Insulinoma
Insulinomas are the most common sporadic endocrine tumor of the pancreas.
On imaging, they usually present as small well-defined hypervascular tumors that may be found anywhere in the pancreas.
Epidemiology
Account for 40% of syndromic pancreatic endocrine tumors.
The overall incidence is of ~0.0003%.
Clinical presentation
Typically insulinomas present with Whipple’s triad consisting of:
fasting hypoglycemia (<50 mg/dL)
symptoms of hypoglycemia (due to subsequent catecholamine release)
immediate relief of symptoms after the administration of IV glucose
As with other endocrine tumors of the pancreas, there is an association with multiple endocrine neoplasia type I (MEN I).
Pathology
They develop from ductal pluripotent cells into unregulated cells secreting insulin. The beta cells of the islets of Langerhans normally secrete insulin. Approximately 10% of insulinomas are multiple and 10% malignant.
Radiographic features
These tumors can be relatively small and multiphase contrast-enhanced thin slice cross-sectional imaging is ideal. Most insulinomas are small (90% are <2 cm at presentation ) and hypervascular. They may contain calcifications. Malignant tumors tend to be larger. Equally distributed between the head, body, and tail of the pancreas.
CT
They tend to be hyperattenuating on arterial phase and, therefore, dedicated protocols with arterial or pancreatic phase imaging may aid in better detection . Some may show calcification.
MRI
Dynamic MRI with fast gradient echo sequences following a bolus injection of contrast medium may aid in the detection of these tumors
T1 C+ (Gd): typically shows enhancement, although contrast enhancement may not improve tumor visualization compared with non-contrast images