Bursa Formation and Synovial Chondrometaplasia Associated with Osteochondromas

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1 Bursa Formation and Synovial Chondrometaplasia Associated with Osteochondromas ANITA M. BORGES, M. D., ANDREW G. HUVOS, M. D., AND JULIUS SMITH, M. D. Borges, Anita M., Huvos, Andrew G., and Smith, Julius: Bursa formation and synovial chondrometaplasia associated with osteochondromas. Am J Clin Pathol 75: , Two adult patients who had synovial chondromatosis occurring within bursae formed around osteochondromas are described. In spite of marked cellular atypia of the cartilage cells, the clinical course was unremarkable, pointing out the discrepancy between histologic changes and subsequent behavior in this condition. Histologic features, in addition, are not always helpful in distinguishing primary from secondary chondrometaplasia. (Key words: Osteochondroma; Synovial chondrometaplasia.) SYNOVIAL CHONDROMETAPLASIA affecting the extraarticular tissues is a rare condition. When it occurs, it usually affects the tendosynovial sheaths of the hands or feet. 2,7 We have recently encountered two adult patients who had synovial chondromatosis occurring within bursae formed around osteochondromas. In addition to the rarity of the condition, these cases presented certain interesting radiographic and pathologic aspects while highlighting pathogenesis. Reports of Two Cases Case I Case 2 A 26-year-old white man in otherwise good health was admitted with a six-month history of pain and stiffness in the muscles of the right thigh on awaking. The pain improved as the day progressed. Clinical examination revealed a hard mass deeply situated in the soft tissue of the posterior aspect of the hip. It was nontende'r, and a full range of movement could be elicited. Results of a neurologic examination were negative. No findings of note were present on routine biochemical and hematologic workup. Radiologic examination of the lumbosacral spine and pelvis revealed a dense, sessile 10-cm bony mass arising from the medial portion of the neck of the right femur (Fig. 1). In addition there were two other bony masses in relation to the inferior pubic ramus. The findings were interpreted as being benign. The radiologic diagnoses considered were multiple ossified osteochondromata and/or myositis ossificans. At surgery a large osteochondroma surrounded by a bursa was found. An oval multinodular bony area embedded in the synovial lining of the bursa was recognized. The osteochondroma and its bursa were excised. Pathologic Examination. Received for histologic examination were: (1) portions of the synovial lining of the bursa; (2) two oval Received July 7, 1980; received revised manuscript and accepted for publication November 24, Address reprint requests to Dr. Huvos: Department of Pathology, Memorial Hospital for Cancer and Allied Diseases, New York, New York Departments of Pathology and Diagnostic Radiology, Memorial Hospital for Cancer and Allied Diseases, New York, New York multinodular masses of bony tissue, the larger measuring 5.2 x 3.5 x 2.7 cm. These had a soft cartilaginous center and thin bony cortex around it. They were completely separate from the main mass; (3) a bony excrescence with an irregular surface having a gray-white glistening cartilaginous appearance. The lesion measured 10.5 x 8 x 6 cm. On section, the core of the specimen was made up of sclerotic bone, while the periphery consisted of irregular masses of translucent cartilage containing dense foci of ossified material. Histologic examination confirmed the presence of a synovium-lined bursa and an osteochondroma with regular, orderly endochondral ossification of the cartilaginous cap. Atypia of the cartilage cells was not present. The bony masses, embedded in the synovial lining and submitted separately, showed the typical features of synovial chondrometaplasia with lobules of calcifying cartilage progressing in an orderly manner to bone formation (Fig. 2). The detached osteochondral fragments of the osteochondroma that initiated the chondrometaplasia were still evident in some sections. Follow-up. The patient is well with no recurrence of disease three and a half years later. A 56-year-old physician's wife had an 18-year history of a left scapular lesion that had been radiologically diagnosed as an osteochondroma. It had been observed by periodic radiologic examinations. Two years before surgical intervention, the lesion was noticed to be increasing in size. The patient had no symptom other than intermittent radicular numbness in both arms. The mass was not palpable. The only physical sign of note was marked crepitus elicited by movement of the left scapula. Radiologic examination revealed an anteriorly placed bony lesion arising from the medial border of the left scapula in relation to the third and fourth ribs (Fig. 3). Multiple calcific foci separate from the mass were similarly seen, and an anomalous synostosis of the fifth and sixth ribs was also detected. At surgery an osteochondroma arising from the medial border of the scapula was found. A bursa surrounded the bony lesion and lay between it and the rib cage. Several hard nodules were found embedded within the synovial membrane. A partial scapulectomy and excision of the bursa surrounding the osteochondroma was performed. Pathologic Examination. Received for histologic examination was a left partial scapulectomy specimen that consisted of the medial portion of the left scapula with the surrounding skeletal muscle and fibroadipose tissue. On the posterior surface of the scapula near the medial edge was a mushroom-shaped flat-topped excrescence with a thin cartilaginous cap. The surface of the lesion measured 3 cm in diameter, and the stalk was 1.9 cm high. Surrounding the bony ex /81/0500/0648 $00.80 American Society of Clinical Pathologists 648

