Cross-sectional imaging in the evaluation of osteogenic sarcoma: MRI and CT

Cross-sectional Imaging in the Evaluation Osteogenic Sarcoma: MRI and CT By Leanne L. Seeger, Jeffrey J. Eckardt, B EFORE the advent of cross-sectional scan- ning techniques, imaging of malignant bone tumors was confined to plain radiography and radionuclide bone scanning. While radiography remains the primary imaging modality for differ- ential diagnosis, magnetic resonance imaging (MRI) and computed tomography (CT) have had a profound impact on the preoperative stag- ing evaluation of bone tumors and their response to therapy. In this article we will define the role of MRI and CT in the work-up of the patient with known osteogenic sarcoma (OGS), stressing imaging strategies that optimize information available to the clinician and assist in therapy planning. In order to achieve these optimal factors, communi- cation with the referring physician and review of available radiographs and radionuclide bone scans before MRI or CT image acquisition is often essential. PREOPERATIVE EVALUATION Under usual circumstances, the diagnosis of OGS should be made with radiographs and confirmed by biopsy, and the detection of skip lesions and distant metastases should be accom- plished with radionuclide bone scanning. The role of MRI and CT scanning, therefore, is not for diagnostic purposes but rather to supply information that is otherwise inapparent or un- available. This basic concept is often forgotten when cross-sectional images are obtained, result- ing in studies that provide “pretty pictures,” but add little or no additional useful information to the clinician who will ultimately be responsible From the Department of Radiological Sciences. Muscu- loskeletal Section, and the Department of Surgery, Division of Orthopaedic Surgery, UCLA School of Medicine, Los Angeles. Leanne L. Seeger: Assistant Professor of Radiological Sciences; Jeffrey J. Eckardt: Associate Professor of Ortho- paedic Surgery; Lawrence W. Bassett: Professor of Radiolog- ical Sciences, UCLA School of Medicine. Los Angeles. Address reprint requests to L.L. Seeger, MD, UCLA School of Medicine. Department of Radiological Sciences, 10833 Le Conte Ave. Los Angeles, CA 90024. 0 I989 by W.B. Saunders Company. 0037-I 98X~89/2403-0003$5.00/0 and Lawrence W. of Bassett for treatment. Magnetic resonance imaging and CT image acquisition should address specific issues that are important to the surgeon and should be tailored according to tumor location and proposed surgical treatment, whether it be amputation or resection with limb salvage proce- dure. The following discussion reflects the scanning principles and techniques we use for evaluating patients with OGS both preoperatively and post- operatively. This was derived from both our own experience and the experience of others as re- ported in the literature. ‘-’ Regional differences in the management of patients with malignant bone tumors may alter this procedure. To become familiar with local treatment protocols, commu- nicate directly with the surgeon who will ulti- mately be responsible for treatment. The goals of cross-sectional imaging of pa- tients with OGS include: (1) determining both the marrow and soft-tissue extent of tumor; (2) defining the relationship of tumor to major neu- ral and vascular structures; (3) evaluating adja- cent joints for intraarticular tumor and/or syn- ovial infiltration; (4) detecting skip lesions; and (5) providing measurements needed for the antic- ipated surgical procedure. It is prudent to image the involved bone in its entirety with MRI or CT. This will do the following: (1) allow evaluation of any additional suspicious-looking lesions on bone scan; (2) allow detection of unsuspected metastases that were not evident on the bone scan; and (3) provide reference points for measurements that aid in surgical planning. Tumor resectability in the extremities will be in part determined by the ability to leave major neural and vascular bundles intact; therefore, limb salvage is not appropriate when tumor has encased or infiltrated these structures. Tumor that is either intraarticular or has extensively involved the synovial barrier also precludes limb salvage. Skip lesions will significantly alter surgi- cal margins for OGS of the extremity. For primary pelvic tumors of the ilium or sacrum, preoperative imaging must identify infiltration into abdominal or pelvic soft tissues and the Seminsrs in Roentgenology, Vol XXIV, No 3 (July), pp 174-