A 59-year-old woman was referred to our hospital for the treatment of a growing tumor detected by computed tomography (CT) with calcification on the ventral side of the duodenum. Six years before the presentation, a nodule with calcification that had grown from 6 mm to 7.5, 15, and 18 mm at 14-, 56-, and 68-month follow-up, respectively, in the CT (Fig. 1a–d). Then she was referred our department for further evaluation and treatment. She had no chief symptoms. She had a history of chronic gastritis, gastroesophageal reflux disease. Her family history was unremarkable. On physical examination, she had a soft and flat abdomen without palpable masses. Laboratory tests, including tumor markers, showed no abnormalities. The tumor showed a faint high-signal intensity on T2-weighted magnetic resonance imaging (MRI) (Fig. 1e) and high-signal intensity on diffusion-weighted MRI (Fig. 1f). No other tumor was detected on endoscopy. The diagnosis was an omental tumor. The tumor was gradually growing and suspected as a malignant lesion. Therefore, laparoscopic surgery was performed.
The patient was placed in the supine position under general anesthesia. Five trocars were introduced, similar to laparoscopic distal gastrectomy. The tumor was easily identified at the omentum near the right gastroepiploic vein (RGV) (Fig. 2). Sharp dissection was accomplished using a Sonosurg™ ultrasonic dissection device (Olympus, Tokyo, Japan). The RGV branch was divided after clipping (Additional file 1: Video S1). The total operative time was 99 min, and the intraoperative blood loss was low.
Macroscopically, tumor showed well-circumscribed brown to black ovoid mass measuring 20 mm (Fig. 3a, b). Histologically, tumor consisted of cuboidal cells with eosinophilic, granular cytoplasm showing trabecular or ribbon architecture. Nucleus of tumor cells had coarsely granular chromatin and mitotic figure (5 cells/10 HPF). No other component, including heterotopic tissue such as aberrant pancreas or lymph node, was seen. Immunohistochemically, tumor cells were positive for chromogranin A, synaptophysin, and CD56, whereas negative for CK7, CK20, estrogen receptor, and progesterone receptor. The Ki-67 index was 5% (Fig. 3c–g). Based on these findings, the tumor was diagnosed as a grade 2 NET, according to the World Health Organization 2019 classification.
The postoperative course was uneventful, and the patient was discharged on postoperative day 3. She developed no signs of recurrence by CT/MRI follow-up at 42 months. No other primary suspected lesion was detected on endoscopic examination. Therefore, we diagnosed the omental NET as the primary lesion.