Carcinoma of unknown primary of neuroendocrine origin: Accurate detection of primary with ⁶⁸Ga-labelled [1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid]-1-NaI3-Octreotide positron emission tomography/computed tomography enterography

We present a case of 73-year-old male patient who presented with the complaints of weight loss and flushing for 6-7 months. Hematological parameters including erythrocyte sedimentation rate, fasting blood sugar and thyroid function tests were normal. An initial abdominal ultrasound revealed multiple hypoechoic lesions in bilateral lobes of liver and multiple enlarged mesenteric lymph nodes. Contrast enhanced computed tomography abdomen and chest revealed the same extent of disease. Patient underwent fine-needle aspiration cytology (FNAC) of liver lesion, which revealed metastatic neuroendocrine tumor. Serum chromogranin A (CgA) level was also elevated (CgA ~ 656.46 U/ml). Colonoscopy was performed in search of primary and found to be normal. Finally the treating oncologist advised ⁶⁸Ga-labelled (1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid)-1-NaI3-Octreotide (⁶⁸Ga-DOTANOC) positron emission tomography/computed tomography (PET/CT) in order to search for primary tumor and to define the disease extent. ⁶⁸Ga-DOTANOC PET/CT was performed which revealed metastatic ⁶⁸Ga-DOTANOC avid lesions in liver and mesenteric lymph nodes [Figure 1a]. Multifocal DOTANOC uptake in the region of distal ileum was also noted [Figure 1b–e]. For better delineation of the small intestinal lesion, we performed PET/CT enterography by orally administrating 100 ml of polyethylene glycol (PEG) mixed in 1 l of water. After 1 h of PEG administration, ⁶⁸Ga-DOTANOC was injected intravenously and a spot view of abdomen was acquired after 45-50 min. The preparation is arranged in a manner that whole procedure including the scan was completed within 2 h. ⁶⁸Ga-DOTANOC PET/CT enterography helped in accurate delineation of the ileal lesions in the background of distended intestinal loops [Figure 1f-i]. FNAC/biopsy was not accessible as the lesions were located in the distal ileum. He was put on somatostatin based therapy in view of metastatic disease.

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Figure 1 ⁶⁸Ga-labelled [1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid]-1-NaI3-Octreotide (⁶⁸Ga-DOTANOC) positron emission tomography/computed tomography (PET/CT) maximum intensity projection PET image and trans-axial PET/CT images revealing DOTANOC avid lesions in liver (a) and multifocal DOTANOC uptake in the distal ileum (b-e, arrow). The ileal lesions after performing ⁶⁸Ga-DOTANOC enterography showed accurate delineation in the background of distended intestinal loops (f-i, arrow)

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⁶⁸Ga-DOTANOC PET/CT is a better modality in patients with carcinoma of unknown primary of neuroendocrine origin.[1] Most of the primary lesions are located in a midgut region and mid gut lesions have a poor resolution due to undistended and overlapping intestinal loops and motility-related artifacts. For better delineation and evaluation of intestinal lesions, a complete evaluation of lumen, wall and adjacent structures of gut is required. Both CT and magnetic resonance enteroclysis depict mucosal abnormalities and extra intestinal complications in a highly accurate way but these fail to show the metabolic status of the disease.[2] Therefore, we conceptualized a fusion of a metabolic imaging technique like PET and an anatomical imaging modality like CT enterography to derive information both on the morphology and the functional activity of the lesions at the same time.[3] Although PET/CT enteroclysis, enterography and colonography have been described with ¹⁸F-fluorodeoxyglucose,[345] PET/CT enterography with ⁶⁸Ga-DOTANOC has not been described in the literature. Here in this case, ⁶⁸Ga-DOTANOC PET/CT enterography was useful in identifying the primary lesion in small intestine with accurate delineation.