PMC7568784_01
(a) Axial abdomen/pelvis CT showing a soft tissue mass (arrow) at the tip of the appendix. (b) Coronal image of the soft tissue mass (arrow) at the tip of the appendix.
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While chest CT did not show any findings of intrathoracic malignancy, abdomen and pelvis CT showed a 2.4 x 3.2 cm soft tissue mass at the tip of the appendix (Figure 1) as well as a 5.3 x 2.5 cm lobular perirectal mass (Figure 2) which were concerning for a malignancy.
(a) Axial abdomen/pelvis CT showing a soft tissue mass (arrow) inseparable from the rectal wall. (b) Sagittal abdomen/pelvis CT showing a soft tissue mass (arrow) inseparable from the rectal wall.
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While chest CT did not show any findings of intrathoracic malignancy, abdomen and pelvis CT showed a 2.4 x 3.2 cm soft tissue mass at the tip of the appendix (Figure 1) as well as a 5.3 x 2.5 cm lobular perirectal mass (Figure 2) which were concerning for a malignancy.
Axial image of MRI pelvis showing a nonspecific rectal mass (arrow).
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MRI of the pelvis was also performed again demonstrating an infiltrative rectal soft tissue mass which was nonspecific (Figure 3).
CT-guided core needle biopsy of the appendiceal mass.
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Three 18-gauge (Figure 4) core needle biopsies of the appendiceal mass were obtained and submitted to the pathology department for evaluation.
(a) Histiocytes with characteristic prominent nucleoli and pale abundant cytoplasm (hematoxylin and eosin, 600x). (b) Histiocytes with emperipolesis (hematoxylin and eosin, 600x). (c) Immunohistochemistry of the appendiceal mass with S-100 highlighting large histiocytes with prominent nucleoli (600x). (d) Immunohistochemistry of the appendiceal mass with CD68 highlighting large areas of histiocytes. (e) Immunohistochemistry of the appendiceal mass with IgG4-positive cells.
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Histologic sections showed a heterogeneous lesion composed predominantly of histiocytes with numerous scattered plasma cells and lymphocytes (Figure 5(a)). Several foci of emperipolesis were also identified (Figure 5(b)). IHC (Figure 5(d)) with CD68 also highlighting large areas of histiocytes. IgG4 IHC staining showed significantly increased positive cells (approximately 53 IgG4-positive cells) in a single 400x field (Figure 5(e)) in a background of predominantly scattered and focally aggregated positive cells.