Thrombus
A thrombus is the formation of a clot within a vein or an artery that is not damaged. As a result, blood flow is altered.
Symptoms and Causes
A thrombus is a solid mass formed by blood coagulation that appears within a blood vessel and remains stationary inside it. When it forms in a damaged vessel, the clot is not dangerous, as it serves to repair the injured tissue. However, when it develops in an intact vessel, it reduces or blocks blood flow, causing a serious health risk.
The clot is formed through the accumulation of platelets and the activation of coagulation factors, a series of proteins that create a fibrin network that strengthens and stabilizes it. Therefore, when it becomes lodged in an undamaged vein or artery, it is difficult to dissolve and restore normal blood flow.
Although they may appear similar, a thrombus refers to the blood clot itself, whereas Thrombosis refers to the process by which the clot forms and obstructs the blood vessel.
Thrombi can be classified into two main types depending on the vessel in which they form:
- Venous thrombus: Forms in vessels that carry blood from organs back to the heart.
- Deep vein thrombus: Located within muscles and running alongside bones.
- Legs: femoral veins (thigh), popliteal veins (behind the knee), posterior and anterior tibial veins, peroneal and soleal veins (calf).
- Pelvis: iliac veins.
- Arms: axillary or subclavian veins.
- Neck: jugular veins.
- Abdomen:
- Portal vein (to the liver)
- Superior mesenteric vein (intestines)
- Splenic vein (spleen, stomach, pancreas)
- Inferior vena cava (from head to lower limbs)
- Deep vein thrombus: Located within muscles and running alongside bones.
- Superficial vein thrombus: Occurs just beneath the skin. It usually affects the legs, mainly the great saphenous vein (from foot to groin) and the small saphenous vein (calf to foot).
- Arterial thrombus: Appears in vessels that carry oxygenated blood from the heart to body tissues.
- Coronary arteries: supply the heart muscle.
- Carotid arteries: supply blood to the brain.
- Aorta: the main artery of the body.
- Pulmonary arteries: supply the lungs.
- Peripheral arteries: located in the lower limbs.
The formation of thrombi is a potentially life-threatening condition that requires early medical attention and prompt treatment to reduce the risk of complications. If not treated in time, the risk increases significantly. The outcomes and recurrence risk after a first episode depend on the patient’s overall health status.
Symptoms
Symptoms of a thrombus that partially or completely obstructs a blood vessel include:
- Sudden, severe pain in the affected area, often worsening over time.
- Skin becomes paler than usual and cold to the touch (in arterial thrombosis).
- In some cases, cyanosis: bluish discoloration of the skin.
- Weak or absent pulse.
- Tingling or numbness sensation.
Signs depending on location:
- Extremities:
- Reduced mobility
- Warm, red/purple or violaceous skin in cases of Deep vein thrombosis
- Swelling (edema), causing tension and pain
- Gangrene: tissue death due to lack of oxygen
- Brain:
- Hemiparesis or unilateral weakness
- Speech difficulties
- Language comprehension impairment
- Visual disturbances or vision loss
- Coordination disorders
- Dizziness, drowsiness, fainting, confusion
- Heart:
- Chest pain radiating to jaw, neck, shoulders, or arms
- Sweating
- Shortness of breath
- Chest tightness
- Lungs:
- Sudden dyspnea
- Pleuritic chest pain
- Tachycardia (increased heart rate)
- Tachypnea (increased respiratory rate)
- Dry cough or hemoptysis
- Dizziness, sweating
- Pelvis:
- Pain when standing
- Heaviness in legs
- Vulvar, perianal, or leg varicose veins
- Dyspareunia (pain during intercourse)
- Dysmenorrhea (painful menstruation)
- Edema, usually in the left leg
- Increased urinary frequency
- Fever in infectious cases (septic pelvic thrombophlebitis)
- Aorta:
- Fever
- Increased heart rate
- Cough
- Bloody sputum
- Thoracic aorta:
- Sharp pain in upper back, neck, chest, or jaw
- Respiratory distress
- Loss of consciousness
- Abdominal aorta: Abdominal or lumbar pain radiating to groin, buttocks, or legs
- Abdomen:
- Acute pain worsened after meals
- Nausea
- Vomiting, sometimes with blood
- Diarrhea
- Blood in stools
- Abdominal distension
- Ascites (fluid accumulation in the abdomen)
- Jaundice
- Esophageal varices
- Jugular vein:
- Neck or headache pain
- Neck or facial swelling
- Palpable vein
- Neck stiffness
- Pain on swallowing
- Visual disturbances
- Local warmth and tenderness over the sternocleidomastoid muscle
Causes
A thrombus develops when blood coagulation is abnormally activated without a vessel injury. It commonly occurs due to:
- Prolonged immobilization (slower circulation, especially in the legs)
- Sedentary lifestyle
- Cancer: tumor-related factors and treatments promote clot formation
- Hormonal changes (pregnancy or postpartum period)
- Obesity
- Hypertension
- Hypercholesterolemia
- Diabetes
- Cardiac arrhythmias
Risk Factors
Risk of thrombus formation is higher in:
- Advanced age
- Genetic predisposition
- Hospitalization
- Long-distance travel
- Post-surgical immobilization
- Hormonal medication (contraceptives or menopausal therapy)
- Pregnancy
- Cancer
- Smoking
- Thrombophilia
Complications
A thrombus may lead to:
- Deep vein thrombus: may lead to deep vein thrombosis.
