cisterna chyli

**Location/Anatomy:** Retroperitoneal, anterior to the L1–L2 vertebral bodies (variable: T11–L2), to the right of the abdominal aorta and posterior/right of the aorta near the right crus of the diaphragm. It is the dilated, saccular origin of the thoracic duct (present in roughly 50–60% of people; in others, the trunks simply converge as a plexus). The thoracic duct ascends through the aortic hiatus of the diaphragm (T12) alongside the aorta and azygos vein, runs in the posterior mediastinum, crosses to the left around T5, and drains into the junction of the left internal jugular and left subclavian veins (left venous angle).

**Tributaries:** - Right and left lumbar (lumbar) lymphatic trunks: drain lower limbs, pelvis, and abdominal wall/pelvic viscera - Intestinal trunk(s): drain the GI tract, pancreas, liver (partly), spleen; carry chyle (lipid-rich lymph absorbed via intestinal lacteals; chylomicrons) - Descending intercostal trunks (variable)

**Drainage:** The thoracic duct drains ~75% of the body's lymph (everything below the diaphragm plus the left upper body: left head/neck, left arm, left thorax). The right lymphatic duct drains the right upper quadrant (right head/neck, right arm, right thorax) into the right venous angle.

**Clinical significance/high-yield associations:** - **Chylous ascites / chylothorax / chyluria:** Injury or obstruction of the cisterna chyli or thoracic duct (trauma, surgery such as esophagectomy, retroperitoneal lymph node dissection, aortic aneurysm repair, lymphoma, malignancy, filariasis, cirrhosis) leads to leakage of chyle. Fluid is milky with high triglycerides (>110 mg/dL) and chylomicrons. Thoracic duct injury above T5 typically causes a left chylothorax; below T5, a right chylothorax. Lymphoma is the most common nontraumatic cause of chylothorax; esophagectomy is a common surgical cause. - **Pleural fluid analysis:** Triglycerides >110 mg/dL (exudate-like lymphocyte-predominant), distinguishing it from pseudochylothorax (high cholesterol, chronic effusions such as TB or rheumatoid pleurisy). - **Management:** Low-fat diet with medium-chain triglycerides (absorbed directly into portal circulation, bypassing lymphatics), octreotide, drainage, thoracic duct ligation/embolization if refractory. - **Metastasis:** Abdominal/pelvic cancers (e.g., testicular cancer spreading to para-aortic nodes, and gastric cancer to the left supraclavicular Virchow node via the thoracic duct) – Virchow node (Troisier sign) reflects thoracic duct drainage into the left venous angle. - **Lipid absorption:** Dietary long-chain fats are packaged into chylomicrons in enterocytes, enter lacteals, travel via the intestinal trunk to the cisterna chyli → thoracic duct → left subclavian vein. Chylomicrons thus bypass the portal circulation and first-pass hepatic metabolism. - **Embryology:** Lymphatic sacs develop from venous endothelium (the retroperitoneal lymph sac gives rise to the cisterna chyli).

**Mnemonic:** "Cisterna chyli = cistern of chyle" – a reservoir where gut lipid-rich lymph meets leg/pelvic lymph at L1–L2, just before the thoracic duct passes through the aortic hiatus at T12.