Limited value of 18F-F-DOPA PET to localize pancreatic insulin-secreting tumors in adults with hyperinsulinemic hypoglycemia

68Ga-DOTA-Exendin-4 PET/CT Demonstrated a Higher Detection Efficacy for Double-Primary Insulinomas Than MRI: A Case Report

ABSTRACT

We presented a 20-year-old woman with gradually increasing lethargy and multiple episodes of dizziness for 5 months. The laboratory examination revealed decreasing level of blood glucose and elevated levels of fasting plasma insulin and C-peptide. The MRI identified a focal nodule in the tail of the pancreas. 68Ga-DOTA-exendin-4 PET/CT revealed 2 intense focal tracer uptakes in the tail of the pancreas, one of which corresponded to the lesion revealed on MRI. The immunohistochemical results of resected samples confirmed the diagnosis of double-primary insulinomas. 68Ga-DOTA-exendin-4 PET/CT demonstrated excellent localization and characterization for double-primary insulinomas in the tail of the pancreas.

Molecular Imaging of Neuroendocrine Neoplasms

The key for molecular imaging is the use of a radiotracer with a radioactive and a functional component. While the functional component targets a specific feature of the tumor, the radioactive component makes the target visible. Neuroendocrine neoplasms (NEN) are a diverse group of rare tumors that arise from neuroendocrine cells found mainly in the gastroenteropancreatic system, lung, thyroid, and adrenal glands. They are characterized by the expression of specific hormone receptors on the tumor cell surface, which makes them ideal targets for radiolabeled peptides. The most commonly expressed hormone receptors on NEN cells are the somatostatin receptors. They can be targeted for molecular imaging with various radiolabeled somatostatin analogs, but also with somatostatin antagonists, which have shown improved imaging quality. 18F-DOPA imaging has become a second-line imaging modality in NENs, with the exception of the evaluation of advanced medullary thyroid carcinoma. Alternatives for NENs with insufficient somatostatin receptor expression due to poor differentiation involve targeting glucose metabolism, which can also be used for prognosis. For the localization of the often-small insulinoma, glucagon-like peptide-1 (GLP-1) receptor imaging has become the new standard. Other alternatives involve metaiodobenzylguanidine and the molecular target C-X-C motif chemokine receptor-4. In addition, new radiopeptides targeting the fibroblast activation protein, the glucose-dependent insulinotropic polypeptide receptor and cholecystokinin-2 receptors have been identified in NENs and await further evaluation. This mini-review aims to provide an overview of the major molecular imaging modalities currently used in the field of NENs, and also to provide an outlook on future developments.

Molecular imaging of endocrine neoplasms with emphasis on 18F-DOPA PET: a practical approach for well-tailored imaging protocols

6-[18F]-L-fluoro-L-3, 4-dihydroxyphenylalanine (¹⁸F-DOPA) PET/CT can be a useful tool for the detection of different neuroendocrine tumors (NETs). The main determinants of ¹⁸F-DOPA uptake and retention by NETs are related to expression of LAT1/LAT2 transporters, expression and activity of AADC and biochemical phenotype, all being intimately inter-connected to their embryological origin. In order to improve sensitivity of ¹⁸F-DOPA PET, it is of main importance to perform indivisualized imaging protocols across primaries. This review provides a practical approach for performing well-tailored imaging protocols and describes the clinical value of the recommended radiopharmaceuticals.

Molecular Imaging in neuroendocrine neoplasias

Molecular imaging, which uses molecular targets due to the overexpression of specific peptide hormone receptors on the tumour surface, has become an indispensable diagnostic technique. Neuroendocrine neoplasms (NENs) especially differentiated NENs or neuroendocrine tumours (NETs) are a rare group of heterogeneous tumours, characterized by the expression of hormone receptors on the tumour cell surface. This property makes them receptive to diagnostic and therapeutic approaches (theranostics) using radiolabelled peptides. Amongst the known hormone receptors, somatostatin receptors (SSTR) are expressed on the majority of NETs and are therefore the most relevant receptors for theranostic approaches. Current research aims to medically upregulate their expression, while other focuses are on the use of different radiopeptides (64Cu and 67Cu) or somatostatin-antagonists instead of the established somatostatin agonists. The GLP-1 receptor is another clinically relevant target, as GLP-1-R imaging has become the new standard for the localisation of insulinomas. For staging and prognostic evaluation in dedifferentiated NENs, 18F-FDG-imaging is useful, but lacks a therapeutic counterpart. Further options for patients with insufficient expression of SSTR involve metaiodobenzylguanidine (MIBG) and the molecular target C-X-C motif chemokine receptor-4 (CXCR4). New targets such as the glucose-dependant insulinotropic polypeptide receptor (GIPR) and the fibroblast activation protein (FAP) have been identified in NENs recently and await further evaluation. For medullary thyroid cancer 18-F-DOPA imaging is standard, however this technique is rather second line for other NENs. In this area, the discovery of minigastrin, which targets the cholecystokinin-2 (CCK2) receptors in medullary thyroid carcinoma and foregut NENs, may improve future management. This review aims to provide an overview of the most commonly used functional imaging modalities for theranostics in NENs today and in the possible future.

Values of 68Ga-DOTATOC and Carbidopa-assisted 18F-DOPA PET/CT for insulinoma localization

To assess the value of ⁶⁸Ga-DOTATOC and carbidopa-assisted ¹⁸F-DOPA in 21 hypoglycaemic patients. Methods: All patients who underwent ⁶⁸Ga-DOTATOC and/or carbidopa-assisted ¹⁸F-DOPA PET/CT for suspicion of insulinoma from January 2019 to January 2021 were retrospectively analysed. Insulinoma final diagnosis was defined according to pathological reports or consensus. Results: During the study period, 21 patients underwent both ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT. A final diagnosis of insulin-secreting tumour was reached in 12 cases, including 11 insulinomas and 1 small mixed neuroendocrine/non-neuroendocrine neoplasm. ¹⁸F-DOPA and ⁶⁸Ga-DOTATOC PET/CT were positive in 5 (45%) and 7 (64%) of 11 cases, respectively, with 4 concordant positive findings. Moreover, 1 insulinoma was visualized exclusively by ¹⁸F-DOPA PET/CT and 3 by ⁶⁸Ga-DOTATOC PET/CT only. ¹⁸F-DOPA and ⁶⁸Ga-DOTATOC PET/CT were falsely positive in 1 non-functioning pancreatic neuroendocrine tumour. Conclusion: When ⁶⁸Ga-exendin-4 is not available, ⁶⁸Ga-SSTR PET/CT should be the first choice for insulinoma functional imaging.

Imaging of Insulinoma by Targeting Glucagonlike Peptide-1 Receptor

"Glucagonlike peptide-1 (GLP-1) receptor imaging, using radiolabeled exendin-4, was recently established for detecting insulinoma in patients with hyperinsulinemic hypoglycemia. It has proven to be a sensitive and specific method for preoperative localization of insulinoma. This review introduces the development, clinical research, and perspective of GLP-1 receptor imaging mainly in insulinoma.

