Chondroblastoma

Background

This is a rare bone tumor which commonly presents within the lower extremities with pain the most common presenting symptom. Symptoms may be present an average of 20 months. Depending upon the location, joint swelling or diminished range of motion may also occur. The cause is unknown and no risk factors are known. The surgical pathologist must distinguish this tumor from other benign bone tumor as well as cartilaginous tumors. A helpful finding is the localization within the epiphyseal cartilage of the long bones.

OUTLINE

Epidemiology

Pathogenesis

Laboratory/Radiologic/Other Diagnostic Testing

Gross Appearance and Clinical Variants

Histopathological Features and Variants

Special Stains/Immunohistochemistry/Electron Microscopy

Differential Diagnosis

Prognosis

Treatment

Commonly Used Terms

Internet Links

EPIDEMIOLOGY CHARACTERIZATION

INCIDENCE/PREVALENCE 1% of all bone tumors

AGE 10-30 years (range 3-73 years)
About 90% of tumors occur in those aged 5-25 years

SEX M:F 2-3:1.

PATHOGENESIS CHARACTERIZATION

Chondroblastoma is an osteoid-forming, but not cartilage-forming neoplasm.

Aigner T, Loos S, Inwards C, Perris R, Perissinotto D, Unni KK, Kirchner T.

Institute of Pathology, University of Erlangen-Nurnberg, Krankenhausstrasse 8-10, D-91054 Erlangen, Germany.
J Pathol. 1999 Dec;189(4):463-9. Abstract quote
Chondroblastoma is defined as a 'benign tumour, characterized by highly cellular and relatively undifferentiated tissue composed of rounded or polygonal chondroblast-like cells' and the 'presence of cartilaginous intercellular matrix' (WHO).

An extensive analysis of the extracellular matrix composition and gene expression pattern of a large series of chondroblastoma cases shows, however, that type II collagen, which is the main component of any cartilage matrix, is not expressed by the neoplastic cells of this tumour entity and is not deposited into the extracellular tumour matrix. Instead, osteoid and fibrous matrix is formed, with its typical biochemical composition. The multifocal expression of aggrecan proteoglycan in most chondroblastomas explains the bluish, pseudo-chondroid appearance of some of the matrix-rich areas of chondroblastomas.

This study did not show chondroid matrix formation or chondroblastic cell differentiation in chondroblastomas, suggesting that chondroblastoma should be classified as a specific bone-forming, rather than cartilage-forming neoplasm.

LABORATORY/RADIOLOGIC/
OTHER TESTS
CHARACTERIZATION

RADIOLOGIC

Chondroblastoma: a clinical and radiological study of 104 cases.

Bloem JL, Mulder JD.

Skeletal Radiol. 1985;14(1):1-9 Abstract quote
The clinical and radiographic findings in 104 patients with chondroblastoma are presented. Pain was an almost constant presenting complaint, often accompanied in the case of para-articular lesions by impaired function of an adjacent joint. The majority (80%) were in long bones with a mean age of presentation of 16 years.

The characteristic radiological image of these lesions was an eccentric radiolucency, having a sharply defined sclerotic margin and containing areas of calcification in approximately a third of cases. They were always related to a growth plate. Nearly half were confined to the affected epiphysis or apophysis itself, but most of the remainder had traversed the growth plate to involve also the adjacent metaphysis. The bones around the knee and the proximal ends of the humerus and femur were the sites of predilection. A minority (20%) affected flat bones and short tubular bones of the hand and foot, with a peculiar affinity for the calcaneus and talus. The mean age of presentation of these was 28 years. The radiological pattern was similar, except for a greater tendency to expand the affected bone.

Complications included the formation of a secondary aneurysmal bone cyst in 16 cases (10 of them in long bones), one malignant chondroblastoma, and one fibrosarcoma developing after radiation of the original chondroblastoma.

GROSS APPEARANCE/
CLINICAL VARIANTS CHARACTERIZATION

GENERAL

Chondroblastoma.

Turcotte RE, Kurt AM, Sim FH, Unni KK, McLeod RA.

Department of Orthopedics, Mayo Clinic, Rochester, MN 55905.
Hum Pathol. 1993 Sep;24(9):944-9. Abstract quote
Chondroblastoma of the bone is a benign tumor that has well-characterized radiographic and histologic features. It tends to affect the epiphyseal ends of long bones in men during the second and third decades of life.

The tumor is located more frequently at other sites in older patients. The treatment of choice is complete curettage with bone grafting, which in our series provided local control in 82% of patients at 2 years' follow-up.

Recurrent tumors usually can be treated in the same manner.

Chondroblastoma of bone.

Kurt AM, Unni KK, Sim FH, McLeod RA.

Department of Orthopedics, Mayo Clinic, Rochester, MN 55905.
Hum Pathol. 1989 Oct;20(10):965-76. Abstract quote
Chondroblastomas are unusual benign lesions of bone. They classically occur at the ends of long bones in young persons. The roentgenographic and histologic features are typical.

