Authors Kunal Jakharia, MD, Pulmonary and Critical Care fellow, University of North Carolina, Chapel Hill Christina MacRosty, DO, Interventional Pulmonary fellow, University of North Carolina, Chapel Hill Jason Akulian, MD MPH, Assistant Professor of Medicine, Division of
Pulmonary Diseases and Critical Care Medicine, University of North
Carolina, Chapel Hill
Case
A 55-year-old female with well controlled HIV on anti-retroviral
therapy, and end stage renal disease, was admitted for hypoxic
respiratory failure. On presentation, she was hypotensive, tachycardic
and febrile to 39C. Initial labs revealed an elevated serum lactate and
leukocytosis. Chest Xray was followed up by a Chest CT, shown below.
Question
What does this patient likely have?
A. Simple parapneumonic effusion B. Empyema C. Lung abscess D. Lymphoma
Answer
B. Empyema
Discussion
This patient’s contrast enhanced computed tomography (CT) scan shows a
split pleura sign (SPS) which is highly sensitive and specific for
empyema1. The SPS occurs due to thickening and separation of
the visceral and parietal pleural layers by collection of infected
pleural fluid.
The collection of pus in the pleural space is defined as empyema.
Empyema are most often seen in the setting of bacterial pneumonia. A
simple parapneumonic effusion forms by movement of interstitial fluid
across the adjacent visceral pleura due to increased capillary vascular
permeability2, 3. This fluid is thought to be sterile.
Bacterial invasion into the pleural fluid leads to an inflammatory
response and fibrin deposition creating a complex fluid space, known as a
complicated parapneumonic effusion. Frank pus within the pleural space
is definitive of empyema, the natural course of which is development of a
fibrous peel that coats the surface of the visceral and parietal
pleura. Organizing fibrin deposition and neovascularization of the
pleural layers causes them to thicken and enhance with contrast3
(Figure 1 - arrows). The lower fluid density of the empyema separating
the thickened/enhanced pleural layers form the basis of the SPS.
Previous study of SPS reported the finding to be associated with a
high accuracy (100%) in differentiating empyema from lung abscess3.
Lung abscesses were noted to abruptly interrupt the bronchovascular
structures whereas empyema would only distort and compress adjacent
lung. Waite et al., reported that 86% of cases found to be empyema had
enhancement of the parietal pleura4. More recently, Tsujimoto
et al., reported that the SPS had a sensitivity and specificity of
80.6% and 74.5% respectively when diagnosing empyema1. In addition, a measure of pleural fluid thickness >30mm along with SPS increased the specificity to 80.9%1.
In our patient, ultrasound evaluation of the pleural effusion
revealed heterogeneous septated fluid. Due to the clinical scenario and
imaging (CT chest and thoracic ultrasound) findings, a 14-french chest
tube was placed under ultrasound guidance. The fluid was observed to be
frankly purulent and had a positive gram stain leading to a diagnosis
of empyema. Blood cultures and pleural fluid culture later grew
streptococcus pyogenes.
We believe that the presence of the SPS should prompt the clinician to intervene swiftly to achieve source control.
References
Tsujimoto N, Saraya T, Light RW, Tsukahara Y, Koide T, Kurai D, et
al. A Simple Method for Differentiating Complicated Parapneumonic
Effusion/Empyema from Parapneumonic Effusion Using the Split Pleura Sign
and the Amount of Pleural Effusion on Thoracic CT. PLoS One. 2015. 10 (6):e0130141
Aquino SL, Webb WR, Gushiken BJ. Pleural exudates and transudates: diagnosis with contrast-enhanced CT. Radiology. 1994 Sep. 192(3):803-8
Stark DD, MP Federle, PC Goodman et al. Differentiating lung abscess
and empyema: radiography and computed tomography. Am. J. Roentgenol.
141, no. 1 (July 1, 1983): 163-167
Waite RJ, Carbonneau RJ, Balikian JP, Umali CB, Pezzella AT, Nash G.
Parietal pleural changes in empyema: appearance at CT. Radiology 1990;
175:145-150.
