Title

Title: Pediatric Free Flap Reconstruction for Head and Neck Defects

Authors: Roasa, Francis V., MD
Castañeda, Samantha S., MD
Mendoza, Daniel Jose C., MD

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Corresponding Author: Mendoza, Daniel Jose C., MD
Department of Otorhinolaryngology – Head and Neck Surgery
Jose R. Reyes Memorial Medical Center
San Lazaro Compound, Rizal Avenue Sta. Cruz, Manila 1003 Philippines
Phone: (+632) 743-6921; (+632) 711-9491 local 320
Email: [email protected]

The authors declared that this represents original material that is not being considered for publication or has not been published or accepted for publication elsewhere, in full or in part, in print or electronic media; that the manuscript has been read and approved by the authors, that the requirements for authorship have been met by each author, and that each author believes that the manuscript represents honest work.
Disclosures: The authors signed disclosures that there are no financial or other relationships, intellectual passion, political or religious beliefs, and institutional affiliations that might lead to a conflict of interest.

Abstract
Purpose of review: To review recent literature on the use of pediatric free flap reconstruction for head and neck defects with focus on skull base reconstruction, reconstruction of congenital defects, mandibular reconstruction and operative considerations of using free flaps in the pediatric population.
Recent findings: Reconstruction of the skull base depends on the defect size, location, bony involvement, and pedicle length with a variety of flaps to choose from. Flaps may be used to cover congenital defects due to facial clefts and syndromic causes requiring tissue bulk. Delayed reconstruction of mandibular defects may be an option especially for patients with malignancy. Chemotherapy and radiation therapy may inhibit growth potential of the mandible. The use of running or coupled arterial anastomosis was associated with the increased immediate complication.
Summary: Pediatric free flap reconstruction is a reasonable option for various head and neck defects such as skull base, congenital, and mandibular defects.
Keywords: pediatric, free flap, skull base, congenital, mandible

Introduction
Microsurgical free flaps were often avoided before in pediatric patients based on presumed increased risks of complications including flap loss, smaller vessels more affected by vasospasm, challenging post-operative management, and concerns regarding donor site morbidity and effects on patient growth 1. Despite the limitation of free flap reconstruction in the pediatric population such as small donor & recipient vessels, studies have shown a high success rate at 96.4% compared to that of adults 2.
Improved microsurgical expertise led to the acceptance of microsurgical free flaps as safe and dependable option for pediatric head and neck reconstruction. This may even be the only option to best restore a child’s form and function 1. A variety of donor sites can be used depending on the type of defect, which can either be soft tissue or bony defects. Soft tissue defects can be reconstructed using radial forearm (RFF), anterolateral thigh (ALT), latissimus dorsi and rectus abdominis free flaps. Fibula, scapular, and iliac crest free flaps are used for bony defect reconstruction 1-3. Pediatric free flaps are used commonly in the reconstruction of defects due to congenital, ablative, burn, and traumatic etiologies. The locations commonly reconstructed are mandible, skull base, midface, scalp, soft tissue, pharynx, and tongue 2.
This review will focus on recent literature regarding free flap reconstruction of the skull base, congenital, and mandibular defects and operative considerations of pediatric patients who will undergo free flap reconstruction of head and neck defects.