We had an opportunity to study a large number of chondroblastomas. Most of the cases came from the consultation file started by Dr D. C. Dahlin at the Mayo Clinic. This method of ascertainment may tend to load our series with unusual and atypical examples. We found some unusual locations, such as the skull and facial bones and the small tubular bones of the hands and feet. We also found some unusual histologic features, such as mitotic activity, necrosis, and cellular atypia.

However, despite the unusual features, the biological behavior of these tumors was that of a benign process with only limited local aggressiveness.

VARIANTS

MULTIFOCAL

Multifocal benign chondroblastomas: report of a case.

Roberts PF, Taylor JG.

Hum Pathol. 1980 May;11(3):296-8. Abstract quote
Benign chondroblastoma is an unusual solitary bone tumor occurring usually in the second decade in a long bone. The tumor is often sited on epiphyseal cartilages. Very few examples of malignant variants have been documented, although local recurrence of benign tumors is not unusual.

We wish to report a patient who developed two chondroblastomas in two distinct anatomical sites (tibia and calcaneus) over the space of seven years, with no clinical or histological features of malignant disease.

SKULL

Chondroblastoma of the skull and facial bones.

Bertoni F, Unni KK, Beabout JW, Harner SG, Dahlin DC.
Am J Clin Pathol. 1987 Jul;88(1):1-9. Abstract quote
A series of 30 chondroblastomas was reviewed: 21 had occurred in the lateral part of the temporal bone, 6 in the mandible, 1 in the parietal bone, and 2 in the region that included the temporal bone and mandible.

Of the 30 patients in the series, 20 were males and 9 were females; the sex of 1 patient was not stated. The ages of 29 patients ranged from 2 years 11 months to 70 years (mean, 43.5 years). Radiologic findings were not suggestive of a specific diagnosis, although the lesions appeared to be benign.

Histologically, most tumors were classic chondroblastomas. However, some showed aneurysmal bone cyst-like areas and nodules of epithelioid cells without chondroid differentiation. Conservative reexcisions were usually curative. Approximately half of the patients had recurrence after curettage.

HISTOLOGICAL TYPES CHARACTERIZATION

GENERAL
Lobulated tumors that consist of grayish-pink soft tissue intermixed with bluish chondroid tissue and calcifications. The lesions may have many hemorrhagic cystic areas.

Sheets of neoplastic mononuclear chondroblasts with eosinophilic cytoplasm and grooved nuclei
Interspersed among the mononuclear cells are osteoclastlike giant cells. The chondroid matrix typically is pink, with the basophilic matrix seen in hyaline cartilage occurring rarely. Others may have a spindle-cell component, which represents either spindle-shaped mononuclear cells or reparative cells of fibroblastic origin. One of the most characteristic findings in the histologic examination of chondroblastomas is linear deposition of calcification surrounding individual chondroblasts, creating a chicken-wire pattern (see Image 6). Calcification may be so extensive that the chondrocytes in the area are not viable. In sections with well-preserved chondroblasts, mitoses may be seen, but atypical mitoses are not present in benign chondroblastoma.

Cystic changes common

Secondary aneurysmal bone cysts in 20-25%

Less frequently are cellular atypia with enlargement and irregularity of chondroblast nuclei, hemosiderin, surrounding cortical and soft tissue permeation, myxoid areas, and vascular invasion

Chondroblastoma: Varied histologic appearance, potential diagnostic pitfalls, and clinicopathologic features associated with local recurrence.

De Silva Mv MC, Reid R.

Ann Diagn Pathol. 2003 Aug;7(4):205-13. Abstract quote
Chondroblastoma is a rare, benign bone tumor. Although it has distinctive clinicopathologic features, its wide morphologic spectrum may pose diagnostic problems.

We present the clinicopathologic features of 42 patients (28 males, 14 females; age range, 8 to 66 years), with emphasis on unusual histologic features, potential diagnostic pitfalls, and factors associated with recurrence. Thirty-four tumors were in long bones, with the most common site being the proximal femur. Unusual histologic features included the presence of atypical, epithelioid, spindle, and foamy cells and necrosis and a diffuse basophilic myxoid matrix. Tumors with focal osteoclast-like giant cell rich areas (n = 11), prominent cystic change (n = 8) and extensive fibromyxoid areas (n = 3) resembled giant cell tumors, aneurysmal bone cysts, and chondromyxoid fibromas, respectively. The diagnosis of referring pathologists was inaccurate in 34% of cases. Six patients (14%) had local recurrence.

The only clinical feature significantly associated with increased risk of local recurrence was duration of symptoms for less than 6 months (log rank P =.003). None of the histologic features was significantly associated with recurrence. These included worrisome features such as cellular atypia, necrosis, and mitoses. None of the patients had metastases.

