A Bilobed Lipoma Presenting in the Post-Excision Space of the Radial Head 5 Years after Radial Head Excision: A Case Report.

INTRODUCTION: Lipoma is the commonest benign soft-tissue tumor, but its occurrence within a surgically created dead space is exceedingly rare. Radial head excision leaves a void in the lateral compartment of the elbow that is ordinarily obliterated by hematoma and fibrous tissue. We report what we believe to be the first case in the indexed literature of a bilobed lipoma arising within this post-excision space. CASE REPORT: A 58-year-old Indian man presented with an 8-month history of progressive pain and swelling over the right elbow. He had undergone right radial head excision 5 years earlier for a traumatic radial head fracture and had been largely symptom-free in the interval. Examination showed a soft, compressible, lobulated swelling over the lateral aspect of the elbow with flexion restricted to 90° and no neurological deficit. Radiographs confirmed absence of the radial head with no other bony abnormality. Magnetic resonance imaging showed a well-defined bilobed homogeneous fatty lesion occupying the ventral and lateral aspects of the post-excision space, with signal suppression on fat-saturated sequences and no features of malignancy. At exploration through the previous lateral approach, a single bilobed, well-encapsulated lipomatous mass was found in the post-excision space, with one lobe ventral and one lateral. The posterior interosseous nerve was free of the mass. The isthmus was divided to permit delivery, and both lobes were excised intact, measuring 8 × 4 and 6.5 × 4 cm. Histopathology confirmed a benign lipoma. At 6 months, the patient was pain-free, flexion had improved to 120° and there was no recurrence. CONCLUSION: A bilobed lipoma can develop within the dead space left by radial head excision after a prolonged latent interval. The bilobed configuration appears to be molded by the architecture of the post-excision void, a novel observation regarding the pathogenesis of post-surgical lipomas. Magnetic resonance imaging is diagnostic and excision with preservation of the posterior interosseous nerve is curative. This entity should be included in the differential diagnosis of late soft-tissue swelling at a previous surgical site, so that it is not mistaken for recurrence or a malignant fatty tumor.