(024) FIRST TIME ASSESSMENT OF HYMENAL TISSUE IMMUNOHISTOCHEMICAL STAINING FROM PATIENTS WITH NEUROPROLIFERATIVE VESTIBULODYNIA

Abstract Introduction Embryologically, the hymen forms at the junction of the endodermal urogenital sinus and the mesodermal primitive vagina. During fetal development the hymen becomes surrounded by the endodermal vestibule distally and the endodermal vagina proximally (Fig. 1) and therefore, is likely to also be of endodermal origin. Neuroproliferative vestibulodynia (NPV) is a provoked vestibular pain disorder associated with excess immunohistochemical (IHC) staining with CD117, a mast cell marker, throughout the entire 1:00-11:00 o’clock as well as 12:00 o’clock vestibular regions. Although the hymen is surrounded by endodermal tissue, to the best of our knowledge, it has not been established whether hymenal tissue of patients with NPV also would have excess IHC staining consistent with mast cells. This is clinically relevant, as some patients have persistent post-operative pain in the region of the unexcised hymen when vestibulectomy is not complete. Objective We wished to assess, for the first time, CD 117 immunostaining in the hymenal tissue of NPV patients and compare the IHC data with that of excised vestibular tissue. Methods Medical records from the patient cohort who underwent complete vestibulectomy between April 1, 2024 and May 31, 2024 were reviewed. For this patient cohort, three separate specimens were sent to pathology for analysis: i) 1:00-11:00 vestibule, ii) 12:00 vestibule and iii) hymenal tissue that had been sharply separated from the 1:00-11:00 excised vestibular specimen (Fig. 2). Slides of IHC-stained vestibular tissue specimens from the 1:00-11:00 and 12:00 vestibule as well as hymen were examined, and images captured using a 3.5 megapixel digital camera attached to a light microscope at 100× magnification. A minimum of 2 photomicrographs were taken for each stained slide, identifying representative regions of the epithelial basement membrane and adjacent subepithelium. A total of 48 photomicrographs of slides stained for CD117 were assessed. Each photomicrograph was assigned a unique identification number. Manual counting of CD117-immunopositive stained cells was performed on these photomicrographs for comparison to Bornstein’s data that >8 mast cells per high power field confirmed the diagnosis of NPV. Results A total of 8 NPV patients (mean age 28 years, range 21–42) were included in the chart review. All had symptoms consistent with NPV, and all had other conditions associated with aberrant mast cell activity. Both 1:00– 11:00 and 12:00 vestibular tissue specimens had >8 mast cells per high power field. The hymenal tissue in all 8 patients also contained >8 mast cells per field at the same magnification (Fig. 3). Median manual mast cell count values were similar in 1:00-11:00 o’clock and 12:00 vestibular regions and the hymen: 45 (range 21-67), 39 (range 19-63) and 43 (range 18-68) mast cells per 100× field, respectively. Conclusions NPV is a field disease of the endoderm, which based on these data, includes all hymenal tissue. To maximize success from complete vestibulectomy for NPV, excision of all hymenal tissue should be considered. Disclosure No.