Extraskeletal Ewing sarcoma primarily arising in the stomach and omentum in children: a case series

Figures

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  Figure 1. CECT of the abdomen and pelvis, demonstrating treatment response in Case 1. (a and b) Pre-treatment images demonstrate a voluminous, heterogeneously enhancing gastric neoplasm centered along the lesser curvature, exhibiting a complex growth pattern with both endophytic and exophytic components. (a) Axial image: The white arrow denotes the peripherally enhancing tumoral rim, and the yellow arrow delineates an internal hypoattenuating component consistent with liquefactive necrosis or cystic degenerative change. (b) Coronal image: The white arrow denotes the predominant exophytic neoplastic mass, while the yellow curved line delineates obliteration of the intervening fat plane with contiguous extension into the adjacent hepatic parenchyma, suggesting direct visceral invasion and resultant luminal compromise. (c and d) Post-treatment images obtained following neoadjuvant systemic therapy demonstrate a substantial partial radiographic response (RECIST criteria), characterized by marked interval reduction in the primary gastric mass and associated components. (c) Axial image: The white arrow demarcates residual hypoattenuating soft tissue proliferation persisting in the gastrohepatic…

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  Figure 2. Gross surgical specimen following wedge gastrectomy, Case 1. A lobulated, exophytic gastric neoplasm with a tan-white, fleshy serosal surface is shown. (a) Serosal aspect demonstrating an outwardly projecting mass arising from the muscularis propria. (b) Luminal aspect demonstrating submucosal protrusion with intact overlying gastric mucosa, consistent with a non-epithelial origin. Colored arrows denote key features: Red, tumor bulk; blue, intact mucosa/serosa; yellow, tumor origin at the muscularis propria. Ruler included for size reference.

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  Figure 3. Serial gross sections of the resected gastric wedge specimen, Case 1. Cross-sections reveal a solid, tan-white, fleshy neoplastic mass with areas of multifocal hemorrhagic degeneration and focal necrosis. Peripheral surgical margin ink is applied for orientation and margin assessment (arrowheads). Sequential slices are numbered (1–8) for topographic mapping and histopathologic correlation; display arrangement is non-chronological relative to anatomic order.

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  Figure 4. Photomicrographs (H&E stain) of the excised wedge gastrectomy specimen, Case 1, highlighting high-risk histopathological features. (a) Low-power magnification demonstrating transmural neoplastic infiltration traversing the full thickness of the gastric wall, extending from the serosal surface (left) through the muscularis propria and submucosa to the mucosa (right) (bracket), consistent with pathologic T4a staging. Representative foci of desmoplastic stroma with irregularly infiltrating tumor cell nests are indicated (arrowheads). (b) High-power magnification demonstrating lymphovascular invasion (LVI), characterized by cohesive neoplastic emboli within thin-walled, endothelial-lined vascular channels (arrows). The intraluminal tumor cell clusters are closely opposed to the endothelium, confirming intravascular tumor involvement, an independent predictor of nodal metastases and decreased survival.

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  Figure 5. Baseline contrast-enhanced CT of the abdomen and pelvis acquired prior to initiation of systemic therapy, demonstrating extensive intra-abdominal and pelvic disease burden. (a) Axial CECT, upper abdomen: A voluminous, heterogeneously enhancing mesenteric mass (arrow) is identified, inducing significant mass effect with resultant displacement and compressive remodeling of adjacent enteric loops. Concomitant moderate-volume hypoattenuating intraperitoneal free fluid (arrow) is observed, consistent with malignant ascites in the appropriate clinical context. (b) Axial CECT, pelvis: A large, lobulated, heterogeneously enhancing soft tissue mass (arrow) occupies the central pelvic cavity, producing mass effect with cephalad and lateral displacement of adjacent pelvic viscera, including the urinary bladder and rectosigmoid colon. This finding is consistent with caudal extension of the dominant intra-abdominal tumor burden into the pelvic compartment. (c) Coronal CECT, abdomen, and pelvis: Diffuse peritoneal carcinomatosis is demonstrated. Circumferential infiltration and nodular thickening of the greater omentum (ellipse) are identified, consistent with omental caking. Multifocal soft…

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  Figure 6. Omental biopsy (H&E preparation, 100× magnification) revealing an infiltrative DSRCT consistent with extraosseous Ewing sarcoma, Case 2. The photomicrograph demonstrates effacement of indigenous omental stroma by cohesive sheets of uniform cells exhibiting a markedly elevated nuclear-to-cytoplasmic (N:C) ratio, finely stippled basophilic chromatin, and attenuated eosinophilic cytoplasm. The neoplastic proliferation, occupying the right aspect of the field (blue arrowheads), directly abuts intact univacuolated mature adipocytes along the left (blue arrowheads). The transition is delineated by a desmoplastic fibrocollagenous band (gold arrowheads) containing hemorrhagic necrosis (red arrowheads), highlighting the aggressive architecture of the tumor as it supplants resident adipose parenchyma.

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  Figure 7. Post-chemotherapy MRI of the abdomen and pelvis demonstrating marked interval cytoreduction with residual multifocal abdominopelvic disease. (a) Coronal T2-weighted/post-contrast image: A substantial quantitative reduction in aggregate neoplastic burden is demonstrated relative to baseline imaging, characterized by significant interval diminution in the dimensions of the dominant intra-abdominal mass. Persistent, T2-hypointense multifocal peritoneal implants (arrows) remain distributed along the mesenteric and serosal surfaces, consistent with residual peritoneal sarcomatosis. A residual pelvic lesion is also identified at the inferior margin. (b) Axial image, upper pelvis: Residual mesenteric and peritoneal soft tissue thickening (arrow) is demonstrated, reflecting a marked longitudinal reduction in disease volume following administration of systemic cytotoxic therapy. The morphologic characteristics of the residual tissue are suggestive of a combination of viable tumor and post-treatment desmoplastic change. (c) Axial image, pelvis: A well-circumscribed residual pelvic mass (arrow) is identified, constituting the principal site of persistent macroscopic disease. Adjacent…