanitski.⁵

We report the successful multidisciplinary management of a pygomelia case associated with an occult lipomeningocele.

CASE Presentation

A 3-month-old female infant, born from a dichorionic-diamniotic twin pregnancy to nonconsanguineous parents, presented with an accessory lower limb identified at birth. Maternal history was notable for two prior spontaneous abortions. Antenatal obstetric ultrasounds failed to detect the anomaly, likely due to multifetal gestation and breech presentation. Delivery was through cesarean section; the twin sibling was healthy.

Physical examination revealed a supernumerary lower limb arising from the left iliosacral region (Figure 1). The limb featured hypoplastic thigh, leg, and foot segments with three distinct joints (hip, knee, and ankle) and four toes. Notably, the accessory limb demonstrated partial mobility, specifically within the toes. Tactile sensitivity was present, but motor function was absent. An oval mass resembling an imperforate vulvar remnant was noted at the commissure between the accessory limb and the native left leg. It was separate from the otherwise normal native external genitalia and anus.

Figure 1.

Clinical photographs of the infant at birth. A, Anterior view demonstrating the native lower extremities, the supernumerary limb, and the associated imperforate vulvar remnant. B, Posterior view illustrating the well-developed accessory limb featuring thigh and leg segments arising from the left iliosacral region. C, Lateral view highlighting the soft-tissue commissure and the junction between the accessory limb and the native left lower extremity.

Radiographs identified a hypoplastic hemipelvis fused to the sacrum and malformed long bones within the accessory limb (Figure 2). MRI was done to evaluate the interface between the supernumerary limb and the host and confirmed a lipomeningocele communicating with a wide posterior sacral arch defect, together with a low-lying tethered cord and a syringomyelia at the L4 level (Figure 3). The supernumerary limb received aberrant left sacral nerve roots arising from the low-lying tethered cord and a vascular pedicle arising from the left internal iliac artery through the sacroiliac defect, with no bony bridge to the host pelvis. Being a closed lipomeningocele rather than an open neural tube defect, the lesion is not typically associated with the Chiari II malformation or hydrocephalus that characterize open myelomeningocele, and the native lower limbs showed a normal neurologic examination. This illustrates how such conspicuous cutaneous findings often mask “hidden” or occult spinal dysraphism.⁶

Figure 2.

Anteroposterior (AP) pelvic radiograph demonstrating the skeletal architecture. The native hips are present with associated pelvic dysmorphism. A well-developed accessory femur is visible, articulating with a hypoplastic accessory hemipelvis. Distal ossification centers within the supernumerary limb represent a tibia and a malformed foot.

Figure 3.

Magnetic resonance imaging (MRI) of the lumbosacral spine and pelvis. A, Sagittal T2-weighted sequence demonstrating the low-lying tethered conus medullaris, the lumbar syringomyelia, and the associated lipomeningocele sac. B, Coronal sequence illustrating the iliosacral origin of the accessory limb and its relationship to the host pelvic wall. C and D, Axial sequences at different levels demonstrating the soft-tissue architecture and internal morphology of the supernumerary limb at the interface with the host.

Abdominal ultrasonography identified bilateral ovarian cysts but ruled out internal visceral duplications.

At 5.5 months, the patient underwent surgical resection. A circumferential incision was made around the base of the supernumerary limb (Figure 4). Intraoperatively, the lipomeningocele sac and the host sacral nerve roots were identified and carefully preserved. As there was no bony bridge to the host pelvis, the limb was released by dividing its soft-tissue and neurovascular attachments and was resected (Figure 5). Skin closure was achieved using 3-0 monocryl (Ethicon, Somerville, NJ).

Figure 4.

Intraoperative photograph demonstrating the surgical planning. Blue markers outline the circumferential incision at the base of the supernumerary limb. This approach was designed to facilitate adequate soft-tissue exposure and provide sufficient skin flaps for primary closure while protecting underlying host structures.

Figure 5.

Specimen radiograph of the resected supernumerary limb. The image confirms the internal bony morphology, demonstrating a hypoplastic femur, a distal segment representing the tibia, and rudimentary ossification centers corresponding to the malformed foot identified clinically.

At the 3-year follow-up, the patient was independently ambulatory and able to run. Clinical examination with the patient in a standing position demonstrated neutral alignment, independent weight-bearing, and a stable sagittal profile (Figure 6). A residual cutaneous bulge persisted at the lipomeningocele site. Although gross motor milestones were met, she had not yet achieved sphincter control, unlike her healthy twin sister. This finding mirrors clinical profiles in recent literature where functional continence remains variable and may be secondary to the associated spinal dysraphism.³

Figure 6.