2 Vol. 75. No. 5 SYNOVIAL CHONDROMATOSIS IN OSTEOCHONDROMA a»i*i.\ 649 (^ Fic. 1. (Upper). Case I. Radiograph of the femur on the left compared with a photograph of the surgical specimens on the right that have been superimposed on an anatomic drawing of bones of the region. Notice the radiologic likeness to myositis ossificans or multiple osteochondromata. Fic. 2. (Lower). Case I. Orderly endochondral ossification in one of the chondrometaplastic lesions in the synovium. Hematoxylin and eosin. x400.

3 650 BORGES, HUVOS, AND SMITH A.J.C.P. May 1981 FIG. 3. Case 2. Radiograph of the left chest showing the irregularly calcified mass with surrounding areas of calcification lying posterior to the ribs and probably arising from the scapula. crescence was a thick-walled membrane-lined sac in which multiple osteocartilaginous nodules and plaques were embedded. This bursa was not lined by synovium and was merely connective tissue surrounding the osteochondroma. A ringlike nodular plaque of osteochondral tissue surrounded the base of the stalk, forming what may be termed a "pseudoarthrosis." Histologically, the osteochondroma had an almost totally eburnated cartilaginous cap (Fig. 4). The synovial lesions showed metaplastic cartilage with areas of ossification (Fig. 5). Most areas revealed an orderly progression of endochondral ossification from fibrocartilage through hyaline cartilage of bone. However, areas of crowding of cartilage cells with cellular atypia and hyperchromatism were seen (Fig. 6). An occasional multinucleate cartilage cell was also present. These changes were alarming and raised the question of malignant change (Fig. 7). Discussion A recognized complication of osteochondromas is the development of a bursa around the cartilaginous cap This is particularly true of large exostoses and exostoses in sites where friction with surrounding unyielding structures is present. McWilliams 1 "' and El- Khoury and Bassett :i each reported a case of subcapsu-

