Introduction

Gastric cancer could metastasize to different sites prior to diagnosis. The rate of bone metastasis has been reported as 1% to 20% for gastric cancer (1,2,3). Detection of gastric cancer bone metastasis is crucial since its presence is an independent prognostic factor (4). In this report, we would like to present a case with gastric cancer bone metastases that could not be shown by ¹⁸F-FDG positron emission tomography/computed tomography (PET/CT).

Case Report

A 58 years old female patient with histopahologically proven gastric mucinous adenocarcinoma was referred to Ankara University Medical Faculty Department of Nuclear Medicine with a request of ¹⁸F-FDG PET/CT for staging. The whole body ¹⁸F-FDG PET/CT imaging was performed approximately 1 hour after intravenous injection of 370 MBq ¹⁸F-FDG. PET/CT images were acquired with GE Discovery ST PET/CT scanner (General Electric, Milwaukee, Wisconsin, USA). Emission PET images were reconstructed with non-contrast CT data for attenuation correction. In the evaluation of ¹⁸F-FDG PET/CT images, there was no pathological uptake in the stomach and whole body except diffuse increase in gastric wall thickness (Figure 1). Multiple sclerotic bone lesions were detected in axial CT images (Figure 2). An ¹⁸F-NaF PET/CT was performed to exclude bone metastases. ¹⁸F-NaF PET/CT images were obtained by the same scanner and parameters with CT, approximately 30 minutes after intravenous injection of 135 MBq ¹⁸F-NaF from vertex to feet. Intense ¹⁸F-NaF uptake was seen in multiple sclerotic bone lesions in the vertebral column, sternum, ribs, scalp and both scapula (Figure 3).

Literature Review and Discussion

¹⁸F-FDG PET/CT is a hybrid imaging modality used in the staging of several cancers. However, the role of ¹⁸F-FDG PET/CT in the detection of bone metastases of gastric cancer is controversial (4,5,6,7,8,9,10). No algorithm has yet been defined to detect bone metastases of gastric cancer.

In our case, bone metastases of gastric cancer could not be shown by ¹⁸F-FDG PET/CT. In our case, we suspected bone metastases of gastric cancer in spite of lack of ¹⁸F-FDG uptake, because absence of uptake in the primary tumor was probably related to the mucinous component and sclerotic pattern of bone lesions. For these reasons an ¹⁸F-NaF PET/CT was performed to evaluate bone lesions, and ¹⁸F-NaF PET/CT confirmed bone metastases.

Conventional staging modalities such as bone scintigraphy are more valuable especially in patients with non ¹⁸F-FDG avid tumors. Various imaging methods including ¹⁸F-FDG PET/CT, whole body bone scintigraphy, magnetic resonance imaging and CT could be utilized to detect bone metastases. Tc-99m MDP bone scintigraphy is the traditional method to evaluate bone metastases of several cancers with low cost (5). The poor spatial resolution and longer duration of the examination result in limitations to bone scintigraphy. High quality images of the skeleton can be obtained within one hour after intravenous injection of 18F-NaF (6). In a recent study, Iagaru et al. (7) have reported that ¹⁸F-NaF PET/CT is superior to ¹⁸F-FDG PET/CT in the detection of bone metastases. An advantage of combined PET/CT systems is that they provide skeletal system evaluation with highly sensitive and specific images (8). During evaluation of ¹⁸F-FDG PET/CT images, skeletal lesions could be seen in CT series and these lesions could be evaluated by other methods to show bone metastases. In patients with non ¹⁸F-FDG avid tumors that could often metastasize to bone, CT series should be carefully evaluated to search bone lesions.

Informed Consent: It was taken, Concept: Çiğdem Soydal, Design: Çiğdem Soydal, Data Collection or Processing: Elgin Özkan, Analysis or Interpretation: Çiğdem Soydal, Özlem Nuriye Küçük, Literature Search: Çiğdem Soydal, Metin Kemal Kır, Writing: Çiğdem Soydal, Peer-review: Externally peer-reviewed, Conflict of Interest: No conflict of interest was declared by the authors, Financial Disclosure: The authors declared that this study has received no financial support.