Definition: The term "subclavian steal" refers to a phenomenon of flow reversal in the vertebral artery ipsilateral (on the same side) to a hemodynamically significant stenosis (narrowing) or occlusion (blockage) of the prevertebral subclavian artery (which includes the subclavian and innominate arteries).
Physiological Significance: This phenomenon represents an appropriate physiological response to proximal arterial disease.
Symptoms: Most individuals demonstrating this phenomenon are asymptomatic (show no symptoms). However, when the condition is termed "subclavian steal syndrome," it implies that there is significant cerebrovascular (brain-related) symptoms due to arterial insufficiency (lack of blood flow) in the brain.
Flow Characteristics: Subclavian steal syndrome describes retrograde (backward) blood flow in the vertebral artery, which is associated with proximal ipsilateral subclavian artery stenosis or occlusion.
Superior Vena Cava (SVC) Syndrome
Definition: Superior vena cava syndrome is a collection of clinical signs and symptoms that result from either partial or complete obstruction of blood flow through the superior vena cava (SVC).
Causes: Obstruction of the SVC is most commonly attributed to the formation of a thrombus (a blood clot) or tumor infiltration into the vessel wall.
Anatomical Context: The superior vena cava is formed at the junction of the left and right innominate (brachiocephalic) veins. Its role is to return deoxygenated blood from the head, neck, upper extremities, and torso back to the heart.
Current Trends: Today, this syndrome is most frequently associated with malignancy (cancer). Recently, there has been an increase in benign (non-cancerous) etiologies as causes of the condition.
Clinical Manifestations: The obstruction due to venous congestion results in elevated pressures in the upper body venous system, leading to several common signs and symptoms, including:
Face or neck swelling
Upper extremity swelling
Dyspnea (difficulty breathing)
Cough
Dilated chest vein collaterals (veins near the chest that become enlarged due to increased blood flow).