Surgical approach to insulinomas: are pre-operative localisation tests necessary?

Insulinoma is a rare, but curable, endocrine tumour. The ability to localise the tumour accurately before or during surgery is an important factor in the management of these elusive lesions, which has been extensively debated. We have reviewed our experience of these lesions to establish the role of localisation tests.

The medical records of 20 consecutive patients who had surgery for sporadic insulinomas since 1985 at this institution were retrospectively reviewed. All the patients had a definite biochemical diagnosis of endogenous hyperinsulinism. Results of pre-operative and intra-operative localisation tests were compared with the final outcome.

Of the 20 patients with sporadic insulinomas reviewed, 17 patients (85%) had multiple pre-operative localising investigations. Overall accuracy of pre-operative localisation tests was 33%. Non-invasive pre-operative localisation tests (ultra-sonography, CT, MRI) had a combined localisation rate of 25% with MRI having the highest sensitivity of 71%. Invasive tests (angiography, transhepatic portal venous sampling [THPVS], endoscopic ultrasound) detected 48% of lesions with THPVS being most sensitive (67%). THPVS was particularly helpful in localising lesions before re-operation. Intra-operative inspection and palpation localised the lesions correctly in 91% and intra-operative ultrasound in 93% of cases. All 5 occult tumours (indeterminate anatomical site before operation) were palpable at surgery and four of these were also correctly identified by intra-operative ultrasound. Site and size of tumour correlated poorly with pre-operative localisation. Operative procedure did not influence outcome with three patients needing re-operation. One patient died (5% mortality) and 9 patients (45%) had complications. Normoglycaemia has been obtained in all but one patient.

Insulinomas can be readily localised by systematic operative exploration. Non-invasive pre-operative investigations (ultrasonography/MRI) may help identify the location of tumour to determine the appropriate surgical procedure. Invasive pre-operative localisation tests like angiography and THPVS may be a valuable adjunct for re-operations. This also helps reduce the costs.