Clinical Presentation

A 64-year-old man presents with weight loss, night sweats, and episodic dizziness. Routine blood work reveals a critically low glucose level of 1.0 mmol/L (18 mg/dL). Fasting blood work is subsequently ordered, yielding a glucose level of 1.2 mmol/L (21 mg/dL) coincident with a serum insulin level of 267 pmol/L (normal, 14–145 pmol/L). While fasting, the patient becomes clammy, sweaty, and generally unwell. He is instructed to consume frequent meals as well as orange juice mixed with sugar. These measures result in a significant reduction in his symptoms.

Fig. 95.1

Fig. 95.2

Technique

• ¹¹¹In-pentetreotide

• If possible, withhold nonradiolabeled octreotide before the scan: withhold 24 hours for short- acting octreotide and 3 to 4 weeks for long-acting formulations.

• The patient should be well hydrated to enhance renal clearance.

• If the patient has an insulinoma, a glucose infusion should be available to treat paradoxical hypoglycemia.

• 6 mCi (222 MBq)

• Slow intravenous injection over 1 minute

• Medium-energy collimator

• 172- and 247-keV photopeaks, 20% window

• SPECT: abdomen and pelvis at 4 hours

• SPECT: chest, abdomen, and pelvis at 24 hours

• Additional images can be obtained at 48 hours if there is uncertainty whether abdominal activity represents pathologic or physiologic uptake.

Image Interpretation