Ferrous Illusion: A Unique Case of Welding Fume Particles Appearing as Metallic Artifacts in MRI.

A rare cause of metallic artifacts over the scalp on magnetic resonance imaging (MRI) is welding fume particles that contain paramagnetic iron oxide particles. These introduce distortion of the magnetic field homogeneity and result in susceptibility artifacts. They may erroneously be reported as a pathology such as calcified lesions; therefore, awareness among radiologists is required. We report a case of a 52-year-old male, an industrial inspector by profession, who presented to the neurology clinic with headaches for which an MRI of the brain without contrast was advised. There was no brain parenchymal signal abnormality; however, numerous small rounded altered signal foci were identified along the scalp, especially in the vertex region, which returned central hypointense and marginal hyperintense signal on all sequences. The imaging signals were suspicious for calcified scalp lesions, and the patient was recalled for clinical examination, which was unremarkable for cutaneous or subcutaneous abnormality on the scalp or elsewhere over the body. A detailed history was taken retrospectively, revealing that the patient had walked through a room where welding was being done before presenting for an MRI exam, without taking a shower. The various altered signal foci over the scalp on MRI based on their shape were hence identified as welding fume particles. These were fine enough not to be visible by the naked eye but determined by the MRI machine because of their magnetic susceptibility artifact. We aim to increase radiologists' awareness of such artifacts that may be seen in patients with occupational exposure to these particles to avoid misdiagnosis of other pathologies.