Patients with solitary plasmacytoma in the spine frequently require a biopsy for diagnosis of their condition. This is an appearance of plasmacytoma in the spine, which is sufficiently pathognomonic to obviate biopsy. Identification of a “mini brain” in an expansile lesion in the spine is characteristic of plasmacytoma. It is important that radiologists note this characteristic because biopsy can be avoided in patients with this appearance. Although biopsy might still be required at many institutions, at some institutions surgeons find this appearance sufficiently pathognomonic to bypass biopsy and start treatment.