title: Significance of the "doughnut" sign.
mesh_terms: D001922:Brain Abscess / Q000175:diagnosis; D001927:Brain Diseases / Q000175:diagnosis*; D001932:Brain Neoplasms / Q000175:diagnosis; D002561:Cerebrovascular Disorders / Q000175:diagnosis; D003937:Diagnosis, Differential; D003951:Diagnostic Errors; D006801:Humans; D009362:Neoplasm Metastasis; D011877:Radionuclide Imaging