An increased awareness of the morphologic spectrum of chondroblastomas will enable pathologists to avoid diagnostic pitfalls. We emphasize the need for a combined clinical, radiologic and histologic approach to the diagnosis of chondroblastomas.

VARIANTS

AGGRESSIVE

Histology and biology of metastatic chondroblastoma. Report of a case with a review of the literature.

Kunze E, Graewe T, Peitsch E.

Pathol Res Pract. 1987 Feb;182(1):113-23. Abstract quote
This case report of a metastasizing chondroblastoma with a review of the literature was undertaken to gain a better understanding of the biologic behavior of this exceedingly rare tumor and thus to facilitate its clinical management. The lung was by far the most frequent metastatic site.

Thus, all 7 patients with a proven metastatic chondroblastoma recorded up to now including the present case had developed multiple pulmonary metastases. The interval between the initial diagnosis of the primary and manifestation of lung metastases proved to be long, with a mean of 8.4 years. The average survival time was at least 12.3 years. The mean interval between diagnosis of metastatic disease and death amounted to at least 6.3 years. The histomorphologic features of metastatic chondroblastoma, its local recurrences and of the metastatic lesions differed in no way from conventional chondroblastomas. Because of the lack of cellular criteria of malignancy it is impossible to predict the potential biologic behavior of chondroblastomas, in particular with respect to their ability to metastasize.

However, the presence of tumor emboli in the primary lesion is highly suggestive of a subsequent development of metastatic disease. The delayed induction of hematogenous metastases is best explained by a limited growth potential of the tumor cells. In case of a large primary tumor--especially in flat bones--with soft tissue invasion or in the presence of tumor emboli an aggressive surgical approach is suggested. When lung metastases have developed their surgical removal is recommended to hopefully prolong live expectancy or even to obtain a curative effect.

NON-EPIPHYSEAL TUMORS

Chondroblastoma arising from a nonepiphyseal site.

Brien EW, Mirra JM, Ippolito V.

Department of Orthopedic Surgery and Pathology, Orthopaedic Hospital, Los Angeles, CA 90007, USA.

Skeletal Radiol. 1995 Apr;24(3):220-2. Abstract quote
Chondroblastoma is a rare, benign primary bone tumor usually involving secondary centers of enchondral ossification. The consistent epiphyseal location in the great majority of chondroblastomas signifies that the tumor may arise from an aberrant germ cell of the physeal plate.

This case report describes a chondroblastoma located in a atypical nonphyseal location, namely in the right fourth metatarsal base. Cases such as these imply that the cell of origin may not exclusively be derived form the physeal plate. The clinical-radiographic significance is that historically chondroblastoma is considered an epiphyseal lesion, but rare cases such as the one reported here and those of the skull demonstrate that this is not always a characteristic of these tumors. T

he implication from a histogenetic standpoint is that chondroblastoma may, on rare occasions, occur in an area of an enchondrally formed bone other than adjacent to the physeal plate.

We are presently investigating the histogenetic relationship of the chondroblastoma (CB) of bone to CB of soft tissue, giant-cell tumor of tendon sheath (GCT-TS), pigmented villonodular synovitis (PVNS) and chondroma of tendon sheath (chondroma of soft parts). We now have collected about 15 cases of GCT-TS and PVNS with extensive areas of chondroid and/or cartilage differentiation that cannot be distinguished from CB of bone by histologic or electron microscopic features alone. From these interesting observations we are developing the histogenetic concept that all of these lesions are interrelated to multipotential mesenchymal and/or synovial cells of the tendon sheath.

SPECIAL STAINS/IMMUNOPEROXIDASE/
OTHER CHARACTERIZATION

SPECIAL STAINS

IMMUNOPEROXIDASE

Chondroblastoma of bone. A clinical, radiological, light and immunohistochemical study.

Edel G, Ueda Y, Nakanishi J, Brinker KH, Roessner A, Blasius S, Vestring T, Muller-Miny H, Erlemann R, Wuisman P.

Gerhard-Domagk-Institute of Pathology, University of Munster, Federal Republic of Germany.

Virchows Arch A Pathol Anat Histopathol. 1992;421(4):355-66. Abstract quote
The clinical and morphological findings of 53 chondroblastomas in the files of the Bone Tumour Registry of Westphalia are presented.

The mean age of all patients was 19.2 years. The male-to-female ratio was 1.5:1. Forty-two of the tumours (79.8%) were located in the long tubular bones and short tubular bones of the hands and were closely related to the growth plate. Six cases (11.3%) were found in the flat bones, 4 cases (7.5%) in the tarsal bones and 1 case (1.9%) in the craniofacial bones.

The characteristic radiological feature of 44 investigated lesions was a mostly eccentric radiolucency with a geographic pattern of bone destruction and matrix calcifications. Periosteal reaction was evident in 9% of the cases. Most tumours demonstrate the typical morphological features of chondroblastoma, but 3 cases resembled a giant cell tumour. In 2 cases a haemangiopericytoma-like growth pattern was observed. Nine of the tumours had an aneurysmal bone cyst-like component. Vascular invasion was seen in 1 case.

