Histologic Hitchhikers: A Review of Common Exogenous Artifacts Encountered During Mohs Micrographic Surgery.

Background: Exogenous artifacts can interfere with accurate histologic tissue evaluation on frozen sections during Mohs micrographic surgery (MMS). Mohs surgeons should be aware of these anomalies to avoid potential misdiagnoses.
Objective: To review exogenous artifacts encountered in frozen tissue pathology during MMS.
Methods: A literature search was conducted in PubMed to identify studies reporting on exogenous artifacts encountered during MMS and a list of previously described exogenous artifacts was compiled. A retrospective examination of frozen histology slides from recent Mohs cases at the authors' institution was performed to obtain illustrative examples of these artifacts, supplemented by formalin-fixed paraffin-embedded samples when frozen examples could not be found.
Results: Exogenous artifacts represent foreign bodies that have been externally introduced into the skin or artifacts resulting from other external factors. If frozen section evaluation is inaccurate, overdiagnosis can occur during MMS, resulting in unnecessary layers, larger margins, and more complex reconstructions. These exogenous tissue changes can mimic inflammatory processes and melanocytic or keratinocyte malignancies on histology.
Conclusion: Exogenous artifacts are common findings during margin assessment in Mohs micrographic surgery. The resulting histological findings can be confusing but correlating them with the clinical and surgical history often reassures surgeons. Recognizing these artifacts facilitates accurate diagnosis and promotes optimal patient care.
(Copyright © 2024 by the American Society for Dermatologic Surgery, Inc. Published by Wolters Kluwer Health, Inc. All rights reserved.)