- Superficial vein thrombus: causes superficial thrombophlebitis.
- Coronary artery thrombus: leads to myocardial infarction.
- Carotid artery thrombus: causes cerebral infarction or a stroke.
- Peripheral arterial embolism
- Acute limb ischemia
- Myocardial infarction
- Stroke
- Renal failure
- Acute aortic syndrome
- Pulmonary arteries: is the cause of:
- Pulmonary embolism
- Chronic pulmonary hypertension
- Pulmonary infarction
- Cor pulmonale (right heart failure)
- Cardiogenic shock
- Sudden cardiac death
- Peripheral arteries: is responsible for:
- Acute limb ischemia
- Chronic non-healing ulcers
- Gangrene
- Amputation in irreversible cases
Which specialist treats thrombus?
Thrombi are diagnosed and treated by Angiology and Vascular surgery and Nuclear medicine. In some cases, Neurology, Pulmonology, or Cardiology may be required.
Diagnosis
A thrombus is diagnosed using the following tests:
- Clinical history: The patient’s family and medical history, general health status, and presenting symptoms are evaluated.
- Blood tests: Various parameters involved in blood coagulation are assessed:
- D-dimer: a protein involved in clot formation.
- Activated partial thromboplastin time (aPTT): measures the time it takes for blood to clot.
- Prothrombin time (PT): measures how long it takes the liquid portion of blood (plasma) to clot.
- Thrombophilia studies: assessment of genetic factors (e.g., Factor V Leiden) or acquired conditions that increase the risk of premature coagulation.
- Doppler ultrasound: the preferred diagnostic test for detecting a thrombus, as it is highly accurate and non-invasive. Ultrasound waves are used to measure the speed and direction of blood flow in real time.
- Pulmonary CT angiography (CT pulmonary angiography): a contrast agent is injected to enhance image visibility, followed by X-rays taken from multiple angles. This provides a detailed representation of the lungs and their arteries.
- Ventilation/perfusion (V/Q) scintigraphy: evaluates airflow (ventilation) and blood flow (perfusion) in the lungs. First, a gas containing a small radioactive component is inhaled and images are taken to assess its distribution in the lungs. Then, a contrast agent is injected into the bloodstream, and once it reaches the pulmonary vessels, gamma rays are used to obtain images of blood flow within the organ.
- Magnetic resonance imaging (MRI): radio waves and a magnetic field are used to generate detailed images of the internal structures of the body. It is a safe test, as it does not use ionizing radiation. It is performed in the area where a thrombus is suspected.
- Computed tomography (CT): X-rays from multiple angles are used to obtain three-dimensional images of the body. It is used when a rapid diagnosis is required, as it is faster than MRI.
Treatment
The primary treatment for a thrombus is pharmacological. Medications are administered to prevent the clot from detaching and migrating to vital organs where it may cause severe complications. The most commonly used drugs are:
- Anticoagulants: These may be administered orally or intravenously. They prevent clot formation or inhibit the growth of existing clots.
- Antiplatelet agents: These prevent platelet aggregation. They are usually administered orally.
- Thrombolytics: These are injected intravenously to dissolve clots and restore normal blood flow. They are used when there is an inadequate response to previous treatments.
When a thrombus causes complications, other approaches are used:
- Compression stockings: These prevent blood from pooling in the legs, thereby reducing edema.
- Inferior vena cava filter: When a patient cannot receive anticoagulant therapy, a mesh-like metallic device is implanted to prevent the thrombus from migrating to the lungs or brain.
- Thrombectomy: A procedure used to remove the clot, performed in the most severe cases.
- Mechanical thrombectomy: A thin, flexible catheter is inserted through a vein, usually in the groin, and advanced to the site of the thrombus to extract it with the assistance of CT, MRI, or fluoroscopy.
- Surgical thrombectomy: When a minimally invasive approach cannot be used, an incision is made in the affected blood vessel, the clot is removed, and the walls of the vein or artery are repaired.