Immunohistochemically most cells in 30 of the cases and fetal chondroblasts in 3 cases were strongly positive with vimentin and S-100 protein. Collagen type II was positive in the chondroid matrix of the tumours and in fetal cartilage tissue; collagen type VI was present focally around individual tumour cells and was always seen in the chondroid matrix of the lesions and in fetal cartilage. These findings support the cartilaginous nature of these tumours. In paraffin sections, 46.6% of the cases revealed a distinct positive reaction of some tumour cells with the monoclonal cytokeratin antibody KL1 (molecular weight 55-57 kDa). Only 4 of them demonstrated a coexpression with the other monoclonal cytokeratin antibody CK (clone MNF 116, molecular weight 45-56.5 kDa). In paraffin sections all fetal chondroblasts were negative with both cytokeratin antibodies. Frozen sections of 3 tumours showed a strong positive reaction with both cytokeratin antibodies in many chondroblasts, indicating an "aberrant" cytokeratin expression. Osteoclast-like giant cells stained positive with leucocyte-common antigen (LCA) and with the macrophage-associated antibody KP1, but were negative with the other macrophage-associated antibody MAC 387.

Recurrence rate was 10.7%. The clinical course of all tumours was benign.

ELECTRON MICROSCOPY

DIFFERENTIAL DIAGNOSIS KEY DIFFERENTIATING FEATURES

CHONDROMA OF SOFT TISSUE

Chondroblastoma-like chondroma of soft tissue: an underrecognized variant and its differential diagnosis.

Cates JM, Rosenberg AE, O'Connell JX, Nielsen GP.

James Homer Wright Pathology Laboratories, Massachusetts General Hospital, Harvard Medical School Boston, Massachusetts, USA.
Am J Surg Pathol. 2001 May;25(5):661-6. Abstract quote
Soft-tissue chondromas are usually composed entirely of mature hyaline cartilage. Infrequently, however, they may exhibit morphologic features that result in diagnostic difficulty.

The authors report a series of eight hypercellular soft-tissue chondromas composed of enlarged chondrocytes within a variable amount of chondroid matrix that often demonstrated delicate calcifications and contained numerous osteoclast-like multinucleated giant cells.

This histologic appearance closely resembles that of chondroblastoma of bone. However, its extraosseous location, dense cellularity, and poorly formed cartilage can cause confusion with more aggressive chondroid neoplasms of soft tissue.

The clinicopathologic features of these chondroblastoma-like chondromas are discussed, emphasizing the characteristics that facilitate their accurate identification.

CHONDROMYXOID FIBROMA

Chondromyxoid fibroma of bone: a clinicopathologic review of 278 cases.

Wu CT, Inwards CY, O'Laughlin S, Rock MG, Beabout JW, Unni KK.

Department of Orthopedics, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.

Hum Pathol. 1998 May;29(5):438-46. Abstract quote
In a study of the clinical, radiographic, and pathological features of chondromyxoid fibroma, the tumor was slightly more common in men, usually in the second decade of life. Almost half of the tumors involved the long bones, although the ilium and the small bones were also common sites.

Roentgenograms showed a sharply marginated, lobulated, lucent defect in the metaphysis. The tumor involved the medullary bone in an eccentric fashion, and the cortex was thinned and expanded. Periosteal reaction and soft tissue extension were uncommon. Mineralization was identified in 13% of the lesions.

Histologically, the tumors were almost always arranged in lobules, which were prominent (macrolobular) or somewhat indistinct (microlobular). The tumor cells were spindle-shaped or stellate and arranged in a myxoid matrix. Calcification was seen in more than one third of the cases but was rarely prominent. Hyaline cartilage and chondroblastoma-like areas were not uncommon. Approximately 18% of tumors showed bizarre nuclei. Permeation of bony trabeculae was uncommon.

Treatment was conservative surgical removal; approximately one fourth of the patients had recurrence.

GIANT CELL TUMOR OF BONE

OSSIFYING FIBROMYXOID TUMOR

OSTEOBLASTOMA

PROGNOSIS CHARACTERIZATION

RECURRENCES

Metastatic chondroblastoma. Report of a fatal case with a review of the literature on atypical, aggressive, and malignant chondroblastoma.

Kyriakos M, Land VJ, Penning HL, Parker SG.
Cancer. 1985 Apr 15;55(8):1770-89. Abstract quote
A boy with metastatic and fatal chondroblastoma is presented. Unlike previously published examples of metastatic chondroblastoma, these metastases developed before any operative manipulation of the primary tumor.

