Endocrine—Insulinoma
Concept
Tumor in the pancreas that releases insulin. Association with MEN I syndrome (pituitary, pancreas, parathyroid) so be sure to ask about family history. Usually less than 2 cm in size, if > 3 cm, be suspicious of malignancy.
Management depends on tumor location, number of tumors, malignancy, and part of MEN syndrome (hyper- parathyroidism, pituitary/pancreatic tumors). Need to r/o other causes for hypoglycemia like liver disorder (cirrhosis, Gaucher’s dx), pregnancy, and exogenous administration.
Way Question May be Asked?
“37 y/o female presents with a history of repeated bouts of weakness and fatigue after meals, with a fasting glucose level of 40.” There are several ways the question can go, but, after ruling out liver disorder, and alcoholism (quickly), start focusing on insulinoma. Rarely will get classic Whipple’s triad:
symptoms with fasting
blood glucose < 60 at time of symptoms symptoms relieved with glucose administration
How to Answer?
Will need to perform complete H&P
History
Syncope Blurred vision
Sweating → brought on by fasting or exercise Palpitations
Weakness Seizures Confusion Wt. gain
Be sure to ask about family history for MEN 1 Early pregnancy could be mistaken for this syndrome
Laboratory Studies
Need to have a fasting glucose level (should be less than 60)
Need to check fasting insulin level (should be greater than 24)
Check insulin to glucose ratio (should be > 0.3)
Check C-terminal peptide level to rule out exogenous insulin administration (will be elevated only with endogenous insulin) may see needle marks on arms/legs
Could also check proinsulin level
Will need to try to localize insulinoma (80% in pan- creas, may be multiple if familial variety, only 10%
malignant)
Localization studies (don’t stop after CT scan!):
(1) CT scan abd/pelvis with thin cuts through pancreas
(2) Arteriogram
(3) Portosplenic vein sampling (be prepared for results of this test!)
(4) Endoscopic U/S (5) MRI
Even if can’t localize (usually won’t be able to), you start the pt on Diazoxide and prepare pt for surgery (be sure okay surgical candidate)
Surgical Treatment
In OR, you need to fully examine pancreas by division gas- trohepatic ligament, Kocher maneuver, medial reflection of spleen, and divide the peritoneum on superior and infe- rior borders of pancreas.
If perform enucleation, dose of secretin intra-op to check for leak, place omental flap, and leave a drain. Don’t try to close defect created by “bovie down” to lesion.
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Then you will be in one of the following situations:
(1) You find tumor in the head of pancreas→enucleation distal pancreas→distal pancreatectomy
(2) You find tumor in pancreas with mets→ debulk- ing surgery, and use somatostatin, diazoxide, and streptozotocin post-op
(3) You can’t find tumor→ intra-op U/S, rapid venous assays
(a) If still can’t find, try to send to outside facil- ity for rapid venous assays to detect drop in insulin level
(b) If examiner won’t let you do→do distal pan- createctomy and send for frozen section and glucose/insulin measurement
(c) Don’t do near total pancreatectomy unless an endocrine expert
(4) MEN 1→ subtotal pancreatectomy because of high incidence of islet cell hyperplasia
Pt may have mild hyperglycemia for 2–3 days post-op.
Common Curveballs
Won’t be able to localize pre-op
Won’t be able to localize intra-op (consider intra-op U/S)
Won’t have facilities to do rapid venous sampling Will find a mass and FNA will be a malignant
adenocarcinoma Will be multiple tumors
Will see pancreatic duct leak after enucleation
Will be exogenous administration if don’t check C-terminal peptide/proinsulin level
Will be part of MEN syndrome
Will be malignant tumor or borderline tumor on final path
Can’t enucleate because deep in head/tail of pancreas (if you do, there will be damage to pancreatic duct Will get into massive hemorrhage during enucleation
Will do distal pancreatectomy and pt still symptomatic.
Examiner will ask you if you regret your decision (stick to your guns if you know you gave the right answer—examiner most likely trying to get at how confident a surgeon you are)
Strikeouts
Whipple procedure for tumor near surface (appropriate if deep in pancreatic head)
Stopping after CT scan and proceeding straight to OR Failing to ask about family history suspicious for MEN
(pituitary, pancreas, parathyroid problems) Failing to rule out exogenous insulin administration Performing too radical a surgery before exhaustive
work-up including venous sampling and possible referral to center specializing in the disease (always better to refer pt to tertiary care center than doing blind near total pancreatectomy)
Not mentioning controlling symptoms pre-op with small, frequent meals or diazoxide pre-op (suppresses insulin secretion with side effect of fluid retention and nausea)
Failing to rule out liver disease
Failing to recognize insulin-producing tumor in pt with hypoglycemic symptoms reversible with sugar intake Not knowing Whipple’s triad
Performing pancreatic resection when tumor near sur- face rather than enucleation
Will be pancreatic duct leak after enucleation
It’s better to say “I don’t perform this procedure, but the key steps are...” than to describe a procedure you don’t do and then get trapped answering questions about technical steps in the procedure.
Describing the exploration and enucleation to be done laparoscopically
Mistaking surgery for gastrinoma for insulinoma and opening up duodenum and palpating for tumor
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