Non-invasive Beta-cell Imaging: Visualization, Quantification, and Beyond

Pancreatic beta (β)-cell dysfunction and reduced mass play a central role in the development and progression of diabetes mellitus. Conventional histological β-cell mass (BCM) analysis is invasive and limited to cross-sectional observations in a restricted sampling area. However, the non-invasive evaluation of BCM remains elusive, and practical in vivo and clinical techniques for β-cell-specific imaging are yet to be established. The lack of such techniques hampers a deeper understanding of the pathophysiological role of BCM in diabetes, the implementation of personalized BCM-based diabetes management, and the development of antidiabetic therapies targeting BCM preservation and restoration. Nuclear medical techniques have recently triggered a major leap in this field. In particular, radioisotope-labeled probes using exendin peptides that include glucagon-like peptide-1 receptor (GLP-1R) agonist and antagonist have been employed in positron emission tomography and single-photon emission computed tomography. These probes have demonstrated high specificity to β cells and provide clear images accurately showing uptake in the pancreas and transplanted islets in preclinical in vivo and clinical studies. One of these probes, ¹¹¹indium-labeled exendin-4 derivative ([Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4), has captured the longitudinal changes in BCM during the development and progression of diabetes and under antidiabetic therapies in various mouse models of type 1 and type 2 diabetes mellitus. GLP-1R-targeted imaging is therefore a promising tool for non-invasive BCM evaluation. This review focuses on recent advances in non-invasive in vivo β-cell imaging for BCM evaluation in the field of diabetes; in particular, the exendin-based GLP-1R-targeted nuclear medicine techniques.

A side-by-side evaluation of [18F]FDOPA enantiomers for non-invasive detection of neuroendocrine tumors by positron emission tomography

Neuroendocrine tumors (NETs) are an extremely heterogenous group of malignancies with variable clinical behavior. Molecular imaging of patients with NETs allows for effective patient stratification and treatment guidance and is crucial in selection of targeted therapies. Positron emission tomography (PET) with the radiotracer L-[¹⁸F]FDOPA is progressively being utilized for non-invasive in vivo visualization of NETs and pancreatic β-cell hyperplasia. While L-[¹⁸F]FDOPA-PET is a valuable tool for disease detection and management, it also exhibits significant diagnostic limitations owing to its inherent physiological uptake in off-target tissues. We hypothesized that the D-amino acid structural isomer of that clinical tracer, D-[¹⁸F]FDOPA, may exhibit superior clearance capabilities owing to a reduced in vivo enzymatic recognition and enzyme-mediated metabolism. Here, we report a side-by-side evaluation of D-[¹⁸F]FDOPA with its counterpart clinical tracer, L-[¹⁸F]FDOPA, for the non-invasive in vivo detection of NETs. In vitro evaluation in five NET cell lines, including invasive small intestinal neuroendocrine carcinomas (STC-1), insulinomas (TGP52 and TGP61), colorectal adenocarcinomas (COLO-320) and pheochromocytomas (PC12), generally indicated higher overall uptake levels of L-[¹⁸F]FDOPA, compared to D-[¹⁸F]FDOPA. While in vivo PET imaging and ex vivo biodistribution studies in PC12, STC-1 and COLO-320 mouse xenografts further supported our in vitro data, they also illustrated lower off-target retention and enhanced clearance of D-[¹⁸F]FDOPA from healthy tissues. Cumulatively our results indicate the potential diagnostic applications of D-[¹⁸F]FDOPA for malignancies where the utility of L-[¹⁸F]FDOPA-PET is limited by the physiological uptake of L-[¹⁸F]FDOPA, and suggest D-[¹⁸F]FDOPA as a viable PET imaging tracer for NETs.

68Ga-DOTA-Exendin PET-MRI Fusion Imaging in a Case of Insulinoma

Persistent hyperinsulinemic hypoglycemia in adults is most commonly caused by insulinomas, which pose a diagnostic challenge to physicians, surgeons, and radiologists and require multimodality imaging for precise localization and staging. PET tracers such as F-FDOPA and glucagon-like peptide 1 receptor analogs have been used for imaging insulinomas. Glucagon-like peptide 1 receptor analogs have recently shown promising results in preoperative localization of these tumors, as all insulinomas express glucagon-like peptide 1 receptors. Ga-DOTA-Exendin PET and MRI done in the present case helped in precise localization and management of the culprit lesion, whereas contrast-enhanced CT and F-FDOPA PET failed to do so.

State of the Art and Recent Developments of Radiopharmaceuticals for Pancreatic Neuroendocrine Tumors Imaging

Background:

Neuroendocrine Tumors (NETs) are relatively rare tumors, mainly originating from the digestive system, that tend to grow slowly and are often diagnosed when metastasised. Surgery is the sole curative option but is feasible only in a minority of patients. Among them, pancreatic neuroendocrine tumors (pancreatic NETs or pNETs) account for less than 5% of all pancreatic tumors. Viable therapeutic options include medical treatments such as biotherapies and more recently Peptide Receptor Radionuclide Therapies (PRRT) with radiolabeled somatostatin analogues. Molecular imaging, with main reference to PET/CT, has a major role in patients with pNETs.

Objective:

The overexpression of specific membrane receptors, as well as the ability of cells to take up amine precursors in NET, have been exploited for the development of specific targeting imaging agents.

Methods:

SPECT/CT and PET/CT with specific isotopes such as [68Ga]-1,4,7,10-tetra-azacyclododecane- N,N’,N’’,N’’’-tetra-acetic acid (DOTA)-somatostatin analogs, [18F]-FDG and [18F]-fluorodopa have been clinically explored.

Results:

To overcome the limitations of SSTR imaging, interesting improvements are connected with the availability of new radiotracers, activating with different mechanisms compared to somatostatin analogues, such as glucagon-like peptide 1 receptor (GLP-1 R) agonists or antagonists.

Conclusion:

This paper shows an overview of the RPs used so far in the imaging of pNETs with insight on potential new radiopharmaceuticals currently under clinical evaluation.

Molecular imaging of β-cells: diabetes and beyond

Since diabetes is becoming a global epidemic, there is a great need to develop early β-cell specific diagnostic techniques for this disorder. There are two types of diabetes (i.e., type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM)). In T1DM, the destruction of pancreatic β-cells leads to reduced insulin production or even absolute insulin deficiency, which consequently results in hyperglycemia. Actually, a central issue in the pathophysiology of all types of diabetes is the relative reduction of β-cell mass (BCM) and/or impairment of the function of individual β-cells. In the past two decades, scientists have been trying to develop imaging techniques for noninvasive measurement of the viability and mass of pancreatic β-cells. Despite intense scientific efforts, only two tracers for positron emission tomography (PET) and one contrast agent for magnetic resonance (MR) imaging are currently under clinical evaluation. β-cell specific imaging probes may also allow us to precisely and specifically visualize transplanted β-cells and to improve transplantation outcomes, as transplantation of pancreatic islets has shown promise in treating T1DM. In addition, some of these probes can be applied to the preoperative detection of hidden insulinomas as well. In the present review, we primarily summarize potential tracers under development for imaging β-cells with a focus on tracers for PET, SPECT, MRI, and optical imaging. We will discuss the advantages and limitations of the various imaging probes and extend an outlook on future developments in the field.

