Elbow Mass in a 52-Year-Old Man With RA

A 52-year-old man with long-standing seropositive, erosive rheumatoid arthritis (RA) presented to our clinic with a mass on his left elbow (at left). He had noticed it 2 years earlier-the mass had been painless, but it had gradually increased in size.

Physical examination revealed a soft, nontender mass with mild erythema and no warmth. There was no synovitis in the patient's elbows, but both had 20° of flexion contracture. Laboratory test results showed a normal erythrocyte sedimentation rate and C-reactive protein level.

MRI T1- and T2-weighted coronal images of the patient's elbow were obtained (at left). What do they show?

What is your diagnosis?

(Find the answer on the next page.)

The differential diagnosis included synovial cyst, rheumatoid nodule, lipoma, and atypical lipomatous tumor. However, synovial cyst was unlikely because of the location of the mass adjacent to but apart from the elbow joint and rheumatoid nodule because of its large size and soft texture.

The MRI T1- and T2-weighted images showed a well-circumscribed fat-containing mass with numerous thick and irregular septations (below top panel, arrows). The mass was excised, and a biopsy specimen showed an abundance of mature adipose tissue intermingled with spindle cells and collagen, with no cytological atypia or lipoblasts (below bottom panel, left). CD34 immunohistochemical staining highlighted the spindle cells and collagen bundles (below bottom panel, right).

These findings were consistent with a diagnosis of spindle cell lipoma. This rare but benign lipoma variant represents 1.5% of lipomatous tumors and often occurs in men aged 45 to 65 y

ears; its incidence in patients with RA has not been described in the literature. It often occurs in the subcutaneous tissue of the posterior neck, shoulder, and back.

Spindle cell lipoma shares many characteristics with liposarcoma. When the radiological findings suggest a complex internal architecture, it is imperative to obtain a biopsy to rule out liposarcoma.¹

In our patient, the mass was completely excised and biopsied. He did well, without recurrence of the mass 6 months after the surgery.

1. Oaks J, Margolis DJ. Spindle cell lipoma of the mediastinum: a differential consideration for liposarcoma. J Thorac Imaging. 2007;22:355-357.