Page 804 - Robbins Basic Pathology by Vinay Kumar, Abul K. Abbas, Jon C. Aster
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790 C H A P T E R 20 Bones, Joints, and Soft Tissue Tumors soft tissue tumors. In comparison, reactive tumor-like lesions
such as ganglions and synovial cysts are much more common
disease. The arthritis may be caused by immune responses than neoplasms; these typically result from trauma or
against Borrelia antigens that cross-react with proteins in degenerative processes. Here we discuss the more common
the joints, but the exact mechanisms are not yet under- or clinically significant tumor-like lesions and neoplasms
stood. The disease tends to be migratory, with remissions of joints and associated soft tissues.
and relapses. It involves mainly large joints, especially the
knees, shoulders, elbows, and ankles, in descending order Ganglion and Synovial Cysts
of frequency. Histologic examination reveals a chronic
papillary synovitis with synoviocyte hyperplasia, fibrin A ganglion is a small cyst (less than 1.5 cm in diameter)
deposition, mononuclear cell infiltrates, and onion-skin located near a joint capsule or tendon sheath; the wrist is
thickening of arterial walls; in severe cases, the morphol- an especially common site. Lesions manifest as firm to fluc-
ogy closely resembles that of rheumatoid arthritis. In only tuant pea-sized nodules that are translucent to light. Micro-
25% of cases do silver stains reveal a sprinkling of organ- scopically, they consist of fluid-filled spaces that lack a true
isms, and formal diagnosis of Lyme arthritis may depend cell lining, apparently because they stem from cystic degen-
on the clinical picture, including history, and/or appropri- eration of connective tissue. Coalescence of adjacent cysts
ate serologic studies. Chronic arthritis with pannus forma- can produce multilocular lesions. The cyst contents resem-
tion and permanent deformities develops in roughly 1 in ble synovial fluid, although often there is no communica-
10 patients. tion with the joint space. Ganglions typically are completely
asymptomatic. Classically, these can be treated by “Bible
S U M M A RY therapy”: Whacking the affected area with a large tome
Arthritis usually is sufficient to rupture the cyst, but reaccumulation
may recur. Despite their name, they have no relationship
• Osteoarthritis (degenerative joint disease) is by far the most to ganglia of the nervous system.
common joint disease; it is primarily a degenerative dis-
order of articular cartilage in which matrix breakdown Herniation of synovium through a joint capsule or
exceeds synthesis. Inflammation is secondary. The vast massive enlargement of a bursa can produce a synovial cyst.
majority of cases occur without apparent precipitating A good example is the Baker cyst that occurs in the popliteal
cause except increasing age. Local production of pro- fossa.
inflammatory cytokines and other mediators (IL-1, TNF,
nitric oxide) may contribute to the progression of the Tenosynovial Giant Cell Tumor
joint degeneration.
Tenosynovial giant cell tumor (TGCT) is a catchall term for
• Rheumatoid arthritis (RA) is a chronic autoimmune inflam- several closely related benign neoplasms of synovium.
matory disease that affects mainly the joints, especially Although these lesions previously were considered reac-
small joints, but can affect multiple tissues. RA is caused tive proliferations (hence the earlier designation synovitis),
by an autoimmune response against self-antigen(s) such as they are consistently associated with an acquired (1;2)
citrullinated proteins, which leads to T cell reactions in translocation that fuses the promoter of the collagen 6A3
the joint with production of cytokines that activate phago- gene to the coding sequence of the growth factor M-CSF.
cytes that damage tissues and stimulate proliferation of Classic examples are diffuse tenosynovial giant cell tumor,
synovial cells (synovitis).The cytokine TNF plays a central previously known as pigmented villonodular synovitis
role, and antagonists against TNF are of great clinical (PVNS), involving joint synovium, and localized tenosyno-
benefit. Antibodies may also contribute to the disease. vial giant cell tumor, also known as giant cell tumor of tendon
sheath. Both types typically arise in people in their 20s to
• Gout and pseudogout. Increased circulating levels of uric 40s, without gender predilection.
acid (gout) or calcium pyrophosphate (pseudogout) can
lead to crystal deposition in the joint space. Resulting MORPHOLOGY
inflammatory cell recruitment and activation lead to car-
tilage degradation, fibrosis, and arthritis. Grossly, TGCTs are red-brown to orange-yellow. In the
diffuse variant the joint synovium becomes a contorted mass
• Either direct infection of a joint space (suppurative arthritis) of red-brown folds, finger-like projections, and nodules (Fig.
or cross-reactive immune responses to systemic infec- 20–23, A). By contrast, the localized type is well circum-
tions (e.g., in some cases of Lyme arthritis) can lead to joint scribed and contained. Tumor cells in both lesions resemble
inflammation and injury. synoviocytes, and numerous hemosiderin-laden macro-
phages, osteoclast-like giant cells and hyalinized stromal col-
JOINT TUMORS AND TUMOR-LIKE lagen also are present (Fig. 20–23, B). The tumor cells spread
LESIONS along the surface and infiltrate the subsynovial compartment.
In localized TGCT, the cells grow in a solid nodular aggregate.
Primary neoplasms of joints are uncommon and usually Other typical findings include hemosiderin deposits, foamy
benign; in general, they reflect the cells and tissue types macrophages, multinucleate giant cells, and zones of
(synovial membrane, vessels, fibrous tissue, and cartilage) scarring.
native to the joints. Benign tumors are much more frequent
than their malignant counterparts. The rare malignant neo-
plasms of these structures are discussed below with the
