PET/CT and PET using [18F]-FDG in a Patient with Soft Tissue Sarcoma

摘要

Fluorine-18 Fluordeoxyglucose Positron Emission Tomography (FDG-PET) is a useful tool in monitoring of sarcoma treatment. Recent data demonstrated an increase of tumour uptake with time compared to a decline in inflammatory lesions in dual time PET scanning. We demonstrate a patient with pulmonary masses 6 months after surgical removement of a mediastinal soft tissue sarcoma. Using PET scans 1h and 3h p.i 320 MBq FDG (,i.e. a combined PET/CT using CT-based attenuation correction and a conventional PET with measured attenuation correction), an increased tracer-uptake was observed in a single pulmonary mass, thus leading to the diagnosis of malignancy. Subsequent CT guided biopsy and further clinical follow-up, however, demonstrated the absence of malignancy and showed inflammatory disease instead. Introduction Adult soft tissue sarcoma is a type of cancer originating from the soft tissue including muscles, connective tissues, vessels, joints, and fat. Soft tissue sarcomas are rare in children and adolescents. The prognosis of a patient with adult soft tissue sarcoma depends on factors such as size, histologic grade, stage, and age of the patient. Factors associated with a poorer prognosis are age older than 60 years, tumours with a diameter of >5 cm, and low differentiation. Although well differentiated tumours usually are curable by surgery alone, higher-grade sarcomas are associated with higher local treatment failure rates and increased metastatic potential. [1,2,3,4,5]Fluorine-18 fluordeoxyglucose Positron Emission Tomography (FDG-PET) is a useful tool in following sarcoma treatment, grading sarcoma, separating benign from malignant masses, selecting biopsy sites, and assessing the extent of sarcomas [6]. Concerning the diagnosis of recurrent disease, literature shows an overall sensitivity of 66 % and specificity of 96 % for FDG-PET (overall patients n=254) [7,8,9,10,11,12]. However, the low anatomical resolution of FDG-PET can be problematic. The intrinsic combination of anatomical and metabolical information as introduced with combined PET/CT [13,14,15] may solve these shortcomings and further improve staging.The pitfalls of dual time FDG-PET for decision making with respect to therapy will be shown in the following case report. Case Report History and Clinical FindingsA 21-year-old male with a history of a soft tissue sarcoma of the mediastinum who underwent surgery 6 months before was referred to the Department of Nuclear Medicine with newly found pulmonary masses detected by CT and MRI. Prior to further treatment planning, metabolic information was desired for the differentiation of benign and malignant lesions. The physical examination showed a normally developed asymptomatic patient with normal physical examinations. Laboratory results were performed without pathological findings.Computed Tomography (CT) ImagingPreoperative CT-imaging of the thorax had been unremarkable. Two months postoperatively five ill-defined lesions of up to two centimetres in size in Segments 1 and 2 of the left upper pulmonary lobe where identified on a CT-scan. Those lesions decreased in size until 6 months after operation when the next CT was carried out. Due to the reduction in size over time without any cytostatic therapy, the lesions in the left upper pulmonary lobe were characterised as inflammatory. There were no signs of local recurrence in the mediastinal region on the postoperative CT-scans.Positron-Emission Tomography and PET/CTOne hour after intravenous injection of 320 MBq [fluorine-18] fluordeoxyglucose (serum glucose at injection 86 mg/dl) a PET scan with attenuation correction was acquired in 3D mode (ECAT HR+, Siemens Medical Solutions, Erlangen, Germany manufactured by CPS, Knoxville TN, USA). Projections from head to proximal femora were obtained. PET showed no pathologies. In particular, there was no pathologic tracer accumulation in the pulmonary lobes (Fig. 1).