A 63-year-old man complained of the back pain for 2 years. The MRI and 18F-FDG PET/CT demonstrated the mass located in the left posterior mediastinum and invaded the spinal canal through the adjacent intervertebral foramen caused the dumbbell shape. The metabolism of the lesion was low with a SUVmax as 3.59 on 18F-FDG PET imaging. The pathology examination revealed the leiomyosarcoma. This case demonstrated that high-grade leiomyosarcoma in the posterior mediastinal can have low 18F-FDG metabolism and dumbbell-shaped tumor in the posterior mediastinal should consider leiomyosarcoma as differential diagnosis.
Keywords: Leiomyosarcoma; Dumbbell Shape; Posterior Mediastinum; PET/CT
The lesion invaded the spinal canal through the intervertebral foramen with adjacent T10 vertebra bone destruction with sclerosis (arrow in E: PET/CT bone fusion imaging), which was diagnosed as suspected malignant neurogenic tumor. In addition, no extra-lesion involvement was observed. Surgical excision of the lesion and vertebral body of T10 was performed. The tumor cells were immu nohistochemically positive for desmin and Caldesmon and negative for SMA, myoD1 and S-100. These findings confirmed the diagnosis of leiomyosarcoma with FNCLCC grade of 3. Primary leiomyosarcoma of the posterior mediastinum is a very rare malignant mesenchyma tumor, which come from the soft tissue of the mediasti num or the great vessels . Dumbbell-shaped tumor is a type of the inner and outer spinal canal tumor and most of these tumors are neurogenic tumors  (Figure 1). Some non-neurogenic dumb bell-shaped tumors occurred in posterior mediastinum including angioma, angiolipoma, chondrosarcoma , desmiod tumor , lymphoma , castleman disease . The posterior mediastinal of leiomyosarcoma caused dumbbell-shape is very rare and there was only one case reported in the literature . Intense 18F-FDG uptake with SUVmax from 5 to 28 observed in leiomyosarcoma had been reported in the literature [7-13] and high-grade leiomyosarcoma may correlated with high SUVmax . However, minimal 18F-FDG uptake in leiomyosarcoma is noteably rare . Interestingly, our patient had the highest FNCLCC of grade 3 but the SUVmax was 3.59. This case demonstrated that high-grade leiomyosarcoma in the posterior mediastinal can have low 18F-FDG metabolism and dumbbell- shaped tumor in the posterior mediastinal should consider leiomyosarcoma as differential diagnosis (Figure 2).
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