Background: Extensive head and neck deformities including bone and soft tissue defects are always challenging for reconstructive surgeons. The purpose of this study was to extend application of the face/scalp transplantation model in rat by incorporation of the vascularized mandible, masseter and tongue, based on the same vascular pedicle, as a new reconstructive option for extensive head and neck deformities with large soft and bone tissue defects. Methods: A total of 12 composite osseomusculocutaneous hemiface/mandible-tongue transplantations were performed in two experimental groups. Group 1 isotransplantation between Lewis rats served as control without treatment (n=6). Group 2 (n=6) composite hemiface/mandible-tongue transplants were performed across MHC barrier between Lewis-Brown Norway (LBN, RT1¹⁺ⁿ) donors and Lewis (RT1¹) recipients. Hemimandibular bone, masseter muscle, tongue and hemifacial flaps were dissected on the same pedicle of external carotid artery and jugular vein and were transplanted to the donor inguinal region. All allogenic transplant recipients received 16mg/kg/day of CsA monotheraphy tapered to 2 mg/kg/day and maintained at this level thereafter. All animals were monitored for sign of rejection such as erythema, edema, hair loss, desquamation. Flap angiography and CT scan evaluated allograft viability. Flow cytometry assessed donor-specific chimerism for MHC class I- RT1ⁿ antigen. H&E staining revealed bone histology and tested inflammatory response and grade of allograft rejection. Results: Isograft controls survived indefinitely. Six hemiface/mandible-tongue allotransplants survived up to 100 days (still under observation). Flap angiography demonstrated intact vascular supply to the bone. No signs of rejection and no flap loss were noted. CT scan and bone histology confirmed viability of bone components of the composite allografts. Viability of tongue was confirmed by pink color, bleeding after puncture and histology. H+E staining determined the presence of viable bone marrow cells within transplanted mandible. Donor-specific chimerism at day 100 posttransplant was evaluated by presence of donor T-cells (2.7% CD4/RT1ⁿ, 1.2% CD8/RT1ⁿ) and (B-cells 11.5% CD45RA/RT1ⁿ). Conclusions: We have introduced a new model of composite osseomusculocutaneous hemiface/mandible-tongue allograft transplant. Long-term allograft acceptance was accompanied by donor specific chimerism supported by vascularized bone marrow transplant of the mandibular component. This model may serve as a new reconstructive option for coverage of the extensive head and neck deformities involving large bone and soft tissue defects performed in one surgical procedure.
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