Preoperative imaging and pathologic classification for pancreatic neuroendocrine tumors

The management of patients with pancreatic neuroendocrine tumor (PNET), whether hormonally secretory or not, is multidisciplinary and often multimodal. Surgical treatment plays a central role because complete resection is the only potentially curative treatment. The choice of the therapeutic plan for a PNET requires precise localization of the primary tumor (which may sometimes be multiple in case of genetic predisposition), confirmation of the diagnosis of PNET, a search for metastases (mainly hepatic), and identification of the main histoprognostic factors. This update focuses on the WHO 2017 histological classification and recent innovations in the preoperative assessment of PNET using conventional and isotopic imaging. The aim is to not only allow the mapping of primary and metastatic lesions but also to predict tumor aggressiveness.

Pancreatic uptake and radiation dosimetry of 6-[18F]fluoro-L-DOPA from PET imaging studies in infants with congenital hyperinsulinism

METHODS

After injecting 25.6 ± 8.8 MBq (0.7 ± 0.2 mCi) of 18F-Fluoro-L-DOPA intravenously, three static PET scans were acquired at 20, 30, and 40 min post injection in 3-D mode on 10 patients (6 male, 4 female) with congenital hyperinsulinism. Regions of interest (ROIs) were drawn over several organs visible in the reconstructed PET/CT images and time activity curves (TACs) were generated. Residence times were calculated using the TAC data. The radiation absorbed dose for the whole body was calculated by entering the residence times in the OLINDA/EXM 1.0 software.

RESULTS

The mean residence times for the 18F-Fluoro-L-DOPA in the liver, lungs, kidneys, muscles, and pancreas were 11.54 ± 2.84, 1.25 ± 0.38, 4.65 ± 0.97, 17.13 ± 2.62, and 0.89 ± 0.34 min, respectively. The mean effective dose equivalent for 18F-Fluoro-L-DOPA was 0.40 ± 0.04 mSv/MBq. The CT scan used for attenuation correction delivered an additional radiation dose of 5.7 mSv. The organs receiving the highest radiation absorbed dose from 18F-Fluoro-L-DOPA were the urinary bladder wall (2.76 ± 0.95 mGy/MBq), pancreas (0.87 ± 0.30 mGy/MBq), liver (0.34 ± 0.07 mGy/MBq), and kidneys (0.61 ± 0.11 mGy/MBq). The renal system was the primary route for the radioactivity clearance and excretion.

CONCLUSIONS

The estimated radiation dose burden from 18F-Fluoro-L-DOPA is relatively modest to newborns.

Molecular imaging in the investigation of hypoglycaemic syndromes and their management

There has been recent progress in molecular imaging using a variety of cellular targets for the investigation of adult non-diabetic hypoglycaemic syndromes and its integration into patient management. These targets include peptide receptors (somatostatin receptors (SSTRs) and glucagon-like peptide-1 receptor (GLP-1R)) the amine precursor uptake and decarboxylation system utilising the diphydroxyphenylaline (DOPA) analogue 6-[¹⁸F]-l-fluoro-l-3,4-dihydroxyphenylalanine (¹⁸F-FDOPA), and glycolytic metabolism with 2-[¹⁸F]fluoro-2-deoxy-d-glucose (FDG). Accurate preoperative localisation and staging is critical to enable directed surgical excision or enucleation with minimal morbidity and preservation of residual pancreatic function. Benign insulinoma has near ubiquitous dense GLP-1R expression enabling accurate localisation with radiolabelled-exendin-4 compounds (e.g. ⁶⁸Ga-NOTA-exendin-4 PET/CT), whilst the rarer and more difficult to manage metastatic insulinoma typically express SSTR and is preferably imaged with radiolabelled-SSTR analogues such as ⁶⁸Ga-DOTA-octreotate (DOTATATE) PET/CT for staging and assessment of suitability for peptide receptor radionuclide therapy (PRRT). Similar to other metastatic neuroendocrine tumours, FDG PET/CT is used in the setting of higher-grade metastatic insulinoma to provide important prognostic information that can guide treatment and determine suitability for PRRT. Interestingly, these three tracers appear to represent a spectrum of differentiation, which we conceptually describe as the 'triple-flop' phenomenon, with GLP-1R > SSTR > FDG in benign insulinoma and the opposite in higher-grade disease. This paper will review the clinical syndromes of adult hypoglycaemia (including a practical overview of the differential diagnoses to be considered), comparison of techniques for insulinoma localisation with emphasis on molecular imaging before discussing its implications for management of metastatic insulinoma.

Molecular imaging in neuroendocrine tumors: recent advances, controversies, unresolved issues, and roles in management

PURPOSE OF REVIEW

The purpose is to review recent advances in molecular imaging of neuroendocrine tumors (NETs), discuss unresolved issues, and review how these advances are affecting clinical management.

RECENT FINDINGS

Molecular imaging of NETs underwent a number of important changes in the last few years, leading to some controversies, unresolved issues, and significant changes in clinical management. The most recent changes are reviewed in this article. Particularly important is the rapid replacement in somatostatin receptor scintigraphy of In-diethylenetriamine penta-acetic acid-single-photon emission computed tomography/computed tomography (CT) by Ga-fluorodopa(F-D)PA), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-peptide-PET/CT imaging, which is now approved in many countries including the USA. Numerous studies in many different types of NETs demonstrate the greater sensitivity of Ga-DOTA-peptide PET/CT, its high specificity, and its impact on management. Other important developments in somatostatin receptor scintigraphy/molecular imaging include demonstrating the prognostic value of both Ga-DOTA-peptide PET/CT and F-fluoro-deoxyglucose PET/CT; how their use can be complementary; comparing the sensitivities and usefulness of Ga-DOTA-peptide PET/CT and F-FDOPA PET/CT; introducing new linkers and radiolabeled ligands such as Cu-DOTA-peptides with a long half-life, enhancing utility; and the introduction of somatostatin receptor antagonists which show enhanced uptake by NETs. In addition, novel ligands which interact with other receptors (GLP-1, bombesin, cholecystokinin, gastric inhibitory polpeptide, integrin, chemokines) are described, which show promise in the imaging of both NETs and other tumors.

SUMMARY

Molecular imaging is now required for all aspects of the management of patients with NETs. Its results are essential not only for the proper diagnostic management of the patient, but also for assessing whether the patient is a candidate for peptide receptor radionuclide therapy with Lu and also for providing prognostic value.

