Evaluation of the temporal relationship between formalin submersion time and routine tissue processing on resected head and neck specimen size

Background: Studies show formalin fixation may shrink resected tissue, altering critical elements such as tumour size and surgical margins. To date, no literature exists examining time-dependent shrinkage of head and neck resection specimens. This paper aims to evaluate the temporal relationship between formalin submersion time and resected specimen size. Methods: Twelve male merino sheep were utilised in this study. In each animal tissue was resected from four locations: tongue, labial mucosa, buccal mucosa and sternocleidomastoid (SCM) muscle. Dimensions of the tissue were recorded immediately post-resection and subsequently after 6, 12, 24, 48, 72 and 96 hours of submersion in formalin. Results: After 96 hours of submersion, median shrinkage of specimen length in relation to initial size was 15.5% (11.56-19.5%; P<0.05) and shrinkage in width was 16.7% (13.2-20%, P<0.05). The rate of shrinkage for both length and width was maximal within the first 24 hours, after which shrinkage was markedly reduced. There was generally no difference in tissue shrinkage between individual regions. Conclusions: These findings indicate formalin fixation time results in measurable and significant changes in specimen size of about 16% which evolves and then plateaus at the 24-hour mark. Based on this study all specimens should be submersed in formalin for 24 hours prior to sectioning, as any further tissue shrinkage is then negligible. Standardised fixation protocols should be considered to allow for accurate comparison of surgical specimens.