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Biopsy of Musculoskeletal Tumors

- Discussion:
    - may be accomplished with a large needle or by open surgical methods; 
    - things to consider before biopsy:
          - has the workup established metastatic dz (most common in patients over 40) vs isolated bone / soft tissue tumor vs infection (osteomyelitis);
          - studies that may be performed prior to biopsy:
                   - MRI of lesion;
                   - CT scan of chest, abdomen, pelvis (assist with work up of metastatic disease);
                          - most common site of skeletal metastasis is the thoracic spine;
                   - bone scan;
                   - CBC, sed rate, CRP, blood cultures, Ca level, Chem 7, PSA, Alk Phos, UA.

    - needle bx:
         - involves less disturbance to tissue & is usually less extensive;
         - where the soft tissue or bone lesion is accessible and near surface, needle biopsy is often a simple matter;
         - when inserting the biopsy needle, it is essential that the pathologist be aware of respecting tissue planes,
         - it is esp helpful technique when the diagnosis can be made on basis of a small number of cells, such as in metastatic cancer;
         - two types of biopsies include: fine needle and core needle biopsies;
         - fine needle biopsy:
                - relies on cytologal interpretation by an experienced pathologist;
                - its accuracy (65 to 95%) is determined in part by the adequacy of the collected tissue sample;
                - it does not allow for immunohistochemical analysis;
         - core needle biopsy:
                - uses trocar cannula system, with a outer sleeve which closes over the trocar, capturing the sample of tissue;
                - provides more tissue than fine needle and allows for immuno-histochemical analysis;
                - accuracy ranges between 75 to 95%;
         - disadvantages of needle bx:
                - are that tissue obtained may be from necrotic portion of tumor and therefore not suitable for dx, or tissue may be reactive in nature and not
                           representative of actual tumor;
                - Skrzynski MC, et al. (1996) recommend caution when a myxomatous tumor is diagnosed by needle biopsy, and recommend and recommend
                           an incisional biopsy for confirmation;
         - references: 
                - Diagnostic accuracy and charge-savings of outpatient core needle biopsy compared with open biopsy of musculoskeletal tumors.
                - Clinical Utility of Percutaneous Biopsies of Musculoskeletal Tumors.
                - Needle biopsy of musculoskeletal lesions. A review of 208 procedures.
                - Aspiration biopsy of primary neoplasms of bone.
                - Diagnosis of eosinophilic granuloma of bone by cytology, histology, and electron microscopy of transcutaneous bone-aspiration biopsy.

     - incisional open bx:
         - where several areas of a tumor must be evaluated (as seen in cartilagenous lesions), larger sample obtained by open biopsy is to be preferred;
         - incisional biopsies are performed (as opposed to excisional biopsies) inorder to minimize contamination of peripheral tissues and to preserve
                  the tumor's pseudocapsule (which facilitates future tumor excision);
         - need for embolization:
                  - some lesions such as suspected renal or thyroid carcinoma should have preoperative embolization, but consideration should be given to embolization
                            if a non compressible lesion is present (such as might occur with a pelvic or acetabular lesions);
         - surgical pitfalls:
                  - as a basic principal, the surgeon must be careful not contaminate tissue planes or compartments outside of the tumor's location;
                            - avoid mistake of placing a drain several cm away from incision site (may place tumor cells along the path of the drain;
                  - likewise transverse incisions will spread tumor cells across compartments; 
                  - incision should go through a single muscle belly when possible (and avoid intermuscular planes);
                  - percutaneous biopsy should avoid crossing compartments, (ie biopsy of a distal femoral lesion through the suprapatellar pouch, or transversing
                            through an intermuscular septum;
                  - it is essential that hemostasis be obtained prior to wound closure;
                  - drains should be placed at either the proximal or distal end of a longitudinally placed incision;
                  - compression dressing is applied postoperatively 
         - reference:
                  - Possible Metastasis of Osteosarcoma to a Remote Biopsy Site: A Case Report
                  - Residual disease following unplanned excision of soft-tissue sarcoma of an extremity.  
                  - Open surgical biopsy most accurate method for soft tissue mass diagnosis

- Considerations for Bone Biopsy:
    - always contour smooth edges;
    - make a circular or a longitudinal oval hole (torsional strength not affected by length of defect);
    - attempt to keep defects less than 10% of bone diameter (maintains over 80% of bone strength);
          - when biopsy size is greater than 20% of bone diameter, torsional strength decreases to 50%;
    - references:
          - The spread of tumor-cell-sized particles after bone biopsy.
          - The effect of biopsy-hole shape and size on bone strength.

The hazards of the biopsy, revisited. Members of the Musculoskeletal Tumor Society.

THE CLASSIC: The Hazards of Biopsy in Patients with Malignant Primary Bone and Soft-Tissue Tumors.