Cross sectional and nuclear medicine imaging of pancreatic insulinomas

Insulinomas are rare neuroendocrine tumors which occur predominantly in the pancreas. Although majority of the insulinomas are benign, over-secretion of insulin by the tumor leads to debilitating hypoglycemic symptoms. The diagnosis is based on clinical and biochemical findings. After the diagnosis is made, the principal challenge lies in locating the tumor because most tumors are solitary and small in size. Locating the tumor is of paramount importance as complete surgical excision is the only curative treatment, and incomplete resection leads to persistence of symptoms. Different preoperative and intraoperative imaging techniques have been used with varying success rates for the insulinoma imaging. Besides localizing the tumor, imaging also helps to guide biopsy, detect metastatic lesions, and perform image-guided therapeutic procedures. This review will discuss the role of different Cross sectional and nuclear medicine imaging modalities in insulinomas.

Tumor Heterogeneity Detected by 68Ga DOTATOC and 18F-FDG PET/CTs in One Malignant Insulinoma With Involvement of the Portal Splenic Confluence and Ovarian Metastases

A 67-year-old woman was referred for staging of an insulinoma. CT has shown a pancreatic tumor, a portal thrombus, and an ovarian mass presumed not to be related with the insulinoma. These three lesions were highly positive on Ga DOTATOC PET/CT, leading to the hypothesis of a malignant insulinoma with neoplastic vein thrombus and ovarian metastasis, which was subsequently confirmed histologically. Despite severe hypoglycemia preventing fasting, F-FDG PET/CT was informative, showing significant uptake by the thrombus, which corresponded to the most aggressive lesion (Ki67 of 3.5% for the primary pancreatic tumor and 19.6% for the thrombus).

Targets and probes for non-invasive imaging of β-cells

β-cells, located in the islets of the pancreas, are responsible for production and secretion of insulin and play a crucial role in blood sugar regulation. Pathologic β-cells often cause serious medical conditions affecting blood glucose level, which severely impact life quality and are life-threatening if untreated. With 347 million patients, diabetes is one of the most prevalent diseases, and will continue to be one of the largest socioeconomic challenges in the future. The diagnosis still relies mainly on indirect methods like blood sugar measurements. A non-invasive diagnostic imaging modality would allow direct evaluation of β-cell mass and would be a huge step towards personalized medicine. Hyperinsulinism is another serious condition caused by β-cells that excessively secrete insulin, like for instance β-cell hyperplasia and insulinomas. Treatment options with drugs are normally not curative, whereas curative procedures usually consist of the resection of affected regions for which, however, an exact localization of the foci is necessary. In this review, we describe potential tracers under development for targeting β-cells with focus on radiotracers for PET and SPECT imaging, which allow the non-invasive visualization of β-cells. We discuss either the advantages or limitations for the various tracers and modalities. This article concludes with an outlook on future developments and discuss the potential of new imaging probes including dual probes that utilize functionalities for both a radioactive and optical moiety as well as for theranostic applications.

Pancreatic Uptake by 18F-FDOPA PET/CT in Patients With Hypoglycemia After Gastric Bypass Surgery Compared With Controls With or Without Carbidopa Pretreatment

PURPOSE

The use of Fluorine-labeled dihydroxy-phenyl-alanine (F-FDOPA) PET/CT in patients with hypoglycemia suspected to be caused by pancreatic disease can be helpful to localize the source of excess insulin production. In this setting, carbidopa pretreatment is not recommended. However, quantitative comparisons of pancreatic tracer uptake in patients with or without carbidopa pretreatment and in diffuse pancreatic disease are lacking. Therefore, we aimed to describe and quantify pancreatic F-FDOPA uptake in patients without pancreatic disease with or without carbidopa pretreatment and in patients with hypoglycemia after gastric bypass surgery.

PATIENTS AND METHODS

This is a retrospective data analysis of F-FDOPA PET/CT scans performed at a university medical center in the period from 2009 to 2015. All scans were reconstructed and calculated based on the European Association of Nuclear Medicine/EANM Research Ltd guidelines. Of 358 patients without evidence of pancreatic disease or hypoglycemic disorders, 344 received carbidopa and 14 did not. Another 9 patients had post-gastric bypass hypoglycemia. The main outcome measurement was F-FDOPA SUVmax for pancreatic head, body, and tail regions.

RESULTS

Carbidopa pretreated patients had a lower median SUVmax (-1.15, -1.20, and -0.84 in pancreatic head, body, and tail [all P < 0.01]) than patients without carbidopa pretreatment. Patients with post-gastric bypass hypoglycemia scanned without carbidopa pretreatment had higher median SUVmax (+1.18, +1.39, and +1.63, all P < 0.03) compared with controls without pretreatment.

CONCLUSIONS

Patients with post-gastric bypass hypoglycemia have increased uptake in all pancreatic regions. Carbidopa pretreatment lowers pancreatic F-FDOPA uptake in the nonaffected pancreas and may therefore mask disease activity in post-gastric bypass hypoglycemia.

Effect of Carbidopa on 18F-FDOPA Uptake in Insulinoma: From Cell Culture to Small-Animal PET Imaging

Patient premedication with carbidopa seems to improve the accuracy of 6-¹⁸F-fluoro-3,4-dihydroxy-l-phenylalanine (¹⁸F-FDOPA) PET for insulinoma diagnosis. However, the risk of PET false-negative results in the presence of carbidopa is a concern. Consequently, we aimed to evaluate the effect of carbidopa on ¹⁸F-FDOPA uptake in insulinoma β-cells and an insulinoma xenograft model in mice.

METHODS

¹⁸F-FDOPA in vitro accumulation was assessed in the murine β-cell line RIN-m5F. In vivo small-animal PET experiments were performed on tumor-bearing nude mice after subcutaneous injection of RIN-m5F cells. Experiments were conducted with and without carbidopa pretreatment.

RESULTS

Incubation of RIN-m5F cells with 80 μM carbidopa did not significantly affect the cellular accumulation of ¹⁸F-FDOPA. Tumor xenografts were clearly detectable by small-animal PET in all cases. Insulinoma xenografts in carbidopa-treated mice showed significantly higher ¹⁸F-FDOPA uptake than those in nontreated mice. Regardless of carbidopa premedication, the xenografts were characterized by an early increase in ¹⁸F-FDOPA uptake and then a progressive reduction over time.

CONCLUSION

Carbidopa did not influence in vitro ¹⁸F-FDOPA accumulation in RIN-m5F cells but improved insulinoma imaging in vivo. Our findings increase current knowledge about the ¹⁸F-FDOPA uptake profile of RIN-m5F cells and a related xenograft model. To our knowledge, the present work represents the first preclinical research specifically focused on insulinomas, with potential translational implications.

Carbidopa-assisted 18F-fluorodihydroxyphenylalanine PET/CT for the localization and staging of non-functioning neuroendocrine pancreatic tumors

OBJECTIVE

CD premedication was found to increase the value of ¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-FDOPA) PET/CT imaging in the detection of adult insulinoma. The aim of this study was to evaluate the performance of CD-assisted ¹⁸F-FDOPA PET/CT in the diagnosis and staging of non-functioning pNETs.

