Fluorine‐18 fluorodeoxyglucose positron emission tomography‐computed tomography for staging of canine insulinoma: 3 cases (2019–2020)

Abstract

Objectives Canine insulinomas are uncommon malignant functional pancreatic neuroendocrine tumours with a high metastatic rate. Diagnostic imaging aids with staging and surgical planning of these tumours; however, identification is unpredictable across modalities. High‐grade human pancreatic neuroendocrine tumours display increased avidity on 18F‐fluorodeoxyglucose positron emission tomography‐CT. Materials and Methods Dogs with clinicopathologic findings consistent with pancreatic insulinoma were prospectively enrolled. Patients underwent 18F‐fluorodeoxyglucose positron emission tomography‐CT and CT angiography, followed by exploratory laparotomy. Results Three patients met the inclusion criteria and had histologically confirmed insulinomas. Both metastatic lesions in patient 1 were mildly avid (SUVmax 2.79 and 3.01). In patient 2, the primary pancreatic insulinoma was minimally avid (SUVmax 2.16). The primary pancreatic lesion in patient 3 had similar avidity to normal pancreatic parenchyma (SUVmax 1.54) and was undetected on 18F‐fluorodeoxyglucose positron emission tomography‐CT. Insulinomas demonstrated variable attenuation and contrast enhancement patterns on CT angiography and certain lesions were more conspicuous than on 18F‐fluorodeoxyglucose positron emission tomography‐CT. Two metastatic lesions not visible on either imaging modality were discovered in patient 2 at surgery. Clinical Significance Canine insulinomas were inconsistently avid on 18F‐fluorodeoxyglucose positron emission tomography‐CT. This finding is likely attributable to the confounding clinicopathological features and multifaceted transformation of these tumours, in addition to the influence of variable tumour size, composition and vascularity. Unpredictable tumoural avidity limits the value of 18F‐fluorodeoxyglucose positron emission tomography‐CT for staging canine insulinomas.

Current Trends in Diagnosis, Treatment and Prognosis of Canine Insulinoma

“…This imaging modality has proven to be effective for the imaging of human malignant insulinomas with 88.9% of human patients having avid lesions on the 18 F-FDG PET-CT images. The three canine insulinomas that were included in the Walczak et al (2022) study, however, were inconsistently avid on the 18 F-FDG PET-CT images, and it was concluded that the unpredictable tumoural avidity limits the value of 18 F-FDG PET-CT for staging canine insulinomas [ 38 ].…”