This video provides a detailed pathological examination of a large joint lesion identified as Lipoma Arborescens (also known as Synovial Lipomatosis). Using low-power microscopy, the specimen is confirmed to be located within a joint space, characterized by the presence of a loosely organized synovial lining and adjacent dense connective tissue. The key feature of the lesion is the massive proliferation of benign mature adipose tissue forming striking, frond-like, polypoid projections that push into the synovial space. Histological clues for this diagnosis include the presence of dilated vessels and mixed inflammatory cells within the fatty tissue. The entity is contrasted with the differential diagnosis of reactive papillary synovial hyperplasia, which lacks the prominent fatty component.
Summary of the Pathological Examination: Lipoma Arborescens
0:06 Low-Power View: The lesion is noted to be dramatically visible even at low power (2X magnification).
0:28 Tissue Identification: Connective tissue is identified, initially appearing as dense regular collagen.
0:38 Synovium Location: The location is confirmed to be a joint space, identified by the presence of synovium. The synovium is described as a non-tight lining of cells (resembling loosely packed histiocytes) attempting to form an epithelial layer.
1:35 Diagnosis: The mass is identified as Lipoma Arborescens (or Synovial Lipomatosis), characterized by mature adipose tissue (benign fat) forming multiple large, polypoid projections pushing into the joint space.
2:15 Gross Appearance: The condition often presents intraoperatively and grossly as polypoid or frond-like protrusions within the synovial space.
2:28 Associated Conditions: The condition may sometimes be seen in conjunction with other synovial diseases, such as Pigmented Villonodular Synovitis (PVNS).
2:52 Key Differential Diagnosis: It is important to distinguish Lipoma Arborescens from Papillary Synovial Hyperplasia, which is a reactive process characterized by polypoid projections of synovium that do not contain the significant fatty component.
3:55 Additional Histological Features: Important secondary features of Lipoma Arborescens include the presence of dilated vessels and mixed inflammatory cells within the adipose tissue.
Takeaway: Lipoma Arborescens is a distinctive, benign proliferation of fat that forms striking, massive, frond-like projections into the synovium-lined joint space.