case_images: PMC11210213_01
case_images: Plain CT imaging [(A), arrow  ] revealed a round soft tissue density lesion in the left lower quadrant abdomen, with the boundary of the lesion with the sigmoid colon not being distinct. On multiphasic contrast-enhanced CT scans [(B-D), arrow  ], the lesion demonstrated mild to moderate enhancement. The CT values for the non-contrast scan phase, arterial phase, venous phase, and delayed phase were 46 HU, 57 HU, 67 HU, and 70 HU, respectively.
case_images: fmed-11-1425112-g001.jpg
case_images: PMC11210213_01_fmed-11-1425112-g001.jpg
case_images: fig1
case_images: The plain CT scan image (Figure 1A) identified a nodular mass with isodensity in the left lower quadrant of the abdomen, measuring approximately 2.3 x 3.1 cm, with an indistinct border in relation to the sigmoid colon. The multiphase contrast-enhanced CT scan images (Figures 1B-D) demonstrated the lesion exhibiting mild to moderate enhancement.
case_images: 18F-FDG PET-CT MIP image [(A), arrow  ] revealed a lesion with increased FDG uptake in the left lower quadrant of the abdomen. Axial CT [(B), arrow  ] and fused axial PET-CT [(C), arrow  ] images depicted an isolated, round soft tissue density mass in the same area, with increased FDG uptake and a SUVmax of 3.6. Coronal and sagittal CT images [(D,F), arrow  ] and their corresponding fused PET-CT counterparts [(E,G), arrow  ] revealed an indistinct boundary between the mass and the sigmoid colon.
case_images: fmed-11-1425112-g002.jpg
case_images: PMC11210213_01_fmed-11-1425112-g002.jpg
case_images: fig2
case_images: The maximum intensity projection (MIP) image (Figure 2A) revealed a focal area of increased FDG uptake in the left lower quadrant of the abdomen. The axial CT and fused axial PET-CT images (Figures 2B,C) revealed an isolated, round, soft-tissue mass with isodensity in the left lower quadrant, showing increased FDG uptake and a maximum standardized uptake value (SUVmax) of 3.6. The corresponding coronal and sagittal CT and fused PET-CT images (Figures 2D-G) demonstrated that the mass had an indistinct margin in relation to the sigmoid colon, suggesting a gastrointestinal stromal tumor (GIST) as a likely diagnosis.
case_images: Histological and immunohistochemical characteristics of sigmoid RDD. The histological section exhibited clusters of histiocytes amidst lymphocytes and plasmacytes, with a fibrotic background. Emperipolesis, characterized by small lymphocytes and plasmacytes within the cytoplasm of the histiocytes, was evident [(A,B); HE 20x]. The large histiocytes were positive for CD68 [(C); HE 40x] and S100 [(D); HE 40x].
case_images: fmed-11-1425112-g003.jpg
case_images: PMC11210213_01_fmed-11-1425112-g003.jpg
case_images: fig3
case_images: The presence of small lymphocytes and plasma cells within the cytoplasm of some histiocytes, a phenomenon known as emperipolesis, was noted (Figures 3A,B). Immunohistochemical analysis confirmed that the histiocytes were positive for CD68 (Figure 3C), S100 (Figure 3D), and CD163, while negative for CK, ALK, CD1a, and Langerin.