MRI without contrast enhancement is a highly accurate method of imaging insulinoma

BACKGROUND: According to the literature, there are contradictory results regarding the diagnostic accuracy of magnetic resonance imaging (MRI) without contrast enhancement (CE) in insulinoma, and studies that analyze the factors influencing the obtaining of false negative results have not been described.

AIM: Evaluation of the operational characteristics of MRI imaging of insulinoma without CE.

MATERIALS AND METHODS: Imaging studies of the abdominal cavity and retroperitoneal space were performed in patients with suspected nondiabetic hypoglycemia (NDH): MRI without CE (index test) and CT with CE (first row reference test). Ultrasound examination was used as a reference test of the second row, and arteriostimulated venous blood sampling was used in the third row. The diagnosis of NDH and insulinoma was established based on the detection of hyperinsulinemic hypoglycemia during laboratory examination and confirmation of the presence of a pancreatic tumor.

RESULTS: 125 patients with insulinoma and 55 patients with other causes of NDH were included. The sensitivity of MRI without CE in the diagnosis of insulinoma was 94%, 95% CI [89%; 98%], specificity — 98%, 95% CI [90%; 100%], prognostic value of a positive result — 99%, 95% CI [95%; 100%], prognostic value of a negative result is 87%, 95% CI [76%; 94%]. The Kappa index of agreement with the final diagnosis was 0.886 (95% CI [0.814; 0.958]), which corresponds to excellent agreement, with CT — 0.750 (95% CI [0.651; 0.850]), which corresponds to significant agreement.

In a comparative analysis of the tomographic and pathomorphological characteristics of insulinoma, in cases with divergent results when using MRI without CE and CT with CE, significant differences in structure, shape, contour features, localization and degree of malignancy of the tumor, as well as the structure of its surrounding parenchyma were not revealed.

In the presented sample, the insulinoma has a median size of 14–15 mm with the median optical density in the native phase of CT 42–44 units.H, hyperintensivity on T2-weighted MRI images in 89%, 95% CI [78%; 95%] cases and low Grade 1 malignancy in 70%, 95% CI [56%; 81%] cases.

CONCLUSION: CT with CE and MRI without CE are characterized by significant agreement in the diagnosis of insulinoma. In this regard, as well as due to the lack of radiation exposure and the strict need for contrast agents, MRI without CE can be recommended as a first-line method on a par with abdominal ultrasound and CT with CE to detect insulinoma.

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