Histopathological findings of the nodule-in-nodule appearance. (a) In the small nodules, the boxed areas in Figure 5(b)
(×20) are marked for further magnifications at the top left-side image. Inset squares B, C, and D are magnified in Figures 6(b)
(×20), and 6(d)
(×20), respectively. (b) More densely packed endometrial stromal cells with a concentric arrangement of the small spiral arteriole-like vessels (indicated by arrows) exhibit an expansile growth pattern. (c) Sex cord-like elements are observed partially within some small nodules. (d) Peripheral areas around the small nodule are more loosely packed with endometrial stromal sarcoma (ESS) cells. Some areas are intermingled with the normal uterine myometrium. (e) ESS cells with the eosinophilic cytoplasm in hematoxylin and eosin (HE) staining are observed to be partially stained positive with cluster of differentiation (CD) 10 immunohistochemistry (IHC) markers. (f) ESS cells with the eosinophilic cytoplasm in HE staining are observed to be partially stained positive with desmin IHC markers. (d), (e), and (f) images result in the diagnosis of low-grade endometrial stromal sarcoma (LG-ESS) with smooth muscle differentiation.