A288 TWO RARE PRESENTATIONS: RECTAL LINITIS PLASTICA AND GASTRIC PNEUMATOSIS BOTH CAUSED BY COLORECTAL SIGNET RING CELL CARCINOMA

Signet ring cell carcinoma represents 1% of all colorectal cancers. While rare, it is likely to be encountered in the course of a gastroenterologists career. This subtype of colorectal cancer affects younger patients, has a more aggressive course, later stage at diagnosis and a very poor prognosis compared to typical colorectal adenocarcinoma. Signet cell tumors often present as rigid thickening of hollow organs termed linitis plastica and can be misinterpreted as fibrosis or inflammation on imaging and biopsy with characteristic delays in diagnosis. To increase awareness of a rare condition that is likely to be encountered but can be challenging to diagnose. Qualitative description of two cases. Case 1: 68 year-old male with progressively thin stools, urinary retention and perineal swelling. He was otherwise well, on no regular medications. Colonoscopy revealed a rigid, tight anal canal with a narrow thickened rectum but normal appearing mucosa. CT and MRI revealed non-specific rectal and bladder wall thickening with no masses or lymphadenopathy. No diagnosis was made and he did not attend follow up for several months before returning to hospital with weight loss, nausea and vomiting. CT and MRI imaging showed progressive thickening of the rectum, bladder and distal stomach with negative EGD with repeated biopsy. Deep retropubic surgical biopsies were eventually performed which confirmed the diagnosis of infiltrative signet ring cell carcinoma and he was palliated shortly thereafter. Case 2: 69 year-old female who presented to the emergency department with several weeks of pain, nausea, hematemesis and unintentional weight loss of 25 pounds. She had successful resection of colorectal signet cell carcinoma with chemotherapy 4 years prior with no signs of recurrence until this presentation. CT showed pneumatosis within the gastric wall, and focal stenosis in the duodenal bulb but no definitive mass or lymphadenopathy. Multiple cautious attempts at EGD were performed and biopsies of an obstructed duodenum eventually confirmed infiltrative signet ring cell adenocarcinoma. She subsequently underwent palliative stenting and passed away shortly there after. Colorectal signet ring cell carcinoma is a rare malignancy comprising approximately 1% of colorectal cancers. Presentation may be atypical and superficial biopsy can be negative making diagnosis difficult. Non-specific thickening is the most common imaging finding and may be interpreted as inflammation, edema or fibrosis. Characteristic findings may be seen on MRI or CT but neither test is highly sensitive. Signet cell should be considered with any infiltrative disease of the GI tract and deep endoscopic or surgical biopsies may be necessary. Prognosis is poor compared to most GI malignancies however early diagnosis can affect 5-year survival. Yellow arrows highlight target-like rectal thickening in MRI of patient in Case 1. Red arrow shows gastric pneumatosis in CT scan from patient in Case 2. None

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