Abstract
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Objectives: Neuroendocrine tumors (NETs) are uncommon but with increasing incidence and prevalence. 68Ga-DOTATATE is a PET radiopharmaceutical for somatostatin receptor (SSR) detection. After reviewing multiple patients with 68Ga-DOTATATE PET/CT, the authors noticed equivocal interpretations of uptake in the tail of the pancreas. The purpose of our study was to measure the uptake semi-quantitatively using SUVs in the tail of the pancreas compared to normal liver parenchyma and SSR-positive lesions.
Methods: We reviewed the 68Ga-DOTATATE PET/low mAs CT images of 35 consecutive patients performed between October 4, 2017 and January 23, 2018. There were 17 male and 18 females ranging in age from 37 to 80 years (mean +/- SD = 57.1 +/- 10.7). SUVs were measured by two observers and the average values between the two observers were compared between normal liver parenchyma and pancreas tail. Normal liver parenchyma SUVaverage with the size of the region of interest (ROI) = 23.48 cm2, the lesion SUVpeak with the size of the ROI = 0.78 cm2, and the tail of the pancreas SUVpeak. An ABR-certified radiologist reviewed the corresponding available diagnostic CTs and MRI of the abdomen to assess the presence of lesions in the tail of the pancreas. Results: The indications for referral to 68Ga-DOTATATE PET/CT were the following: 1. Evidence of a new lesion in the pancreas (n=9), restaging (n=5), NET metastases (n=11), and elevated tumor markers (n=10). Twenty-four patients had resection or biopsy of a lesion diagnostic of NET prior to and nine had tissue acquisition after the 68Ga-DOTATATE PET/CT. The average normal liver parenchyma SUVaverage was 3.9 +/-1.0. The median SUVpeak of the lesions was 17.65 (interquartile range: 5.55, 24.35). In the 31 patients with a tail of the pancreas without anatomical lesions, the average SUVpeak was 3.7 +/- 1.1. There was no significant difference (p=0.59) between the SUVaverage of normal liver parenchyma and the SUVpeak of normal tail of the pancreas. There were five patients with uptake in the tail of the pancreas slightly above that of normal liver parenchyma that were interpreted equivocally as cancer. One of these patients had 68Ga-DOTATATE uptake in a peripancreatic lymph node in addition to the tail of the pancreas. The fine needle aspiration of the lymph node demonstrated neuroendocrine tumor. He underwent a distal pancreatectomy and pathologic examination revealed islet cell hyperplasia. Conclusion: We observed that 68Ga-DOTATATE uptake in the tail of the pancreas above that of normal liver parenchyma was consistent with a SSR-avid lesion. 68Ga-DOTATATE uptake in the tail of the pancreas equal to the liver can be normal. Patients with 68Ga-DOTATATE uptake equivalent to the liver parenchyma should undergo further imaging with either contrast-enhanced CT or MRI before procedural intervention to confirm the presence of a pathological lesion. Figure 1: 68GA-DOTATATE PET/CT of a 43 year-old man who presented with carcinoid syndrome: A. CT transmission, B. Fusion PET/CT image, C. 68Ga-DOTATATE PET, D. Maximum intensity projection (MIP). An outside CT without contrast demonstrated a 1 cm retroperitoneal lymph node at the level of the renal vessels. A fine needle aspiration revealed neuroendocrine tumor. The 68Ga-DOTATATE PET images demonstrated uptake in the retroperitoneal lymph node seen on the MIP. A transaxial image demonstrated uptake in the tail of the pancreas at the same level as normal liver parenchyma (arrow).