1. ¹Department of Scientific Laboratories, Armed Forces Institute of Pathology, Washington, DC, USA
2. ²Bio-Quick Inc., Silver Spring, MD, USA
3. ³Department of Genitourinary Pathology, Armed Forces Institute of Pathology, Washington, DC, USA
4. ⁴Center for Prostate Disease Research, Rockville, MD, USA
5. ⁵Department of Neuropathology, Armed Forces Institute of Pathology, Washington, DC, USA
6. ⁶Department of Hematopathology, Armed Forces Institute of Pathology, Washington, DC, USA

Correspondence: Dr W-S Chu, MD, Department of Scientific Laboratories, Armed Forces Institute of Pathology, Washington, DC 20306-6000, USA. E-mail: chu@afip.osd.mil

^*Deceased.

Received 9 September 2004; Revised 22 October 2004; Accepted 24 October 2004; Published online 17 December 2004.

Abstract

Formalin fixation and paraffin embedding are conventional tissue preservation and processing methods used for histologic diagnosis in over 90% of cases. However, formalin fixation has three disadvantages: (1) slow fixation (16–24 h) hinders intraoperative decision making, (2) slow quenching of enzymatic activity causes RNA degradation, and (3) extensive molecule modification affects protein antigenicity. Applying high-frequency, high-intensity ultrasound to the formalin fixative cuts fixation time to 5–15 min. Fixation of various tissues such as lymph node, brain, breast, and prostate suggests that, compared to the conventional method, implementation of ultrasound retains superior and more uniform tissue morphology preservation. Less protein antigenicity is altered so that rapid immunohistochemical reactions occur with higher sensitivity and intensity, reducing the need for antigen retrieval pretreatment. Better RNA preservation results in stronger signals in in situ hybridization and longer RNA fragments extracted from fixed tissues, probably due to rapid inhibition of endogenous RNase activity. Molecules extracted from ultrasound-fixed tissues are of greater integrity and quantity compared to conventionally fixed tissues, and thus better support downstream molecular analyses. Overall, ultrasound-facilitated tissue preservation can provide rapid and improved morphological and molecular preservation to better accommodate both traditional and molecular diagnoses.