diagnostico con ct del derrame

7/27/2019 Diagnostico Con CT Del Derrame

1/6

Suzanne L. Aquino, MD {149}W. Richard Webb, MD {149} ryan J. Gushiken, MD

Pleural Exudates

and

Transudates:

Diagnosis with Contrast-enhanced CT

803

Thoracic Radiology

PURPOSE:

To determine the accu-

racy of computed tomography CT) in

enabling differentiation of pleural

exudates from transudates.

MATERIALS AND METHODS:

Eighty consecutive patients 86 effu-

sions) underwent contrast-enhanced

CT. Thoracentesis was performed to

measure pleural and serum total pro-

tein and lactate dehydrogenase LDH)

values. Effusions were classified as

exudates with accepted criteria. CT

scans were evaluated for the pres-

ence and appearance of parietal pleu-

ral and extrapleural fat thickening.

RESULTS: Fifty-nine effusions

were

exudates and 27 were transudates.

Thirty-six of the 59 exudates 61 )

were associated with parietal pleural

thickening. All cases of empyema

and 56 of the parapneumonic exu-

dative effusions had pleural thicken-

ing. The specificity of this finding in

diagnosing the presence of an exu-

date is 96 .

CONCLUSION: Parietal pleural

thickening at contrast-enhanced CT

almost always indicates the presence

of a pleural exudate. A pleural exu-

date in the absence of pleural thick-

ening occurs most frequently in pa-

tients

with malignancy or uncompli-

cated parapneumonic effusion.

Index terms: Pleura, CT

{149} le ura , dise ase s,

66.335, 66.693, 66.773 {149} leura, fluid, 66.693,

66. 76 , 66. 773 {149} leura, infection, 66.76 {149} leura,

neoplasms, 66.335

Radiology 1994; 192:803-808

I

From the Department of Radiology, Univer-

sity of California, 505 Parnassus Ave. San Fran-

cisco, CA 94143-0628. Received December 29,

1993; revision requested February 28, 1994; revi-

sion received April 5; accepted April 25. Address

reprint requests to S.L.A.

RSNA, 1994

C OMPUTED

tomography CT) is fre-

quently used to assess patients

with pleural abnormalities associated

with neoplasm, asbestos exposure,

pneumonia, and empyema. It has

been recently reported that the find-

ing of parietal pleural thickening at

contrast-enhanced CT can help distin-

guish pleural effusions representing

exudates or empyema from those rep-

resenting transudates 1). Transuda-

tive pleural effusions and a large per-

centage of malignant exudates do not

show parietal pleural thickening or

enhancement. Also, several studies

have described extrapleural fat thick-

ening and edema in association with

pleural thickening or effusion, al-

though it was unclear whether chest-

tube placement had preceded these

findings in many of the cases.

We reviewed the appearance of

the pleura on contrast-enhanced CT

scans

obtained in 80 consecutive pa-

tients with pleural effusions to deter-

mine the accuracy of CT in enabling

differentiation of pleural exudates

from transudates on the basis of pari-

etal pleural thickening. The appear-

ance of extrapleural fat was also

assessed.

MATERIALS AND METHODS

Eighty consecutive patients with 86

pleural effusions were evaluated with con-

trast-enhanced CT and diagnostic thora-

centesis. Patients were selected for the

study if they

met the following criteria:

a

presence of a pleural effusion at con-

trast-enhanced CT, b

pleural lactic dehy-

drogenase LDH), total protein, glucose,

and serum LDH and total protein values

obtained at thoracentesis, and c

results

from pleural effusion culture and cytologic

examination. There were

25

female pa-

tients and 55 male patients aged 10-88

years mean, 58 years). The 86 effusions

represented a variety of diagnoses but

most were pleural effusions associated

with malignancy or pneumonia Table 1).

No patients had previously undergone

placement of a pleural drainage tube or

sclerotherapy.

Thoracentesis was performed an aver-

age of 4.3 days range, 0-20 days) before or

after the CT examination. For the pur-

poses of this study, a pleural effusion was

classified as an exudate or a transudate in

accordance with definitions proposed by

Light 2). Modifications of Lights criteria

have been shown to increase the specific-

ity in detecting exudates 3); however, we

chose to adhere to the original criteria,

which is followed at our institution and at

the hospital laboratory. To be classified as

an exudate, an effusion met at least one of

the three following criteria: a) a pleural

fluid total protein/serum total protein ra-

tio of more than 0.5, b

a pleural fluid

LDH/serum LDH ratio

of more than 0.6,

or

c

pleural fluid LDH greater than two-

thirds of the upper limits of normal for

serum LDH. At our institution, the upper

limit of normal for serum LDH is 200 IU.

