Diagnosis and localisation of insulinoma: the value of modern magnetic resonance imaging in conjunction with calcium stimulation catheterisation

Context: Preoperative localisation of insulinoma improves cure rate and reduces complications, but may be challenging. Objective: To review diagnostic features and localisation accuracy for insulinomas. Design: Cross-sectional, retrospective analysis. Setting: A single tertiary referral centre. Patients: Patients with insulinoma in the years 1990-2009, including sporadic tumours and those in patients with multiple endocrine neoplasia syndromes. Interventions: Patients were identified from a database, and case notes and investigation results were reviewed. Tumour localisation by computed tomography (CT), magnetic resonance imaging (MRI), octreotide scanning, endoscopic ultrasound (EUS) and calcium stimulation was evaluated. Main outcome measure(s): Insulinoma localisation was compared to histologically confirmed location following surgical excision. Results: Thirty-seven instances of biochemically and/or histologically proven insulinoma were identified in 36 patients, of which seven were managed medically. Of the 30 treated surgically, 25 had CT (83.3%) and 28 had MRI (90.3%), with successful localisation in 16 (64%) by CT and 21 (75%) by MRI respectively. Considered together, such imaging correctly localised 80% of lesions. Radiolabelled octreotide scanning was positive in 10 out of 20 cases (50%); EUS correctly identified 17 lesions in 26 patients (65.4%). Twenty-seven patients had calcium stimulation testing, of which 6 (22%) did not localise, 17 (63%) were correctly localised, and 4 (15%) gave discordant or confusing results. Conclusions: Preoperative localisation of insulinomas remains challenging. A pragmatic combination of CT and especially MRI predicts tumour localisation with high accuracy. Radionuclide imaging and EUS were less helpful but may be valuable in selected cases. Calcium stimulation currently remains useful in providing an additional functional perspective.