An ectopic or accessory limb attached to the back is an extremely rare and strange condition, and there are only a few documented cases in the worldwide literature. The first case was described by Jones and Larkin (1889). There are several theories regarding the origin of this condition. Asymmetric conjoined twinning which is located dorsally in the vertebral column (rachipagus) is the most probable diagnosis of our patient. Conjoined twinning is very rare and the incidence is 1 per 50 000 live births. Rachipagus is even rarer, with no more than 30 case reports so far (Chadha et al. (1993, 2006)). In this report, we present a patient who underwent successful surgical excision of a third arm attached to the back in the midline over the low-dorsal region. Differential diagnoses including teratoma and fetus in fetu are discussed.
A female baby was born by C/S after an uncomplicated full-term pregnancy, weighing 3500 g with Apgar scores 8 and 9 at the first and fifth minutes, respectively. The patient did well; she was referred to our Pediatric Care Unit.
Antenatal course was uneventful and no history of maternal medication or harmful drug use or exposure to radiation during pregnancy was reported. Her mother was followed up during pregnancy. She had several prenatal ultrasound examinations, but her daughter’s abnormality was diagnosed postnatally.
On physical examination, a malformed accessory extremity, resembling a rudimentary structure like a tiny arm, was attached to the back, in the upper-dorsal region of the vertebral column (Figures
A malformed accessory arm attached to the back; it is immobile. There are three small buds originating from just below the root of the arm (a). Note that hemorrhagic area is located caudal to this accessory extremity (arrow).
Abdominal and cranial ultrasonography (USG), thoracic computed tomography, and magnetic resonance imaging (MRI) were performed. Cranial USG showed no abnormality. Brain and medulla spinalis were normal in MRI except a 2 cm lipoma located at the same level with the origin of the ectopic extremity. There was no associated meningocele or myelocele. Abdominal organs appeared normal on USG. Thoracic CT revealed spina bifida from 5th cervical to 7th dorsal vertebrae level (Figure
Axial tomographic section (a) shows spina bifida adjacent to the root of the ectopic extremity (arrow). Coronal reformatted image (b) shows two hypoplastic metacarpals and three phalangeal bones of the hand (arrow).
The MRI demonstrated that medulla spinalis terminated between L3 and L4 vertebraes. Ectopic arm was originated from subcutaneous soft tissues and it did not extend to deeper neural elements. It ended with interspinous ligament (Figures
T1-weighted sagittal (a) and T2-weighted coronal (b) images. Arrow points that the lipoma is located at the same level of the ectopic extremity. Medulla Spinalis terminates between L3 and L4 vertebrae. Ectopic extremity originates from subcutaneous soft tissues and it does not extend deeper neural elements. It ends interspinous ligament. Coronal T2-weighted image shows dorsally located extremity, composed of fat and muscle tissue. Note that cerebral structures are in normal limits.
Surgical operation was performed when the baby was two months old. Midline skin incision was performed between the first and the seventh thoracic vertebrae of the dorsal region. Incision extended around the accessory extremity so that the periphery of the mass and its globular appendages were liberated. The mass was attached firmly to the laminae of the dorsal vertebrae. It was excised totally. There was no relationship between the mass and the underlying dura mater, and intraspinal structures. A significant closure defect was observed at the level of the fifth thoracic vertebrae, and a single level laminectomy was made using a Kerrison punch. Dura mater was incised and a spinal lipoma was observed. However, it was wrapped tightly around the nerve fibers; thus it could not be excised. Finally, closure of the subcutaneous tissues and skin was performed. The infant did not require postoperative ventilation and made an uneventful recovery. She began oral feeding with no complications on the same day, six hours after the operation. She was discharged on the fourth day of hospitalization. Histopathological examination revealed normal muscle tissue extending along the ectopic extremity and three bones resembling metacarpal bones and phalanges. There were no neural, cartilaginous, or vascular tissues. At the bottom of the mass, the lesion was covered by a thin-walled hemorrhagic mucosa. Microscopically, a primitive type intestinal mucosa resembling colonic mucosa was noted in this region. DNA analysis was performed. DNA samples from the blood and hair of the autosite and from the skin and muscle of the parasitic twin were extracted using the rapid Chelex-100 method. A sex locus (amelogenin gene) and 15 STR loci were amplified using the Powerplex TM 16 system. DNA analysis revealed that the parasitic twin in this report had an identical genotype to the autosite, which indicated that it was of monozygotic origin. The patient is currently 14 months old and completely healthy.
Heteropagus is a term used to describe the development of an asymmetrical form of twinning when one of the twins monopolizes the placental blood at the expense of other fetus with consequent ischaemic atrophy of the latter [
Based on the typical appearances and histological results, diagnosis of rachipagus is made easily but rarely the differential diagosis may be required from teratoma and fetus in fetu [
Neural tube defects associated with ectopic limbs have been reported in a few cases. Krishna et al. reported accessory legs associated with spina bifida and rudimentary external genitalia [
In summary, a case of rachifagus is presented herein, which had the limb buds very similar to extremities, was located at the midline of the dorsal region, and attached to the vertebral column. The literature of this amazing condition was reviewed. We concluded that this anomaly was limited to the infant’s dorsum. Nevertheless, other midline pathologies including vertebral column, medulla spinalis, and heart should be kept in mind. Thus, careful preoperative examination of the patient is essential for a good postoperative outcome.