Varicose<unk>  are normal<unk>  that have become dilated beyond 3mm. They usually occur in lower limbs. 
The superficial and deep<unk>  are connected by perforating<unk>  (also have valves), which also prevent the backflow of blood from deep to superficial<unk> . Due to obesity, pregnancy, intra-abdominal mass, post-thrombotic destruction of the perforating<unk> ' valves, etc. sustained high pressures can develop in superficial<unk> .  This causes dilation of superficial<unk>  and the development of varicose<unk>  over time. If unattended, they worsen over time and might be associated with pain, discomfort, localized dermatitis, discoloration, and/or ulceration. Because of slowed blood flow, they can also be associated with the formation of blood clots in the dilated<unk> .
Varicose veins pathophysiology
Deep vein thrombosis pathophysiology
Portal vein thrombosis pathophysiology
Thrombosis pathophysiology
Varicose veins risk factors
Stent thrombosis risk factors
Varicose veins differential diagnosis
Varicose veins epidemiology and demographics