Anesthetic challenges in the separation of a rare occipital heteropagus twin: A case report

INTRODUCTION

A heteropagus is a conjoined twin with an underdeveloped asymmetric twin (parasite), dependent on the completely developed autosite.^[1] This parasitic attachment may be at epigastric, thoracic, pelvic, or cranial sites. The incidence of conjoined twins is 1 in 50,000–200,000 live births. The conjoined twins are usually classified as per the site of fusion, which may be ventral at the thorax (thoracopagus), abdomen (omphalopagus), or pelvis (ischiopagus); dorsal at the sacrum (pygopagus), vertebral column (rachipagus), or skull (craniopagus); or lateral (parapagus). Heteropagus twins are <5% of these conjoined twins, with varied anatomical presentations.^[2] Occipital heteropagus has an incidence of <1/10 million live births.^[3] This case report details the perioperative anesthetic challenges during the separation of a parasitic craniopagus twin.

CASE REPORT

A 3-year, 9-month-old girl, the sixth child of a multigravida mother, presented to our institute with irregular swelling at the back of her head and neck for excision of the mass. This swelling, though noticed immediately after birth, had grown with the child.

The child, though apprehensive, was active with regular facial features, age-appropriate milestones, and vital signs. Her height, weight, and head circumference were 95 cm, 14 kg, and 49 cm, respectively. Her systemic examination and echocardiogram were unremarkable. The swelling behind the head covered the neck with restriction in extension and had a limb-like projection [Figure 1]. The magnetic resonance imaging showed incomplete fetal parts, predominantly lower limb bones with a bony pelvis-like structure fused with occipital bone, receiving supply from the left vertebral artery, and documented a cervical meningomyelocele sac measuring 3.8 × 1.8 × 2 cm with cervical cord tethering between C2 and C3.

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Figure 1:

(a) Lateral head and neck radiograph showing heteropagus twin with a bony pelvic like structure (red arrow) (b) Magnetic resonance imaging: Sagittal section of the head demonstrating the occipital attachment of the parasitic twin (red arrow) (c) 3D reconstruction of the cranium with the bony pelvic like structure of the parasitic twin (red arrow).

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The anesthesiologist discussed the perioperative plan with a multidisciplinary team consisting of a neurosurgeon and neurophysiologist. We identified perioperative challenges, including anticipated difficult airway, prone positioning, shared airway, potential blood loss, hypothermia, hemodynamic instability, the need for neuromonitoring, prolonged surgical duration, and the anticipation of post-operative mechanical ventilation and intensive care. We planned to support the child’s back on a blanket platform on the operation theater (OT) table, raising the body and head on a roll, with the growth hanging in the gap to facilitate laryngoscopy. For airway management, Plan A was video laryngoscopy-guided intubation after inhalational induction using succinylcholine after confirmation of bag mask ventilation. Plan B was pediatric fiberoptic bronchoscope-guided oral intubation with the preservation of spontaneous ventilation.

After the parents gave written informed consent, the child was distracted by cartoons on a smartphone and brought into the prewarmed OT with her father. After attaching standard American Society of Anesthesiologists (ASA) monitors and para-oxygenation through a nasal cannula, the child was premedicated with intravenous ketamine 10 mg, glycopyrrolate 65 mcg, and injection of midazolam 0.4 mg and positioned as planned [Figure 2]. Depth of anesthesia was monitored with bispectral index (BIS). After giving analgesia with two micrograms/kg of fentanyl, incremental sevoflurane induction was performed, and once bag-mask ventilation was confirmed, a 20 mg dose of succinylcholine was administered intravenously. Video laryngoscopy showed an anterior glottic opening with a percentage of glottic opening score of 20%. Negotiation of an age-appropriate size 4 mm ID armored tube through the subglottic space failed. With bag-mask ventilation with sevoflurane, intubation with a size 3.5 cuffed armored tube was successful on the second attempt. Dexamethasone 0.1 mg/kg was given. For anesthetic depth maintenance, we used 0.5 minimum alveolar concentration (MAC) isoflurane in blended oxygen (50%) and propofol infusion (50–100 mcg/kg/min) to target a BIS value between 40 and 60. Hourly aliquots of 1 mcg/kg fentanyl were given. Non-depolarizing neuromuscular relaxant boluses were stopped an hour before electromyography recording. After left radial artery cannulation, ultrasound-guided left internal jugular vein catheterization was done (4.5 Fr). A wide-bore peripheral intravenous cannula was inserted in the lower limb. After proning and pin fixation of the head, we padded the pressure points and initiated forced air warming of the rest of the body. Significant hypotension was seen immediately after proning and at the time of surgical dissection, which was managed by titrating intravenous fluids and phenylephrine boluses to target a systolic pressure variation of <12% and a mean pressure of 50–60 mmHg. Low ionized calcium levels on arterial blood gas (ABG) were corrected with intravenous calcium gluconate 20 mg/kg. Intraoperatively, a transfusion of 40 mL of packed red blood cells was done. Correction of electrolyte imbalances was done per serial ABG analysis. After careful dissection, the surgical team excised the parasitic twin en bloc, with assistance of ultrasound doppler to check for vascularity, and repaired the cervical lipo meningocele. After surgery, the armored tube was changed to a cuffed polyvinyl chloride (PVC) endotracheal tube, and the child was electively ventilated because of glottic edema. The trachea was extubated uneventfully on the 1^st post-operative day. Further recovery was uneventful, and the child was discharged on the 6^th postoperative day from the hospital.

