Case presentation

An 80-year-old female was admitted with a six-month history of right-sided abdominal pain, moderate in intensity, with no relieving factors, aggravated on bending over and decreased bowel habits. Physical examination revealed a vague abdominal lump in the right iliac fossa (RIF) extending towards the umbilicus, measuring approximately 7 × 5 cm. The mass had a smooth surface, ill-defined margins, was non-tender, firm in consistency, did not move with respiration, and had restricted mobility.

Contrast-enhanced computed tomography (CECT) of the whole abdomen demonstrated a well-defined, circumscribed soft tissue density mass lesion in the RIF within the mesentery, measuring 7.1 × 4.4 × 5.3 cm. The mass received vascular supply from branches of the superior mesenteric artery (SMA). A stalk was identified extending from the mesenteric mass to the terminal ileum. No regional lymph node involvement was identified (Figures 1, 2). CT imaging showed a heterogeneous enhancement on post-contrast study, suggesting a hypervascular tumor.

Figure 1: Contrast-enhanced computed tomography (CECT) Abdomen (coronal view)Demonstrating a well-defined soft tissue mesenteric mass (7.1x4.4x5.3 cm) in the right iliac fossa with vascular supply from the superior mesenteric artery.

Figure 2: Contrast-enhanced computed tomography (CECT) Abdomen (axial view)Showing mesenteric mass in right iliac fossa.

The patient underwent diagnostic laparoscopy, which identified a vascular mass of approximately 7 × 5 cm adherent to the ileal mesentery, located approximately 80 cm proximal to the ileocaecal junction. Thorough exploration of the abdominal cavity revealed no evidence of additional masses or lesions involving the small or large intestine, stomach, liver, pancreas, or intraperitoneal rectum. The tumor was laparoscopically excised en masse, with ligation of all adhesions and the supplying vasculature (Figure 3).

Figure 3: Intraoperative ImagesIntraoperative gross images of the mesenteric neuroendocrine tumor showing the laparoscopic appearance before excision (A), the intact excised specimen (B), and the cut section of the specimen (C).

The postoperative course was complicated by severe hypertension refractory to oral and intravenous antihypertensive medications, necessitating intravenous nitroglycerin (glyceryl trinitrate) infusion. Blood pressure normalized within 72 hours and the patient was discharged following satisfactory postoperative recovery.

Gross pathological examination of the excised specimen revealed a globular soft tissue mass measuring 6 × 4.5 × 3.5 cm. Microscopic examination demonstrated a WHO Grade I well-differentiated NET (G1), comprising neoplastic cells arranged in nests, trabeculae, and rosettes (Figure 4). Lymphovascular emboli were identified; however, resection margins were tumor-free. Immunohistochemistry demonstrated positivity for pan-cytokeratin, synaptophysin, chromogranin, INSM1, and CD56, with negativity for S100 and DOG-1, consistent with a diagnosis of NET (Table 1, Figure 5).

Figure 4: Histopathological examination (HPE) images(A, B) HPE shows a malignant neoplasm comprising neoplastic cells arranged in nests, trabeculae and rosettes, separated by collagenous stroma (A. x40, B. x100, H&E)(C) HPE shows presence of lymphovascular emboli (x100, H&E)(D) HPE shows tumor cells having round to ovoid predominantly monomorphic nuclei with focal abrupt anisonucleosis, fine stippled chromatin, inconspicuous nucleoli, 1-2 mitoses per 10 high-power fields (HPFs) and moderate amount of eosinophilic cytoplasm (x400, H&E).

Marker | Result
Pan-cytokeratin | Positive
Synaptophysin | Positive
Chromogranin A | Positive
INSM1 | Positive
CD56 | Positive
S100 | Negative
DOG-1 | Negative
Ki67 | Low

Figure 5: Immunohistochemistry (IHC)IHC shows tumor cells staining positive for (A) Pan-cytokeratin, (B) Synaptophysin, (C) Chromogranin, (D) CD56, and (E) INSM1, along with negative staining for (F) DOG1, (G) S100 and (H) a low Ki67 of <2% (x400, IHC).

During the first two postoperative weeks, the patient remained asymptomatic. Technetium-99m somatostatin receptor scintigraphy and ⁶⁸Ga-DOTATATE positron emission tomography (PET)-CT were planned to assess for residual tumor and somatostatin receptor expression status; however, the patient was subsequently lost to follow-up.