 Introduction/Background Acute onset of a cold, painful leg, also known as acute limb ischemia (ALI), describes the sudden loss of perfusion to the lower extremity and carries significant risk of morbidity and mortality. The pathophysiology primarily relates to acute arterial ischemia, in which there is often insufficient vascular collateralization to perfuse the lower extremity. A minority of cases may be related to a severe presentation of venous thrombotic disease. Known as phlegmasia cerulea dolens, this condition presents with lower extremity dusky discoloration, massive swelling, and pain. These clinical differences allow for differentiation from acute arterial ischemia. ALI requires rapid identification and treatment. The objectives of diagnostic imaging include confirmation of diagnosis, identifying the location and extent of vascular occlusion, and preprocedural/presurgical planning. The published literature regarding imaging of peripheral artery disease (PAD) focuses almost exclusively on patients with chronic PAD. This includes asymptomatic PAD, leg pain with exertion (ie, intermittent claudication), and critical limb ischemia (defined as chronic leg or foot pain at rest, skin ulceration, or gangrene). By comparison, the literature on imaging patients with ALI is very limited. Consequently, the following discussion relies heavily on studies of patients with chronic PAD. This document has separated imaging appropriateness based on the clinical scenario of suspected ALI for which signs and symptoms may include pain, pallor, paresthesia/paralysis, poikilothermia, and pulselessness, or more rarely with symptoms of phlegmasia cerulea dolens as described above, acknowledging that some patients may present with any combination of the above or other comorbidities that may require imaging. Additionally, compartment syndrome also induces acute ischemia via a separate mechanism of tissue pressurization within a fixed volume, often in the setting of trauma or other injury.
Sudden Onset of Cold Painful Leg.  Introduction/Background Acute onset of a cold, painful leg, also known as acute limb ischemia (ALI), describes the sudden loss of perfusion to the lower extremity and carries significant risk of morbidity and mortality. The pathophysiology primarily relates to acute arterial ischemia, in which there is often insufficient vascular collateralization to perfuse the lower extremity. A minority of cases may be related to a severe presentation of venous thrombotic disease. Known as phlegmasia cerulea dolens, this condition presents with lower extremity dusky discoloration, massive swelling, and pain. These clinical differences allow for differentiation from acute arterial ischemia. ALI requires rapid identification and treatment. The objectives of diagnostic imaging include confirmation of diagnosis, identifying the location and extent of vascular occlusion, and preprocedural/presurgical planning. The published literature regarding imaging of peripheral artery disease (PAD) focuses almost exclusively on patients with chronic PAD. This includes asymptomatic PAD, leg pain with exertion (ie, intermittent claudication), and critical limb ischemia (defined as chronic leg or foot pain at rest, skin ulceration, or gangrene). By comparison, the literature on imaging patients with ALI is very limited. Consequently, the following discussion relies heavily on studies of patients with chronic PAD. This document has separated imaging appropriateness based on the clinical scenario of suspected ALI for which signs and symptoms may include pain, pallor, paresthesia/paralysis, poikilothermia, and pulselessness, or more rarely with symptoms of phlegmasia cerulea dolens as described above, acknowledging that some patients may present with any combination of the above or other comorbidities that may require imaging. Additionally, compartment syndrome also induces acute ischemia via a separate mechanism of tissue pressurization within a fixed volume, often in the setting of trauma or other injury.