Ferromagnetic MRI artifact secondary to a previous mandibular modified condylotomy

Abstract

The presence of artifact on diagnostic radiographs can sometimes lead to misinterpretation and misdiagnosis. Artifacts are often caused by improper handling or processing of radiographic film. Panoramic radiographs often exhibit shadows or ‘ghost’ images cast by the presence of objects, such as earrings, that were present on the patient while the film was being exposed. Computerized tomography (CT) scans may display a significant ‘scatter’ effect if metallic dental restorations, implants, or rigid fixation hardware are present. Magnetic resonance imaging (MRI) is also degraded by the presence of both ferromagnetic and non-ferromagnetic metal implants. 1,2 The use of steel surgical instruments, such as drills and saws, may result in a ferromagnetic artifact caused by the deposition of minute metallic particles into the surrounding bone and soft tissue. 3‐5 Ferromagnetic artifacts have been previously reported following orthopaedic and neurosurgical osteotomies, 2‐5 but not after facial bone osteotomies. Recently, at our institution, we encountered a case where a large ferromagnetic MRI artifact occurred in the area of a previous mandibular osteotomy. No rigid fixation or other metallic hardware was present in this area to explain the artifact. The patient was a 32-year-old white male who originally presented with internal derangement of his right temporomandibular joint. When conservative therapy for this complaint failed, a right modified condylotomy with a postoperative period of maxillomandibular fixation was performed. The osteotomy was performed using an electric oscillating saw with a stainless steel blade (Stryker Instruments, Kalamazoo, MI) and copious irrigation. The patient returned 5 months postoperatively with complaints of pain, swelling and trismus associated with the right side of the mandible. Examination showed a large, firm, tender, non-fluctuant swelling superficial to the right angle of the mandible with associated cervical lymphadenopathy. An ultrasound examination failed to show a fluid accumulation in the area. An MRI of the area was obtained in order to determine an explanation for the soft tissue swelling. Evaluation of the MRI showed a dramatic artifact associated with the mandibular ramus that made interpretation of the soft tissue in the area impossible. This artifact consisted of multiple halo-appearing areas joined centrally like the spokes on a wheel. These halos were not uniform in size, but all appeared to be teardrop shaped in appearance. The artifact was associated with the entire mandibular ramus, both medially and laterally, in the area of the previous osteotomy and was visible on both axial and coronal views (Figs 1 & 2). Upon consultation with the radiology service, it was determined that the abnormal appearance of the area was consistent with a ferromagnetic artifact. There was no macroscopic ferromagnetic or nonferromagnetic hardware located in this area to explain this phenomenon. Surgical exploration of the area failed to show any gross anatomic abnormality and no purulence was demonstrated. Several small hard and soft tissue specimens were obtained from the area. Histologic examination with both standard light microscopy and polarized light microscopy failed to reveal any foreign bodies in the tissue. The presence of microscopic metal particles could not be ruled out however, due to the relatively small size of the tissue specimens. Large MRI artifacts will result from the presence of even minute ferromagnetic particles present within the scanner’s radiofrequency coils. 3 Stainless steel saws and drills may deposit microscopic ferromagnetic debris in the tissue after their use. 3‐5 Even these tiny particles can lead to a significant change in the local magnetic susceptibility of the tissue which in turn leads to local distortions of the homogeneity of