Mapping the Tumor: Imaging and Staging for ZES

Locating a gastrinoma is often described as a “detective story.” While your blood tests may confirm that a tumor is producing too much gastrin, these tumors are frequently less than 1 centimeter in size—about the size of a pea—making them incredibly difficult to find with standard hospital equipment ^[1][2].

The Gastrinoma Triangle

Because gastrinomas can technically form in various parts of the body, doctors focus their search on a specific anatomical region called the gastrinoma triangle ^[3]. The vast majority of gastrinomas are found within this zone, which is bounded by:

• The junction of the cystic and common bile ducts (near the gallbladder).
• The junction of the second and third parts of the duodenum (the beginning of the small intestine).
• The neck of the pancreas ^[3].

Functional Imaging: Ga-68 DOTATATE PET/CT

A highly useful tool for finding a gastrinoma today is the Ga-68 DOTATATE PET/CT (or DOTATOC) ^[4][5]. Gastrinomas are typically somatostatin-receptor positive, meaning they have special “docking stations” on their surface ^[6].

Before the scan, you are injected with a tiny amount of a radioactive tracer that specifically seeks out and sticks to these receptors. On the PET scan, receptor-bearing tissue “lights up”, which helps localize the tumor and assess staging ^[7]. However, while this technology is excellent, its sensitivity varies depending on the tumor’s size, grade, and receptor expression. Small duodenal gastrinomas can still remain occult (hidden), and uptake alone is not a definitive pathology diagnosis ^[4][5].

Endoscopic Ultrasound (EUS)

If a tumor is suspected in the pancreas, your doctor may use Endoscopic Ultrasound (EUS) ^[1]. In this procedure, a doctor passes a flexible tube with a tiny ultrasound probe down your throat while you are sedated.

Because the probe is positioned directly next to the stomach and pancreas, it can provide high-resolution images that a scan from outside the body might miss ^[8]. EUS is particularly effective at finding pancreatic tumors, though it is less reliable for finding very small tumors hidden in the walls of the duodenum ^[1][8].

Traditional Mapping: CT and MRI

Standard CT (Computed Tomography) and MRI (Magnetic Resonance Imaging) scans provide a “roadmap” of your anatomy ^[7]. While they may miss the primary small tumor, they are excellent at identifying:

• Hypervascular lesions: Tumors that have a high blood supply ^[9].
• Lymphadenopathy: Swollen lymph nodes that may indicate the tumor has begun to spread ^[9].
• Liver involvement: MRI is often the preferred tool for looking specifically at the liver to check for any spread ^[9][7].

The Challenge of the “Negative” Scan

It is important to understand that a “negative” scan does not mean you don’t have ZES ^[2]. In many cases—especially in patients with MEN1—the tumors are so small that they evade imaging ^[1][2].

If your biochemical tests confirm ZES but scans are negative, a high-volume neuroendocrine tumor (NET) team will weigh your biochemical certainty, whether you have sporadic or MEN1 disease, suspected tumor burden, operative risks, and patient goals. They may recommend exploratory surgery, where an expert surgeon can often find “hidden” tumors by manually feeling the tissue, or they may recommend watchful waiting ^[10][11]. Exploratory surgery is a major decision and is not an automatic next step for everyone.

Staging and Grading

When mapping the tumor, doctors look at both stage and grade.

• Stage refers to where the disease is located: Local (only in the duodenum/pancreas), Regional (spread to lymph nodes), or Distant (spread to the liver or bones) ^[7][12].
• Grade refers to how fast the cells appear to grow under a microscope. This is often measured by a Ki-67 index or mitotic rate. A low-grade tumor grows very slowly, while a higher-grade tumor grows faster.

Treatment decisions are never made based on stage alone. Your team will evaluate the stage, grade, receptor expression, and your overall health to determine the best path forward ^[13][14].