The histologic characteristics of the primary, metastatic, and locally recurrent tumors were those of a conventional chondroblastoma. A review of published cases of atypical, aggressive, and malignant chondroblastoma is presented with current follow-up information. Although some metastatic chondroblastomas may result from operative manipulation of the primary tumor and are clinically benign, other histologically benign chondroblastomas exist that are capable of pursuing a malignant course.

The authors designate these as malignant chondroblastomas. No histologic criteria exist for the separation of these tumors.

Aggressive chondroblastoma. Report of a case with multiple bone and soft tissue involvement.

Hull MT, Gonzalez--Crussi F, DeRosa GP, Graul RS.
Clin Orthop. 1977 Jul-Aug;(126):261-5. Abstract quote
A 14-year-old male had a recurrent chondroblastoma in his right talus which involved the right calcaneus and the soft tissue of that ankle. While the initial lesion had a typical, benign appearance, the recurrent lesion and the soft tissue nodules showed a significantly elevated mitotic rate.

Although some extraosseous involvement by chondroblastomas may be secondary to soft tissue or hematogeneous seeding at the time of surgery, and aggressive variant of chondroblastoma appears to exist. Previous reports of these aggressive cases show a poor correlation between histologic appearance and biologic behavior.

When objective quantitation of cytologic features such as mitotic rate are made, we believe that these features may serve as a marker for identification of those cases of chondroblastoma which have a propensity for aggressive behavior.

TREATMENT CHARACTERIZATION

GENERAL Curettage, with or without autograft or allograft bone grafting

Henry JB. Clinical Diagnosis and Management by Laboratory Methods. Twentieth Edition. WB Saunders. 2001.
Rosai J. Ackerman's Surgical Pathology. Eight Edition. Mosby 1996.
Sternberg S. Diagnostic Surgical Pathology. Third Edition. Lipincott Williams and Wilkins 1999.
Robbins Pathologic Basis of Disease. Sixth Edition. WB Saunders 1999.
DeMay RM. The Art and Science of Cytopathology. Volume 1 and 2. ASCP Press. 1996.
Weedon D. Weedon's Skin Pathology Second Edition. Churchill Livingstone. 2002
Fitzpatrick's Dermatology in General Medicine. 5th Edition. McGraw-Hill. 1999.
Weiss SW and Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors. Fourth Edition. Mosby 2001.

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GROSS APPEARANCE/ CLINICAL VARIANTS	CHARACTERIZATION
GENERAL
Chondroblastoma. Turcotte RE, Kurt AM, Sim FH, Unni KK, McLeod RA. Department of Orthopedics, Mayo Clinic, Rochester, MN 55905.	Hum Pathol. 1993 Sep;24(9):944-9. Abstract quote Chondroblastoma of the bone is a benign tumor that has well-characterized radiographic and histologic features. It tends to affect the epiphyseal ends of long bones in men during the second and third decades of life. The tumor is located more frequently at other sites in older patients. The treatment of choice is complete curettage with bone grafting, which in our series provided local control in 82% of patients at 2 years' follow-up. Recurrent tumors usually can be treated in the same manner.
Chondroblastoma of bone. Kurt AM, Unni KK, Sim FH, McLeod RA. Department of Orthopedics, Mayo Clinic, Rochester, MN 55905.	Hum Pathol. 1989 Oct;20(10):965-76. Abstract quote Chondroblastomas are unusual benign lesions of bone. They classically occur at the ends of long bones in young persons. The roentgenographic and histologic features are typical. We had an opportunity to study a large number of chondroblastomas. Most of the cases came from the consultation file started by Dr D. C. Dahlin at the Mayo Clinic. This method of ascertainment may tend to load our series with unusual and atypical examples. We found some unusual locations, such as the skull and facial bones and the small tubular bones of the hands and feet. We also found some unusual histologic features, such as mitotic activity, necrosis, and cellular atypia. However, despite the unusual features, the biological behavior of these tumors was that of a benign process with only limited local aggressiveness.
VARIANTS
MULTIFOCAL
Multifocal benign chondroblastomas: report of a case. Roberts PF, Taylor JG.	Hum Pathol. 1980 May;11(3):296-8. Abstract quote Benign chondroblastoma is an unusual solitary bone tumor occurring usually in the second decade in a long bone. The tumor is often sited on epiphyseal cartilages. Very few examples of malignant variants have been documented, although local recurrence of benign tumors is not unusual. We wish to report a patient who developed two chondroblastomas in two distinct anatomical sites (tibia and calcaneus) over the space of seven years, with no clinical or histological features of malignant disease.
SKULL
Chondroblastoma of the skull and facial bones. Bertoni F, Unni KK, Beabout JW, Harner SG, Dahlin DC.	Am J Clin Pathol. 1987 Jul;88(1):1-9. Abstract quote A series of 30 chondroblastomas was reviewed: 21 had occurred in the lateral part of the temporal bone, 6 in the mandible, 1 in the parietal bone, and 2 in the region that included the temporal bone and mandible. Of the 30 patients in the series, 20 were males and 9 were females; the sex of 1 patient was not stated. The ages of 29 patients ranged from 2 years 11 months to 70 years (mean, 43.5 years). Radiologic findings were not suggestive of a specific diagnosis, although the lesions appeared to be benign. Histologically, most tumors were classic chondroblastomas. However, some showed aneurysmal bone cyst-like areas and nodules of epithelioid cells without chondroid differentiation. Conservative reexcisions were usually curative. Approximately half of the patients had recurrence after curettage.

