Chondroblastoma is a rare, benign tumor derived from
chondroblasts. It is found in the epiphysis of long bones, usually of
the lower extremity. The most common site is the distal femur followed
by the proximal femur, proximal humerus and proximal tibia. The tumor
has a preference for males over females and the mean age of presentation
is approximately 20 years old. The tumor may have behavior not normally
associated with benign tumors including pulmonary metastases as well as
local invasion of bone and soft tissue.
Clinically, chondroblastoma presents as pain near a joint without history
of trauma. A secondary synovitis can be induced by the tumor, but pathological
fracture is extremely rare.
The diagnosis of chondroblastoma can usually be made
by radiograph. when the age of the patient and location of the lesion
are considered. The most common site for chondroblastoma is the epiphysis.
The lesion is lytic with well defined margins and can be from 1-6cm in
size. Scalloping or expansion of cortical bone may be present. Fine calcifications,
either punctate or in rings, may be visible. Cysts are present about 20%
of the time and both MRI and CT can define the fluid levels. CT is also
useful for defining the relationship of the tumor to the joint, integrity
of the cortex, and intralesional calcifications. The differential diagnosis
includes enchondroma, central chondrosarcoma and aneurysmal bone cyst.
On gross examination, a chondroblastoma has a lobulated,
round form and is made up of friable, soft, grayish pink tissue that may
be gritty. If present, the cystic fluid is rust or straw-colored.
Chondroblastoma is made up of uniform, polygonal cells that are closely
packed. These primitive cells are derived from the epiphyseal cartilage
plate and have abundant cytoplasm. There is little mitotic activity. A
scant chondroid matrix may be superimposed by a pericellular deposit of
calcification that appears like "chicken-wire".
The rapid proliferation of immature chondrocytes does not create lacunae
or formal cartilage matrix. Giant cells are often present.
Treatment of chondroblastoma is biopsy and curettage
with possible use of adjuvant liquid nitrogen or phenol, or a mechanical
burr. It may be necessary to reconstruct articular surfaces due to subchondral
erosion. Any joint invasion is usually secondary to previous instrumentation.
All pulmonary nodules should be excised.
Bulloughs, Peter, Orthopaedic Pathology (third edition), Times Mirror
International Publishers Limited, London, 1997.
Huvos, Andrew, Bone Tumors: Diagnosis, Treatment and Prognosis, W.B. Saunders,