The influenza vaccine is increasingly available to the general public and mandated by many employers in the United States. The prevalence of post-vaccination complications is likely on the rise. Complications are well known to general clinicians, but are under-reported in the imaging literature. We present four cases of post-vaccination shoulder pain with magnetic resonance imaging (MRI) findings. An intrasubstance fluid-like signal in deep muscular and/or tendinous structures was the most common finding on MRI of these four cases. Focal bone marrow signal within the humeral head and inflammatory changes in the subacromial/subdeltoid bursa were also observed. The most likely reason for a humeral intraosseous edema-like signal was presumed injection of vaccine substance directly into osseous structures that might lead to focal osteitis. In the published literature, there is little emphasis on the imaging of local injection site complications accompanying influenza vaccination. We intended to increase familiarity of MRI findings in the setting of prolonged or severe clinical symptoms following influenza vaccination through the imaging findings of these four cases.

The medical management of patients requiring imaging of the head is often complex. This is confounded by growth and development of neuroimaging technology. Summarizing established guidelines and provided answers to commonly asked questions about neurovascular imaging may aid in providing efficient medical care. Noncontrast head computed tomography (CT) is usually the first line in imaging because of its speed and wide-spread availability. More advanced techniques are reserved for more specific questions or when the CT head is non-diagnostic. MRI is the modality of choice for indications that include chronic headache, pulsatile tinnitus, and cerebrovascular diseases including stroke in the subacute or chronic setting. The imaging of stroke is evolving and many advanced techniques including CT and magnetic resonance perfusion are playing an increasing role in diagnosis. Digital subtraction angiography is widely accepted as the gold standard for evaluation of vascular pathology including aneurysm, vascular malformations, Moyamoya syndrome, carotid stenosis and dissection; and offers treatment options. Alternatives such as MR angiography, MR venography, and CT angiography offer similar sensitivity and specificity to conventional digital subtraction angiography. Safety considerations are an important concern. When using iodinated and gadolinium contrast agents, there are potential complications including allergic reactions, lactic acidosis, and nephrogenic systemic fibrosis. Impaired renal function requires modification in the use of contrast during neuroimaging. Neuroimaging during pregnancy is also discussed.