Clinical photographs at 3-year follow-up. A, Standing anterior view demonstrating symmetric development, neutral alignment of the native lower extremities, and independent weight-bearing. B, Standing posterior view illustrating successful wound healing and the residual cutaneous bulge. C, Standing lateral view showing the stable sagittal profile and the posterior projection of the preserved neural sac.

Discussion

The embryogenesis of externally attached supernumerary limbs remains unresolved, with theories suggesting either parasitic twinning or the CDS spectrum.^2,3 Three overlapping models are advanced. Parasitic (rachipagus) conjoined twinning attributes the limb to an incompletely separated, nonviable monozygotic twin that persists on the dorsal axis of the autosite.^3,7 The caudal duplication syndrome spectrum invokes a disturbance of the caudal cell mass between the third and seventh weeks of gestation, variably affecting the hindgut, genitourinary tract, and distal neural tube.² A third view situates such cases within the axial mesodermal dysplasia spectrum, a regional disturbance of secondary neurulation and caudal patterning that links dysraphism, vertebral and pelvic dysgenesis, and supernumerary limb formation.⁶

CDS involves a broad morphogenetic disturbance affecting gastrointestinal, genitourinary, and spinal systems.²

In our case, the constellation of a skin-covered lipomeningocele, a tethered cord with syringomyelia, a duplicated hemipelvis, and an accessory labial remnant favors a regional caudal dysgenesis rather than an isolated limb-bud duplication, overlapping the CDS and parasitic-twin constructs. The absence of hindgut or anorectal duplication, however, argues against a complete CDS phenotype, underscoring that these entities lie on a continuum rather than in discrete categories.

A critical clinical pearl is that accessory limbs are frequently markers for occult spinal dysraphic anomalies.⁶

Mohindra et al.⁶ emphasized that such conspicuous cutaneous findings necessitate high-resolution preoperative MRI to delineate the relationship between the supernumerary limb and the host.

Surgical planning was dictated by the neurovascular interface between the supernumerary limb and the host, defined on multiplanar MRI. Because the accessory limb derived its innervation from aberrant host sacral roots arising from the tethered cord and its blood supply from the internal iliac system through the sacroiliac defect, the principal objective was preservation of these host neural elements rather than radical excision. Accordingly, the lipomeningocele sac was deliberately left intact and not repaired, the residual bulge being an acceptable trade-off for neurologic safety. Although 3D skeletal reconstructions were not available, the multiplanar 2D MRI sequences provided sufficient anatomic details to identify the neurovascular pedicle and the dural interface and to plan a safe resection. Multidisciplinary planning involving orthopaedic and neurosurgical teams is essential to achieve an excision that addresses both skeletal and dural attachments while preserving host neurologic function.^7,8

Surgical ablation remains the standard treatment and was established as the definitive management for achieving functional ambulation in landmark orthopaedic reports.^4,5

Recent series suggest that early intervention allows for concurrent limb removal and dural repair.^3,9

Long-term follow-up data from Freitas et al.³ indicate that even patients with early postoperative bladder incontinence can achieve favorable sensory and motor outcomes by school age.

Our 3-year follow-up results confirm that independent standing and running are achievable goals (Figure 6), confirming the success of early surgical reconstruction.

However, urogenital milestones require longitudinal multidisciplinary monitoring to track developmental trajectories.¹⁰

Beyond its rarity, this case illustrates how established reconstructive principles can be transferred to an unfamiliar deformity. The imaging-first definition of the neurovascular pedicle, the protection of host neural tissue over completeness of resection, and staged multidisciplinary execution are the same tenets that govern excision of any complex parasitic or duplication anomaly. Where such cases demand modification is in accepting a deliberate, planned residual—here the preserved dysraphic sac—when neurologic function would otherwise be jeopardized. Framed this way, the rare deformity becomes generalizable: It is managed by applying, and selectively adapting, principles already familiar to the orthopaedic surgeon.

Conclusion

Pygomelia is a rare marker for complex spinal and pelvic dysmorphogenesis. Preoperative imaging must prioritize the identification of occult neural tube defects. Combined multidisciplinary resection ensures host neurologic preservation and supports excellent long-term ambulation and psychomotor development at a 3-year follow-up.