4 Vol. 75 No. 5 SYNOVIAL CHONDROMATOSIS IN OSTEOCHONDROMA 651 \V Fie. 4. Case 2. A whole-mouth section of the osteochondroma, which has a flat-topped mushroom shape. The cartilaginous cap is almost totally eburnated. lar exostosis with adventitious bursa formation quite similar to our Case 2. However, neither of their cases showed synovial chondrometaplasia of the bursal lining. Interestingly, the patient reported by El-Khoury and Bassett 3 also had demonstrable crepitus on scapulothoracic manipulation. The occurrence of osseocartilaginous metaplasia in the synovial lining of bursae around exostoses is distinctly uncommon. Dahlin,' in a large series of osteochondromas from the Mayo Clinic, reported three cases involving loose bodies in the accompanying bursae. Apart from the rarity of these lesions, the two cases were of clinicopathologic interest because the clinical and radiologic appearances of both cases and the histologic picture in Case 2 could be mistaken for a more serious condition, chondrosarcoma. In an adult, pain in the region of an osteochondroma, especially if associated with abnormal calcification in the adjacent tissues, should be viewed with alarm. In Case 1, although no malignant diagnosis was entertained preoperatively, the correct diagnosis was not considered in the differential diagnoses, testifying to the rarity of the lesion. In Case 2, the radiologic appearances of the osteochondroma had been followed for 18 years, and a recent increase in size and new calcifications were noticed. These were considered to be ominous signs. Radiologists should consider the possibility of bursa formation with osteocartilaginous metaplasia when irregularities in the cartilage cap or new calcifications appear around an osteochondroma. El-Khoury and Bassett 3 advocate the use of ultrasound to diagnose and outline the bursa. Pathologically, Case 1 is a typical example of secondary synovial osteochondromatosis, where synovial chondrometaplasia occurred around a recognizable osteochondral fragment. The metaplastic cartilaginous areas showed chondrocytes of quiescent, uniform appearance, with orderly maturation to bone in some areas. In Case 2, however, the disorder occurred in an older individual (56 years), and the cartilage in the synovial nodules had a disturbing histologic appearance. Cellu-

5 FIG. 5. Case 2. One of the synovial chondromas with intralesional ossification. -%.**; '-' r : **.-- FIG. 6. Case 2. The synovium-lined fibrocartilage matures into hyaline cartilage and then to bone in a typical synovial chondroma. Hematoxylin and eosin. (x64).

6 Vol. 75 No. 5 SYNOVIAL CHONDROMATOSIS IN OSTEOCHONDROMA 653 Fic. 7. Case 2. Cellular crowding, pleomorphism, and irregularity in the synovial chondrometaplasia. Areas such as these may be mistaken for malignant change. Hematoxylin and eosin. (x 160). larity was increased; focal cellular atypia and cell crowding were present. Areas of disorderly arrangement of the cells were also seen. These features are those usually considered criteria for malignant transformation of a cartilaginous tumor. However, we are in agreement with Smith, 8 Jaffe,4 and Lichtenstein and Goldman 5 that occasional microscopic fields showing hyperchromatism, atypical cells, and increased cellularity cannot be used as criteria for malignant change in synovial chondrometaplasia. True malignant change in synovial chondrometaplasia is very rare. Villacin and associates 10 in a recent paper suggested that atypical histologic features were of help in distinguising cases of primary and secondary chondrometaplasia; i.e., atypical features were present in the former and not in the latter condition. We feel that although in most instances this is true, a case like ours demonstrates that atypical changes can also occur in chondrometaplasia following a recognized initiating factor, which in this instance was eburnation of the cartilage cap of the osteochondroma by friction against the rib cage. References 1. Dahlin DC: Bone tumors. Springfield, Illinois, Thomas, 1978, p Dahlin DC, Salvador AH: Cartilaginous tumors of the soft tissues of the hands and feet. Mayo Clin Proc 49: El-Khoury GY, Bassett GS: Symptomatic bursa formation with osteochondromas. AJR 133: , Jaffe HL: Tumors and tumorous conditions of the bones and joints. Philadelphia, Lea & Febiger, 1958, pp Lichtenstein L, Goldman RL: Cartilage tumors in soft tissues, particularly in the hand and foot. Cancer 17: , McWilliams CA: Subscapular exostosis with adventitious bursa. JAMA 63: , Sim FH, Dahlin DC, Ivins JC: Extraarticular synovial chondromatosis. J Bone Joint Surg [Am] 59: , Smith CF: Synovial chondromatosis. Orthop Clin North Am 8: , Smithius T: Exostosis bursata. J Bone Joint Surg [Br] 46:544545, Villacin AB, Brigham LN, Bullough PG: Primary and secondary synovial chondrometaplasia. Hum Pathol 10: , 1979