Microscopic polyangiitis involves small vessels, typically capillaries. Kidneys and lungs are commonly involved, but many organs can be affected. There may be an underlying immune disease, chronic infection, or drug reaction. Giant cell arteritis typically involves arterial branches of the external carotid, most often the temporal artery. Micro abscesses may be present with an infectious process, or with thromboangiitis obliterans (Buerger disease), which typically involves lower extremities. Mycotic aneurysms occur when a focus of infection, often from a septic embolus, weakens an arterial wall so that it bulges out. Perivascular eosinophilic infiltrates may be seen with Churg-Strauss syndrome, which typically involves the lungs.