Diagnostic modalities in vascularized composite allotransplantation: from histopathology to multimodal strategies.

Background: Vascularized composite allotransplantation (VCA) of the face and limbs restores form and function after devastating injury but, as in other transplant settings, remains limited by the precision of its diagnostic tools. Current surveillance relies on skin biopsy histology, which addresses acute cellular but not antibody-mediated or chronic rejection. More than a decade of clinical experience has revealed persistent diagnostic gaps, including sampling bias and interobserver variability. Methods: Published studies describing histopathologic, molecular, and imaging approaches in human VCA were reviewed to summarize diagnostic advances and identify emerging tools. Results: The Banff 2022 revision introduced vascular modifiers to capture chronic vascular injury. Comparative work indicates that mucosal rejection may occur earlier or more severely than cutaneous rejection. Molecular assays such as donor-derived cell-free DNA, miRNA profiling, and proteomic and transcriptomic panels show promise for early and minimally invasive detection. Discussion: Key challenges in VCA diagnostics include variability in biopsy interpretation across centers, absence of validated molecular and biomarker criteria, and limited integration of multimodal data into clinical workflows. Coordinated multicenter efforts are needed to standardize evaluation and improve early, accurate diagnosis.