Small bowel obstruction secondary to ileal tumor

HISTOPATHOLOGY

CLINICAL NOTES: Ileo-colic resection (tight stricture with perforation terminal ileum) -> gross peritonitis. Further clinical history: ileal thickening noted 10 years ago and thought clinically to be Crohn's disease. Not biopsied.

MACROSCOPIC DESCRIPTION:

"Bowel": A right hemicolectomy including extended ileectomy (400mm), unremarkable appendix (60x10mm), proximal large bowel (190mm) and attached mesentery up to 70mm. There is firm white diffuse thickening of the ileal wall up to 10mm over a 90mm length located 260mm from the proximal margin and 90mm from the ileocolic junction. Within this region is a full thickness wall defect with an area of 3x2mm. The bowel and mesenteric serosa is diffusely coated with a thin light cream sheet. The adjacent mesentery contains three firm cream nodules up to 22mm and other nodules up to 20mm. The proximal ileum is dilated to a diameter of 60mm. Within the ascending colon there is a region of multiple sessile polypoid lesions up to 20mm all containing brown friable fecal-type material (area 60x30mm), all located 20mm from the proximal margin. BLOCK DESIGNATION: A - bowel margins, LS. B-C - composite TS ileal stenosis (B) and adjacent mesentery (C). D - ileal stenosis. E - interface between ileal stenosis and normal ileum. F - appendix. G-H - polypoid ascending colon area. I-J - mesenteric nodules, 1x TS each. K-M - mesenteric nodules, 1x TS each N-O - ileum proximal (N) and distal (O) to stenosing lesion. P - ascending colon. Q - mesenteric vessels.

MICROSCOPIC DESCRIPTION: Sections of the ileal stenosis show a tumor circumferentially involving all layers of the bowel wall. The tumor is composed of nests and trabeculae as well as small groups of cells in pools of mucin. The mucinous component accounts for about 60% of the tumor. Tumor cells are cuboidal with cytoplasmic mucin including signet-ring cell type changes. Tumor nuclei are large, round to oval with fine chromatin and small frequent nucleoli. The overlying ileal mucosa is extensively ulcerated. No ileal epithelial dysplasia is identified although at the edges of ileal stenosis the tumor is centered within the lamina propria. Tumor extensively involves mesenteric fat and focally invades through to the serosa at the macroscopically identified perforation. Several foci of tumor are present in the appendiceal mesentery and muscularis propria. There are foci of lymphovascular invasion including distant sites such as the ascending colon and small foci of perineural invasion.

By immunohistochemistry tumor cells are CK7-, CK20+, CDX2+, TTF1-, PSA-, PSAP-, synaptophysin-, chromogranin- and CD56-. This phenotype is consistent with a primary ileal adenocarcinoma with no evidence of neuroendocrine differentiation. Mismatch repair protein (MLH1, MSH2, MSH6, PMS2) expression is normal. Metastatic tumor is seen within six of eleven mesenteric lymph nodes up to 20mm in maximum dimension. The metastatic tumor morphology is somewhat different to the main tumor in that it forms predominantly sheets and trabeculae with large amounts of mucinous eosinophilic cytoplasm. The longitudinal margins are clear. The serosa is covered with an acute inflammatory exudate. The other regions of the bowel show no evidence of inflammatory bowel disease.

DIAGNOSIS: Right hemicolectomy and partial iliectomy: * Mucinous adenocarcinoma - Stenotic and perforated lesion involving ileum. - Maximum dimension - 90mm. - Invasion - perforates serosa. - Lymphovascular invasion - present. - Perineural invasion - present. - Lymph nodes - metastatic tumor in 6/11 mesenteric lymph nodes. - Normal mismatch repair protein expression. - AJCC pT4, N2, MX Stage IIIB