Coexisting Somatostatin Receptor Expressing Gastric Neuroendocrine Tumor Primary and Lymph Nodal Tuberculosis on ⁶⁸Ga-DOTANOC Positron Emission Tomography/Computed Tomography

A 34-year-old man who presented with abdominal discomfort, decreased appetite, and weight loss on evaluation was found to have gastric polyps on endoscopy, elevated serum antiparietal cell antibody (titer 1:20), plasma chromogranin A level of 527 ng/ml (normal <76.3 ng/ml), and serum gastrin level of 977 pg/ml (13–115 pg/ml). He underwent ⁶⁸Ga-DOTANOC positron emission tomography/computed tomography (PET/CT) for the evaluation of gastric neuroendocrine tumor (G-NET). The scan [Figure 1] revealed somatostatin receptor (SSTR) expressing polypoidal lesion (maximum standardized uptake value [SUVmax]: 25.7) in gastric fundus [Figure 1a-c, arrowhead] and also noted enlarged right paratracheal lymph nodes (SUVmax: 5.23) [Figure 1d-g, white arrow]. Endoscopic biopsy of gastric lesion [Figure 2a-d] shows small round cell tumor [Figure 2a], with immunohistochemistry positive for synaptophysin [Figure 2b], chromogranin [Figure 2c], and Ki-67 index <1% [Figure 2d, white arrow], suggesting well-differentiated neuroendocrine tumor (NET) (Grade 1). Histopathology of paratracheal lymph node revealed necrotizing epithelioid cell granulomatous inflammation with Langhans giant cell [Figure 2e and f, black arrows]. Considering the clinical, imaging, and node histopathology findings, the patient was started on antitubercular therapy. Follow-up ⁶⁸Ga-DOTANOC PG-NET done 3 months after starting antitubercular therapy (ATT) revealed a reduction in size and SSTR expression of previously involved lymph nodes [Figure 3d-3g, white arrow] suggesting response to ATT and no significant interval change in gastric carcinoid [Figure 3a-3c, arrowhead].

Close

Figure 1 ⁶⁸Ga-DOTANOC positron emission tomography/computed tomography, maximum intensity projection image (a), axial (b-e) and coronal sections (f,g) revealing somatostatin receptor expressing polypoidal lesion (maximum standardized uptake value: 25.7) in gastric fundus (b, c: arrowhead). Enlarged right paratracheal lymph nodes with somatostatin receptor expression (maximum standardized uptake value: 5.23) (d-g, white arrow)

Export to PPT

Close

Figure 2 Histomicrophotograph of sections from gastric lesion (a), showing neuroendocrine tumor (H and E, ×100), on immunohistochemistry, tumor cells are positive for synaptophysin (b), chromogranin (c) with Ki-67 proliferative index less than 1% (d), suggesting well-differentiated neuroendocrine tumor (typical carcinoid, Grade 1). Lymph node biopsy reveals necrotizing epithelioid cell granulomatous inflammation with Langhans cell histiocytosis (e, f: black arrow)

Export to PPT

Close

Figure 3 Follow-up ⁶⁸Ga-DOTANOC positron emission tomography/computed tomography, 3 months after starting antitubercular treatment, maximum intensity projection (3a), axial (3b-3e) and coronal sections (3f,3g), showing no significant interval change in gastric carcinoid (3c: white arrow),with reduction in size and somatostatin receptor expression of involved lymph nodes (3e, 3g: white arrow) suggesting response to antitubercular therapy

Export to PPT

G-NET is classified into four clinical types. Type 1 is most common with a lower risk of lymph nodal and distant metastases resulting in good overall prognosis.[12] Well-differentiated NET is known to express SSTR.[3] SSTR expression (⁶⁸Ga-DOTANOC uptake) can also be seen in granulomatous pathologies including tuberculosis (TB), fungal, bacterial, and protozoan infections and noninfectious diseases including sarcoidosis, Crohn's disease, and Wegener's granulomatosis.[4] In chronic inflammatory pathologies, including TB, this ⁶⁸Ga-DOTANOC avidity is due to the SSTR expression on activated lymphocytes and macrophages present in granulomas.[5] Although the presence of this uptake opens a window to image granulomatous pathologies as shown by Vanhagen et al., this might result in false-positive results in patients with NET having coexistent granulomatous pathologies; hence, the understanding of the false-positive sites is important for correct decision-making.[6] Sometimes, even after thorough histological examination and special stains, obvious infectious etiology resulting in granulomatous inflammation cannot be found, but Few histology features are suggestive of tuberculosis, such as granuloma formation by epithelioid histiocytes and Langhans type giant cells.[789] The diagnosis of extrapulmonary TB is sometimes difficult when bacteriological proof is lacking, but in areas with high prevalence like India (very high pretest probability), it can be assumed that granulomatous lymphadenitis is of tubercular origin after taking clinical and imaging features into consideration.[1011] Regarding the management of Type 1 G-NETs, endoscopic resection and follow-up is an acceptable treatment option.[12] In view of nonmetastatic Grade 1 gastric carcinoid in our patient, he is planned for endoscopic removal of gastric polyp and has shown good response to ATT for lymph node TB which was incidentally detected on ⁶⁸Ga-DOTANOC PET/CT.