HISTOLOGICAL TYPES	CHARACTERIZATION
GENERAL	Lobulated tumors that consist of grayish-pink soft tissue intermixed with bluish chondroid tissue and calcifications. The lesions may have many hemorrhagic cystic areas. Sheets of neoplastic mononuclear chondroblasts with eosinophilic cytoplasm and grooved nuclei Interspersed among the mononuclear cells are osteoclastlike giant cells. The chondroid matrix typically is pink, with the basophilic matrix seen in hyaline cartilage occurring rarely. Others may have a spindle-cell component, which represents either spindle-shaped mononuclear cells or reparative cells of fibroblastic origin. One of the most characteristic findings in the histologic examination of chondroblastomas is linear deposition of calcification surrounding individual chondroblasts, creating a chicken-wire pattern (see Image 6). Calcification may be so extensive that the chondrocytes in the area are not viable. In sections with well-preserved chondroblasts, mitoses may be seen, but atypical mitoses are not present in benign chondroblastoma. Cystic changes common Secondary aneurysmal bone cysts in 20-25% Less frequently are cellular atypia with enlargement and irregularity of chondroblast nuclei, hemosiderin, surrounding cortical and soft tissue permeation, myxoid areas, and vascular invasion
Chondroblastoma: Varied histologic appearance, potential diagnostic pitfalls, and clinicopathologic features associated with local recurrence. De Silva Mv MC, Reid R.	Ann Diagn Pathol. 2003 Aug;7(4):205-13. Abstract quote Chondroblastoma is a rare, benign bone tumor. Although it has distinctive clinicopathologic features, its wide morphologic spectrum may pose diagnostic problems. We present the clinicopathologic features of 42 patients (28 males, 14 females; age range, 8 to 66 years), with emphasis on unusual histologic features, potential diagnostic pitfalls, and factors associated with recurrence. Thirty-four tumors were in long bones, with the most common site being the proximal femur. Unusual histologic features included the presence of atypical, epithelioid, spindle, and foamy cells and necrosis and a diffuse basophilic myxoid matrix. Tumors with focal osteoclast-like giant cell rich areas (n = 11), prominent cystic change (n = 8) and extensive fibromyxoid areas (n = 3) resembled giant cell tumors, aneurysmal bone cysts, and chondromyxoid fibromas, respectively. The diagnosis of referring pathologists was inaccurate in 34% of cases. Six patients (14%) had local recurrence. The only clinical feature significantly associated with increased risk of local recurrence was duration of symptoms for less than 6 months (log rank P =.003). None of the histologic features was significantly associated with recurrence. These included worrisome features such as cellular atypia, necrosis, and mitoses. None of the patients had metastases. An increased awareness of the morphologic spectrum of chondroblastomas will enable pathologists to avoid diagnostic pitfalls. We emphasize the need for a combined clinical, radiologic and histologic approach to the diagnosis of chondroblastomas.
VARIANTS
AGGRESSIVE
Histology and biology of metastatic chondroblastoma. Report of a case with a review of the literature. Kunze E, Graewe T, Peitsch E.	Pathol Res Pract. 1987 Feb;182(1):113-23. Abstract quote This case report of a metastasizing chondroblastoma with a review of the literature was undertaken to gain a better understanding of the biologic behavior of this exceedingly rare tumor and thus to facilitate its clinical management. The lung was by far the most frequent metastatic site. Thus, all 7 patients with a proven metastatic chondroblastoma recorded up to now including the present case had developed multiple pulmonary metastases. The interval between the initial diagnosis of the primary and manifestation of lung metastases proved to be long, with a mean of 8.4 years. The average survival time was at least 12.3 years. The mean interval between diagnosis of metastatic disease and death amounted to at least 6.3 years. The histomorphologic features of metastatic chondroblastoma, its local recurrences and of the metastatic lesions differed in no way from conventional chondroblastomas. Because of the lack of cellular criteria of malignancy it is impossible to predict the potential biologic behavior of chondroblastomas, in particular with respect to their ability to metastasize. However, the presence of tumor emboli in the primary lesion is highly suggestive of a subsequent development of metastatic disease. The delayed induction of hematogenous metastases is best explained by a limited growth potential of the tumor cells. In case of a large primary tumor--especially in flat bones--with soft tissue invasion or in the presence of tumor emboli an aggressive surgical approach is suggested. When lung metastases have developed their surgical removal is recommended to hopefully prolong live expectancy or even to obtain a curative effect.
NON-EPIPHYSEAL TUMORS
Chondroblastoma arising from a nonepiphyseal site. Brien EW, Mirra JM, Ippolito V. Department of Orthopedic Surgery and Pathology, Orthopaedic Hospital, Los Angeles, CA 90007, USA.	Skeletal Radiol. 1995 Apr;24(3):220-2. Abstract quote Chondroblastoma is a rare, benign primary bone tumor usually involving secondary centers of enchondral ossification. The consistent epiphyseal location in the great majority of chondroblastomas signifies that the tumor may arise from an aberrant germ cell of the physeal plate. This case report describes a chondroblastoma located in a atypical nonphyseal location, namely in the right fourth metatarsal base. Cases such as these imply that the cell of origin may not exclusively be derived form the physeal plate. The clinical-radiographic significance is that historically chondroblastoma is considered an epiphyseal lesion, but rare cases such as the one reported here and those of the skull demonstrate that this is not always a characteristic of these tumors. T he implication from a histogenetic standpoint is that chondroblastoma may, on rare occasions, occur in an area of an enchondrally formed bone other than adjacent to the physeal plate. We are presently investigating the histogenetic relationship of the chondroblastoma (CB) of bone to CB of soft tissue, giant-cell tumor of tendon sheath (GCT-TS), pigmented villonodular synovitis (PVNS) and chondroma of tendon sheath (chondroma of soft parts). We now have collected about 15 cases of GCT-TS and PVNS with extensive areas of chondroid and/or cartilage differentiation that cannot be distinguished from CB of bone by histologic or electron microscopic features alone. From these interesting observations we are developing the histogenetic concept that all of these lesions are interrelated to multipotential mesenchymal and/or synovial cells of the tendon sheath.

