Bone mass of the calvarium

Plasmacytoma of the calvarium is very rare, accounting forthe 0.7 % of all plasmacytomas [1–5]. The most commonlocations are the thoracic and lumbar spine (30–40 % ofcases). Involvement of the hip, femurs, and ribs is lessfrequent [6].Plasmacytoma of the calvarium can be indistinguish-able from other lytic lesions, especially metastatic dis-ease. Meningioma, eosinophilic granuloma, anddermoid cysts can have similar appearances, althoughusually in a different clinical context [10, 11]. Histo-pathological examination and laboratory tests are nec-essary to make a definitive diagnosis of plasmacytoma(Fig. 1).The typical features on imaging are a lytic lesion on X-rayexamination(Fig.1 question) [1, 6]. On computedtomography (CT), plasmacytoma presents as a lyticpunched-out lesion with interspersed residual thickened bonytrabeculae. Cortical thinning and focal destruction are typical(Fig. 2 question) [2]. On magnetic resonance imaging (MRI),bone plasmacytoma of the calvarium presents as an intra-medullary lesion of low to intermediate intensity on T1-weighted images and high intensity on T2-weighted images.Contrast enhancement is usually mild [4–9].In the presented case, the calvarium plasmacytomapresents a “mini-brain” appearance, due to the presence oflow-intensity hypertrophic residual trabeculae interspersedin a relatively homogeneous mass, mimicking the brainsulci.Major et al. first described the “mini-brain” appearanceof plasmacytoma in a series of ten patients with spinal