Myometrial hyperplasia: proposed criteria for a discrete morphological entity.

Myometrial hyperplasia is not a well-established morphological entity. Technical obstacles regarding uterine weight, myometrial cellularity, and myometrial cell orientation have made it difficult to establish objective criteria for diagnosis. In this study, 15 slides that had been interpreted as within normal limits on routine examination were reevaluated because there were areas of myometrium that stood out as relatively blue on scanning magnification of H&E-stained sections. Morphometrically, they all had increased myometrial cellularity, compared with normal myometrium elsewhere on the same slide (P < 0.05), and an increased nucleus/cell ratio (P < 0.001). They occurred in three patterns. The diffuse inframucosal form and the subserosal plaque-like form sometimes corresponded to grossly detectable inframucosal bulges or subserosal ridges. There was also an occult, microscopic intramural pattern of myometrial hyperplasia, which differed from seedling leiomyomas by its lack of nodularity and compression of adjacent myometrium. We propose that these criteria may permit an objective diagnosis of myometrial hyperplasia. We believe that it will be of interest to explore the clinical significance, cell biology, and pathogenesis of this distinctive variation in myometrial structure.