History
A 63-year-old female patient (BMI 19.57 kg/m²), with a history of hypothyroidism, fatigue, weakness, loss of appetite and hypoglycemia, was referred to the Department of Radiology for evaluation. A calcium stimulation challenge test showed diffuse insulin secretion throughout the pancreas. A pancreatic insulinoma was suspected. However, a previous CT examination performed with an Energy Integrating Detector CT (EID-CT) did not reveal any pancreatic lesion. A contrast CT scan with a dual source photon-counting detector CT (PCD-CT), NAEOTOM Alpha®, was performed for further evaluation.
Diagnosis
Virtual monoenergetic images (VMIs), displayed at 50 KeV, revealed a hypervascular nodular lesion in the pancreatic body in the arterial phase, measuring 1 cm in size. The lesion was also seen in the iodine maps and the VNC/iodine fused images. In the virtual non-contrast (VNC) images, it appeared isodense, and in the standard image reconstructions, it was inevident. Subsequently, the lesion was confirmed by a Dotatate PET/CT scan as well as an Endoscopy Ultrasound (EUS) examination. The patient underwent a distal pancreatectomy with splenectomy. The pathology result confirmed the diagnosis of a G1 well-differentiated neuroendocrine tumor with insulin hyperproduction.
Fig. 1: An axial VMI, acquired in the arterial phase and displayed at 50 keV, show a small hypervascular nodular lesion in the pancreatic body (Fig. 1c, arrow). The lesion is neither shown in a previous EID-CT image (Fig. 1a) nor evident in a standard image reconstruction (Fig. 1b).
Fig. 2: An iodine map (Fig. 2b) and a VNC/ iodine fused image (Fig. 2c) show a contrast enhanced lesion (arrows) in the pancreatic body. The lesion appears isodense in the VNC image (Fig. 2a).
Fig. 3: A Dotatate PET/CT image shows a small lesion spotted in the pancreatic body (Fig. 3a, arrow). The lesion is clearly seen in a cinematic VRT image created with UHR images as well (Fig. 3b, arrow).
Comments
Insulinoma is a type of functional pancreatic neuroendocrine tumor (pNET) originating from the endocrine cells of the pancreas. It is often confined to the pancreatic gland and characterized by hypersecretion of insulin causing hypoglycemia. Surgery is the only potentially curative therapeutic strategy in localized disease, and generally, small pancreatic insulinomas have a very good prognosis. [1] The challenge, though, lies in the identification of the primary tumor due to its small size.
PCD-CT provides energy-resolved CT data with increased spatial resolution and inherent spectral information. [2] Tissue contrast is optimized by a combination of missing down-weighting of the lower energy X-ray photons and absence of electronic noise. In this case, an ultra-high resolution (UHR) mode was performed, using a fine collimation of 120 x 0.2 mm, in the arterial phase. This mode uses smaller sub-pixels, defined by a strong electric field without further mechanical separation, which are read out separately to increase the spatial resolution. VMIs are then reconstructed at 0.4 mm and displayed at 50 keV to enhance the contrast. The small insulinoma, initially missed by EID-CT, is clearly visualized owing to the combination of increased spatial resolution and tissue contrast. This facilitates an appropriate surgical planning and thereby an optimal patient outcome.
Examination Protocol
