Islet β-cell tumor is a functional adenoma or carcinoma formed by pancreatic islet β cells. It commonly occurs between the ages of 20 and 50, is usually solitary, and 90% are benign. Occasionally, it may be part of type I multiple endocrine neoplasia.

bubble_chart Etiology

Pancreatic islet cell tumors are relatively rare, with most being benign and a few malignant. They are divided into two main categories: functional and non-functional. The most common type is insulinoma, accounting for 60-90% of cases. These tumors often occur in the body and tail of the pancreas, are usually small, and most measure less than 2.0 cm. The second most common is gastrinoma, making up about 20% of cases. These tumors are often multiple and can occur outside the pancreas, frequently in the duodenum and stomach wall. Other rare pancreatic islet cell tumors include glucagonoma, vipoma, and somatostatinoma. Non-functional pancreatic islet cell tumors are typically large and can even exceed 10 cm in size.

bubble_chart Clinical Manifestations

Clinically, insulinomas primarily manifest as hypoglycemic syndrome with elevated serum insulin levels. Gastrinomas can cause Zollinger-Ellison syndrome, presenting as refractory gastrointestinal ulcers. Nonfunctional pancreatic islet cell tumors are generally asymptomatic, but in the late stage (third stage), symptoms such as abdominal pain, weight loss, and jaundice may occur due to tumor growth, peripancreatic infiltration, and distant metastasis.

bubble_chart Auxiliary Examination

1. During an episode, blood glucose is <2.8 mmol/L (50 mg/dl).
2. Serum insulin and C-peptide: Plasma insulin and C-peptide levels are elevated during hypoglycemia, with an insulin index (insulin/glucose) >0.3. A value >1.0 confirms the diagnosis. Fasting plasma insulin >200 uU/ml is diagnostic.
3. Oral glucose tolerance test: Typically shows a flat curve, with some cases exhibiting impaired glucose tolerance. A minority may show early hypoglycemia or a normal glucose tolerance curve.
4. Fasting test: A positive result aids diagnosis. The test can only be performed if fasting blood glucose is >2.8 mmol/L. Hypoglycemia can be induced in over 90% of cases after 24–36 hours of fasting. A minority require 48–72 hours of fasting, with exercise added 2 hours before ending the fast to induce hypoglycemia. If hypoglycemia is not induced after 72 hours of fasting, the disease can be ruled out.
5. Conventional X-ray: In gastrinoma, barium meal examination of the digestive tract may reveal multiple
6. recurrent ulcers in the stomach and duodenum.
7. Ultrasound findings: Lesions are located at the edge of the pancreas or within the pancreas, appearing as round or oval masses with hypoechoic interiors and clear margins. Malignant islet cell tumors have irregular borders and heterogeneous internal echoes.
8. CT findings:
   1. Non-contrast scans show isodense masses within the pancreas, usually small, which may be embedded in the pancreas or protrude locally from its surface.
   2. Since functional islet cell tumors, whether benign or malignant, are hypervascular and richly perfused, early-phase contrast-enhanced scans (during the hepatic arterial phase) show significant enhancement of the mass as a high-density nodule, denser than the surrounding normal pancreas.
   3. Non-functional tumors are usually larger, with homogeneous or heterogeneous density, often occurring in the body or tail of the pancreas. About 20% exhibit calcification within the tumor. Post-contrast enhancement may occur, with density slightly higher than normal pancreas, and central cystic changes may be present.
   4. If accompanied by local lymphadenopathy, involvement of adjacent organs, or metastasis, these are signs of malignancy.
9. Angiography: During the parenchymal phase, the tumor shows sustained increased density, with clearly defined tumor staining, which is a characteristic feature.

bubble_chart Diagnosis

The onset is slow, and a minority of cases take a long time to be diagnosed. Prolonged misdiagnosis can lead to permanent brain damage. Clinical manifestations include:

1. Whipple's triad:
   1. Hypoglycemic symptoms occurring after hunger or exercise;
   2. Blood glucose <2.8mmol/L (50mg/dl) during episodes;
   3. Immediate relief after glucose injection.
2. Hypoglycemic episodes often become more frequent as the disease progresses, with prolonged duration and increased severity of hypoglycemia, and may even be triggered postprandially. Most cases are accompanied by gradual obesity and declines in memory and reaction ability.

bubble_chart Treatment Measures

1. Surgical removal of the tumor is performed. If the tumor cannot be located during the operation, subtotal pancreatectomy may be considered.
2. For patients with surgical contraindications, those who refuse surgery, or those with unresolved or recurrent symptoms postoperatively, diazoxide can be administered at 100–200 mg/day, divided into 2–3 doses. Concurrent use of diuretics can prevent water retention side effects. Phenytoin sodium and propranolol also have some inhibitory effects on insulin secretion. Adrenocortical hormones may also alleviate symptoms.
3. For unresectable or metastatic islet cell carcinoma, streptozocin can be used, with 50% of patients achieving symptom relief or prolonged survival. During drug therapy, it is important to increase meal frequency and consume more sugar- and fat-rich foods. Adrenocortical hormones may be added as needed to prevent hypoglycemic episodes.