METHODS

Twenty consecutive patients with low-grade pNETs who underwent CD-assisted ¹⁸F-FDOPA PET/CT imaging and ¹¹¹In-somatostatin receptor scintigraphy (SRS) were evaluated. Histology was considered as the gold standard. In case where no surgical resection was performed, the diagnosis of pNET was made by the confrontation of the different available imaging modalities.

RESULTS

CD-assisted ¹⁸F-FDOPA PET/CT was positive in 18/20 cases (90 %), whereas SRS was positive in 13/19 cases (68 %). When considered the 19 patients underwent both nuclear medicine examinations, ¹⁸F-FDOPA PET/CT was significantly more sensitive then SRS for primary tumor detection (p = 0.049). False-negative results of both ¹⁸F-FDOPA PET/CT and SRS were observed in 2 cystic pNETs. SRS failed to detect one additional cystic tumor and 3 pNETs of 10, 12 and 17 mm, respectively. ¹⁸F-FDOPA PET/CT correctly identified all patients with lymphatic, visceral and bone metastases. SRS failed to detect lymphatic spread and was falsely negative in one patient with splenic metastasis.

CONCLUSIONS

Contrary to widely held assumptions, our study further expands the application of CD-assisted ¹⁸F-FDOPA PET/CT for non-functioning pNETs when ⁶⁸Ga-radiolabeled somatostatin analogs are not available.

Giant insulinoma in a 15-year-old man: A case report

•

Giant insulinomas are extremely rare, especially among young patients.

•

Tumor resection is the treatment of choice for giant insulinomas with benign features.

•

Long-term follow-up is essential in benign giant insulinoma to detect the recurrence in the future

Introduction

Giant insulinomas are extremely rare pancreatic neuroendocrine tumor.

Presentation of case

A 15-year-old man presenting with acute onset of lightheadedness was found to have serum glucose of 1.5 mmol/L. The blood collected from the hypoglycemic episode showed an inappropriately high insulin and C-peptide level. Abdominal computerized tomography showed a 12.5 cm well-defined, lobulated hypervascular mass at pancreatic tail, without any evidence of metastasis. En bloc resection with distal pancreatectomy, and splenectomy was successfully performed. The pathological examination confirmed insulinoma, with benign characteristics. Follow-up after the procedure revealed neither hypoglycemic, nor hyperglycemia.

Conclusion

We report the youngest case of a giant insulinoma. Despite the size of the tumor, the pathological report confirmed the benign characteristics. However, long-term follow-up is still essential to detect recurrence in the future.

Preoperative localization of an insulinoma: selective arterial calcium stimulation test performance

PURPOSE

Preoperative localization of an insulinoma is recommended to improve the cure rate, but non-invasive procedures can fail to detect the tumour. The objective of the study was to assess the performance of a selective arterial calcium stimulation test in the preoperative localization of insulinomas that were not detected by conventional imaging procedures.

METHODS

We conducted a monocenter retrospective case review of 13 patients who had endogenous hyperinsulinism and were treated between 1994 and 2013. Patients were selected on the basis of negative or doubtful non-invasive preoperative imaging. A selective arterial calcium stimulation test was performed by pancreatic and hepatic arteriography with selective intra-arterial calcium stimulation and hepatic venous sampling in order to obtain the plasma insulin measurement. We evaluated the efficacy of the test by comparing the results with an endoscopic ultrasound.

RESULTS

Twelve of the 13 patients underwent surgery, and the presence of an insulinoma was proven in 11 patients by pathological analysis of the tumour. An endoscopic ultrasound was consistent with surgery in 71.4 % of cases, while selective arterial calcium stimulation was consistent with surgery in 90.9 % and allowed detection of an insulinoma in two additional patients with a negative endoscopic ultrasound. One false-negative and one false-positive arterial calcium test were observed. No adverse events were recorded except transient skin flush following calcium injection in one patient.

CONCLUSION

The selective arterial calcium stimulation test is a sensitive diagnostic procedure for localizing insulinomas and may be considered when non-invasive radiological imaging does not allow the detection of an occult insulinoma.

Gastroenteropancreatic neuroendocrine tumours (GEP-NET) - Imaging and staging

Detection of gastroenteropancreatic neuroendocrine tumours (GEP-NETs) and monitoring of treatment response relies mainly on morphological imaging such as computed tomography (CT) and magnetic resonance imaging (MRI). Molecular imaging techniques also in combination with CT (hybrid imaging) greatly benefit patient management, including better localization of occult tumours and better staging. Somatostatin receptor scintigraphy (SRS) and somatostatin receptor (SSTR) positron emission tomography (PET) play a central role in the diagnostic work-up of patients with well-differentiated GEP-NETs. SSTR PET/CT is superior to SRS and should be used whenever available. (18)F-DOPA and (18)F-FDG PET/CT is inferior to SSTR PET/CT at least in patients with well-differentiated GEP-NETs. Both SSTR PET/CT and SRS have limitations, such as relatively low detection rate of benign insulinomas, poorly differentiated GEP-NETs and liver metastases. New innovations such as SSTR PET/MRI, radiolabelled SSTR antagonists and glucagon-like peptide-1 receptor (GLP-1R) agonists might further improve imaging of GEP-NETs.

Selective Arterial Calcium Stimulation With Hepatic Venous Sampling Differentiates Insulinoma From Nesidioblastosis

CONTEXT

In adult patients with endogenous hyperinsulinemic hypoglycemia and negative or inconclusive noninvasive imaging, insulinoma and non-insulinoma pancreatogenous hypoglycemic syndrome (NIPHS) resulting from diffuse nesidioblastosis must be considered in the differential diagnosis. It is not known whether the biochemical results of selective arterial calcium stimulation (SACST) with hepatic venous sampling can differentiate insulinoma from diffuse nesidioblastosis.

OBJECTIVE

To determine the specificity of SACST with hepatic venous sampling in differentiating insulinoma from diffuse nesidioblastosis.

DESIGN

Retrospective review (January 1996 to March 2014).

SETTING

Tertiary referral center.

PATIENTS OR OTHER PARTICIPANTS

A total of 116 patients with biochemical evidence of endogenous hyperinsulinemic hypoglycemia and negative or inconclusive noninvasive imaging who were subsequently shown at surgery to have insulinoma (n = 42) or nesidioblastosis (n = 74) after undergoing SACST with hepatic venous sampling.

INTERVENTION(S)

SACST with hepatic venous sampling before pancreatic exploration.

MAIN OUTCOME MEASURE(S)

Receiver operating characteristic curves were generated from the biochemical results of SACST to determine the specificity of the maximum hepatic venous insulin concentration (mHVI) and the relative-fold increase in hepatic venous insulin concentration (rHVI) over baseline after calcium injection from the dominant artery in differentiating insulinoma from nesidioblastosis.

