The use of an 18F-dihydroxyphenylalanine (DOPA) positron emission tomography (PET)/computed tomography (CT) scan led to the diagnosis of mediastinal adenopathies and the detection of a low-grade neuroendocrine tumor in the appendix in a patient with medullary thyroid carcinoma (MTC) who had undergone radical surgical resection, according to a recently published case report in the Spanish Journal of Nuclear Medicine and Molecular Imaging.
Radiological findings are of vital importance in the decision-making process of malignant diseases such as MTC. Several studies have shown that 18D-DOPA PET/CT is a sensitive tool for the detection of local, regional, and distant metastases in MTC.
Read more about MTC diagnosis
The levodopa analog 18F DOPA crosses the cellular membrane, binding to specific amino acid receptors on the cell surface. After undergoing enzymatic transformation, which is increased in neuroendocrine tumors, the resulting L-amino acid-aromatic decarboxylase (AADC) is stored in cellular vesicles, which are later detected through PET and CT imaging.
The case involved a 23-year-old female who underwent total thyroidectomy and emptying of the bilateral laterocervical and esophagotracheal lymph nodes due to an MTC diagnosis in the context of multiple endocrine neoplasia type 2B (MEN2B). Despite surgical intervention, the patient had rising calcitonin levels without any abnormalities detected on conventional imaging studies.
The attending physicians conducted an 18F-DOPA PET/CT scan, which revealed the presence of mediastinal adenopathies as well as a hypermetabolic focus in the right pelvis. The findings led to endoscopic intervention followed by surgical resection of a tumor located at the base of the appendix.
A subsequent biopsy revealed chromogranin-positive tumoral cells with a Ki67 index below 3%, suggestive of a low-grade neuroendocrine tumor compatible with MEN2B.
“PET/CT with 18F-DOPA is considered first-line in the diagnosis of midgut G1-[neuroendocrine tumor grade 2] being a specific radiotracer for this type of tumor, which has made it possible to detect the appendicular lesion,” the authors wrote.
Amaya J, Repetto A, Rubí S, Fuster J, Martínez M, García-Granero A. 18F-DOPA PET/CT: diagnosis of a synchronous appendiceal neuroendocrine tumor in a patient with medullary thyroid cancer. Rev Esp Med Nucl Imagen Mol (Engl Ed). Published online March 25, 2023. doi:10.1016/j.remnie.2023.03.003