In their article, Mohr et al. compare the ability of ultrasonography-guided vacuum-assisted biopsy (a technique that has become widely utilized for breast biopsy and can be performed in an outpatient setting) and open incisional biopsy (which is performed in the operating room) to characterize soft-tissue tumors encountered in orthopaedics. They examine selected cases in which chemotherapy or radiation therapy was not used prior to the biopsy and excision was performed shortly after the biopsy, thus narrowing the number of vacuum-assisted biopsy cases from 116 to seventy-five and the number of open biopsy cases from 110 to seventy-four. The vacuum-assisted biopsy technique achieved results that were comparable to those of the open technique, albeit with slightly lower accuracy, sensitivity, and negative predictive value. A diagnostic sample was successfully obtained in 99% of the vacuum-assisted biopsy cases.
This is an interesting and compelling article in that it challenges the current approach to diagnosis of these tumors, which involves either open biopsy or core needle biopsy without imaging guidance, with use of computed tomography (CT) imaging for guidance of core needle biopsy or fine needle aspiration biopsy generally reserved for difficult-to-access or recurrent lesions.
First and foremost, the authors are to be applauded for focusing attention on the conceptually simple but sometimes neglected step of making a diagnosis prior to excision of a soft-tissue mass. In selected cases, such as lipomas and cysts, a diagnosis of a soft-tissue mass may be arrived at on the basis of the history and clinical examination, sometimes supplemented by imaging. However, if a diagnosis cannot be arrived at on the basis of the preoperative clinical evaluation and imaging, the consensus among orthopaedic oncologists is that biopsy should precede excision. Mankin et al. twice documented the potential ill effects of poorly planned excisions and biopsies performed prior to referral to a tumor center, and such problems continue to be encountered by orthopaedic oncologists and to adversely affect tumor patients1,2.
There is less consensus on the biopsy technique that should be used for soft-tissue masses or on who should perform the biopsy3. However, open biopsy and core needle biopsy are the predominant techniques. Open biopsy is typically performed by the surgeon in the operating room. Core needle biopsy is usually performed by the clinician in the office when the patient initially presents. Fine needle aspiration biopsy is preferred at a limited number of centers where expert cytopathologists are readily available. Both core needle biopsy and fine needle aspiration biopsy may be performed by pathologists or interventional radiologists as well as by surgeons. To date, imaging guidance for biopsy of soft-tissue masses has usually employed CT and has generally been reserved for difficult locations, for small, deep tumors, and for tumors located adjacent to vital structures.
Reports on the use of ultrasonography-guided biopsy for soft-tissue tumors have recently begun to appear in the literature. In a 2010 retrospective study of 115 such biopsies, De Marchi et al. reported 97.1% sensitivity and 92.5% specificity for the 94.8% of specimens that were adequate for diagnosis4. Soudack et al. reported similarly high sensitivity, specificity, positive predictive value, and accuracy (97%, 99%, 99%, and 98%, respectively) in distinguishing malignant from benign lesions in 183 patients. However, thirteen patients (7.1%) required more than one biopsy, and the overall diagnostic accuracy was only 91%5. Earlier, smaller series have also reported similar findings6-9.
In their review of the available evidence-based literature regarding biopsy of soft-tissue masses for the Musculoskeletal Tumor Society, Rougraff et al. concluded that open biopsy has higher diagnostic accuracy than core needle biopsy and that both have better accuracy than fine needle aspiration biopsy3. They found no evidence of differences in accuracy among biopsies performed by general surgeons, orthopaedic surgeons, radiologists, or pathologists3. The preponderance of evidence in this area was Level IV. There was only one Level-I study, a prospective comparison of core needle biopsy with simultaneous fine needle aspiration biopsy that showed that core needle biopsy yielded substantially better accuracy (83% compared with 64%)10. One Level-II study indicated a diagnostic accuracy of 84% for core needle biopsy and 94% for open biopsy11. There were three Level-III studies (retrospective, case-control studies of nonconsecutive patients); one evaluated core needle biopsy, one evaluated fine needle aspiration biopsy, and one compared these two techniques12-14. There were fifteen Level-IV studies of the results of core needle biopsy, one additional study that compared the results of core needle and open biopsy, eleven studies of the results of fine needle aspiration biopsy, three studies that compared the results of core needle and fine needle aspiration biopsy, and one study in which the combined results of core needle and fine needle aspiration biopsy were presented3.
In essence, what Mohr et al. report is a retrospective controlled study indicating that vacuum-assisted biopsy with ultrasonographic guidance yielded results comparable with those of open biopsy but with a trend toward lower sensitivity. The combination of vacuum assistance and ultrasonographic guidance potentially allows selection of non-necrotic, nonvascular areas on the basis of the ultrasonographic imaging as well as use of only a single needle insertion using the vacuum-assisted technique. However, despite its excellent results in the current study and its obvious theoretical advantages, we still do not know how this technique stacks up to either CT-guided core needle biopsy or office-based core needle biopsy. There are theoretical advantages to both ultrasound-guided and traditional in-office core biopsy (Table I).
The most important question that remains unanswered is the appropriate role for vacuum-assisted, ultrasonography-guided core needle biopsy. Given the additional cost of a $35,000 vacuum device, $100 single-use needles, an ultrasonography facility, and support staff to operate the equipment, implementing this technique in facilities in which it does not already exist will require a substantial investment. Vacuum-assisted biopsy appears to be a cost-effective alternative for breast lesions, but the estimated number of breast cancer cases in the United States in 2011 (232,620) dwarfs the number of soft-tissue sarcomas (10,980)15. Consequently, vacuum-assisted biopsy of soft-tissue masses is not likely to quickly replace the simpler, quicker, and less costly alternative of office-based core needle biopsy in orthopaedics. Even in facilities in which the vacuum-assisted ultrasonography-guided technique is routinely used for breast biopsy, will a greater scheduling delay for this technique compared with core needle biopsy in the office setting offset the potentially increased diagnostic accuracy? It is not clear whether this technique is even intended to supplant office-based core needle biopsy. Mohr et al. suggest that ultrasonographic guidance is not required for large superficial tumors but may avoid vascular injury and improve accuracy for small, deep lesions. If that is true, should use of this technique be limited to vascular lesions and small, deep lesions that are difficult to access? At present, patients with such lesions would probably be sent to a radiology department for a CT-guided core needle biopsy, begging the question of whether this technique should replace CT-guided needle biopsy.
In institutions in which a very good imaging core facility with a highly motivated in-house ultrasonographer and support staff are available on short notice to perform a biopsy at the request of the orthopaedic oncologist, it will perhaps supplant both office-based and CT-guided core needle biopsy. In institutions in which difficult core needle biopsies are already referred to an interventional radiologist for CT-guided core needle biopsy, it will be interesting to see how the radiologist directs us regarding the relative merits of the two techniques. Clearly, ultrasonography eliminates the radiation exposure that CT requires, and ultrasonographic guidance has been readily adopted for breast biopsy—but, as already noted, breast imaging centers that perform vacuum-assisted biopsy on a regular basis often have dedicated personnel to operate the necessary equipment. Ultimately, access to such existing facilities will probably guide the adoption of this technique by musculoskeletal oncologists in many centers. As in the case of imaging-guided needle biopsy performed by a radiologist, communication between the orthopaedic oncologist and the radiologist regarding desired needle track placement will remain crucial to avoid poor placement that might complicate subsequent safe excision of the biopsy track with the tumor. Ultrasonography-guided vacuum-assisted biopsy will no doubt find its niche, but it may be some time before it replaces office-based core needle biopsy.