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Three patients with histologically differing lesions of synovial origin and two with synovial cysts, one of which was a dissecting popliteal cyst, were examined by magnetic resonance imaging (MR) and computerized tomography (CT). The three histologically proven synovial lesions were synovial sarcoma, diffuse giant cell tumor of tendon sheath, and synovial chondromatosis. In two of the five patients MR provided better anatomic and morphologic appreciation than CT, while in the others they were of equal value. CT demonstrated calcification in two of the lesions while on MR calcification could be identified in only one patient where it outlined the mass. MR did not demonstrate calcification in the substance of the diffuse giant cell tumor of tendon sheath. Coronal, transverse, and sagittal images of magnetic resonance graphically demonstrated the extent of the soft tissue masses and their relationship to bone, vessels, and soft tissue structures. Synovial sarcoma had a shorter T1 than diffuse giant cell tumor of tendon sheath (these two lesions being of comparable size) and also had a uniformly longer T2. The dissecting popliteal cyst showed the most intense signals on the T1 weighted images, while the uncomplicated synovial cyst showed a long T1. On the T2 weighted images, each type of cyst showed a long T2. The variance and overlap of intensity of MR signals suggest limited specificity in predicting the histologic nature of the synovial lesion.

Following an abnormal radiograph, an initial 34 patients had both computed tomography (CT) and magnetic resonance (MR) to further characterize and stage a solitary tumor. This experience determined the choice between CT and MR in evaluating the next 55 solitary tumors. The choice of examination depends on the radiologist's ability to characterize the lesion from the radiograph as to its morphology, matrix, and probable histologic nature. The anatomic location, in turn, frequently influences the ability to characterize the lesion. Lesions in long bones can almost always be successfully characterized by radiography and, in these instances, only the MR examination is required to stage the tumor. Radiographic characterization of tumors in flat bones such as the scapula, certain portions of ribs, vertebrae, and pelvis is often difficult or incomplete. In these cases, CT is the preferred initial examination, and if further staging is required to establish the relationship of the tumor to soft tissues or neurovascular structures, the MR examination is done. Because of MR's superiority in staging the tumor and CT's superiority in characterizing the lesion, the initial choice between the two examinations should depend on the radiologist's ability to characterize the lesion from the radiograph. When radiographic depiction of tumor permits assessment of its morphology, matrix and probable histologic nature, (characterization) MR ought to be the next examination solely for staging purposes. It is the anatomic location of the tumor and the radiologist's ability to characterize it that ought to govern the choice of the next examination. Surgical and histopathological findings were known in all patients in this study.

On T1 weighted pulsing sequences, the majority of soft tissue masses are of low signal intensity and show high intensity signals on T2 weighting. There however is a subset of soft tissue masses of varied histology that shows high signal intensity on T1 weighted pulsing sequences. These masses have either fat or blood in their substance. Lipomatous and hemangiomatous lesions that did not show high-signal intensity on T1 weighting were also encountered and are discussed. Present experience with MRI of soft tissue masses suggests that there is a limited spectrum of entities that produce high-signal intensity T1 weighted soft tissue masses.

Early magnetic resonance (MR) experience in the evaluation of 14 consecutive long bone intramedullary osteosarcomas demonstrates the need for T1 and T2 weighted pulsing sequences in the staging of this disease. Intramedullary disease is best depicted by coronal T1 weighted pulsing sequences and subtle extra-compartmental disease by T2 weighted axial imaging. Both high intensity and low intensity intra-medullary signals were noted on T2 weighting, while all T1 weighted pulsing sequences showed intra-medullary disease to have low signal intensity. Extraosseous tumor on T2 weighting usually had a high signal, and disease extent was therefore sharply demarcated from uninvolved muscle and its relationship to vessels confidently assessed. MR appears optimally suited for local staging of osteosarcoma, further enhancing the role of radiology in planning limb-salvage surgical techniques.

Synchronous multicentric aggressive fibromatosis does not appear to have been previously reported. Two such cases are described. The tumors were identified by magnetic resonance (MR) imaging. The incidence of synchronous multicentric aggressive fibromatosis is not known. It is anticipated that increased use of coronal MR imaging will reveal more tumors of this type, both synchronous and metachronous. In a patient with known or suspected aggressive fibromatosis, every other soft tissue nodule or mass in the same limb has to be regarded as an additional tumor of the same histology.