Shrinkage of skin excision specimens: formalin fixation is not the culprit

Discrepancies between cutaneous specimen sizes reported by the dermatosurgeon and the pathologist are important to evaluate because of their legal implications for malignant tumours and the downcoding of surgical acts.

The objective of this study was to determine the magnitude of changes in size and the factors influencing the retraction of routine skin excision specimens.

Three measurements of 82 skin excision specimens--consisting of length and width of the planned surgical excision (in vivo), length, width and depth of the specimens following excision (ex vivo) and of the specimens after formalin fixation (in vitro)--were performed and compared using a nonparametric paired test. Factors (age, sex, type and location of the lesions and initial measures) that could influence the amount of shrinkage were analysed using multiple linear regression models.

The mean in vivo to in vitro shrinkage was 16% for length and 18% for width (P<0.001). The shrinkage was significant between in vivo and ex vivo measures (P<0.001), while no difference was observed between ex vivo to in vitro measures. In multivariate analysis, length shrinkage increased significantly with initial length (regression coefficient of 0.24, P=0.001) and limb location (1.25, P=0.048), and decreased significantly with initial width (-0.19, P=0.016). After adjusting for initial width, width shrinkage was neither significantly associated with type of lesion (malignant or not, P=0.20), nor with location (P=0.35).

Shrinkage of skin excision specimens occurred immediately after surgical excision and prior to formalin fixation. Patients' age, sex and type of skin lesion did not influence the amount of shrinkage. Length shrinkage was more important for specimens excised from the extremities and increased with initial length and smaller width.