CONCLUSION
We present here three unique clinical cases, each of which highlights both advantages and limitations to the use of68Ga-DOTATATE PET, 18F-FDG PET, and123I-MIBG SPECT/CT in the evaluation of patients with PPGL. In these patients, who frequently have complex clinical manifestations of their disease, no single imaging technique can be forwarded as the single “best test”. Rather, as the cases shown here emphasize, different clinical considerations necessitate a customized choice of functional imaging techniques. The proposed algorithm may serve as a guideline for physicians when determining which of the available imaging selections is best suited to an individual patient’s care.
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FIGURE LEGENDS
Figure 1 : Metastatic paraganglioma. Fused axial PET and CT images from 18F-FDG PET/CT at diagnosis (A) demonstrate a large heterogeneous retroperitoneal mass (circle) with central photopenia and hypoattenuation suggestive of necrosis (*). Multiple lung nodules were seen by CT (B, white arrow), the largest of which were FDG avid (C, black arrow), consistent with metastatic disease. Coronal MIP image shows no FDG avid disease elsewhere (D). Coronal MIP image from 68Ga-DOTATATE PET/CT (E) shows widespread skeletal metastatic disease (red arrows), none of which was present on the 18F-FDG PET/CT (D). Coronal static planar image from 123I-MIBG scan (F) revealed MIBG-avid metastatic disease in the calvarium, axial, and appendicular skeleton, although the image quality is inferior to the DOTATATE PET/CT and the overall disease burden is underestimated by123I-MIBG. Although some lesions not seen by planar imaging were discernable by SPECT/CT, many lesions seen by68Ga-DOTATATE PET, for example in the liver, ribs, humeral shafts, femoral shafts, and tibiae (arrows) were not evident by123I-MIBG scintigraphy.
Figure 2: Cancer predisposition with SDHC germline mutation and co-existing GIST and paraganglioma.18F-FDG PET MIP images (A) demonstrates diffuse metastatic disease from the patient’s known gastrointestinal stromal tumor. Axial contrast-enhanced CT and 18F-FDG PET images (B, C) highlight numerous hepatic masses with varying degrees of18F-FDG avidity (red arrows), complicating the detection of new lesions with a different histology. Axial non-contrast CT and 68Ga-DOTATATE PET images (E, F) reveal an intensely avid mass in the porta hepatis (circle), consistent with paraganglioma. The adjacent lesions that had been FDG-avid on the earlier 18F-FDG PET/CT (white arrow) showed no DOTATATE uptake, indicating co-existing GIST and paraganglioma in the same patient. The paraganglioma was resected surgically; the patient continues on medical therapy for his metastatic GIST.
The low attenuation region near the periphery that has neither FDG nor DOTATATE uptake (*) represents a site of prior RF ablation.
Figure 3: Cancer predisposition associated with polycythemia and multiple functional paragangliomas (Pacak-Zhuang syndrome).18F-FDG PET/CT was obtained for restaging after surveillance wbMRI revealed new sites of disease. Coronal18F-FDG PET MIP image (A) and axial fused PET/CT images (D) from 18F-FDG PET/CT, demonstrate increased18F-FDG uptake in the left suprarenal mass (B, arrow) seen by MRI. Multiple additional foci of FDG uptake, for example in an aortocaval lesion (A, D: circle), were also concerning for paraganglioma, and even in retrospect were difficult to convincingly see by MRI (C).
18F-FDG PET/CT obtained six months later when serum catecholamine and chromogranin A levels were continuing to rise, was markedly limited for evaluation of metastatic lesions, secondary to intensely FDG-avid hypermetabolic brown adipose tissue uptake, best illustrated on the coronal MIP image (E) from the FDG PET/CT.
Given the patient’s hyper-catecholamine secreting state resulting from her underlying HIF2A activating mutation, she was started on molecularly targeted therapy. 68Ga-DOTATATE PET/CT, obtained just 17 days after drug initiation (F), showed no background brown fat uptake and demonstrated the suprarenal lesion (arrow) and aorto-caval lesion (circle), with the suprarenal lesion having already decreased slightly in size in response to targeted therapy. She continues on treatment and has been monitored by surveillance MRI and68Ga-DOTATATE PET/CT.
Figure 4: Proposed algorithm for68Ga-DOTATATE imaging children with known PPGL or PPGL predisposition syndrome.