Skull base reconstruction
Skull base reconstruction is difficult in itself more so in the pediatric population. Anatomic factors to be considered are 1) smaller craniofacial complex, cranial fossa, and paranasal sinuses, 2) stage of tooth eruption, 3) absence of anatomic landmarks such as the superior orbital fissure and mastoid pneumatization, and 4) the fragility of neurovascular elements. Reconstruction needs to consider 1) craniofacial skeleton ; soft tissue growth 2) donor site morbidity and 3) psychosocial issues 4.
Free flaps are used in skull base reconstruction for large defects or with orbitomaxillary resection 4. They postulated an algorithm based on literature review although most of the studies available were retrospective with small sample size ; heterogeneous sample (Table 1). Computer-aided design and computer-aided manufacturing (CAD/CAM) is a valuable tool in pre-operative virtual surgery for the best possible outcome for the patient. CT angiography of the leg is also useful in fibular free flap surgery of the skull base so that the osteotomy may be planned beforehand. Surgical navigation also lessens complications.
Free flap reconstruction of the skull base provides adequate tissue bulk with a rich, reliable blood supply, allowing for improved healing, decreased hospitalization, and decreased complications including CSF leak and meningitis. The choice in free tissue donor site is dictated by defect size, location, need for bony restoration, and pedicle length. Frequently utilized flaps include the RFF, rectus abdominis, and latissimus dorsi free flaps. Additional options include the fibula, anterolateral thigh, gracilis muscle, scapula, lateral arm, ulna, serratus anterior, and superficial temporal fascia free flap. The most commonly used recipient vessels are the superficial temporal ; facial. Free flaps are generally used in large defects such as in cases with orbital, midface ; maxilla defects to obliterate the dead space 4. Vascularized bone flaps also provide an osteogenic environment and remain viable even in cases with infection or will undergo chemotherapy or radiotherapy 3.

Congenital defect
Congenital facial anomalies requiring free tissue transfers include Romberg hemifacial atrophy, hemifacial microsomia, facial clefts, and Treacher-Collins syndrome. The use of local flaps or bone grafts in these cases is limited due to the high probability of infection and/or bone extrusion. Scapular ; para-scapular flaps along with the fascia are used in cases of reconstruction of Romberg atrophy because of their bulk ; the fascia can be anchored to the underlying bone to prevent migration. The disadvantage is hypertrophy of the scar at the donor site. The radial forearm flap may be also used in cases of wide palatal fistula after failed primary repair 3.

Mandibular Reconstruction
In the reconstruction of the pediatric mandible, growth of the neo-mandible needs to be considered. In a systematic review by Zhang et al. 5 on mandibular growth after pediatric mandibular reconstruction using the fibular free flap, growth potential was noted in 83.3% of patients in the 8-12 years old age group. The condyle needs to be preserved to have growth potential (81.5%). However, patients who underwent radiotherapy or chemotherapy may have inhibited growth potential at 16.7 % and 36.3%, respectively 5. The mechanical stresses on the vascularized bone at the recipient site induces periosteal ; endosteal bone growth 6.
In pediatric patients with extensive mandibular defects such as in malignancy or big benign tumors, Hu et al. 7 advocate secondary reconstruction after the puberty growth spurt. This is due to unpredictable mandibular growth, possible donor site morbidity ; tumor recurrence. Elledge et al. 6 also stated that mandibular reconstruction in the pediatric population may be precluded due to the length of the defect, irradiation, scarring of the tissue bed and the potential for infection at the recipient site. Hu et al. 7 recognize that secondary reconstruction is very challenging ; advise close follow up with use of an inclined bite plate postoperatively. All of their 6 cases had preserved condyle. They used free flap (2 iliac crests, 2 fibulae, 2 scapulae) along with orthognathic surgery. All patients were satisfied with their appearance post-operatively with relatively stable ; good occlusion except for 1 patient who developed osteoradionecrosis.
Donor site considerations are possible donor site morbidity. Fibula harvested before 9 years old tend to cause valgus deformity although with no functional impairment in gait or ankle stability. Gait instability is noted in iliac crest free flaps if harvested before the second decade of life. Scapular flap harvested before the end of adolescence causes asymmetrical growth 6.
In our own experience, we have had 3 mandibular reconstructions in pediatric patients with long-term follow-up. All cases were primary reconstruction after removal of benign mandibular tumors (2 ameloblastoma ; 1 osseous fibroma). 2 patients had preserved condyle ; had growth of the mandible as assessed by cephalometric X-Ray at 6 months ; 3 years post-surgery. The 2 patients had no gait abnormalities but 1 had slight weakness of dorsiflexion at the ankle (Figures 1 ; 2). One patient who had removal of her condyle had asymmetric growth of her mandible with class III malocclusion. She also had compartment syndrome 4th-day post-op due to a primary closure of the harvest site even if a skin paddle was harvested. She was noted to have a 2-cm discrepancy in leg length ; with ankle inversion 2 years post-operation (Figures 3, 4, 5).

