Edema-like marrow signal intensity: a narrative review with a pictorial essay

The termedema-likemarrowsignal intensity (ELMSI) represents a general termdescribing an area of abnormal signal intensity atMRI. Its appearance includes absence of clear margins and the possibility of exceeding well-defined anatomical borders (forexample, physeal scars). We can define “ELMSI with unknown cause” an entity where the characteristic MR appearance isassociated with the absence of specific signs of an underlying condition.However, it ismore often an important finding indicatingthe presence of an underlying disease, and we describe this case as “ELMSI with known cause.” It presents a dynamic behaviorand its evolution can largely vary. It initially corresponds to an acute inflammatory response with edema, before being variablyreplaced by more permanent marrow remodeling changes such as fibrosis or myxomatous connective tissue that can occur overtime. It is important to study ELMSI variations over time in order to evaluate the activity state and therapeutic response of aninflammatory chronic joint disease, the resolution of a trauma, and the severity of an osteoarthritis. We propose a narrative reviewof the literature dealing with various subjects about this challenging topic that is imaging, temporal evolution, etiology, differentialdiagnoses, and possible organization, together with a pictorial essay.