Assessing the Quality of Long-Term Stored Tissues in Formalin and in Paraffin-Embedded Blocks for Histopathological Analysis

INTRODUCTION: Formalin is the most commonly used fixative which enables for long-term storage of specimens and preserves morphologic features allowing the microscopic evaluation for future research analysis. Archival collections of the tissue serve as a reliable tool for diagnostic research purpose. They have an important role in on-going patient care, allows for evaluation of recurrent cases for diagnostic purpose and rare case specimens can also be used as an educational tool as well as for further biomedical research purposes. However, studies assessing quality and their usefulness for such purposes are scanty. Hence, the present study is aimed at evaluating and comparing the tissue changes after long-term storage in formalin as well as in paraffin-embedded blocks. METHODOLOGY: Three study groups include specimens stored in formalin for a minimum of 5 years (long-term fixed tissue) and their corresponding paraffin-embedded old tissue blocks along with freshly fixed tissues taken as controls which were subjected to routine histopathological procedures and were assessed for macroscopic and microscopic evaluation.Chi-square test and Z-proportion tests were considered for statistical analysis. RESULTS: Prolonged storage of the tissues in formalin showed variation in color and consistency, difficulty in cutting during grossing with inadequate sectioning characters, loss of tissue integrity and architecture, and inadequate nuclear and cytoplasmic details. CONCLUSION: On histological analysis, prolonged formalin-stored specimens showed deleterious effects than archival blocks. Hence, it can be proposed that tissues are better preserved in paraffin blocks rather than in formalin for further biomedical research purposes.