Localization of insulinomas to regions of the pancreas by intraarterial calcium stimulation: the NIH experience

Abstract

Context: Selective intraarterial calcium injection of the major pancreatic arteries with hepatic venous sampling [calcium arterial stimulation (CaStim)] has been used as a localizing tool for insulinomas at the National Institutes of Health (NIH) since 1989. The accuracy of this technique for localizing insulinomas was reported for all cases until 1996.

Objectives: The aim of the study was to assess the accuracy and track record of the CaStim over time and in the context of evolving technology and to review issues related to result interpretation and procedure complications. CaStim was the only invasive preoperative localization modality used at our center. Endoscopic ultrasound (US) was not studied.

Design and setting: We conducted a retrospective case review at a referral center.

Patients: Twenty-nine women and 16 men (mean age, 47 yr; range, 13-78) were diagnosed with an insulinoma from 1996-2008.

Intervention: A supervised fast was conducted to confirm the diagnosis of insulinoma. US, computed tomography (CT), magnetic resonance imaging (MRI), and CaStim were used as preoperative localization studies. Localization predicted by each preoperative test was compared to surgical localization for accuracy.

Main outcome: We measured the accuracy of US, CT, MRI, and CaStim for localization of insulinomas preoperatively.

Results: All 45 patients had surgically proven insulinomas. Thirty-eight of 45 (84%) localized to the correct anatomical region by CaStim. In five of 45 (11%) patients, the CaStim was falsely negative. Two of 45 (4%) had false-positive localizations.

Conclusion: The CaStim has remained vastly superior to abdominal US, CT, or MRI over time as a preoperative localizing tool for insulinomas. The utility of the CaStim for this purpose and in this setting is thus validated.

Figure 1

Top, Right hepatic vein (RHV) insulin concentration before and after intraarterial calcium injection at the dominant artery for 45 patients who underwent CaStim at NIH from 1996–2008. Bottom, Fold increase in right hepatic vein insulin concentration after calcium injection of dominant artery according to diagnosis. Dotted line denotes 2-fold response. Continuous line denotes median response for each group.

Figure 2

CaStims with multiple positive responses. A 2-fold step-up may be seen in more than one arterial injection. In case 1, a 421-fold increase in baseline insulin is seen when the SMA is injected, and a 72-fold step-up is seen on injection of the GDA. Both responses regionalize to the head. If a positive response, defined as a greater than 2-fold step-up in baseline insulin, is seen in more than one injected artery, the dominant response is taken as the site of tumor localization. Case 2 illustrates a CaStim with multiple positive responses that fails to regionalize. Positive responses are seen in ProxSplenic (4-fold), SMA (3-fold), and GDA (3-fold). Responses are seen in multiple pancreatic regions (e.g. SMA/GDA = head/neck, and ProxSplenic = body/tail), but no clearly dominant response is seen. This CaStim was performed in the work-up of a patient who was later found to be abusing repaglinide surreptitiously (41).

Figure 3

Localization sensitivity of preoperative tests.