Intraoperative tissue staining of invaded oral carcinoma.

The purpose of this study was to assess the ability of intraoperative tissue staining with consecutive application of 0.4% indigo carmine and 0.5% Congo red to demonstrate the extent and border of oral carcinoma invasion. Seventeen patients were included in the study. Once the oral tumor was resected, a vertical section of surgical specimen was taken from the central part of the tumor. The extent and border of the invaded carcinoma were assessed on digital microscopic examination with tissue staining. The results of assessments were compared with corresponding results of conventional histopathological analysis with HE staining, which is considered the gold standard. Tissue staining produced a brown-black stain on normal muscle, connective, and salivary tissues but not tumor and epithelial tissues. It clearly demonstrated the extent and border of tumor invasion in 13 of 17 patients (76.5%); however, detection of remnant vital tumor cells in scar tissue after neoadjuvant chemotherapy, and distinction between the tumor and adipose tissue scattered in the muscle tissue was difficult. The results of this study showed that intraoperative tissue staining was a possible method in demonstrating the extent and border of carcinoma deeply invaded in the soft tissue and selecting the site for additional frozen section analysis, although the method needed some refinement.