RESULTS

The mHVI (21.5-fold; P < .001) and rHVI (3.9-fold; P < .001) were significantly higher in the insulinoma group compared to the nesidioblastosis group. The areas under the receiver operating characteristic curve for mHVI and rHVI were excellent (0.94; P < .0001) and good (0.83; P < .0001), respectively, for differentiating insulinoma from nesidioblastosis. mHVI cutoffs of > 91.5 and > 263.5 μIU/mL were 95 and 100% specific for insulinoma, respectively. A 19-fold increase in rHVI over baseline was 99% specific for insulinoma.

CONCLUSIONS

These data suggest that the mHVI and rHVI at SACST may be useful in differentiating insulinoma from nesidioblastosis with high specificity in patients with hyperinsulinemic hypoglycemia and negative or inconclusive noninvasive imaging.

Transcriptomic and Immunohistochemical Profiling of SLC6A14 in Pancreatic Ductal Adenocarcinoma

We used a target-centric strategy to identify transporter proteins upregulated in pancreatic ductal adenocarcinoma (PDAC) as potential targets for a functional imaging probe to complement existing anatomical imaging approaches. We performed transcriptomic profiling (microarray and RNASeq) on histologically confirmed primary PDAC tumors and normal pancreas tissue from 33 patients, including five patients whose tumors were not visible on computed tomography. Target expression was confirmed with immunohistochemistry on tissue microarrays from 94 PDAC patients. The best imaging target identified was SLC6A14 (a neutral and basic amino acid transporter). SLC6A14 was overexpressed at the transcriptional level in all patients and expressed at the protein level in 95% of PDAC tumors. Very little is known about the role of SLC6A14 in PDAC and our results demonstrate that this target merits further investigation as a candidate transporter for functional imaging of PDAC.

Role of (18) F-FDOPA PET/CT imaging in endocrinology

(18) F-FDOPA (6-[18F]-L-fluoro-L-3, 4-dihydroxyphenylalanine)-based PET/CT imaging can be a useful tool for the detection of different neuroendocrine tumours (NETs). (18) F-FDOPA is taken up into the cells via the neutral amino acid transporter (LAT1/4F2hc). This transporter is also coupled to the mammalian target of rapamycin (mTOR) signalling pathway. (18) F-FDOPA PET/CT may be performed for confirmation of diagnosis of pheochromocytoma/paraganglioma, staging at initial presentation, restaging and follow-up of patients. In SDHx-related syndromes, (18) F-FDG PET/CT should be performed in addition to (18) F-FDOPA PET/CT. (18) F-FDOPA PET/CT is also invaluable in the detection staging/restaging of carcinoid tumours and has greater sensitivity as compared to somatostatin receptor scintigraphy. (18) F-FDOPA PET/CT can also distinguish between focal vs diffuse CHI. It is not as useful in adult hyperinsulinism due to increased background uptake, but the problem may be overcome with the help of premedication with carbidopa. It has limited use in pancreatic NETs. (18) F-FDOPA PET/CT is a good modality for detection of persistent and residual medullary thyroid cancer (MTC), but (18) F-FDG PET/CT may be needed in aggressive tumours. In summary, F-DOPA PET/CT has widespread utility in the diagnosis of different neuroendocrine tumours.

18F-FDOPA PET/CT imaging of insulinoma revisited

PURPOSE

(18)F-FDOPA PET imaging is increasingly used in the work-up of patients with neuroendocrine tumours. It has been shown to be of limited value in localizing pancreatic insulin-secreting tumours in adults with hyperinsulinaemic hypoglycaemia (HH) mainly due to (18)F-FDOPA uptake by the whole pancreatic gland. The objective of this study was to review our experience with (18)F-FDOPA PET/CT imaging with carbidopa (CD) premedication in patients with HH in comparison with PET/CT studies performed without CD premedication in an independent population.

METHODS

A retrospective study including 16 HH patients who were investigated between January 2011 and December 2013 using (18)F-FDOPA PET/CT (17 examinations) in two academic endocrine tumour centres was conducted. All PET/CT examinations were performed under CD premedication (200 mg orally, 1 - 2 h prior to tracer injection). The PET/CT acquisition protocol included an early acquisition (5 min after (18)F-FDOPA injection) centred over the upper abdomen and a delayed whole-body acquisition starting 20 - 30 min later. An independent series of eight consecutive patients with HH and investigated before 2011 were considered for comparison. All patients had a reference whole-body PET/CT scan performed about 1 h after (18)F-FDOPA injection. In all cases, PET/CT was performed without CD premedication.

RESULTS

In the study group, (18)F-FDOPA PET/CT with CD premedication was positive in 8 out of 11 patients with histologically proven insulinoma (73 %). All (18)F-FDOPA PET/CT-avid insulinomas were detected on early images and 5 of 11 (45 %) on delayed ones. The tumour/normal pancreas uptake ratio was not significantly different between early and delayed acquisitions. Considering all patients with HH, including those without imaging evidence of disease, the detection rate of the primary lesions using CD-assisted (18)F-FDOPA PET/CT was 53 %, showing 9 insulinomas in 17 studies performed. In the control group (without CD premedication, eight patients), the final diagnosis was benign insulinoma in four, nesidioblastosis in one, and no definitive diagnosis in the remainder. (18)F-FDOPA PET/CT failed to detect any tumour in these patients.

CONCLUSION

According to our experience, CD administration before (18)F-FDOPA injection leads to low residual pancreatic (18)F-FDOPA activity preserving tumoral uptake with consequent insulinoma detection in more than half of adult patients with HH and more than 70 % of patients with a final diagnosis of insulinoma. If (18)F-FDOPA PET/CT is indicated, we strongly recommend combining CD premedication with early acquisition centred over the pancreas.

Strengths and limitations of using 18fluorine-fluorodihydroxyphenylalanine PET/CT for congenital hyperinsulinism

¹⁸fluorine-fluorodihydroxyphenylalanine (FDOPA) PET/CT is currently the first-line imaging technique to distinguish between focal and diffuse forms of congenital hyperinsulinism (CHI) and to accurately localize focal forms. However, this technique has a number of limitations, mainly the very small size of focal forms or inversely a very large focal form mimicking a diffuse form, and misinterpretation of physiologic uptake masking hot spots or inversely mimicking focal forms. The other limitation is the limited availability of the radiopharmaceutical. FDOPA PET/CT has no recognized competitor to date among the available morphologic and functional imaging techniques. Other potential approaches using specific tracers for positron emission tomography (PET) are discussed, using radiopharmaceuticals specific for β cell mass or targeting somatostatin receptors. These radiopharmaceuticals can be labeled with gallium-68, a PET emitter readily available in PET centers equipped with 68Ge/68Ga generators.

