MRCS Part B (OSCE) - Online Resources

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• The azygos system, a valveless system, running up the right side of the thoracic vertebral column, drains the posterior thoracoabdominal wall.
• Formed by the union of the ascending right lumbar veins and the right subcostal veins at the level of the 12^th thoracic vertebrae.
• Ascends in the posterior mediastinum, arches over the right main bronchus posteriorly at the root of the right lung, to join the SVC.
• Connects the systems of the SVC and IVC and, thus provides an alternative path for blood to the right atrium when either venae cavae is blocked.
• Named the azygos vein as it has no symmetrical anatomical equivalent on the other side of the body.
• Its main tributaries are the bronchial veins, cardiac veins and posterior right intercostal veins. It also communicates with the vertebral venous plexuses.
• The azygos vein is an important component of the portocaval anastomoses via its connection with the left gastric vein.

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• Together, the accessory hemiazygos and hemiazygos veins essentially serve as the left side equivalent of the azygos vein.
• Accessory hemiazygos vein runs to the left of the vertebral column and drains the 5^th- 8^th intercostal spaces on the left side of the thorax.
• The hemiazygos vein usually begins in the left ascending lumbar or renal vein, drains the left lower intercostals spaces and enters the thorax through the left crux of the diaphragm.
• Ascends on the left side of the vertebral column around the level of T9 vertebra, behind the aorta, oesophagus and thoracic duct to empty into the azygos vein.
• Its tributaries include the 9^th- 11^th posterior intercostal veins, the subcostal vein of the left side and some oesophageal and mediastinal branches.

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"The thoracic duct is the largest lymph channel in the body. It drains most of the body’s lymph into the venous system except the right thorax, right arm and, right side of the head and neck. "

"The thoracic duct originates from the cisterna chyli in the abdomen opposite the L2 vertebral body. "

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• The thoracic duct enters the thorax through the aortic hiatus in the diaphragm at the level of T12 vertebra.
• It ascends in the posterior mediastinum with the aorta on its left, azygos vein on the right, oesophagus anteriorly and vertebral bodies posteriorly.
• At the manubriosternal junction (T4-T5) the thoracic duct crosses from the right to the left, ascends in the superior mediastinum and drains at the angle (confluence) of the left internal jugular vein and the left subclavian vein (at the root of the neck).

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"The right lymphatic duct drains lymph from the right side of the thorax, right arm and right side of the head and neck. The right lymphatic duct usually drains into the right subclavian or the right internal jugular veins. "

"Chylothorax results from leakage of lymphatic fluid into the pleural space usually from thoracic duct injury. The most common non-traumatic cause is malignancy (especially lymphoma). Other causes include left heart failure, infection and Down’s syndrome. "

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• Drainage / aspiration.
• Pneumoperitoneal shunting.
• Surgical or chemical pleurodesis.
• Medical treatment with an octopeptide such as Octreotide.
• Reduce chyle production by instituting total parenteral nutrition or a fat-restricted oral diet supplemented with medium-chain triglycerides.
• In 50% of patients the thoracic duct leak may close spontaneously

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"The sympathetic trunk is a ganglionated chain arising from the thoracolumbar regions’ (T1-L2), lateral horn of grey matter and emerge via the ventral root. It is located ventral and lateral to the spinal cord and is part of the autonomic nervous system. "

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The aim of thoracoscopic sympathectomy is to disrupt the sympathetic chain resulting in denervation of the 2^nd and 3^rd thoracic ganglia. Indications for thoracoscopic sympathectomy include:

• Palmar hyperhidrosis.
• Buerger’s disease/ small vessel disease with digital gangrene.

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