Radionuclide Imaging of Soft Tissue Neoplasms Felix S. Chew, Terry M. Hudson, and William F. Enneking Two classes of radiopharmaceuticals may be used for imaging tumors of the musculoskeletal system. The first is comprised of soft tissue or tumor- specific agents such as gallium-67, bleomycin, and radionuclide-labeled antibodies, which may be useful for detecting and localizing these tumors. The other class of tracer is comprised of those with avidity for bone. The ~SmTc-labeled-phosphate skeletal imaging compounds have been found to localize in a variety of soft tissue lesions, including benign and malignant tumors. In 1972, Enneking began to include bone scans in the preoperative evaluation of soft tissue masses. Later, he and his associates reported that these scans were useful in planning operative treat- ment of sarcomas by detecting involvement of bone by the tumors. Nearly all malignant soft tissue tumors take up bone-seeking radiopharmaceuticals, and bone involvement was indicated in two-thirds of the scans we reviewed. About half of benign soft tissue lesions had normal scans, but the other half showed uptake within the lesion and a few also showed bone involvement. Careful, thorough imag- ing technique is essential to proper evaluation. Multiple, high-resolution static gamma camera images in different projections are necessary to adequately demonstrate the presence or absence of soft tissue abnormality and to define the precise relationship of the tumor to the adjacent bone. T WO TYPES of radiopharmaceuticals may be used for imaging soft tissue tumors of the musculoskeletal system. First are those agents intended specifically for localization in soft tissue tumors, such as gallium and bleomy- cin. Second are the technetium-99m-labeled phosphate compounds intended for imaging of the skeleton. After the introduction of these bone-seeking agents, reports of localization in tumors and other lesions of soft tissues began to appear, and now a large number of neoplastic and inflammatory lesions of the soft tissues are known to accumulate the skeletal tracers. Our review of a large number of bone scans has shown that such soft tissue uptake is not only common, it is typical of most malignant and many benign soft tissue tumors and can be of value in diagnosis and in surgical treatment planning. SOFT TISSUE IMAGING AGENTS Gallium-67-Citrate Hayes ~ has recently reviewed the history of the development of 67Ga citrate, including its evolution into an agent used specifically to study soft tissue malignancies and inflammatory processes. Lepanto et al. 2 reported positive From the Departments of Radiology and Orthopedic Surgery and the W. Thaxton Springfi'eld Center for Orthopedic Study and Research, University of Florida Medical Center, Gainesville, Fla. Reprint requests should be addressed to Dr. Terry M. Hudson, Box J-374 J.H.M.H.C., Department of Radiology, University of Florida, Gainesville, Fla. 32610. 9 1981 by Grune & Stratton, Inc. 0001-2998/81/1104-0005502.0(9/0 gallium scans in 4 of 8 sites of soft tissue sarco- mas, but only 2 positive scans of 8 sites of bone metastases from these lesions. A report by Kauf- man et al. 3 included gallium scans of 27 soft tissue sarcomas, of which 25 were positive. This included 10 tumors that arose in the extremities and limb girdles. Nine of the latter scans were positive. Bitran et al. 4 reported a series of gallium scans that included 29 soft tissue sarco- mas. The accuracy of the scans varied with the specific diagnosis. In one group of 16 tumors, including malignant schwanoma, rhabdomyo- sarcoma, and undifferentiated sarcoma, 29 of 31 sites of tumor were positive on the scan: a 94% sensitivity. However, in another group of 13 tumors, including liposarcoma, leiomyosarcoma, malignant fibrous histiocytoma (MFH), and synovioma, only 5 of 16 sites of tumor were positive: a sensitivity of only 31%. In 1978, Teates et al. 5 reviewed the literature dealing with 67Ga-citrate scanning. Fourteen of 15 scans were positive in patients with MFH, rhabdomyo- sarcoma, or liposarcoma. They found 59 positive gallium scans in 65 patients with sarcomas, but many of these were thoracic or abdominal tumors, not musculoskeletal soft tissue tumors. At least some of the patients they included were among those reported by Lepanto and Kaufman. Pinsky and Henkin 6 discussed the use of 67Ga- citrate in scanning soft tissue tumors, the tech- nique of scanning, and the interpretation of normal scans, and listed the nontumor causes of increased uptake, including abscess, sarcoid, rheumatoid arthritis, Paget's disease, fracture, surgery, and others. They concluded that gallium is still "the best available isotope" for 266 Seminars in Nuclear Medicine, Vol. XI, No. 4 (October), 1981