Normal biodistribution pattern and physiologic variants of 18F-DOPA PET imaging

Dihydroxyphenylalanine (DOPA) is a neutral amino acid that resembles natural l-dopa (dopamine precursor). It enters the catecholamine metabolic pathway of endogenous l-DOPA in the brain and peripheral tissues. It is amenable to labeling with fluorine-18 (¹⁸F) for PET imaging and was originally used in patients with Parkinson’s disease to assess the integrity of the striatal dopaminergic system. The recent introduction and use of hybrid PET/CT scanners has contributed significantly to the management of a series of other pathologies including neuroendocrine tumors, brain tumors, and pancreatic cell hyperplasia. These pathologic entities present an increased activity of l-DOPA decarboxylase and therefore demonstrate high uptake of ¹⁸F-DOPA. Despite these potentially promising applications in several clinical fields, the role of ¹⁸F-DOPA has not been elucidated completely yet because of associated difficulties in synthesis and availability. Unfortunately, the available literature does not provide recommendations for procedures or administered activity, acquisition timing, and premedication with carbidopa. The aim of this paper is to outline the physiological biodistribution and normal variants, including possible pitfalls that may lead to misinterpretations of the scans in various clinical settings.

Insulinoma: only in adults?-case reports and literature review

Insulinomas first presenting as refractory seizure disorders are well documented in adulthood but rarely found in children. Only a few cases of childhood insulinoma have been reported so far. We report on two adolescents with hyperinsulinaemic hypoglycaemia, initially misdiagnosed as epilepsy and migraine accompagnée, and compare those to other cases published. Localization of insulinoma was challenging and, in one patient, angiography with selective arterial calcium stimulation and hepatic venous sampling in addition to CT and MRI was necessary. In these patients, long-term recovery was achieved by laparoscopic distal pancreatic resection in one and by conventional enucleation in the pancreatic head in the second patient. In contrast to adults, macrosomy and a decrease in school performance were the main symptoms and, during fasting, impaired cognitive function occurred after a relatively short period and at a higher glucose threshold or lower insulin/glucose ratio, respectively. Neuroglycopenic signs may be attributed to behaviour abnormalities or seizure disorders but in children and adolescents may already be caused by insulinoma. In these cases, timely diagnosis as well as tumour resection ensure long-term cure.

Insulinoma in childhood: clinical, radiological, molecular and histological aspects of nine patients

BACKGROUND

Insulinomas are a rare cause of hyperinsulinaemic hypoglycaemia (HH) in children. The clinical features, investigations, management and histology of these rare pancreatic tumours in children have not been described in a large cohort of patients.

METHODS

We conducted a retrospective review of cases diagnosed between 2000 and 2012, presenting to two referral centres in the United Kingdom. Clinical, biochemical, imaging (magnetic resonance imaging (MRI) and 6-L-¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-DOPA) PET/CT scanning) and histological data were collected.

RESULTS

Nine children (age range 2-14.5 years) were diagnosed during the study period at Great Ormond Street Hospital (n=5) and Royal Manchester Children's Hospital (n=4). The combination of abdominal MRI scan (7/8) and ¹⁸F-DOPA PET/CT scan (2/4) correctly localised the anatomical location of all insulinomas. Before surgery, diazoxide therapy was used to treat hypoglycaemia, but only four patients responded. After surgical resection of the insulinoma, hypoglycaemia resolved in all patients. The anatomical localisation of the insulinoma in each patient was head (n=4), uncinate process (n=4) and tail (n=2, one second lesion) of the pancreas. Histology confirmed the diagnosis of insulinoma with the presence of sheets and trabeculae of epithelioid and spindle cells staining strongly for insulin and proinsulin, but not for glucagon or somatostatin. Two children were positive for MEN1, one of whom had two separate insulinoma lesions within the pancreas.

CONCLUSIONS

We describe a cohort of paediatric insulinoma patients. Although rare, insulinomas should be included in the differential diagnosis of HH, even in very young children. In the absence of a single imaging modality in the preoperative period, localisation of the tumour is achieved by combining imaging techniques, both conventional and functional.

¹⁸F-DOPA PET/computed tomography imaging

18F-DOPA is a radiopharmaceutical with interesting clinical applications and promising performances in the evaluation of the integrity of dopaminergic pathways, brain tumors, NETs (especially MTCs, paragangliomas, and pheochromocytomas), and congenital hyperinsulinism. 18F-DOPA traces a very specific metabolic pathway and has a very precise biodistribution pattern. As for any radiopharmaceutical, the knowledge of the normal distribution of 18F-DOPA, its physiologic variants, and its possible pitfalls is essential for the correct interpretation of PET scans. Moreover, it is important to be aware of the potential false-positive and false-negative episodes that can occur in the various clinical settings.

Childhood insulinoma masquerading as seizure disorder

A 9 year old girl presented with seizures, weight gain and early morning behavioural changes. She had been commenced on anticonvulsants and was subsequently diagnosed with hyperinsulinaemic hypoglycaemia. This case demonstrates the importance of blood glucose monitoring in children presenting with new-onset seizures and/or with early morning or fasting behavioural changes, the challenges in localizing the lesion, as well as the difficulties in achieving normoglycaemia prior to, and immediately following, surgery.

18F-fluorodihydroxyphenylalanine PET/CT in patients with neuroendocrine tumors of unknown origin: relation to tumor origin and differentiation

This work was performed to evaluate the performance of (18)F-fluorodihydroxyphenylalanine ((18)F-FDOPA) PET/CT in detecting primary neuroendocrine tumors (NETs) occult on morphologic and functional imaging, in relation to tumor origin and differentiation.

METHODS

A retrospective study of NET patients who were investigated with (18)F-FDOPA PET/CT imaging in 2 academic endocrine tumor centers was conducted. Only patients with negative conventional and somatostatin receptor scintigraphy (SRS) results were studied.

RESULTS

Twenty-seven patients were evaluated with (18)F-FDOPA PET/CT, 23 at their initial staging and 4 during their follow-up. The primary occult NET was localized by (18)F-FDOPA PET/CT in 12 patients (overall sensitivity, 44%; 52% in patients evaluated at initial diagnosis), leading to tumor resection in all cases. The primary tumors were distributed and graded as follows: 1 duodenum G2 lesion, 7 ileum G2 lesions, 2 terminal ileum G1 lesions, 1 pancreas G2 lesion, and 1 gallbladder G3 lesion. Patients with positive (18)F-FDOPA PET/CT results had higher values of serum chromogranin A (100% vs. 20%, P = 0.0003), serotonin, or urinary 5-hydroxyindolacetic acid (83% vs. 20%, P = 0.003). Two false-negative results were related to poorly differentiated duodenal and prostatic NETs (G3). (18)F-FDOPA PET/CT showed more metastatic anatomic regions than SRS in 17 patients.

CONCLUSION

(18)F-FDOPA PET appears to be a sensitive functional imaging tool for the detection of primary NETs occult on SRS, especially tumors with a well-differentiated pattern and serotonin secretion.

