Sharjeel Usmani  ( Department of Nuclear Medicine, Kuwait Cancer Control Center (KCCC), Khaitan, Kuwait. )
Najeeb Ahmed  ( Department of Nuclear Medicine, Jack Brignall PET/CT Centre, Castle Hill Hosptial, Cottingham, United Kingdom. )
Samreen Muzaffar  ( Department of Nuclear Medicine, Jack Brignall PET/CT Centre, Castle Hill Hosptial, Cottingham, United Kingdom. )
Fareeda al Kandari  ( Department of Nuclear Medicine, Kuwait Cancer Control Center (KCCC), Khaitan Kuwait. )

18F- Sodium Fluoride (NaF) is an excellent bone imaging agent used for skeletal staging but can also be localized in extra osseous calcifying lesions. We report a case of a 38-year-old woman with breast carcinoma referred for 18F-NaF PET-CT to evaluate possible metastatic lesions. 18F-NaF PET-CT detected incidental focal soft tissue tracer uptake in the right cerebellum with no sign of calcification seen on CT images. Subsequent MRI show high intensity signal lesion confirming brain metastasis. Extra osseous 18F-NaF uptake may provide important diagnostic information that might alter patient management.

Keywords: 18F-NaF PET-CT, Breast cancer, PET/MRI, Extra osseous uptake, Metastasis.

A 38-year-old woman was recently diagnosed with breast carcinoma. 18F-NaF PET-CT was performed after injecting 4.1mCi of 18F-NaF for skeletal staging. a) 18F-NaF Maximum intensity Projection image b) cross-sectional 18F-NaF PET-CT images show incidental soft tissue 18F-NaF uptake in the right cerebellum (black arrow) with no sign of calcification seen on CT images. d,e) MRI confirms the cerebellar metastasis with high intensity signal lesion with corresponding increased tracer uptake (white arrow) on separately acquired; fused PET/MRI image (f).

18F-NaF is a promising bone-imaging agent attributable to high bone uptake, rapid single-pass extraction, minimal binding to serum proteins, and fast renal clearance.¹ 18F-NaF PET-CT is more sensitive for detecting skeletal metastases in adults as compared to conventional bone scintigraphy.² 18F-NaF can also localize in extra osseous lesions due to accumulation of 18F-NaF in tumour calcification or calcifications within necrosis.³ The mechanism of 18F-NaF uptake in calcified metastatic lesions is its direct incorporation into the hydroxyapatite crystal.⁴ However, it is not clear how 18F-NaF is taken up in non-calcified metastasis. Sheth et al.⁵ reported 18F-NaF  uptake in metastatic lymph nodes, which might be related to the presence of microscopic calcifications. We report a case of incidentally detected extra osseous 18F-NaF uptake in non-calcified brain metastasis. Extra osseous 18F-NaF uptake is often encountered. Acknowledgment of extra osseous 18F-NaF uptake might be significant for correct interpretation and diagnosis.

Conflict of Interest: There are no potential conflicts of interest to disclose.

References

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2.      Löfgren J,  Mortensen J, Rasmussen SH, Madsen C, Loft A, Hansen AE, et al. A Prospective Study Comparing 99mTc-Hydroxyethylene-Diphosphonate Planar Bone Scintigraphy and Whole-Body SPECT/CT with 18F-Fluoride PET/CT and 18F-Fluoride PET/MRI for Diagnosing Bone Metastases. J Nucl Med. 2017; 58:1778-1785.

3.      Usmani S, Gnanasegaran G, Marafi F, Esmail A, Ahmed N, Van den Wyngaert T. The clinical significance of incidental soft tissue uptake on whole body 18F-Sodium Fluoride (NaF) Bone PET-CT: Pictorial Review. Clin Radiol. 2019; 74:95-110.

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