Age / Sex : 58 / F

Chief complaint: Left wrist pain for 2 days

What is your impression?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).

Courtesy of Yun Sun Choi, MD, Eulji Hospital, Eulji University

Discussion

Answer: Osteoid osteoma of the capitate

Findings:

Anteroposterior radiograph of the left wrist shows a sclerosis area in the distal pole of the capitate. Coronal T1-weighted FSE MR image shows a well-circumscribed lesion with a central low signal in the capitate. On coronal and axial fat-suppressed T2-weighted FSE MR images, this lesion shows a low signal center (calcified nidus) surrounded by the thin high signal rim in the volar aspect of capitate. There is edema in the remaining capitate bone, as well as joint effusion and synovitis in the midcarpal and carpometacarpal joints.

Differential Diagnosis:

1. Osteoblastoma


2. Osteonecrosis


3. Osteomyelitis


4. Bone island

Diagnosis: Osteoid osteoma of the capitate

Discussion:

Osteoid osteoma of the wrist is rare with reported incidences ranging between 2.8 and 10.2%. In the carpal bones, an osteoid osteoma is commonly found in the capitate or the scaphoid and usually arises in the medullary spongiosa. The diagnosis of an osteoid osteoma of the wrist and hand is often delayed because typical clinical (e. g. responding to nonsteroidal anti-inflammatory drugs) and radiological findings are lacking. The latter is due to the fact that either the reactive sclerosis of the adjacent bone is lacking or the nidus itself appears as an area of extensive sclerosis more than of radiolucency. This explains why approximately 25% of these tumors are not detected on radiographs, making osteoid osteoma of the wrist a difficult lesion to diagnose. MRI shows a well-circumscribed lesion in the capitate bone. The focal nature of the lesion and the marked enhancement of the non-sclerotic parts of the nidus after contrast agent injection favors a highly vascularized tumorous lesion. The dense calcification of the nidus is hypointense on all sequences. The presence of an adjacent bone marrow edema is also well known in osteoid osteoma and may be due to elevated prostaglandin levels in the nidus which, together with a stimulation of bradykinin, leads to an increased permeability of the capillaries. Occasionally, the aggressive appearance of the edema can be misleading. Thin-slice CT scan is considered as the reference imaging technique for the diagnosis of osteoid osteoma and is particularly useful when the nidus is hidden by complex anatomy.

References:

1. Murray PM, Berger RA, Inwards CY. Primary neoplasms of the carpal bones. J Hand Surg Am. 1999;24(5):1008-1013


2. Al Shaikhi A, Hébert-Davies J, Moser T, Maillot E, Danino AM. Osteoid osteoma of the capitate: a case report and literature review. Eplasty. 2009;9:e38


3. Kreitner KF, Löw R, Mayer A. Unusual manifestation of an osteoid osteoma of the capitate. Eur Radiol. 1999;9(6):1098-1100