Lymphatic Anatomy in the Abdomen and Thorax

The cisterna chyli forms posterolateral to the right of the aorta and anterior to the vertebral bodies of T12, L1, L2, and L3 as lymphatic channels from the mesentery, intercostals, and lumbar region join in the retroperitoneal space. At approximately L1, the ampullary cisterna chyli ascends, becoming the thoracic duct. The duct travels in a cephalad direction, crossing with the aorta into the thorax through the aortic hiatus. The duct then enters the right posterior mediastinum, crosses at T4 or T5 into the left retropleural space, and continues in a cephalad direction. The thoracic duct enters the venous system and empties the lymph into the blood stream (Figure 1) where the left subclavian and internal jugular veins unite, 2 to 3 cm above the left clavicle. The thoracic duct enters the venous system and empties the lymph into the blood stream.

This system drains lymph from the entire body except the head, neck, arm, and thorax on the right side (which instead use the right bronchomediastinal, jugular, and subclavian lymph trunks to form the right lymph duct). Of the 4 L of lymph carried in the thoracic duct and cisterna chyli daily, more than 50% originates in intestinal and hepatic lymphatic channels. This is subject to great anatomic variation. Ikard documented that up to 50% of individuals did not have a distinct cisterna chyli, having instead a convergence of small lymphatic channels at the second lumbar vertebra to form the thoracic duct. These variations could play a role in the formation of chyloperitoneum and chylothorax after aortic reconstruction.

Diagnosis of Chyoperiotneum and Chylothorax

Because of the relatively low incidence of these complications, their diagnosis is often delayed. However, once suspected, it is readily confirmed by the characteristic appearance of chyle. As patients improve postoperatively and begin eating and drinking normally, chylous circulation increases from less than 1 mL/min in the fasting state to more than 225 mL/min. Early subclinical leaks in the lymphatic circulation then become symptomatic.

Patients with chyloperitoneum most often present 1 to 2 weeks after operation with nausea, vomiting, early satiety or anorexia, abdominal discomfort, and dyspnea as a result of accumulation of chylous fluid causing abdominal distention and pressure on the visceral structures and diaphragm. Shortness of breath and pleural effusion caused by chyle impinging on the lungs and surrounding tissues are the hallmarks of chylothorax. A high ventilation pressure may be noted in patients requiring respiratory support. Mediastinal shift compromising the contralateral lung and encroaching on cardiac function can occur with large unilateral chylothoraces. Physical examination supplemented with computed tomography and/or ultrasound studies in this setting reveals large collections of intraabdominal fluid. Lymphangiography and lymphoscintigraphy can be used to more precisely localize the source of the leakage.

A definitive diagnosis requires a paracentesis or thoracocentesis. The aspirated fluid is odorless and has a milky appearance that separates into a creamy layer upon standing. Laboratory analysis of the fluid can yield a specific gravity greater than 1.012, a pH greater than 7.0, triglyceride levels above 2.25 mmol/L, low cholesterol levels with an ascites-to-serum ratio less than 1, total protein between 25 and 70 g/L, serum-ascites albumin gradient less than 11 g/L, and lactate hydrogenase between 110 and 200 IU/L. The fluid is also sterile and contains fat globules when lipophilic stains such as Sudan III are used. A white blood cell count differential of the aspirated fluid yields predominately lymphocytes, and it has been suggested that a significant decrease in the number of lymphocytes in a patient’s total white blood count may be used as a prognostic factor for the development of chylous ascites.