PURPOSE: Chylothorax is an uncommon form of pleural effusion which usually results from disruption or obstruction of the thoracic duct. The biochemical parameters of chylous pleural fluids have not been adequately analyzed.
METHODS: We retrospectively reviewed 74 cases of chylothorax (defined by the presence of chylomicrons) evaluated over a 10-year period from 1997 to 2006. The biochemical parameters and appearance of the fluid assessed during diagnostic evaluation were analyzed.
RESULTS: There were 37 men and 37 women. The median age was 61.5 years (range, 20–93 years). Chylothorax was caused by surgical procedures in 51%. The chylous pleural fluid appeared milky in only 44%. Pleural effusion was exudative in 64 patients (86%) and transudative in 10 patients (14%). However, pleural fluid protein and lactate dehydrogenase levels varied widely. Transudative chylothorax was present in all 4 patients with cirrhosis but was also seen with other causes. Mean (±SD) triglyceride level was 728 ± 797 mg/dL and mean cholesterol value was 66± 30 mg/dL. Pleural fluid triglyceride value was <110 mg/dL in 10 patients (14%) with chylothorax and 2 of these patients had a triglyceride value <50 mg/dL.
CONCLUSION: We conclude chylothoraces may present with variable pleural fluid appearance and biochemical characteristics. Non-milky appearance is common. Chylous effusions can be transudative, most commonly in cirrhotic patients. Traditional diagnostic criteria, relying on triglyceride cutoff values to exclude the presence of chylothorax, may be falsely negative in fasting patients, particularly in the postoperative state.
CLINICAL IMPLICATIONS: In conclusion, we note that chylothoraces may present with variable pleural fluid appearance and biochemical characteristics. Non-milky appearance is a common presentation and may cause the diagnosis of chylothorax to be overlooked; particularly in post-surgical patients. Chylous effusions may be associated with a wide range of total protein and LDH value resulting in a transudative character by currently employed classification criteria. Because triglyceride level also varies in patients with chylothorax, traditional triglyceride cutoff values used in excluding the presence of chylothorax may miss the diagnosis in fasting patients, particularly in the postoperative state.
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