Imaging: Imaging |

Can CT Attenuation (Hounsfield Unit) Differentiate Between Transudative or Exudative Pleural Effusions? A Controversial Question FREE TO VIEW

Raminderjit Sekhon, MD; Zeron Ghazarian, MD; Tapan Pandya, MD; Michael Hanna, MD; Mourad Ismail, MD
Author and Funding Information

St. Joseph's Regional Medical Center, Paterson, NJ

Copyright 2016, American College of Chest Physicians. All Rights Reserved.

Chest. 2016;150(4_S):663A. doi:10.1016/j.chest.2016.08.757
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SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 26, 2016 at 01:30 PM - 02:30 PM

PURPOSE: Rates of pleural effusion detection in the hospital setting have increased over the past decade with the use of more imaging modalities such as CT scans. Effusions are classified as exudative or transudative based on Modified Light’s criteria by analyzing the fluid obtained through thoracentesis which helps establish the need for further invasive measures such as tube thoracostomy placement. While Modified Light’s criteria have high specificity and sensitivity to determine effusion type, it requires an invasive procedure. Studies have shown mixed results regarding the utility of CT attenuation in addition to Modified Light’s criteria in identifying effusion type. The goal of our study is to identify if CT attenuation (Hounsfield unit) can help classify tranusdative effusions without the need for a thoracentesis to decrease the number of invasive procedures.

METHODS: A retrospective study was conducted on patients admitted during 2014-2015 to St. Joseph’s Health Care System in New Jersey, who underwent bedside thoracentesis and had a CT Scan of the chest within twenty-four hours prior to the procedure. Charts of eligible patients were identified through billing codes. Data was collected to classify the pleural effusion based on Modified Light’s criteria as an exudate or transudate. These variables included both lactate dehydrogenase (LDH) and total protein (TP) from the pleural fluid and serum. Calculations of their respective ratios were then recorded to classify them as a transudative or exudative effusion. In addition, using PACS imaging a Hounsfield unit (HU) average was obtained in axial plane at the most dependent part of the hemithorax ipsilateral to the effusion.

RESULTS: In our study 20 patients were identified who underwent a bedside thoracentesis and had CT imaging of the chest within twenty-four hours prior to the procedure, 15 were identified as exudates and 5 transudates based on Modified Light’s criteria. Statistical analysis revealed a significant difference of the TP ratio and LDH ratio between transudates and exudates (p=0.003 and 0.001), which was similar to Modified Light’s criteria. T-test analysis of HU between effusion type showed mean values of 12.4 and 9.6 for exudates and transudates respectively with no significant difference (p=0.318).

CONCLUSIONS: Our results showed that CT attenuation (HU) difference was not statistically significant between exudative and transudative effusions, which preclude its utility prior to thoracentesis. From our experience, when used in conjunction with Light’s criteria, Hounsfield unit calculation cannot be a helpful parameter to help physicians need to proceed to more invasive procedures.

CLINICAL IMPLICATIONS: Although our study has a small patient cohort and does not account for artifact limitation for attenuation calculation including loculation of pleural fluid, Hounsfield number threshold may not accurately add diagnostic value in classifying effusion type. Larger patient cohort studies may be warranted to assess if there is any role of Hounsfield units to identify transudative effusions.

DISCLOSURE: The following authors have nothing to disclose: Raminderjit Sekhon, Zeron Ghazarian, Tapan Pandya, Michael Hanna, Mourad Ismail

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