What is the gold standard diagnostic test for gastrin-secreting tumors (gastrinomas)?

• A. Serum gastrin level
• B. CT scan abdomen
• C. Somatostatin receptor scintigraphy
• D. Endoscopic ultrasound

Answer: (C)

Gastrinomas are neuroendocrine tumors that commonly express somatostatin receptors, so imaging that targets those receptors provides the most sensitive way to locate them throughout the body.

Somatostatin receptor scintigraphy uses a radiolabeled somatostatin analog (such as octreotide) injected into the patient. The labeled compound binds to somatostatin receptors on tumor cells, and a scan detects where these signals come from. This approach offers a whole-body survey, enabling detection of primary tumors and metastases that may be too small or occult for purely anatomical imaging. It also helps with staging and planning treatment, including surgical approaches and peptide receptor radionuclide therapy.

While measuring serum gastrin confirms excess hormone production, it doesn’t reveal tumor location. CT or MRI provides anatomical detail but can miss small neuroendocrine tumors. Endoscopic ultrasound is excellent for pancreatic lesions but is limited to the local region. Modern practice may use Ga-68 DOTATATE PET-CT, which is even more sensitive, but the principle remains receptor-targeted imaging.