Qualitative Comparison of Cryostat- versus Snap-Frozen Neurosurgical Intraoperative Consultations

Abstract

Background: Frozen sections (FS) are common in neurosurgery to address varied clinical concerns. Artifacts in central nervous system (CNS) FS can be severe and affect or hinder interpretation. We performed a case-control study using a semiquantitative scale: the Histologic Preservation Score (HPS), and a quantitative scale: the Ice Crystal Vacuolization Score (ICVS), to compare the histologic quality yielded by snap- versus cryostat freezing techniques. Material and Methods: All specimens were sectioned in 2 halves, one half was used for FS and the other for permanent evaluation. HPS assigns a distortion score to the FS sample using the non-frozen half as the comparator: 1 = minimal, 2 = slight, 3 = moderate, 4 & 5 = severe. The ICVS is the average size in µm of the 5 largest vacuoles/0.05 mm2, evaluated on digitized slides. Results: 86 CNS-FS were collected: 22 snap- and 64 cryostat-FS. Significant differences in HPS: 2.28 versus 2.84 ( p <0.05) and ICVS 7.47 versus 14.56 ( p < 0.001) were obtained for snap- versus cryostat-FS, respectively. HPS and ICVS showed a strong correlation: R2 = 0.63, p < 0.0001. Histologic distortion was worse for neuroglial than mesenchymal tissue by both methods; however, a significant difference was only observed in cryostat-FS: HPS: 3.23 versus 2.33, p < 0.001; ICVS: 16.86 μm versus 10.26 μm, p < 0.001. Conclusion: Snap-FS yields better histologic quality than cryostat-FS for CNS-FS, and the difference is more pronounced in neuroglial samples. HPS and ICVS correlate strongly, indicating that the histologic quality is inversely proportional to water-crystallization. These results may apply to other areas of surgical pathology.

Letter to the Editor - Saline is Detrimental to Brain Frozen Sections

“…Morphologically, saline-induced ice crystal artefact appears as variously sized vacuoles causing cellular and fiber distortion, 2 similar to that depicted in figure 3 of the article. 1 A second artefact that may not be appreciated can be seen especially in frozen muscle sections. If tissue is kept at −20 °C for an extended period of time (as might occur in a cryostat), sublimation occurs.…”

“…I read with interest the paper written by David Priemer and his team on the qualitative comparison of cryostat- versus snap-frozen neurosurgical intraoperative consultations. 1 They introduced two assessment scales: a semiquantitative Histologic Preservation Score (HPS) and a quantitative Ice Crystal Vacuolization Score (ICVS), to compare the histologic quality yielded by snap- versus cryostat freezing techniques. The authors have concentrated on the analytical issues of tissue freezing and have not mentioned the pre-analytical factors that can affect their assessment scores.…”

“…Morphologically, saline-induced ice crystal artefact appears as variously sized vacuoles causing cellular and fiber distortion, 2 similar to that depicted in figure 3 of the article. 1…”