Splenunculus Masquerading as a Neuroendocrine Tumor of the Pancreatic Allograft in a Kidney-Pancreas Recipient

Primary pancreatic neuroendocrine tumors (NETs) are rare neoplasms arising from the endocrine pancreas and are classified based on the predominant hormone secreted. They are sporadic but can be associated with hereditary endocrinopathies such as multiple endocrine neoplasia type 1 (1). Patients may present with a hormonal syndrome suggestive of pancreatic NETs or be discovered incidentally. Diagnostic imaging includes contrast computerized axial tomography (CT) scan or magnetic resonance imaging, Octreoscan, and positron emission tomography (PET) using the radiotracer 68Ga-DOTA-TATE (Fig. 1). Intrapancreatic splenunculi are increasingly recognized and can mimic pancreatic NETs on contrast-enhanced CT and on PET 68Ga-DOTA-TATE scans. This is the first reported case of an intrapancreatic splenunculus in a pancreatic allograft mimicking a NET.FIGURE 1: Anterior view of maximum intensity projection of PET/CT images. This image demonstrates normal physiologic uptake and excretion of 68Ga-DOTA-TATE as well as the focal pathologic uptake in the superior pole (tail) of the transplanted pancreas in the right lower abdomen (arrow). The transplanted kidney in the left pelvis also has excreted activity of 68Ga-DOTA-TATE uptake (☆). 68Ga-DOTA-TATE PET/CT scan (A, axial CT images; B, axial PET images; C, axial PET/CT images) demonstrating marked increase in tracer uptake in the superior pole of transplanted pancreas representing a suspected primary NET in the transplanted pancreas (arrows).CASE REPORT A 43-year-old woman with type 1 diabetes mellitus 4 years after kidney-pancreas transplantation on tacrolimus, mycophenolate mofetil, and prednisolone presented with a 4-month history of worsening postprandial abdominal pain and diarrhea with frequent symptoms for 3 weeks before admission. Stools were watery with no mucus or blood. She had intermittent night sweats and significant weight loss. She had diabetic microvascular complications, peripheral vascular disease with bilateral above-knee amputations, and celiac disease. The differential diagnoses of diarrhea were autonomic dysfunction, a mycophenolate mofetil side effect, mesenteric ischemia and celiac disease and posttransplantation lymphoproliferative disorder. Documentation regarding splenosis and donor lymph node was not available in records. There was no significant travel history. She had a normal barium swallow and esophagogastroduodenoscopy. She was scheduled for a colonoscopy to evaluate ongoing diarrhea, but due to associated increasing pain and abdominal distension she had a Doppler of the mesenteric arteries. This showed proximal-middle superior mesenteric artery stenosis with more than 50% diameter reduction and critical stenosis of the celiac axis. She had small bowel wall thickening and mesenteric engorgement, confirmed on a CT abdominal angiogram. She deteriorated with signs of acute small bowel obstruction and needed an emergency laparotomy with a partial small bowel resection and lymph node excision. Histology showed inflammatory stenosis of the small bowel and nonspecific reactive hyperplasia of the mesenteric lymph nodes. Pain resolved, but diarrhea persisted after surgery. Two months later, with ongoing diarrhea, patient had a PET 68Ga-DOTA-TATE to evaluate the contrast-enhancing lesion seen on previous imaging (Fig. 2).FIGURE 2: CT arteriographic phase showing contrast-enhancing lesion tail of pancreatic transplant (arrow).CT angiography revealed critical multifocal calcific stenoses of the celiac and mesenteric axes and a contrast-enhancing lesion on the upper pole of the transplanted pancreas (corresponding to the anatomical tail), suggestive of a NET. There were no features of a splenic artery aneurysm or arteriovenous fistula of pancreatic graft vessels mimicking nodule. Stool cultures remained nondiagnostic and the hormone screen was negative apart from a elevated gastrin (Gastrin 750; normal <100 ng/L) and chromogranin A (464 U/L; normal 0–17.2 U/L). The suspected NET in the tail of the pancreatic allograft demonstrated intense 68Ga-DOTA-TATE uptake (specificity 83%) and “confirmed” the diagnosis. 68Ga-DOTA-TATE is a somatostatin analogue which, where available has replaced conventional octreotide scintigraphy. A 18-fluorodeoxyglucose PET scan was also performed to grade the lesion and guide the need for surgical intervention. Low 18-fluorodeoxyglucose uptake indicated that the lesion was well differentiated with low glucose metabolism. Although active observation was recommended, the patient insisted on surgery to avoid living with a possible malignancy. A well-circumscribed lesion was resected with a margin of normal appearing pancreas. She had an uneventful postoperative course and recovery. The histology revealed benign splenic tissue consistent with a splenunculus, 1.5×1.2×1 cm and weighing 0.95 g. A postoperative negative 68Ga-DOTA-TATE scan confirmed that an impalpable NET had not been missed within the residual pancreas. Her pancreatic and renal graft function before and after surgery remained stable with average blood glucose of 5 mmol/L and creatinine of 140 μmol/L. Currently, 10 months later, this patient has gained weight and remains well. She is euglycemic and has stable renal function. DISCUSSION Accessory spleens or splenunculi are found in about 10% of the population (2). Although 80% of accessory spleens that occur at the splenic hilum are mainly located in the tail of the pancreas, they may arise anywhere within the peritoneal cavity between the diaphragm and the pelvis (2), mimicking gastric/pancreatic malignancy. Intra pancreatic accessory spleens, although rare, are increasingly identified. The radiologic diagnosis can still be challenging, as appearances on CT and magnetic resonance imaging may be similar to NETs (3). Somatostatin receptors present within the splenic tissue can bind octreotide with high affinity giving false positives on conventional octreotide scintigraphy (4, 5) or 68Ga-DOTA-TATE PET scans, as with our patient. A differential diagnosis of an intrapancreatic splenunculus should be considered with lesions of the tail of pancreas delineated with contrast CT or 68Ga-DOTA-TATE PET scans. Technetium-99m heat-damaged red blood cell or technetium-99m sulfur colloid scans will show positive uptake with a splenunculus but will be negative with NETs. Thus, these tests will help avoid further surgical intervention (3, 4). Janaki T. Mohandas 1 Aravind S. Ravi Kumar2,3,5 Dwarakanathan Ranganathan1 Helen Healy1 Yu-Ting Huang3 Barry O’Loughlin4 Jeremy Chapman5 George T. John1 1 Department of Nephrology Royal Brisbane and Women’s Hospital Brisbane Queensland, Australia 2 Department of Nuclear Medicine Royal Brisbane and Women’s Hospital Brisbane Queensland, Australia 3 Specialised PET Services Queensland Brisbane Queensland, Australia 4 Department of General Surgery Royal Brisbane and Women’s Hospital Brisbane Queensland, Australia 5 Department of Nephrology Westmead Hospital Sydney New South Wales, Australia 6 School of Medicine University of Queensland Brisbane Queensland, Australia ACKNOWLEDGMENT The authors thank Mr. John Kachel, Medical Illustrator, HMMU, Brisbane.