The radiologic staging of a soft tissue tumor is a vital part of a patient’s evaluation (1, 2). As previously noted in Chapter 3, accurate staging is essential to determine appropriate clinical treatment and prognosis. Complete staging typically requires information that is not available at the time of initial patient presentation, such as tumor grade and presence or absence of metastases. The local extent of disease, however, is a critical part of tumor staging and is accurately defined with magnetic resonance (MR) imaging at initial patient presentation (2). Inherent in the determination of local extent of disease for staging is the concept of anatomic compartments.

Anatomic compartments are defined by natural barriers that prevent the spread of tumor (3). These barriers include major fascial septa, periosteum, cortical bone, joint articular cartilage, and joint capsules (3). Lesions that are confined to a specific anatomic space defined by these barriers are considered to be intracompartmental. This designation has clinical implications in that intracompartmental lesions are lower stage than similar grade extracompartmental lesions; therefore, they generally have an improved prognosis. Extracompartmental lesions are those that have spread beyond the boundaries of the compartment of origin. Mechanisms of extracompartmental spread include direct tumor extension, contamination from hemorrhage, or inappropriate open or percutaneous biopsy (3, 4).

Accurate delineation of the local tumor extent and compartmental status is essential, not only in local staging, but also in planning definitive surgery and in planning surgical or percutaneous biopsy. As a general rule, image-guided biopsy is usually done using the shortest path between the skin and the lesion, avoiding vital structures such as vessels and nerves (3). The biopsy of musculoskeletal lesions and specifically soft tissue tumors, however, has additional requirements. It is essential that the biopsy needle path does not violate any uninvolved compartment, neurovascular structure, or joint (3), and that the biopsy path coincides with that of the planned surgical incision (5). Definitive surgery includes complete removal of the biopsy needle tract, which is considered to be contaminated tissue, and consequently, the biopsy needle tract should ideally be made along the same path as the incision for definitive surgery (3).

As radiologists, we are often called on to perform imageguided biopsies. To ensure optimum patient care, biopsy of a soft tissue tumor should never be undertaken without prior consultation with the surgeon who will perform the definitive surgery (6, 7). Accordingly, percutaneous biopsy should be planned as carefully as the definitive surgery (6). In a 1982 landmark study, Mankin et al. surveyed members of the Musculoskeletal Tumor Society and reported the accuracy of diagnosis and incidence of complications associated with biopsy of musculoskeletal tumors (6). This study of 329 patients noted that the optimum treatment plan had to be altered as a result of biopsy-related problems in 8.2% of patients, unnecessary amputation was performed as a result of problems with biopsy in 4.5%, and the patient prognosis and treatment outcome were adversely affected in 8.5%. A similar study was performed in 1992 involving 597 patients and showed almost identical results (8). Although these studies did not specifically address percutaneous image guided biopsies and were done prior to the availability of current sophisticated techniques, they served as a poignant reminder of the potential harm of inappropriate biopsy, such as violating compartmental anatomy or crossing tissue planes that may compromise subsequent definitive surgery.

This chapter reviews the anatomic compartments of the musculoskeletal system and the basic principles for musculoskeletal tumor percutaneous biopsy. This knowledge is required for the local staging of soft tissue tumors and for the planning and performing of percutaneous image-guided biopsy.