Hounsfield units are a useful predictor of pleural effusion cytological type in dogs but not in cats

Abstract

All categories of pleural effusion subjectively display as soft tissue opacity on computed tomography (CT). Quantitative measurement using Hounsfield units (HU) has the potential to bring additional information regarding the nature of the fluid in a noninvasive way. The purposes of this retrospective cross-sectional analytical study were to compare Hounsfield units of different pleural effusion categories in dogs and cats, assess association between specific cytologic parameters and Hounsfield units, and evaluate the effect of dependent vs. nondependent aspect of the effusion pool on Hounsfield unit. A total of 111 patients (74 dogs and 37 cats) with pleural effusion, that underwent thoracic CT and diagnostic thoracocentesis, were included in the study. Effusions were cytologically categorized as exudate, transudate, modified transudate, hemorrhage, or chyle. Significant differences existed in Hounsfield units between categories in dogs (P < 0.0001) but not in cats (P = 0.334). Canine chylous effusion (6.1 ± 4.7 HU (mean ± standard deviation)) and transudate (5.6 ± 2.0) were significantly lower than exudate (20.3 ± 9.5) and hemorrhage (21.4 ± 9.2). No significant differences were found between modified transudate (13.6 ± 10.3) and other categories. Significant, weak linear correlation was identified in dogs between Hounsfield units and total protein (P = 0.018, R = 0.089), red blood cells (P = 0.021, R = 0.077), and total nucleated cells (P = 0.013, R = 0.089). The Hounsfield units of dependent effusion was not significantly higher than the nondependent effusion, except for canine chylous effusion (P = 0.008). Fourteen Hounsfield units was identified as the most clinically useful threshold: <14 HU identified transudate or chylous effusion with a sensitivity of 100% and a specificity of 69%. A threshold >14 HU had a specificity of 100% and a sensitivity of 69% for identifying exudate, modified transudate, or hemorrhage.

Computed tomographic and clinical findings in a dog with suspected liver lobe torsion, secondary disseminated intravascular coagulation and multiorgan infarction

“…This case also had evidence of a large‐volume pleural effusion. Considering the low attenuation (4 HU) on CT and the serosanguinous nature, it likely represented a transudate 34 35. Pleural effusion has been previously reported in two dogs with LLT 1 13.…”

“…Considering the low attenuation (4 HU) on CT and the serosanguinous nature, it likely represented a transudate. 34 35 Pleural effusion has been previously reported in two dogs with LLT. 1 13 The most likely cause suggested in one of the reports was vasculitis secondary to significant inflammation.…”

“…Total bilirubin was within normal limits (5.0 μmol/l; RI: <5). A coagulation profile revealed mildly prolonged prothrombin time (PT) of 15 seconds (RI: 7-12), but normal activated partial thromboplastin time of 21.6 seconds (RI: [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Fibrinogen was reduced (0.77 g/l; RI: 1-5) and D-dimers were severely increased (3.518 µg/ml; RI: <0.25).…”

A Retrospective Study on Bacteriology, Clinicopathologic and Radiographic Features in 28 Cats Diagnosed with Pyothorax

“…In comparison to radiography, computed tomography would yield a more detailed assessment of underlying parenchymal and pleural abnormalities, avoid the superimposition of images, provide details with regard to severity and provide an opportunity for the assessment of mediastinal, sternal and tracheobronchial lymph node enlargement [ 9 ]. A previous study reported that computed tomographic attenuation values can be a possible predictor of the type of pleural fluid [ 33 , 34 ]. Nevertheless, this method might not be feasible and can be inconsistent in sensitivity due to the technological and technical difference of the respective computed tomography scanner used.…”

Nodules and masses are associated with malignant pleural effusion in dogs and cats but many other intrathoracic CT features are poor predictors of the effusion type

“…There are fewer studies in veterinary medicine assessing pleural abnormalities on CT in dogs and cats with pleural effusion with some studies simply describing nonspecific thickening of the parietal and/or visceral pleura . Several studies assess pleural abnormalities in more detail, including the assessment of Hounsfield units in different types of pleural effusion and assessing various types of pleural thickening (eg, smooth, irregular, nodular, mass), such as those seen with mesothelioma, carcinomatosis or other malignancies or with infectious pleuritis/mediastinitis associated with pyothorax such as secondary to foreign body migration or bronchopneumonia . One study assessed whether pleural abnormalities on CT in dogs can distinguish malignant from inflammatory (pyothorax and chylothorax) effusions and found that there were many overlapping pleural features, although the presence of any pleural thickening, marked pleural thickening involving only the parietal pleura and thoracic wall invasion, supported a diagnosis of malignancy .…”