Preoperative Assessment of the Lesion

There are three different types of situations in musculoskeletal interventional radiology: soft-tissue lesions, mixed density osseous lesions, and intraosseous lytic lesions. Each one of these situations requires a slightly different approach and technique. Logan et al. devised a structured algorithm to workup lesions pertaining to each separate category (3). In their proposed scheme, there is an arbitrary cutoff diameter of 3 cm, after which the authors start using automated cutting needles. We believe with Jelinek et al. (4) that the size of the lesion should not be a decisive factor, provided the stroke margin is appropriate.

As in any other part of the anatomy, fine-needle aspiration biopsies may provide enough cellular material to diagnose a lesion. Malignancy can be demonstrated in many cases without need for histologic specimens. However, a more thorough evaluation of the lesion is obtained by simultaneously sampling histologic core specimens. Biopsy cores preserve the architecture of the tissue, raising their diagnostic yield. In addition, in the musculoskeletal system, purely sclerotic lesions make poor candidates for fine-needle sampling, and require a trephine bone biopsy needle.

Moulton et al. showed that the systematic addition of histologic analysis to fine-needle aspiration samples increases the accuracy of percutaneous biopsies by providing a more specific diagnosis. Cutting needles provide more consistent specimens, lessening the result dependency on the ability of the operator and the availability of an experienced cytopatholo-gist. Cutting needles have the greatest impact on the diagnosis of benign lesions (5). Schweitzer et al. further reflect on the appropriateness of using automated cutting needles in lytic lesions of the musculoskeletal system. The study is based on 25 biopsies, with 24 final diagnoses obtained with the use of a gun, despite obtaining only two cores (6).

Soft-tissue lesions can be reliably sampled with a fine-needle aspiration [van Sonnenberg or Franseen (Cook, Bloomington, Indiana, U.S.A.)], or a spring-loaded core-biopsy device (Fig. 4A) (reusable gun or disposable single-use devices such as Achieve (Allegiance, Mc Gaw Park, Illinois, U.S.A.) (3,7). Spring-loaded core-biopsy needles have a predetermined stroke related to the size of the collecting area and the bevel in front of it. Ideally, the collecting area

FIGURE 4 (A) Core-biopsy cutting needles are most suitable for sampling soft-tissue lesions. (B) Bone biopsy needles do not have a capturing collecting area, and when attempting to sample soft-tissue lesions, the yield is often limited to serosanguineous material.

should be deployed entirely within the lesion (Fig. 5). Therefore, the stroke margin should be larger than the needle stroke. Although needle strokes are variable, the most widely used needles have a throw of approximately 2.5 cm. When the presence of vital structures behind the lesion limit the stroke margin, adequate cores can be obtained with a needle design consisting of a stylet tightly fitted into the cutting cannula, providing a suction effect upon progressive withdrawal of the stylet. The operator manually exerts in-and-out excursions of the needle at each progressive interval withdrawal of the stylet. Eventually a core is suctioned within the cutting cannula [Vacu-Cut (Bard, Covington, Georgia, U.S.A.)] (Fig. 6). Alternatively, needles which retract rather than advance can be utilized, although these types of needles yield overall poorer specimens.

For limb-salvage surgery to be an option in cases of soft-tissue sarcomas, it is essential that the compartmental anatomy be respected during the percutaneous procedure. Violation of fascial planes at the time of the biopsy may alter the eventual surgical approach by limiting therapy to amputation. To minimize the chances of inadvertently violating compartments, Anderson et al. summarize several guidelines: always choose the shortest possible route to the lesion; use the same path that the surgeon will select for resection if the lesion is proven malignant; and avoid transgressing fascial planes or passing close to a neurovascular bundle (8). Also important, large soft-tissue lesions tend to necrose and produce cystic cavities, which are prone to lower the yield of the biopsy. Consequently, it is important to obtain a contrast-enhanced MR or CT before performing the biopsy to select a solid-appearing part of the mass.

Open-ended type needles with a serrated edge (trephine needles), on the other hand, afford dependable purchase on sclerotic bone lesions, avoiding the need for a capturing mechanism. Not only sclerotic neoplastic lesions, but also end plate biopsies in patients with

FIGURE 5 Core-biopsy cutting needles capture tissue in a predetermined trough in the inner stylet, over which the outer cutting cannula is advanced.
FIGURE 6 Vacuum-assisted core-biopsy needle (Vacu-Cut®, Bard, Covington, Georgia, U.S.A.).

suspected vertebral osteomyelitis, are good indications for the use of this type of needle. Although most possess a diamond-shaped or beveled tip, there are also models with a hollow introducer that allows advancement over a fine needle. Traditionally, bone biopsies are performed with Ackerman (Cook, Bloomington, Indiana, U.S.A.) (Fig. 4B and Fig. 7) or Jamshidi-type needles (MDTech Bone Marrow Biopsy Needle, Gainesville, Florida, U.S.A.). This latter type precludes the use of a coaxial system, practically limiting the biopsy to one single pass. Threaded-tip needles provide a more controlled and gradual introduction, usually without as much physical demand on the operator [Ostycut (Bard, Covington, Georgia, U.S.A.)]. However, the use of reusable handgrips facilitates the introduction of Ackerman-type needles.

A subset of lesions is basically composed of soft tissue, yet they lie entirely within the medullary cavity of the bone, sheltered by an intact cortex. These lesions are better accessed in two separate steps, (Fig. 8) as described by White et al. in a coaxial approach with a trephine needle used to penetrate the cortex, and the final tissue sampling performed with a biopsy gun (9). Notably, in their description, a Van Sonnenberg needle was used to guide the Ackerman to the cortex, and to negotiate the 18-g introducer for the biopsy gun beyond the created hole in the cortex. However, this Seldinger exchange over the Van Sonnenberg can be obviated with the use of eccentric drilling needles (10).

FIGURE 7 Metastatic urethral carcinoma to the left iliac bone producing minimal changes in the underlying bone (A), sampled with an Ackerman needle (B).

FIGURE 8 A metastatic focus on hypernephroma with overlying intact cortex is accessed in two stages. Initially, the cortex is transgressed with an eccentric drill, allowing the introducer to be secured past the cortical bone (A). After removing the eccentric drill, several passes are obtained with a spring-loaded needle, shown with the collecting chamber open in (B).

FIGURE 8 A metastatic focus on hypernephroma with overlying intact cortex is accessed in two stages. Initially, the cortex is transgressed with an eccentric drill, allowing the introducer to be secured past the cortical bone (A). After removing the eccentric drill, several passes are obtained with a spring-loaded needle, shown with the collecting chamber open in (B).

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