The “Mini Brain” Sign in a Case of Vertebral Hemangioma Mimicking Solitary Plasmacytoma of the Spine

Excerpt

Solitary plasmacytoma of bone is a rare unifocal tumor of monoclonal plasma cells located anywhere in the skeleton, with negative markers of systemic involvement. It accounts for 3–7% of plasma cell neoplasms and most commonly affects the axial skeleton, namely vertebral bodies, due to the rich red marrow content, in which cases it is designated as solitary plasmacytoma of the spine (SPS) [1]. Although definitive diagnosis requires a histopathologic examination, specific imaging features of SPS could be helpful and guide diagnostic investigations of isolated vertebral lesions. The “mini brain” sign was coined by Major et al. in 2000 regarding a characteristic appearance of SPS on magnetic resonance imaging (MRI) [2]. It consists of curvilinear low signal intensity structures on all imaging sequences, extending partially through the invaded vertebral body from a relatively preserved cortical rim and resembling the sulci and gyri of the brain as seen on axial images. These curvilinear structures represent thickened and remodelled trabecular bone in continuity with cortical struts surrounding a hypointense T1-weighted image (T1WI) and hyperintense T2WI tumor mass and this “mini brain” appearance can be seen equally in the computed tomography (CT) scan [3]. In the same year, an independent case series by Shah et al. described the same features in four out of six SPS patients [1]. This sign has since been repeatedly evoked as a highly specific and even pathognomonic sign of SPS [2‐8]. Frequently mentioned differential diagnoses of SPS imaging include vertebral metastases and hemangioma but no reports to date have been published about the presence of the “mini brain” sign in lesions other than SPS, with the exception of two non-neoplastic cases of spondylodiscitis, in which the clinical history and presentation contributed to an accurate diagnosis [2, 8]. Indeed, some institutions omit a biopsy for histopathological confirmation and start treatment based on this imaging feature alone [2, 3]. …