|
DIAGNOSIS:
1. First carpometacarpal joint arthrosis with laxity and/or lateral subluxation. This is accompanied by a diffuse capsulitis and likely accounts for the patient's symptoms.
2. Incidental solitary first metacarpal enchondroma.
DISCUSSION:
A solitary enchondroma is a benign tumor of cartilage located within the medullary cavity. It originates from a cartilage rest displaced from the epiphyseal plate secondary to failure of normal endochondral ossification.
Microscopically, the cellularity of the lesion is variable but never reaches that of a chondrosarcoma. However, it is often difficult to distinguish a low grade chondrosarcoma from an enchondroma. The major tissue is hyaline cartilage, the lobules of which are separated by fibrous septae. Lesions in the axial skeleton have a greater propensity to become malignant than those in the appendicular skeleton. An enchondroma usually becomes latent in adulthood and less than 2% of asymptomatic solitary enchondromas will transform to chondrosarcoma.
Enchondroma is a common tumor. The incidence is greatest between the second and fifth decades of life and is equally frequent in men and women. Lesions, particularly those in the hand, usually are asymptomatic or associated with painless swelling. The appearance of pain should arouse the suspicion of malignant transformation, a complication that, although infrequent, is noted more commonly in the long tubular bones and especially in the bones of the pelvic and shoulder girdles.
The short tubular bones of the hand are affected in approximately 40-65% of patients; solitary enchondroma is the most common tumor of the bones of the hand.
The origin of the tumor in a tubular bone is usually the central metaphysis, with apparent migration down the shaft. It may extend into the epiphysis only after fusion of the growth plate.
The radiographic appearance of solitary enchondromas in the hand usually is characteristic. A well defined, medullary lesion with some degree of calcification, a lobulated contour, and endosteal scalloping allow a precise diagnosis in most cases. Cortical expansion or thickening and pathologic fracture are other potential radiographic characteristics.
MR imaging shows replacement of marrow fat on T1 weighted sequences by the low signal intensity of the well circumscribed tumor. High signal intensity on T2 weighted spin echo images is characteristic of the cartilaginous portion of the lesion. A lobulated configuration is typical. Calcific foci, if dense enough, are seen as a signal void. Gadolinium enhanced T1 weighted images show rings and arcs of enhancement reflecting the lobulated growth pattern of the tumor.
Asymptomatic solitary enchondromas may be followed non operatively with serial radiographs as the prognosis is excellent. If solitary or multiple enchondromas become symptomatic or begin to enlarge, they may require biopsy and/or tumor excision with a wide margin to reduce recurrence. When complicated by a fracture, in most cases the fracture is allowed to heal with closed treatment. Curettage and bone grafting is then required after fracture healing.
REFERENCES:
1. Pomeranz, Stephen J: Gamuts and Pearls in MRI, 2nd Ed. MRI-EFI Publications 1993
2. Greenfield, George B: Imaging of Bone Tumors. JB Lippincott Co 1995, pp 193-201.
3. Resnick, Donald: Diagnosis of Bone and Joint Disorders. WB Saunders Co 1995, pp 3699-3705.
4. Flemming DJ, Murphey MD: Enchondroma and chondrosarcoma. Seminars Musculoskeletal Radiology. 2000; 4 (1): 59-71.
5. Robbin MR, Murphey MD: Benign chondroid neoplasms of bone. Seminars Musculoskeletal Radiology. 2000; 4 (1): 45-58.
6. Marco RA, Gitelis S, Brebach GT, Healey JH: Cartilage tumors:evaluation and treatment. Journal American Academy Orthopedic Surgery. 2000 Sep-Oct; 8 (5): 292-304.
7. Wheeless CR: Wheeless Textbook of Orthopaedics, 1996. Enchondroma. | 
