Pancreatic Pathology Online
Pathology of Beta cell Tumours (Insulinomas)
Dr Sampurna Roy MD July 2016
Beta cell tumours are the most common of the islet cell neoplasms.
The functional variant releases sufficient insulin to induce severe hypoglycemia ( serum glucose less than 50 mg/dl ) and a syndrome of sweating, nervousness, and hunger, which may progress to confusion, lethargy, and coma.
Attacks are promptly relieved by glucose feeding or infusion.
Since the symptoms are often relieved by eating, it is common for patients to be overweight.
Frequently, the diagnosis is delayed by the prominence of symptoms of abnormal behavior that cause some patients to be under psychiatric care.
Most cases are characterized by only a mild hypoglycemia, and in some the tumour is not functional, which may delay the diagnosis.
Neoplastic beta cells, unlike their normal counterparts, are not regulated by the blood glucose level and continue to secrete insulin autonomously even when the level of glucose is very low.
Most beta cell tumours are benign solitary adenomas (70%) in the body or tail of the pancreas, 10% are multiple adenomas, 10% are metastasizing carcinomas, and the remainder are diffuse islet hyperplasia and adenomas in ectopic pancreatic tissue.
They may be minute, as small as 1 mm in diameter to greater than 2 cm diameter lesions, usually encapsulated, firm, yellow-brown nodules composed of cords and nests of well-defined beta cells, with typical beta cell granules by electron microscopy.
Diffuse hyperplasia is characteristic of infants born to diabetic mothers, subjected to sustained hyperglycemia in utero.
In the majority surgical enucleation is accompanied by a rapid disappearance of symptoms.
Histologically, the insulinoma cells usually resemble normal beta cells.
The tumour has the typical histological features of an islet cell tumour cuboidal cells with compact nuclei and eosinophilic granular cytoplasm arranged in ribbons.
The only absolute criteria for malignancy in islet cell tumours are invasion and metastasis at presentation.
Stromal amyloid and psammoma bodies may be present.
These are rarely seen (although they are said to be more frequently associated with somatostatinomas).
The diagnosis is established by the demonstration of high levels of insulin in the blood and in the tumour cells.
Clinical and biochemical information will usually reveal what product(s) the tumour is secreting, prior to pathological examination.
This is important information because it affects malignant potential.
For example, only 10% of insulinomas are malignant where as 4 - 60% is usually quoted as the malignancy rate for gastrinomas in or around the pancreatic region.
The pro-insulin in insulinomas stains with aldehyde fuschin and other dyes which bind to -SH groups.
Immunohistochemistry is the method of choice for demonstrating secretory products.
Electron microscopy of the tumor is also valuable which usually shows the pleomorphic, paracrystalline cores surrounded by a clear halo that are typical of insulin stored in normal beta cells.
Rarely, the insulin granules are atypical.
With the exception of insulin (which forms rectangular crystals as the dense core of neurosecretory granules) the other secretions form round granules which are only partially distinguished by size.
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