Fig. 1.
A 20-year-old man underwent a whole-body 18F-FDG PET/CT scan for the re-evaluation for recurred metastatic osteosarcoma of T2-T5 with paravertebral extraosseous soft tissue extension to the bilateral neural foramen and paravertebral soft tissues (blue arrows) shown on axial (a) and sagittal (b) magnetic resonance images. Three months ago, he had undergone a corpectomy of T3 with laminectomy of T2-T5, and posterior arthrodesis due to metastatic osteosarcoma after limb salvage surgery, and adjuvant chemotherapy for primary osteosarcoma of his right tibia. In addition to recurring tumors, axial tomographic (c-e) and maximum intensity projection (f) images of 18F-FDG PET/CT show asymmetric increased uptakes (red arrows) in the fatty tissues of the left cervical, supraclavicular, axillary, and thoracic paravertebral spaces, which were considered as increased brown fat activities
Fig. 2.
Three days later, a repeat 18F-FDG PET/CT scan was conducted without any treatment in a warm environment, achieved by outfitting air-conditioned facilities with blankets and portable heaters, thereby ensuring optimal conditions for the procedure. The scan reveals the lack of the brown fat activity on axial (a-c) and maximum intensity projection (d) images without a change in hypermetabolic activities of metastatic tumors (blue arrows). Based on his medical history, he presented absent sweating on the contralateral side of the arm, face, and chest, which may have been caused by damage to the sympathetic trunk during the previous surgery. Brown adipose tissue exhibits distinguishing features such as small cell size, multilocularity, a high mitochondrial count, enhanced vascularity, and substantial sympathetic noradrenergic innervation, in contrast to the more prevalent white adipose tissue [1]. Brown adipose tissue contributes to thermoregulation in response to cold conditions, primarily attributed to its expression of uncoupling protein-1 (UCP1) located in the mitochondrial inner membrane. UCP1 plays a pivotal role in heat generation. While heat production typically results from ATP synthesis through oxidative phosphorylation in the mitochondrial respiratory chain, UCP1, involved in non-shivering thermogenesis, induces heat by uncoupling the mitochondrial respiratory chain [2]. The regulation of thermogenesis involves the action of norepinephrine, which is released by the sympathetic nervous system and primarily interrelates with beta-adrenergic receptors located in brown adipocytes. Brown fat activity in 18F-FDG PET/CT is typically found in the cervical, supraclavicular, paravertebral, and mediastinal areas [1, 3–6]. Denervation of sympathetic pathways can be caused by several etiologies, including a tumor mass, vascular dissection, and iatrogenic injury [7–9]. Although there are several case reports available on unilateral patterns of brown fat activity in 18F-FDG PET/CT scans following surgical sympathetic denervation [10–12], we report an interesting case showing the disappearance of brown fat activity on a repeat scan in warm conditions
Authors’ Contributions
The study was designed by Joon Ho Choi and Jin-Sook Ryu. Material preparation and data collection were performed Joon Ho Choi. The first draft of the manuscript was written by Joon Ho Choi and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Funding
This work was supported by Soonchunhyang University Research Fund. The funders had no role in study design, data collection, analysis, and interpretation, or preparation of the manuscript.
Data Availability
Not applicable.
Declarations
Conflict of Interest
Joon Ho Choi and Jin-Sook Ryu declare that they have no conflict of interest.
Ethics Approval
All procedures performed in study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Consent to Participate
The institutional review board of our institute approved this retrospective study, and the requirement to obtain informed consent was waived.
Consent for Publication
The institutional review board at our institution approved this retrospective study, and the requirement to obtain informed consent was waived.
Footnotes
Publisher's Note
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Associated Data
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Data Availability Statement
Not applicable.