Pure intramuscular osteolipoma

Abstract

Ossified lipoma or osteolipoma are rarely reported. It is defined as a histologic variant of lipoma that has undergone osseous metaplasia. Osteolipoma presents with a dominant osseous component within a lipoma. We report a case of a histologically confirmed osteolipoma on the nuchal ligament independent of bone. The patient was a 51-year-old female who presented with a 5-year history of a painless, progressively enlarging mass on the posterior neck. Computed tomography and magnetic resonance imaging showed a circumscribed mass compatible with fat between the C2 and C6 spinous processes with a large calcified irregular component. The mass with dual components was totally removed under general anesthesia and no recurrence was observed after 6 months of follow-up. We also reviewed the clinicopathologic features of previously reported osteolipomas in the literature and suggest that although osteolipoma is a rare variant of lipoma, it should be considered in the differential diagnosis when a lipoma of the posterior neck mixed with a bony component is encountered.

Keywords: Lipoma; Lipomatous tumor; Ossified lipoma; Ossifying lipoma; Osteolipoma.

Fig. 1

Preoperatively CT (A: sagittal) and sagittal MRI (B: T1-weighted, C: T2-weighted) revealing a irregular calcification involving posterior neck within soft tissue mass compatible with fat tissue.

Fig. 2

Whole body bone scan (A: anterior, B: posterior) shows an amorphous calcification mass with increased uptake, and no bone metastases.

Fig. 3

Grossly, the tumor consists largely of fat and calcification presented with the red bone marrow (black arrow).

Fig. 4

There is a large foci of osseous metaplasia (white star) and at the periphery of the mass, the bony portion is surrounded by mature adipose tissue (black star) [A: hematoxylin & eosin (H-E), ×40]. Microscopic appearance of red bone marrow shows a meshwork of bone trabeculae (white star) and hematopoietic marrow elements (B: H-E, ×100).