Image-Guided Percutaneous Biopsy of Musculoskeletal Lesions

Indications

• Establish whether a musculoskeletal lesion is benign or malignant.

• Obtain material for microbiologic analysis in patients with known or suspected infection.

• Stage patients with known or suspected malignancy when local spread or distant metastasis is suspected.

• Determine the nature and extent of systemic diseases (e.g., connective tissue diseases).

Histopathologic studies are often needed in patients with musculoskeletal lesions to establish a definitive diagnosis of tumor, infection, or systemic process. A lytic or blastic lesion may occur in a patient without a history of cancer and may appear malignant or indeterminate; PNB in this setting is requested for clarification. More commonly, however, a lytic or blastic bone lesion or soft tissue mass appears in a patient with a history of malignancy. PNB is needed to establish the diagnosis of metastasis for staging and initiation of radiation or adjuvant therapy. In addition, in a patient with known cancer and a lesion developing more than 10 years after the initial diagnosis, PNB is needed to distinguish whether the lesion is the same histology as the original tumor or a new neoplasm. Another common indication for PNB is a bone or soft tissue lesion in a patient whose history, physical examination, laboratory values, and imaging point to infection. Treatment in such a case relies on determining the cause of infection, and biopsy allows identification of the organism in question. The rarest indication for PNB is a systemic disease such as a connective tissue disorder; PNB is performed to exclude other more insidious processes.

Contraindications

There is no absolute contraindication to PNB, but several factors can be considered relative contraindications because they render PNB unsafe to perform.

• Known coagulopathy that cannot be corrected adequately

• Inability of the patient to cooperate or be positioned for the procedure

• Known adverse reaction to potential medication given during the procedure

• Hemodynamic instability

• Lack of a safe pathway to the lesion

• Pregnancy

Biopsy should be delayed until critical parameters, including coagulopathy, infection, and hemodynamic instability are satisfied. Technical considerations such as lack of a safe pathway to the lesion, adverse reaction to potential medications given during the procedure, and inability of the patient to cooperate or be positioned for the procedure, as well as pregnancy, have to be addressed before initiating or proceeding with PNB. Careful review of imaging and clinical correlation are critical to avoid unnecessary biopsy of a classic “do-not-touch” lesion such as traumatic avulsion of an apophysis in young patients, evolving myositis ossificans, and subchondral geodes that may appear histologically aggressive and confuse clinical management.

Equipment

Percutaneous needle biopsy may be performed under fluoroscopic, ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI) guidance. The imaging choice depends primarily on the location and imaging characteristics of a lesion and, to a lesser degree, on the available imaging modalities and patient positioning.

For a superficial soft tissue lesion or a lesion with cortical disruption that allows an acoustic window for passage of a needle, ultrasound may be used ( Figs. 107.1 and 107.2 ). Ultrasound provides real-time visualization, minimal patient and preprocedure preparation, and no radiation exposure to the patient. Obviously, poor sound penetration or a hard surface precludes the use of ultrasound for deep medullary bone lesions. Moreover, deep soft tissue lesions also preclude ultrasound use because poor sound penetration may lead to unknowing disruption of critical soft tissue compartments.

For a radiographically identifiable lesion that does not require careful negotiation of neurovascular structures, fluoroscopy allows fast multidirectional real-time visualization with ease of use and less cost than CT or MRI ( Fig. 107.3 ). However, low soft tissue contrast makes fluoroscopy less ideal for lesions with large cystic or necrotic areas.

For a deep lesion or a lesion adjacent to neurovascular bundles, CT and MRI are ideal for creating high-resolution road maps of compartmental anatomy. In practice, CT is routinely used for lytic or blastic lesions with or without a soft tissue component, whereas MRI is often used for lesions that are not identified on other imaging modalities and for targeting a focal marrow abnormality ( Figs. 107.4 and 107.5 ). However, conventional CT can occasionally be a slow, arduous modality because of the lack of real-time visualization and the requirement for repeated scanning during needle manipulation and positioning. CT fluoroscopy allows the combined convenience of real-time guidance and instantaneous cross-sectional anatomy. Although MRI guidance requires MRI-compatible (high nickel content) needles (E-Z-EM Inc., Westbury, NY; Somatex, Berlin, Germany; MD Tech, Gainesville, FL; InVivo, Berlin, Germany), imaging with frequency encoding parallel to the needle path reduces susceptibility artifact, and specialized monitor devices and platforms are being developed for MRI-guided procedures ( Figs. 107.6 and 107.7 ).

Sampling should be performed by fine-needle aspiration (FNA) along with CNB. For FNA, a 25- or sometimes 22-gauge needle is typically used. For CNB, options depend on whether the lesion is composed of soft tissue or bone. For bone lesions, 11- to 15-gauge trephine needles are typically used. These needles consist of a coaxial system with an outer trocar that remains fixed in the cortex and an inner trephine needle that makes multiple passes through the lesion without requiring repositioning. For a longer segment of bone, a drill-based trephine needle can be used.

For soft tissue lesions, biopsy can be performed with cutting needles or core biopsy devices such as automated core biopsy guns and vacuum-assisted needles. Needle sizes range from 14 to 22 gauge, although for the diagnosis of sarcomas, 14- to 16-gauge needles are optimal. An outer introducer sheath is affixed in the lesion to minimize repeated imaging and localization, followed by the use of cutting needles and devices. The commonly used biopsy devices offer adjustable throw lengths and are lightweight, thus allowing single-handed operation.

An important consideration when choosing appropriate needle systems is the amount of tissue expected to be required for accurate pathologic diagnosis. A 25- or 22-gauge FNA needle will inevitably yield a smaller amount of specimen for diagnosis than a 14-gauge Ackerman needle will. However, FNA is used for rapid on-site cytopathologic assessment of the adequacy and diagnostic nature of specimens to guide additional sampling with CNB, because CNB samples require 2 or more days for preparation before samples can be interpreted. Given the limitations of FNA and CNB, many interventionalists find that the two methods have complementary roles and perform both during each biopsy procedure. There are also instances in which the diagnosis will be made by one technique and not the other. Frequently, having both a cytopathologic and a histopathologic specimen increases diagnostic accuracy.