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case_images: Abdominal imaging demonstrates a low-density mass involving the rectosigmoid colon.. The rounded thick-walled structure measures approximately 4 cm (
  arrow). There is some adjacent inflammation in the presacral space as well as prominent lymph nodes. Given the radiological findings the differential diagnosis includes transmural abscess versus inflammatory carcinoma of the sigmoid colon.
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case_images: Computerized tomography (CT) imaging of the abdomen and pelvis showed a sigmoid mass indicating a differential diagnosis of a transmural abscess versus a malignant inflammatory process in the sigmoid colon ( Figure 1).
case_images: Pathology of the rectal mass demonstrates a squamous carcinoma.. At medium and high power magnification, hematoxylin and eosin (HE) staining reveals sheets of poorly differentiated squamous cells invading the surrounding submucosal tissue (HE x40 and x100). Immunohistochemical staining for the squamous cell marker CK5/6, visualized by a cytoplasmic red-chromogen reaction, is positive (CK5/6 x40 and x100). Together histopathology and immunostaining show a poorly differentiated squamous cell carcinoma originating from rectal tissue.
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case_images: The malignant cells showed strong cytokeratin 5/6 (CD5/6) immunoreactivity ( Figure 2).
case_images: PET scans demonstrate a rectal malignancy.. Imaging reveals a large focus of hypermetabolic activity in the rectosigmoid colon with a SUV of 16 and diffuse stranding in the region (
  arrows). There are multiple slightly prominent perirectal lymph nodes with the maximal SUV of 3.3 (
  arrowheads). There is presacral fat stranding and retroperitoneal lymphadenopathy, none of which exhibit hypermetabolism. No evidence of malignancy is noted above the diaphragm. Expected physiologic uptake of F-18 fluorodeoxyglucose is observed in the kidneys and brain. Given these findings, the rectal tumor was determined to be stage III rectal squamous cell carcinoma.
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case_images: For tumor staging and evaluate for distant metastatic disease, the patient had a positron emission tomography (PET) scan, which showed a rectosigmoid mass in the colon with a standardized uptake value (SUV) of 16 and multiple PET-avid pelvic lymph nodes with SUVs of 2-3 ( Figure 3).
case_images: Case report timeline.. Presented according to CARE guidelines.
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case_images: Given the patient's good response to chemotherapy and radiation, she was started on adjuvant chemotherapy with FOLFOX (leucovorin, 5-FU, and oxaliplatin) ( Figure 4). The patient remains alive, healthy, and in complete remission following cessation of FOLFOX chemotherapy three years ago ( Figure 4).