Multi-Observer Study on the Assessment of Pediatric Gonadal Tumors Using Higher Harmonic Generation Microscopy as Compared to Conventional Histology

Background/Objectives: Pediatric gonadal tumors are rare tumors, and germ cell tumors (GCTs) are the most common subgroup. GCTs are heterogeneous tumors and have different subtypes that can be either benign or malignant. Therefore, extensive sampling of the resected tumor is required to obtain an accurate diagnosis. Higher harmonic generation microscopy (HHGM) is an innovative imaging technique that enables rapid visualization of fresh tissue without the need for preparation or staining. This makes it particularly valuable for sample selection, as the tissue can be reused for further analysis. This study aims to evaluate the accuracy of pathologists detecting normal gonadal tissue, germ cell tumors, and other pediatric gonadal tumors in HHGM images. Methods: Twenty-eight samples of twenty-two patients with a germ cell tumor or other gonadal tumor were imaged with the HHG microscope and subsequently processed for histology. Overview images of the samples were made in 10 s per mm², and high-quality images in 1 min per mm². A multi-observer study was performed with five expert pathologists. Results: Pathologists were able to differentiate between tumor and non-tumor tissue with an accuracy of 75% (21/28) on the HHGM images versus an accuracy of 89% (25/28) on the corresponding histology. Discrepancies mainly concerned teratoma cases for HHGM as well as H&E, indicating that sampling errors of these heterogeneous tumors affected the outcomes of this study adversely. Conclusions: Although the sample size was limited by the rarity of these tumors, our data show that HHGM is a promising technique for the rapid assessment of pediatric gonadal tumor samples, particularly in evaluating their representativeness.