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Figure 2:

Heteropagus twin in supine (left) and prone (right) position on the operating theater table.

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DISCUSSION

The anesthetic management of a child with a parasitic twin is challenging due to the varied presentation concerning age, site of attachment, and surgical plan. Isolated cases of heteropagus twins, ranging from the lumbosacral attachment of parasitic twins to ischiopagus (twins conjoined at the hip), have been reported in Africa, with ages up to 17 years.^[4] In the Indian context, Dahiya et al. reported 5 cases of parasitic conjoint twins, most delivered preterm, with no survivors.^[5] Menon et al. reported 5 cases of parasitic twinning (two internal retroperitoneal and three external, with the most common location being lumbar, sacrococcygeal, or lower abdominal wall), with age ranging from 1 day to 6 months.^[6] Separation surgery is usually advised after 4–11 months of age to avoid the high risk associated with the neonatal period.^[7] Pati et al.^[8] reported a rachipagus parasitic twin attached at the upper cervical spine level in a term baby, along with multisystemic involvement. Although disarticulation of the accessory limbs and management of dorsal meningomyelocele were attempted, the child succumbed on post-operative day 35.^[8] We report the successful management of a rare presentation of a heteropagus twin with the attachment of the parasitic limb at the occiput (craniopagus).

The emphasis on ergonomics of the OT, use of positioning aids with available resources, appropriate Plan A and B for difficult airway management, role allocation, and teamwork resulted in smooth, streamlined anesthetic induction. Both intravenous and inhalation induction may be used, depending on the presence of an intravenous line. We used inhalation induction due to the anticipated difficult airway, using a depolarizing muscle relaxant only after confirmation of bag-mask ventilation. Anticipating difficult cooperation, we utilized audio-visual distraction with cartoons and parental presence to facilitate attachment of ASA monitors and paraoxygenation.

Drug dosages are usually calculated separately for each twin in such cases. Since our case was of a vestigial parasitic twin, drugs were prepared according to the ideal body weight of the fully developed autosite. Intraoperative blood loss and fluid management were other challenges guided by dynamic indices and serial ABG assessments.

Surgical positioning may vary as per the site of the parasitic twin. As per the available resources, individualized positioning strategies with airway pressure monitoring are necessary. In our case, we secured adequate invasive monitors, intravenous access, and the use of an armored tube to facilitate ventilation, administration of drugs, and beat-to-beat monitoring in the prone position.

Electromyography posed the challenge of avoiding the use of muscle relaxants, which was addressed through the use of propofol infusion and BIS monitoring. Temperature monitoring is a pivotal concern in these patients due to the large wound size and long duration, which may cause hypothermia. We prewarmed the OT and used fluid warmers and warming blankets to prevent hypothermia.

Although reporting each such rare case of occipital heteropagus twins is crucial, this case report has limitations, including being a single case with a short follow-up time until hospital discharge and limited neuromonitoring due to the shared space. Hence, each such patient may have unique challenges, making it difficult to generalize our findings. The CARE checklist is attached as a supplementary file.

CONCLUSION

Anesthetic challenges in the case of conjoined twins are many. Proper communication with a multidisciplinary surgical team, meticulous planning, and anticipation of perioperative challenges and intensive care can pave the way for a successful outcome.