case_images: PMC8182168_01
case_images: (a) Magnification in hematoxylin-eosin staining x 10: retro-gastric
  mass biopsy: tumor proliferation with small round cells arranged
  in diffuse layers, separated by thick fibrous spans; (b)
  magnification in hematoxylin-eosin staining x 40: small tumor
  cells with a high cytoplasmic ratio, the nuclei are
  hyperchromatic with some mitosis patterns, the cytoplasm is
  sparsely abundant; (c) CD 99 positivity in tumor cells
  (magnification x40).
case_images: 10.1177_2050313X211022426-fig1.jpg
case_images: PMC8182168_01_10.1177_2050313X211022426-fig1.jpg
case_images: fig1-2050313X211022426
case_images: The anatomic pathology examination concluded a relapse of her ES for both the sites (Figure 1).
case_images: MRI T1 sequence, axial cut: (a) retro gastric mass in contact with
  the tail of the pancreas in distinctly hyposignal T1 and
  measuring 4.41 x 1.51 cm in its greatest diameter; (b) MRI T1
  Fat-Sat sequence, axial cut: retro-gastric mass in contact with
  the tail of the pancreas presents an intermediate signal; (c)
  MRI T1 Fat-Sat Gadolinium, axial cut: spiculated fibrous mass
  with a transverse thickening at the gastric post side, this mass
  presents a peripheral enhancing.
case_images: 10.1177_2050313X211022426-fig2.jpg
case_images: PMC8182168_01_10.1177_2050313X211022426-fig2.jpg
case_images: fig2-2050313X211022426
case_images: T1 and T2 with non-gadolinium-enhancing (Figures 2 and 3). These findings invoked a fibrous lesion.
case_images: Axial cut: retro-gastric mass in contact with the tail of the
  pancreas in distinctly hyposignal T2.
case_images: 10.1177_2050313X211022426-fig3.jpg
case_images: PMC8182168_01_10.1177_2050313X211022426-fig3.jpg
case_images: fig3-2050313X211022426
case_images: T1 and T2 with non-gadolinium-enhancing (Figures 2 and 3). These findings invoked a fibrous lesion.
case_images: Specimen of caudal splenopancreatectomy, showing the tail of
  pancreas and the spleen resected in monobloc.
case_images: 10.1177_2050313X211022426-fig4.jpg
case_images: PMC8182168_01_10.1177_2050313X211022426-fig4.jpg
case_images: fig4-2050313X211022426
case_images: We performed an excision of the tumor with distal pancreatectomy and splenectomy (Figure 4).
case_images: Magnification in hematoxylin-eosin staining x 20: (a)
  fibro-hemorrhagic areas of the peripancreatic parenchyma without
  detectable tumor residue. Magnification in hematoxylin-eosin
  staining x 20; (b) deposition of hemosiderin in a mononuclear
  inflammatory infiltrate. Magnification in hematoxylin-eosin
  staining x 20; (c) extensive hemorrhagic areas in the presence
  of ectatic vessels in a fibrous stroma. Magnification in
  hematoxylin-eosin staining x 20; and (d) no evidence of tumor
  proliferation in the pancreatic and peripancreatic
  parenchyma.
case_images: 10.1177_2050313X211022426-fig5.jpg
case_images: PMC8182168_01_10.1177_2050313X211022426-fig5.jpg
case_images: fig5-2050313X211022426
case_images: The anatomic pathology examination concluded a complete therapeutic effect within the resected mass (Figure 5).