MRI Findings in Muscles of Mastication in Patients with Temporomandibular Joint Disorder (TMD)

Introduction: Along with clinical examination Magnetic Resonanz Imaging (MRI) has become a standard tool in Temporomandibular joint disorder diagnosis. Even though MRI diagnosis usually focuses on pathologies of the joint directly, pathological alterations of the muscles can be found as well. Objectives: Is there evidence for correlations between MRI muscle findings and clinical symptoms of TMD? Material and Methods: Digital MR- Images of 65 patients treated for TMD at the dental clinic of Goethe University Frankfurt, Germany between 2004- 2012 have been evaluated. One patient showing noticeable alterations in MR muscle appearance between right and left muscles was defined as reference for the muscle alterations of interest. Fibrous, lipomatic and edematic alterations were recorded and the width of the masseter, medial and lateral pterygoid muscle was measured in the axial plane. Those findings were then matched with clinical findings of palpation, limitation or hypermobility in jaw opening and klicking, deviation and deflexion. Results: Just like in the clinical examinations most alterations in MR signaling were found in the masseter muscle. 93% showed at least one of the alterations of interest while 46% of the masseter were painful on palpation. Still, statistically this was not significant (p> 0,05). With 17% alterations in MR signaling and 13% of clinical symptoms, findings in the medial pterygoid muscle were less frequent. Here as well, there was no proof of correlation between MR - and clinical findings (p> 0,05). Most of the MR- findings in lateral pterygoid muscles (42%) were of lipomatic nature. They were correlated with clinical findings of klicking, limitation or hypermobility in jaw opening and deviation or deflexion but no statistically significant correlations were found (p> 0,05). Conclusion: Although MR findings of muscle alteration such as fibrosis, liposis or edema can be detected quite frequently in patients with TMD, there is no evidence of correlations between MR signaling and clinical symptoms. Therefore a thoroughly performed clinical examination is inevitable. Since no differenciation has been made between severeties of muscle alterations, further investigation is needed to determine if the severness of signal alterations correlates with clinical symptoms. Keywords: MRI pathologies, TMD, masticatory muscles