Pre-operative localisation of insulinoma remains clinically challenging but may shorten operative time and risk of complications by directing exploration and supporting laparoscopic resection where possible. Intra-arterial calcium stimulation testing (IACS) is a well established, albeit invasive modality, that is sometimes used in pre-operative identification of biochemically proven insulinoma. We report the detection rates of IACS as compared to other methods utilised at our centre.

DESIGN:

We conducted a retrospective review of insulinoma cases at our hospital between 2000 – 2012. We contrast the tumour detection rates of IACS with ultrasound (U/S), computed tomography (CT), endoscopic ultrasound (EUS) and intraoperative localisation by both palpation and intraoperative U/S.

RESULTS:

In this time frame 16 patients had histologically proven insulinoma. From this cohort, 14 patients underwent IACS. Of these, 11/14 (79%) IACS studies were consistent with presence of insulinoma and correlated with anatomical location based on arterial distribution with 91% accuracy. Interestingly, of the 3 cases where IACS was unable to localise the tumour, 2 were in the early years after introduction of this method at our hospital. Furthermore, in 3 of our cases, IACS was the only modality able to detect insulinoma.

Localisation of insulinoma was significantly less sensitive using non-invasive imaging: 1/3 (33%) for ultrasound, 9/15 (60%) for CT and 3/6 (50%) for EUS. In this case series, 2 MRI and 2 PET scans were also performed and all failed to detect the tumour. Tumour was located in all cases by intraoperative palpation and confirmed with intraoperative U/S (100% in the 10 cases this was performed). None of our patients required a blind resection or surgical re-exploration for failed localisation.

CONCLUSIONS:

IACS is a high yield test in locating insulinoma. Our detection rates have improved over time. Given the rarity of this tumour, maintaining local expertise in this technique is essential.