Role of PET/CT in the functional imaging of endocrine pancreatic tumors

Endocrine pancreatic tumors (EPTs) are a heterogeneous group of neoplasms with variable clinical and biological features and prognosis, ranging from very slow-growing tumors to highly aggressive and very malignant ones. As other neuroendocrine tumors, EPTs are characterized by the presence of neuroamine uptake mechanisms and/or peptide receptors at the cell membrane and these features constitute the basis of the clinical use of specific radiolabeled ligands, both for imaging and therapy. The more widespread use of hybrid machines, i.e., positron emission tomography/computed tomography (PET/CT), allows to perform imaging with high resolution and high diagnostic accuracy especially for small lesions, and to correlate anatomic location with function. The recent WHO recommendations for classification and prognostic factors help the selection of tracers likely to show a positive image on PET; therefore, tracers exploiting specific metabolic patterns ((18)F-DOPA and (11)C-5-HTP) or specific receptor expression ((68)Ga-DOTA-peptides) are suited to well-differentiated tumors, while the use of (18)F-FDG is preferred for poorly-differentiated neoplasms with high proliferative activity and loss of neuroendocrine features. In differentiated EPTs, (11)C-5-HTP performs better than (18)F-DOPA even though its use is hampered by its complex production and limited availability and experience; (68)Ga-peptides are indicated for all type of gastroenteropancreatic (GEP) neuroendocrine tumors, regardless of their functional activity. In addition, (68)Ga-DOTA-peptides play a distinctive role in planning peptide receptor radionuclide therapy.

18F-fluorodihydroxyphenylalanine vs other radiopharmaceuticals for imaging neuroendocrine tumours according to their type

6-Fluoro-(¹⁸F)-L-3,4-dihydroxyphenylalanine (FDOPA) is an amino acid analogue for positron emission tomography (PET) imaging which has been registered since 2006 in several European Union (EU) countries and by several pharmaceutical firms. Neuroendocrine tumour (NET) imaging is part of its registered indications. NET functional imaging is a very competitive niche, competitors of FDOPA being two well-established radiopharmaceuticals for scintigraphy, ¹²³I-metaiodobenzylguanidine (MIBG) and ¹¹¹In-pentetreotide, and even more radiopharmaceuticals for PET, including fluorodeoxyglucose (FDG) and somatostatin analogues. Nevertheless, there is no universal single photon emission computed tomography (SPECT) or PET tracer for NET imaging, at least for the moment. FDOPA, as the other PET tracers, is superior in diagnostic performance in a limited number of precise NET types which are currently medullary thyroid cancer, catecholamine-producing tumours with a low aggressiveness and well-differentiated carcinoid tumours of the midgut, and in cases of congenital hyperinsulinism. This article reports on diagnostic performance and impact on management of FDOPA according to the NET type, emphasising the results of comparative studies with other radiopharmaceuticals. By pooling the results of the published studies with a defined standard of truth, patient-based sensitivity to detect recurrent medullary thyroid cancer was 70 % [95 % confidence interval (CI) 62.1–77.6] for FDOPA vs 44 % (95 % CI 35–53.4) for FDG; patient-based sensitivity to detect phaeochromocytoma/paraganglioma was 94 % (95 % CI 91.4–97.1) for FDOPA vs 69 % (95 % CI 60.2–77.1) for ¹²³I-MIBG; and patient-based sensitivity to detect midgut NET was 89 % (95 % CI 80.3–95.3) for FDOPA vs 80 % (95 % CI 69.2–88.4) for somatostatin receptor scintigraphy with a larger gap in lesion-based sensitivity (97 vs 49 %). Previously unpublished FDOPA results from our team are reported in some rare NET, such as small cell prostate cancer, or in emerging indications, such as metastatic NET of unknown primary (CUP-NET) or adrenocorticotropic hormone (ACTH) ectopic production. An evidence-based strategy in NET functional imaging is as yet affected by a low number of comparative studies. Then the suggested diagnostic trees, being a consequence of the analysis of present data, could be modified, for some indications, by a wider experience mainly involving face-to-face studies comparing FDOPA and ⁶⁸Ga-labelled peptides.

Malignant insulinoma misdiagnosed and treated as epilepsy

Pancreatic neuroendocrine tumors (PNET) are extremely rare, and although insulinomas are the commonest, less than 10% of insulinomas are malignant. Most patients with insulinomas present neuroglycopenic symptoms. Because of the rarity of the condition, we report the case of a 56-year-old man with malignant insulinoma, which was misdiagnosed as epilepsy. Timely diagnosis of this disease is of paramount importance to prevent neurologic sequelae of hypoglycemia. Insulinomas should be regarded from the beginning as potentially malignant, although the majority of malignant insulinomas progresses slowly.

Hepatocellular carcinoma and gastroenteropancreatic neuroendocrine tumors: potential role of other positron emission tomography radiotracers

18F-Fluorodeoxyglucose avidity for gastroenteropancreatic neuroendocrine tumors and hepatocellular carcinoma is variable, depending on the underlying tumor biology. Experience with non-fluorodeoxyglucose (FDG) tracers (eg, 18F-labeled amine precursors l-dihydroxyphenylalanine and 68Ga-DOTA-peptides for gastroenteropancreatic neuroendocrine tumors and radiolabeled acetate or choline for hepatocellular carcinoma) is evolving and expanding rapidly. This article reviews the role of FDG and non-FDG radiotracers in the imaging evaluation of patients with gastroenteropancreatic neuroendocrine tumors or hepatocellular carcinoma.

Hyperinsulinism presenting in childhood and treatment by conservative pancreatectomy

OBJECTIVE

To describe the uncommon presentation of hyperinsulinism in an 8-year-old boy.

METHODS

We describe the patient's clinical findings, results from biochemical and imaging studies, surgical approach, and outcome. The discussion encompasses a review of literature that provided the basis for the diagnostic and surgical approach applied to this patient's case.

RESULTS

An obese 8.5-year-old boy initially presented with hypoglycemic seizures after initiation of dietary changes to treat obesity. Biochemical analysis indicated hyperinsulinism. Endoscopic ultrasonography showed no pancreatic lesions suggestive of insulinoma. Genetic studies identified no known mutations in the ABCC8, KCNJ11, GCK, or GLUD1 genes. Selective arterial calcium stimulation and hepatic venous sampling did not document a focal source for hyperinsulinism in the pancreas, and positron emission tomography with 18-fluoro-L-3,4-dihydroxyphenylalanine showed diffusely increased uptake in the pancreas. The patient ultimately required partial pancreatectomy because of continued hypoglycemia while taking diazoxide and octreotide. Intraoperative glucose monitoring directed the extent of surgical resection. A 45% pancreatectomy was performed, which resolved the hypoglycemia but led to impaired glucose tolerance after surgery.

CONCLUSION

The unusual presentation of hyperinsulinism in childhood required a personalized approach to diagnosis and surgical management using intraoperative glucose monitoring that resulted in a conservative pancreatectomy.