PROGNOSIS	CHARACTERIZATION
RECURRENCES
Metastatic chondroblastoma. Report of a fatal case with a review of the literature on atypical, aggressive, and malignant chondroblastoma. Kyriakos M, Land VJ, Penning HL, Parker SG.	Cancer. 1985 Apr 15;55(8):1770-89. Abstract quote A boy with metastatic and fatal chondroblastoma is presented. Unlike previously published examples of metastatic chondroblastoma, these metastases developed before any operative manipulation of the primary tumor. The histologic characteristics of the primary, metastatic, and locally recurrent tumors were those of a conventional chondroblastoma. A review of published cases of atypical, aggressive, and malignant chondroblastoma is presented with current follow-up information. Although some metastatic chondroblastomas may result from operative manipulation of the primary tumor and are clinically benign, other histologically benign chondroblastomas exist that are capable of pursuing a malignant course. The authors designate these as malignant chondroblastomas. No histologic criteria exist for the separation of these tumors.
Aggressive chondroblastoma. Report of a case with multiple bone and soft tissue involvement. Hull MT, Gonzalez--Crussi F, DeRosa GP, Graul RS.	Clin Orthop. 1977 Jul-Aug;(126):261-5. Abstract quote A 14-year-old male had a recurrent chondroblastoma in his right talus which involved the right calcaneus and the soft tissue of that ankle. While the initial lesion had a typical, benign appearance, the recurrent lesion and the soft tissue nodules showed a significantly elevated mitotic rate. Although some extraosseous involvement by chondroblastomas may be secondary to soft tissue or hematogeneous seeding at the time of surgery, and aggressive variant of chondroblastoma appears to exist. Previous reports of these aggressive cases show a poor correlation between histologic appearance and biologic behavior. When objective quantitation of cytologic features such as mitotic rate are made, we believe that these features may serve as a marker for identification of those cases of chondroblastoma which have a propensity for aggressive behavior.

Epidemiology
Pathogenesis
Laboratory/Radiologic/Other Diagnostic Testing
Gross Appearance and Clinical Variants
Histopathological Features and Variants
Special Stains/Immunohistochemistry/Electron Microscopy
Differential Diagnosis
Prognosis
Treatment
Commonly Used Terms
Internet Links

EPIDEMIOLOGY	CHARACTERIZATION
INCIDENCE/PREVALENCE	1% of all bone tumors
AGE	10-30 years (range 3-73 years) About 90% of tumors occur in those aged 5-25 years
SEX	M:F 2-3:1.

