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[(18)F]fluorodeoxyglucose positron emission tomography (FDG PET) is used to evaluate the metabolic activity of intermediate- to high-grade soft tissue sarcomas prior to the initiation of chemotherapy. FDG PET and MRI are repeated after chemotherapy to assess treatment response and to correlate this with the histologic response. This case report highlights discrepant results between the final histologic diagnosis (tumor response) and the percent change in maximum standard uptake variable (SUV(max)). Further investigation of the resected specimen identified the significant difference in tumor response assessment to be due to the heterogeneity of the tumor and heterogeneity in its response to treatment. FDG PET imaging has an important role in evaluating tumor metabolic activity and has played an increasingly important part in evaluating the response to neoadjuvant chemotherapy in sarcomas. Evaluating the heterogeneity of the tumor at baseline and after response to therapy can provide insight into prognosis and treatment planning.

Objective. Radiation therapy is often used to treat bone und soft tissue neoplasms, and commonly results in soft tissue edema in the radiation field. However, the time course, distribution and degree of this edema have not been well characterized. Our study was carried out to better define these features of the edema seen following neutron and photon radiation therapy. Design and patients. Two hundred and twenty-six patients underwent radiation therapy as part of combined modality management for musculoskeletal sarcomas between 1985 and 1993. Of these, 15 had surgical resection of their neoplasm, had no clinical evidence of recurrent disease, and had adequate MR follow-up that allowed sequential assessment of soft tissue following irradiation. Ten patients received photons with an average dose of 52.8 Gy. Five patients received neutrons with an average dose of 17.3 nGy. Sequential MR follow-up was available in these patients for an average of 22.8 months following radiation therapy. On each of the serial MR imaging studies, subcutaneous fat, muscle, and the intramuscular septa/fascial planes were graded subjectively as to size and signal intensity. Results. In general, soft tissue signal intensity in the radiation field initially increased over time, peaking at about 6 months for neutron-treated patients and at about 12–18 months for photon-treated patients. Signal intensity then decreased slowly over time. However, at the end of the follow-up period, signal intensity remained elevated for most patients in both groups. Signal intensity in a particular tissue was greater and tended to persist longer on STIR sequences than on T2-weighted sequences. Survival analysis of signal intensity demonstrated much longer edema survival times for neutron-treated patients than for photon-treated patients. Signal intensity increase in the intramuscular septa persisted for much longer than for fat or muscle. A mild increase in size was noted in the subcutaneous fat and intramuscular septa. Muscle, on the other hand, showed a decrease in size following treatment. This was mild for the photon-treated group and more marked for the neutron-treated group. Conclusions. There is a relatively wide variation in the duration and degree of post-irradiation edema in soft tissues. This edema seems to persist longer in the intramuscular septa than in fat or muscle. Although the duration of follow-up was limited, our study suggests that this edema resolves in roughly half the photon-treated patients within 2–3 years post-treatment and in less than 20% of neutron-treated patients by 3–4 years post-treatment. Muscle atrophy was seen in both photon- and neutron-treated patients, but was more severe in the neutron-treated group.

Cryotherapy is an increasingly popular mode of therapy adjunctive to surgical curettage in the treatment of certain skeletal neoplasms, such as giant cell tumors or chondrosarcomas. The magnetic resonance (MR) findings following cryotherapy have not been previously reported. We reviewed the MR findings in seven patients with skeletal neoplasms following curettage and cryotherapy. In six cases we found a zone of varying thickness extending beyond the surgical margins, corresponding to an area of cryoinjury to medullary bone. This zone displayed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, consistent with the presence of marrow edema. This zone of edema almost certainly reflects underlying thermal osteonecrosis. This zone may vary in size and intensity over time as the area of cryoinjury evolves or resolves. MR is currently the imaging procedure of choice for follow-up of most musculoskeletal neoplasms. Knowledge of the MR findings following cryotherapy should help prevent confusion during the interpretation of follow-up MR examinations.