Presentation
Abdominal pain and distension.
Patient Data
Ileocolic intussusception with a hyperdense bowel mass appearing as the lead point. Adjacent serosal nodule with calcification and mesenteric desmoplastic reaction. Upstream bowel dilatation in keeping with obstruction.
The patient went on to an urgent right hemicolectomy.
Histology
MACROSCOPIC: Small bowel – a right hemicolectomy specimen comprising terminal ileum 300mm, cecum and ascending colon 150mm with attached appendix 35 x 5mm and mesentery 50mm wide. Arising in the terminal ileum adjacent to the ileocecal valve there is an exophytic yellow polypoid tumor 45 x 25mm. It is approximately 300mm from the proximal margin and 160mm from the distal margin. The tumor invades through the wall of small bowel and extends into the mesenteric fat for a distance of approximately 15mm. The anatomy in the ileocecal valve region is difficult to determine, the ileocecal valve telescopes into the cecum where the tumor appears to invade through the wall of the terminal ileum and the surrounding cecum into the mesenteric fat. The overlying serosa appears uninvolved. Approximately 50mm from the proximal margin there is a probable Meckel's diverticulum 40 x 15mm.
MICROSCOPIC: The sections of small bowel show a well differentiated neuroendocrine tumor. It comprises variably sized nests and anastomosing trabeculae of cells with indistinct cell borders, pale eosinophilic cytoplasm and round to oval nuclei with stippled chromatin. Mitoses are very infrequent, but focally 2 mitoses are found in a 2mm2 area. The tumor shows strong expression of neuroendocrine markers synaptophysin and chromogranin. The tumor invades through the muscularis propria into mesenteric fat. There is no involvement of the serosa. Extensive retraction artefact is present but no convincing lymphovascular or perineural invasion is identified. There is no necrosis. Metastatic neuroendocrine tumor is identified within 1 of 20 lymph nodes. A Meckel's diverticulum is noted in the proximal ileum. The margins are clear.
DIAGNOSIS:
Tumor type (WHO 5th ed. 2019): Well–differentiated neuroendocrine tumor, NET G2
Histological differentiation: Well differentiated
Histological grade: Grade 2 (2 mitoses per 2 mm², Ki67 3% in the area of greatest proliferative activity)
Depth of invasion: Invades through muscularis propria into mesenteric fat
Serosal involvement: Not identified
Lymphovascular invasion: Not identified
Perineural invasion: Not identified
Tumor deposits: Two of the tissue fragments sampled as lymph nodes are tumor deposits without evidence of an associated lymph node
Lymph node involvement: There is metastatic neuroendocrine tumor involving 1 of 20 lymph nodes.
Margin status: Clear
(AJCC 8th Edition) TNM stage: pT3 pN1
Hyperdense terminal ileum mass. No mesenteric lymphadenopathy or desmoplastic reaction.
Case Discussion
In adults, intussusception should always prompt a careful search for a mass as the lead point although the typical appearances of this small bowel neuroendocrine tumor are readily seen. Interestingly, this mass was present 10 years earlier but is hard to call as a mass given the density is similar to other small bowel luminal density.
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