Gastrointestinal ImagingInsulinoma
most common endocrine
tumour of the pancreas arising from the
B cells of the pancreatic islets that secrete excessive amounts of insulin and cause a distinct syndrome characterized by symptoms due to hypoglycaemia. Exceptionally, insulinoma may develop in ectopic pancreatic tissue located in the gastrointestinal tract. It occurs more commonly in women and in the age group above 40 years.
Insulinomas are frequently small and vary in diameter at the time of diagnosis between 5 mm and several cm, but the majority are about 1 - 2 cm. In about 80 - 90% of cases they are solitary. In some patients, mainly young children, generalized islet cell hyperplasia is the cause of the hypersecretion of insulin. In rare instances they are part of the MEN syndrome.
Grossly, insulinomas are yellow-coloured well circumscribed firm nodules. Histologically, they are composed of well-differentiated B cells with the same histological characteristics as the cells present in the normal islet. Insulinomas are usually benign but it is assumed that 10 - 15% may be malignant. The diagnosis of malignancy is based on local invasion of peripancreatic tissue and on the presence of metastasis rather than on histological features because cellular and nuclear atypia are very limited in these malignant insulinomas.
Clinical symptomatology of insulinoma is characterized by spontaneous hypoglycaemia during fasting or exercise relieved by oral ingestion or parenteral administration of glucose. The hypoglycaemic episodes occur at irregular intervals and become manifest as sweating, sensation of weakness, tachycardia, mental confusion and even seizures. The diagnosis is based mainly on simultaneous demonstration of a fall in blood glucose and a rise in insulin and C-peptide levels during the spontaneous or provoked development of symptoms.
The role of radiological imaging consists mainly in the exact anatomical localization of the lesion, see islet cell tumour.
ALB