GI Endocrine Tumors
GENERAL:
Most are classified as functional or non-functional depending if the clinical syndrome is due to a hormone release
Non-functioning tumors are generally reported as incidental finding during surgery or autopsy
GI endocrine tumors are uncommon; Most to least common: carcinoid, gastrinomas, insulinomas, VIPoma, glucagonoma, somatostatinoma
Their origin is thought to be from endodermal stem cells of the neuroendocrine system; most are slow growing
Detection of tumors is difficult: <1 cm have a detection rate of <10% and >3 cm have a detection rate of ˜50%
Any imaging modality (CT, U/S, MRI) detect <40% of all tumors
Somatostatin receptors are present in: 90% of Gastrinomas, VIPomas, Glucagonomas, Somatostatinomas; >75% Carcinoids
This is the basis for radiolabeled somatostatin analoge (i.e. octreotide) scintigraphy or octreotide scanning (except with Insulinomas)
This is also the basis of therapy to alleviate symptoms and slow tumor growth
These tumors may occur in sporadic (nonfamilial) form or as part of MEN Syndrome Type 1 (pituitary, parathyroid, pancreas)
CARCINOID TUMORS: See Bowel- Carcinoid Tumors (Chapter 2.08)
ZOLLINGER-ELLISON SYNDROME (GASTRINOMA): See Esophagus/Gastric- ZES (Chapter 1.23)
INSULINOMA
Definition:
Insulin secreting tumors that cause symptoms of hypoglycemia (almost always originate in the betacells of the pancreas)
Epidemiology:
Patients are typically (60%) female and age range from 20-75 years
Pathophysiology:
Beta-cell tumors that arise in or adjacent to the pancreas; Mostly are solitary (2% multiple) and arise evenly in head, body, tail
Should raise the question of MEN-1
Clinical Manifestations/Physical Exam:
Signs and symptoms of hypoglycemia, including neurological manifestations (“neuroglycopenic symptoms”): confusion, diplopia, dizziness
Catecholamine-mediated (from hypoglycemia): anxiety, weakness, fatigue, headache, palpitations, sweating especially during fasting
Weight gain in 40% because patients learn to eat to control the symptoms
If you don’t think about symptoms and the possibility of an Insulinoma, you won’t diagnose it (25% are not diagnosed for 3 years)
Laboratory Studies:
Fasting glucose and insulin levels (See Diagnostic Sudies below)
Possibly:
Sulfonylurea levels
Antibodies to insulin
C-peptide: exogenous insulin has no C-peptide, so Insulinoma patients have high or normal C-peptide levels
Plasma proinsulin levels: in most patients with Insulinomas, proinsulin comprises more than 20% of the circulating insulin
Diagnostic Studies:
Combination of: low fasting glucose level and inappropriately high plasma insulin level (Only 65% of patients present with these findings)
If negative and diagnosis still considered: 72-hour fast with blood glucose and insulin levels, including when symptoms develop
Test is positive in 75% of patients in 24 hours and virtually 100% in 72 hours
Caution: other causes of hypoglycemia need to be excluded: exogenous insulin use, sulfonylurea use, autoantibodies to insulin
CT scan: most tumors are small, so detection is 50%
EUS: detects 80-90%
MRI: detects liver metastases in 80%, which is important for determining candidacy for surgical resection
Other:
Angiography with venous sampling for insulin has a sensitivity of 80%Related posts:
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