General Pre-operative, Intra-operative and Post-operative considerations
Co-morbidities which may affect flap outcome are rarely seen in children. However, obesity, genetic disorder or syndrome, atopic disease, and psychiatric disease should be screened and examined. Pre-operative radiation and chemotherapy for patients with malignant tumors such as sarcoma may contribute to possible complications 1.
Intraoperatively, flap harvest and microsurgical anastomosis are done to reconstruct the defect. Flap harvest can be done with the aid of loupe magnification or microscopes to avoid injury to small perforators supplying the flap such as in ALT free flap harvest. Venous and arterial anastomosis is commonly performed in end-to-end using interrupted suture technique. Running or coupled arterial anastomosis was associated with increased immediate complications. Venous coupler device can also be used in children 1.
Improved outcome in the pediatric population is noted when surgery is done in high volume centers 3. Post-operative monitoring is essential in this population because there is a thrombosis rate of 6.8%. Monitoring is a combination of clinical observation, conventional Doppler ultrasonography and surface temperature probe 6. Implantable doppler can also be used for monitoring 1. A study by Starnes-Roubaud et al. 1 showed an immediate complication rate of 15.6% with wound infection as the highest at 3.7%. Late complications were delayed union or non-union (n = 5, 4.6%), wound healing issues requiring operative intervention (2.8%), and fistula formation (2.8%).

Conclusion
The use of free flaps in the pediatric population for various head and neck defects such skull base, congenital defect, and mandibular reconstruction is highly feasible and reliable with success rate comparable to adults.

Key points
• Pediatric free flap reconstruction for head and neck defects is
• Pre-operative assessment tools such as CAD/CAM and CT Angiography of legs may aid in optimal free flap reconstruction in pediatric skull base defects.
• Delayed mandibular reconstruction after growth spurt may be an option especially for patients with malignancy or extensive mandibular defects
• Running or coupled arterial anastomosis was associated with increased immediate complications

I cant paste the pictures here. I don’t know what I doing wrong. Will send the pictures by email
Figure 1. Patient J.A. pre-operation (A) and 6 months post-operation (B)
Figure 2. Panoramic x-ray showing the bony union of the fibula w native mandible (A) & good occlusion on cephalometry (B)
Figure 3. Patient N.T. pre-operation (A) and 1 year and 8 months post-operation (B).
Figure 4. The left leg of Patient N.T. with blisters due to compartment syndrome 4 days post-operation (A) and 1 yr 8 months post-operation (B)
Figure 5. Panoramic x-ray showing the bony union of the fibula w the native mandible. Note condylar resection done (A). Cephalometric x-ray showing class 4 malocclusion (B)

References:
1. Starnes-Roubaud MJ, Hanasono MM, Kupferman ME, et al. Microsurgical reconstruction following oncologic resection in pediatric patients: a 15-year experience. Ann Surg Oncol 2017; 24:4009-4016.
2. Markiewicz MR, Ruiz RL, Pirgousis P, et al. Microvascular free tissue transfer for head and neck reconstruction in children: part I. J Craniofac Surg 2016; 27:846-856.
3. Izadpanah A. Moran SL. Pediatric microsurgery a global overview. Clin Plastic Surg 2017; 44:313-324.
4. Duek I, Pener-Tessler A, Yanko-Arzi R, et al. Skull base reconstruction in the pediatric patient. J Neurol Surg B 2018; 79:81-90.
5. Zhang WB, Liang T, Peng X. Mandibular growth after pediatric mandibular reconstruction with the vascularized free fibula flap: a systematic review. Int J Oral Maxillofac Surg 2016; 45:440-447.
6. Elledge R, Parmar S. Free flaps for head and neck cancer in pediatric and neonatal patients. Curr Opin Otolaryngol Head Neck Surg 2018; 26:127-133.
7. Hu L, Yang X, Han J, et al. Secondary mandibular reconstruction for pediatric patients with long-term mandibular continuity defects: a retrospective study of six cases. Int J Oral Maxillofac Surg 2017; 46:447-452.