The venous drainage of the head and neck is organized into six primary axes: the internal jugular, external jugular, anterior jugular, posterior jugular, vertebral, and inferior thyroid veins.

1. Dural Venous Sinuses and the Internal Jugular Vein (IJV)

The internal jugular vein is the principal collector for the cranial cavity, the orbit, and parts of the face. Its origin lies in the dural venous sinuses, which are unique, inextensible, and valve-less channels situated between the layers of the dura mater.

• Postero-superior Group: Includes the superior sagittal, inferior sagittal, rectus, transverse, sigmoid, and marginal sinuses. These typically converge at the confluent of sinuses (Pressoir d’Hérophile).

• Antero-inferior Group: Centered on the cavernous sinus, located on the sides of the sphenoid body. It receives the ophthalmic veins and the central vein of the retina and drains via the superior and inferior petrous sinuses toward the IJV.

• The Internal Jugular Vein (IJV): Beginning at the jugular foramen as a continuation of the sigmoid sinus, it descends within the carotid sheath. Its major tributaries include the thyro-linguo-facial trunk, pharyngeal veins, and the middle thyroid vein.

2. Superficial Cervical Veins

• External Jugular Vein: Formed in the parotid gland by the union of the superficial temporal and maxillary veins, it descends across the sternocleidomastoid muscle to enter the subclavian vein.

• Anterior Jugular Vein: Originates in the subhyoid region and descends near the midline before turning laterally to join the subclavian or external jugular vein.

II. Systems of the Venae Cavae

1. Superior Vena Cava (SVC) System

The SVC is the trunk collector for the supra-diaphragmatic portion of the body. It is formed by the union of the two brachiocephalic veins.

• Azygos System: This system provides a critical link between the SVC and IVC. The azygos vein ascends on the right side of the vertebral column and describes an arch over the right lung root before entering the SVC. It receives the hemiazygos and accessory hemiazygos veins from the left side.

2. Inferior Vena Cava (IVC) System

The IVC drains all infra-diaphragmatic blood. It is formed by the junction of the common iliac veins at the level of the 5th lumbar vertebra.

• Tributaries: The IVC receives parietal branches (lumbar and inferior phrenic veins) and visceral branches (renal, right suprarenal, right testicular/ovarian, and hepatic veins).

• Note: The left renal vein is longer than the right and typically receives the left suprarenal and left gonadal veins.

III. The Portal Vein System

The portal vein directs blood from the digestive tract, spleen, and pancreas to the liver.

• Formation: It results from the union of the superior mesenteric vein and the splenic vein (which receives the inferior mesenteric vein) behind the neck of the pancreas.

• Porto-Caval Anastomoses: These are vital clinical sites where the portal system communicates with the systemic venous system. Key sites include the esophageal (left gastric to azygos), rectal (superior rectal to middle/inferior rectal), and peri-umbilical regions.

IV. Venous Drainage of the Limbs

1. Upper Limb

• Deep Veins: Usually follow the arteries in pairs (e.g., radial, ulnar, brachial) and terminate in the axillary vein.

• Superficial Veins: The cephalic vein (lateral) and basilic vein (medial) are the primary vessels. At the elbow, they often form an "M" shape through the median cubital vein.

2. Lower Limb

• Deep Veins: Include the tibial, popliteal, and femoral veins.

• Superficial Veins: The great saphenous vein originates anterior to the medial malleolus and joins the femoral vein in the thigh (saphenous opening). The small saphenous vein originates behind the lateral malleolus and typically drains into the popliteal vein