68Ga-DOTANOC Focal Pulmonary Activity With No Corresponding CT Abnormality

Hot Embolus Artifact Mimicking Disease Progression in Post-therapy 177Lu-DOTATATE Scan: Incremental Value of SPECT/CT

Peptide receptor radionuclide therapy (PRRT) has become an established treatment for patients with inoperable and/or metastatic, well-differentiated neuroendocrine tumors with overexpression of somatostatin receptor type 2 (SSTR-2). The post-therapy 177Lu-DOTATATE whole-body scan not only assesses the biodistribution of the lesions seen on pre-therapy 68 Ga-SSTR PET/CT scan but also provides a quick assessment of disease status and dosimetry during treatment. Like any other radionuclide scan, the whole-body 177Lu-DOTATATE scan may also show abnormal radiotracer uptake, which may require further imaging to establish its exact etiology. Though radiotracer emboli mimicking focal pulmonary lesions have been described with 18F-FDG and 68 Ga-DOTANOC PET/CT scans, similar artifacts with post-therapy 177Lu-DOTATATE scans have not been described. Herein, we report two cases of hot emboli in the post-therapy 177Lu-DOTATATE scans.

68Ga-DOTATOC Embolus Manifestation and Spontaneous Resolution by PET/CT

⁶⁸Ga-labeled somatostatin receptor analogs physiologic distribution patterns have become recognizable among nuclear medicine physicians because of the increasing routine clinical use of this modality in the work-up of neuroendocrine tumors. Some pitfalls during ⁶⁸Ga-labeled somatostatin receptor PET/CT have recently been reported as causes of misdiagnoses. Iatrogenic microembolism as a cause of ¹⁸F-FDG embolus is well-established; however, 68Ga-DOTATOC embolus is not well documented in the literature. In the current case, the presence and the spontaneous resolution of the ⁶⁸Ga-labeled somatostatin receptor analogs embolus during sequential PET/CT are nicely demonstrated. Awareness of this incidental finding would avoid misdiagnosis and unnecessary investigations.

Unusual Focal Lung Uptake without CT Abnormality on a Bone Scan: What Might It Mean?

A 48-year-old woman was referred for a bone scan as an assessment of bone metastasis from breast cancer. Surprisingly, two hot spots of lung uptake were present in the left lung without any abnormality on CT slices. No history of pulmonary disease was observed. An optimized CT scan with fine slices performed the same day was strictly normal (without any micronodule). A lung ventilation/perfusion scintigraphy showed no significant perfusion defect. A follow-up bone scan performed eight months later was normal and without any lung uptake. After exclusion of the main etiologies described in the literature, such as amylosis, sarcoidosis, abscess, or hypercalcemia, radiotracer microembolism seems to be the most likely hypothesis in this patient.

68Ga-Prostate-Specific Membrane Antigen Focal Pulmonary Activity With No Corresponding CT Abnormality

ABSTRACT

We describe a case of 68Ga-prostate-specific membrane antigen PET/CT scan with focal tracer concentration in the lung without any abnormalities in the CT part. 18F-FDG focal uptake in lungs without corresponding CT lesions is described. Two possible mechanisms proposed to explain this finding in FDG PET/CT scans are iatrogenic pulmonary microembolism and 18F-FDG-avid infection or inflammation that precedes structural findings. Logically, these proposed mechanisms seem to be applicable to 68Ga-prostate-specific membrane antigen as well. In our case, there were no features of any lung infection/inflammation, and the most plausible explanation would be iatrogenic microembolism.

Iatrogenic Lung Microembolism Resulted in Extraosseous Uptake of 99mTc-MDP

A 61-year-old woman diagnosed with left breast cancer underwent a bone scan for the evaluation of possible bone metastases. Multiple foci of elevated activity were noticed in the spine and pelvis. In addition, a focus of intense activity was observed in the right lung on the SPECT/CT images without corresponding anatomic abnormality.