Case 12

A 72-year-old female presented with a four-month history of an increasing mass in the popliteal fossa.
    A: The mass was soft but fixed and was nontender.
    B: A lateral radiograph of the knee There is a subtle ill-defined soft tissue mass
    C: Magnified Magnification shows no evidence of calcification within the mass or involvement of adjacent bone.
    D: Regional isotope scan. Diffuse increased isotope uptake in the region of the mass probably represents vascularity of the mass.
    E: A first generation axial CT image. The mass is adjacent to the posterior condyles with no apparent bone involvement.

An angiogram was done to evaluate the relationship between the mass and the popliteal neurovascular bundle.
    F: The lateral aspect of the mid-venous phase. The mass contains a significant amount of neovacularity and displaces the neurovascular bundle posteriorly.
    G: Magnified. A magnified view of the venous phase shows compression of the popliteal vein by the mass. An arthrogram was done to evaluate the possibility of intra-articular extension.
    H: The lateral aspect of the arthrogram. The white contrast media surrounds several small dark circular areas suggesting involvement within the joint. An incisional biopsy of the mass was done through a postero-lateral approach. The tissue was taken from just posterior to the femoral condyle. The articular cartilage of the condyle was visible through the biopsy defect.

    I: The appearance of the biopsy specimen. The tissue adjacnt to the articular cartilage was smooth and shiny with a distinctive reddish-brown coloration.
    J: A panoramic view of the specimen. This field is composed of many strands of tissue with a distinctive villous pattern.
    K: A low power field from the previous panoramic view. At this power the villi are seen to be bordered by cuboidal synovial cells.
    L: A medium power field. Within the field are many large macrophages, several in the lower left corner with hemosiderin in their cytoplasm. Several giant cells are evident.
    M: An adjacent medium power field. Here geat amounts of hemosiderin are present aand the vascularity can be easily appreciated.
    N: A high power gield from the previous field. Granules of hemosiderin are clearly seen at this magnification.
Although the staging studies showed the extent of the popliteal mass and its relationship to the neurovascular bundle the arthrogram also demonstrated multiple irregularities within the joint.
The biopsy showed a villous vascular mass composed of a background of bland mesenchymal cells, proliferations of macrophages and giant cells with abundant amounts of hemosiderin in their cytoplasm.
Diagnosis: Pigmented Villonodular Synovitis.

Accordingly a posterior synovectomy was done.

    The external surface of the mass
    The internal surface had the classic, brownish seaweed appearance of pigmented villonodular synovitis.