Inter- and intra-observer variation in the histopathological reporting of cervical squamous intraepithelial lesions using a modified Bethesda grading system

Objective 1. To assess inter- and intra-observer variation in the histopathological reporting of cervical colposcopic biopsies using a histologic modification of the cytological Bethesda grading system; 2. to determine the histologic profile of those cases which resulted in diagnostic disagreement. Methods Consecutive cervical colposcopic biopsies (n = 125) were assessed independently by six experienced histopathologists. Cases were classified as normal, low-grade squamous intraepithelial lesion or high grade squamous intraepithelial lesion, Six months later the process was repeated. The degree of inter and intra-observer variation was assessed by kappa statistics. All cases in which there was less than perfect inter and intra-observer agreement were reviewed by the coordinator of the study. Results In the first round of the study inter-observer agreement was generally poor, with unweighted and weighted kappa values ranging from 0.15 to 0.58 (average 0.30) and from 0.21 to 0.61 (average 0.36) respectively. In the second round inter-observer agreement was better, with unweighted and weighted kappa values ranging from 0.08 to 0.55 (average 0.33) and from 0.22 to 0.59 (average 0.42). Ten of the 15 pairs of observers achieved fair inter-observer agreement using weighted kappa analysis. The degree of intra-observer agreement was better, unweighted and weighted kappa values ranging from 0.26 to 0.61 (average 0.47) and from 0.34 to 0.62 (average 0.51) respectively. Two of the six participants achieved fair intra-observer agreement and two achieved good intra-observer agreement using weighted kappa analysis. There were marked difficulties in the separation of normal squamous epithelium from low grade squamous intraepithelial lesion and in the separation of low grade from high grade squamous intraepithelial lesions. Histopathological review revealed that many of the difficulties in the separation of normal and low grade squamous intraepithelial lesion were in the distinction between superficial vacuolated cells and true koilocytes. Difficulties also resulted in the separation of basal cell hyperplasia, inflammatory associated changes and immature squamous metaplasia from low grade squamous intraepithelial lesion. Conditions which resulted in difficulty in the separation of low grade and high grade squamous intraepithelial lesions included florid koilocytotic change and immature metaplastic squamous epithelium with atypia. In some cases, there was a full spectrum of diagnoses from normal to high grade squamous intraepithelial lesion. These were largely cases of immature metaplastic squamous epithelium with atypia and of thin or atrophic squamous epithelium with atypia. Conclusions Most pairs of observers can achieve fair inter-observer agreement in the reporting of cervical colposcopic biopsies using a modified Bethesda system. Intra-observer agreement is also generally fair to good using this system. It may be that a two tier grading system is more appropriate for the histopathological reporting of these biopsies than the traditional three-tier intraepithelial neoplasia (CIN) system.