SPECIAL STAINS/IMMUNOPEROXIDASE/ OTHER	CHARACTERIZATION
SPECIAL STAINS
IMMUNOPEROXIDASE
Chondroblastoma of bone. A clinical, radiological, light and immunohistochemical study. Edel G, Ueda Y, Nakanishi J, Brinker KH, Roessner A, Blasius S, Vestring T, Muller-Miny H, Erlemann R, Wuisman P. Gerhard-Domagk-Institute of Pathology, University of Munster, Federal Republic of Germany.	Virchows Arch A Pathol Anat Histopathol. 1992;421(4):355-66. Abstract quote The clinical and morphological findings of 53 chondroblastomas in the files of the Bone Tumour Registry of Westphalia are presented. The mean age of all patients was 19.2 years. The male-to-female ratio was 1.5:1. Forty-two of the tumours (79.8%) were located in the long tubular bones and short tubular bones of the hands and were closely related to the growth plate. Six cases (11.3%) were found in the flat bones, 4 cases (7.5%) in the tarsal bones and 1 case (1.9%) in the craniofacial bones. The characteristic radiological feature of 44 investigated lesions was a mostly eccentric radiolucency with a geographic pattern of bone destruction and matrix calcifications. Periosteal reaction was evident in 9% of the cases. Most tumours demonstrate the typical morphological features of chondroblastoma, but 3 cases resembled a giant cell tumour. In 2 cases a haemangiopericytoma-like growth pattern was observed. Nine of the tumours had an aneurysmal bone cyst-like component. Vascular invasion was seen in 1 case. Immunohistochemically most cells in 30 of the cases and fetal chondroblasts in 3 cases were strongly positive with vimentin and S-100 protein. Collagen type II was positive in the chondroid matrix of the tumours and in fetal cartilage tissue; collagen type VI was present focally around individual tumour cells and was always seen in the chondroid matrix of the lesions and in fetal cartilage. These findings support the cartilaginous nature of these tumours. In paraffin sections, 46.6% of the cases revealed a distinct positive reaction of some tumour cells with the monoclonal cytokeratin antibody KL1 (molecular weight 55-57 kDa). Only 4 of them demonstrated a coexpression with the other monoclonal cytokeratin antibody CK (clone MNF 116, molecular weight 45-56.5 kDa). In paraffin sections all fetal chondroblasts were negative with both cytokeratin antibodies. Frozen sections of 3 tumours showed a strong positive reaction with both cytokeratin antibodies in many chondroblasts, indicating an "aberrant" cytokeratin expression. Osteoclast-like giant cells stained positive with leucocyte-common antigen (LCA) and with the macrophage-associated antibody KP1, but were negative with the other macrophage-associated antibody MAC 387. Recurrence rate was 10.7%. The clinical course of all tumours was benign.
ELECTRON MICROSCOPY

DIFFERENTIAL DIAGNOSIS	KEY DIFFERENTIATING FEATURES
CHONDROMA OF SOFT TISSUE
Chondroblastoma-like chondroma of soft tissue: an underrecognized variant and its differential diagnosis. Cates JM, Rosenberg AE, O'Connell JX, Nielsen GP. James Homer Wright Pathology Laboratories, Massachusetts General Hospital, Harvard Medical School Boston, Massachusetts, USA.	Am J Surg Pathol. 2001 May;25(5):661-6. Abstract quote Soft-tissue chondromas are usually composed entirely of mature hyaline cartilage. Infrequently, however, they may exhibit morphologic features that result in diagnostic difficulty. The authors report a series of eight hypercellular soft-tissue chondromas composed of enlarged chondrocytes within a variable amount of chondroid matrix that often demonstrated delicate calcifications and contained numerous osteoclast-like multinucleated giant cells. This histologic appearance closely resembles that of chondroblastoma of bone. However, its extraosseous location, dense cellularity, and poorly formed cartilage can cause confusion with more aggressive chondroid neoplasms of soft tissue. The clinicopathologic features of these chondroblastoma-like chondromas are discussed, emphasizing the characteristics that facilitate their accurate identification.
CHONDROMYXOID FIBROMA
Chondromyxoid fibroma of bone: a clinicopathologic review of 278 cases. Wu CT, Inwards CY, O'Laughlin S, Rock MG, Beabout JW, Unni KK. Department of Orthopedics, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.	Hum Pathol. 1998 May;29(5):438-46. Abstract quote In a study of the clinical, radiographic, and pathological features of chondromyxoid fibroma, the tumor was slightly more common in men, usually in the second decade of life. Almost half of the tumors involved the long bones, although the ilium and the small bones were also common sites. Roentgenograms showed a sharply marginated, lobulated, lucent defect in the metaphysis. The tumor involved the medullary bone in an eccentric fashion, and the cortex was thinned and expanded. Periosteal reaction and soft tissue extension were uncommon. Mineralization was identified in 13% of the lesions. Histologically, the tumors were almost always arranged in lobules, which were prominent (macrolobular) or somewhat indistinct (microlobular). The tumor cells were spindle-shaped or stellate and arranged in a myxoid matrix. Calcification was seen in more than one third of the cases but was rarely prominent. Hyaline cartilage and chondroblastoma-like areas were not uncommon. Approximately 18% of tumors showed bizarre nuclei. Permeation of bony trabeculae was uncommon. Treatment was conservative surgical removal; approximately one fourth of the patients had recurrence.
GIANT CELL TUMOR OF BONE
OSSIFYING FIBROMYXOID TUMOR
OSTEOBLASTOMA