Intraosseous Lipoma of the Calvaria in the Early Stage Resembling Normal Fatty Marrow

Abstract

Intraosseous lipoma (IOL) is a benign bone tumor that usually arises from the lower limb and rarely arises from the skull. Radiological diagnosis of a typical case is not problematic due to its characteristic calcification and marginal sclerosis. Here, we report a case of calvarial IOL in the early stage lacking conventional radiopathological features. The patient is a 7-year-old girl who presented with a slow-growing protuberance on the vertex of the head. Computed tomography displayed a low-density mass without calcification that was continuous with the surrounding diploe. The mass was resected piece by piece for diagnostic and cosmetic reasons. Histologically, the specimen consisted of bony trabeculae and intertrabecular adipose tissue, which resembled normal fatty marrow. However, adipose tissue was considered neoplastic since it lacked hematopoietic elements. The final diagnosis of IOL was made by radiopathological correlation. This case suggests that IOL should be included in the differential diagnosis of diploic expansion, even if calcification is absent. The histology of an early-stage IOL resembles normal fatty marrow, but recognizing the absence of hematopoietic elements aids the diagnosis. Also, our literature review indicates that such cases are likely to be encountered in the calvaria than cranial base.

Keywords: calvaria; diploe; early; intraosseous; lipoma; skull.

Fig. 1

Illustrated midsagittal section of the skull. Calvaria is filled with horizontal wave pattern; cranial base is filled with vertical stripe pattern. Facial skeleton is unfilled.

Fig. 2

Plain lateral ( A ) and frontal ( B ) skull radiographs display a radiolucent mass at the vertex of the skull. Sagittal computed tomography (CT) scan ( C ) illustrates a spindle-shaped low-density mass expanding the diploe, and three-dimensional CT reconstruction ( D ) renders the mass located at the intersection of the coronal and the sagittal suture. Magnetic resonance imaging shows high signal intensity on sagittal T1- ( E ) and T2-weighted ( F ) images.

Fig. 3

Intraoperative photograph reveals the expanded diploe resembling a normal cancellous bone.

Fig. 4

Microscopic image of the lesion, which consists of mature adipose tissue and trabeculae of lamellar bone resembling a normal fatty marrow ( A ). Intertrabecular adipose tissue seems monotonous and lacks hematopoietic elements ( B ). The area that is regarded as a preexisting marrow ( C ) contains hematopoietic elements ( D ).