This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of Adrenal Gland, Subject name: Medicine
Which is the initial Imaging modality of choice for Insulinoma? 
Select and explain. 
A. USG, B. CT abdomen, C. Somatostatin Receptor Scan (SRS), D. E.U.S
D: E.U.S
Answer: D: E.U.S 
Explanation: For PETs in the pancreas, EUS is highly sensitive, localizing 77-100% of insulinomas, which occur almost exclusively within the pancreas. Tests for location of pNET: Somatostatin Receptor Scintigraphy is the initial imaging modality but is less available. Helical CT scan has a sensitivity of 82-94%. Gadolinium based MRI has sensitivity of 85%. If above scans are negative, then Endoscopic ultrasound will be able to pick up the insulinoma which is usually <1.5 cm in size. If all the above tests turn negative then calcium stimulated angiography can be used to localize the tumor. The intra-aerial calcium test also allows differentiation of the cause of the hypoglycaemia and indicates whether it is due to an insulinoma or a nesidioblastosis.