Diagnosis:
Enchondroma

Findings: (Images 1 - 7)
Within the proximal metaphysis and diaphysis of the 1st metacarpal is an eccentrically located, lobulated, expansile lesion. The cortex is intact (image 03a-T1) with no evidence of pathologic fracture. The imaging characteristics are representative of a chondroid tumor and, when correlated with the plain film radiographs, are consistent with an enchondroma. No evidence for a collateral ligament injury associated with the 1st metacarpophalangeal joint is present.

Discussion:
Although the diagnosis could be made on plain film, the patient's pain warranted further evaluation. No aggressive characteristics are seen within or associated with the lesion. The lesion is typically low to intermediate signal on T1 (images 01a, 03a, 04a) and high on T2 (images 02a and 05a). The internal calcifications seen frequently on plain film may be difficult to identify on MR. The lobulated contour and characteristic location should allow the diagnosis to be made. These are frequently seen incidentally on MR, when plain films are unavailable.

Enchondromas of the hands and feet are typically benign, even when they expand or erode the cortex. The clinical behaviour of these lesions is benign and have an excellent prognosis. Despite this histological examination of such lesions is either benign or is similar to a low grade chondrosarcoma. Therefore radiological and pathological correlation is vital in diagnosis and prognostication. Malignant change is rare in the hand or foot, but note that Ollier's and Mafucci's diseases have a higher rate of malignant transformation, even in the periphery.