Effusions were classified as transudates

if they that did not meet any of the above

criteria. Patients were excluded from the

study if there were insufficient laboratory

data with which to evaluate the nature of

the effusion. On the basis of these criteria,

59

of 86 effusions were classified as exu-

dates. Twenty-seven effusions were classi-

fled as transudates Table 1).

Pleural effusions were also analyzed for

the presence of infectious organisms by

means of staining including gram, fungal,

and mycobacterial stains), culture aerobic,

anaerobic, fungal, and mycobacterial), and

cytologic examination. Parapneumonic

effusions are usually defined as those asso-

ciated with pneumonia, lung abscess, or

bronchiectasis, and an empyema is consid-

ered to be a complicated parapneumonic

effusion in which pus is present and the

culture is positive 2,4). Complicated para-

pneumonic effusions necessitating chest-

tube drainage are also considered to be

those with very high LDH > 1,000 LU),

low pH < 7.0 ), or low glucose

< 40 mg/

dL) values 2). In our study, effusions were

considered to be empyemas only if culture

results were positive. Otherwise, all effu-

sions associated with pulmonary infec-

tions were classified as parapneumonic

effusions. Malignant effusions were de-

fined by the presence of positive cytologic

results. Effusions with negative cytologic

Abbreviation: LDH = lactic dehydrogenase.


2/6

Diagnosis

No. of

Effusions

No. of

Exudates

No. of

Transudates

Malignancy

Positive cytologic findings 14

14 0

Negative cytologic findings 17 9 8

Parapneumonic effusion 25 18 7

Empyema

Liver transplantation 4 0 4

Congestive heart failure 3 0 3

Dressler syndrome 2

2 0

Contralateral empyema 2 0 2

Sepsis 1 0 1

FocalLIP 1

1 0

Asbestos exposure

1 1

0

Trauma 1 1 0

Pulmonary embolus 1 1 0

Hypoalbuminemia 1 0 1

Undiagnosed

Total

3 2 1

86 59

27

Note-LIP =

lymphocytic

i nt er st it ia l pneumon ia .

Table 2

Thickness of Parietal Pleura in 59

Exudative Ef fusions

Note-LIP = lymphocytic interstitial pneu-

monia.

8 4 {149}adiology

September 994

results were classified as effusions associ-

ated with malignancy, in distinction to

the truly malignant effusions.

Contrast-enhanced CT was performed

in all patients with either a GE 9800 scan-

ner (GE Medical Systems, Milwaukee,

Wis) or an Imatron Cine CT scanner (Ima-

tron, San Francisco, Calif). Contiguous 10-

mm-thick sections were obtained with the

GE scanner, and contiguous 6-8-mm-thick

sections were obtained with the Imatron

scanner. All patients received 60-200 mL

of iohexol (Omnipaque 300 or 350; Win-

throp-Breon Laboratories, New York, NY)

at a rate of 1.7 mL/sec.

CT scans were reviewed blindly by two

observers who reached a consensus. Stud-

ies were evaluated for the presence of pa-

rietal and visceral pleural thickening. Pan-

etal pleural thickening was diagnosed

only if a pleural line was visible internal to

the nibs, in areas in which pleural effusion

was also seen (5). When visible, the thick-

ness of parietal pleura was measured and

its extent and appearance classified as fo-

cal or diffuse and irregular on smooth.

Pleural thickening was considered diffuse

if it was visible in all locations in which

fluid was visible. The presence of visceral

pleural enhancement and thickening adja-

cent to fluid collections was also assessed.

Effusions were described as either cres-

centric and uniloculan or loculated. Cres-

centric, unilocular effusions were defined

as collections of pleural fluid that accu-

mulated in the dependent portion of the

chest seen without septations. Conversely,

loculation was used to describe any effu-

sion that had septations, was compant-

mentalized in the pleural space, or was

accumulated in the fissures, away from

most of the effusion.

The extrapleural fat adjacent to the ribs

was evaluated for visibility, thickness,

asymmetry, and attenuation. Because ex-

trapleural fat can be seen in healthy sub-

jects, for the purposes of this study, the

presence of extrapleural fat was arbitrarily

considered normal if it was less than 2 mm

thick. The attenuation of the extrapleural

fat was estimated to be the same as that of

the chest wall fat, the same as that of the

musculature of the chest wall, or intenme-

diate, between that of fat and musculature.

RESULTS

Fifty-nine exudates were evaluated

with CT (Table 1). Thirty-six showed

focal or diffuse parietal pleural thick-

ening (Table 2). Thus, the sensitivity

of parietal pleural thickening as seen

at CT in the detection of the presence

of a pleural exudate was 61 (confi-

dence interval, 47 -73 ) (Table 3).

Pleural thickness measured 2-4 mm

in 30 of the 36 cases with thickening,

and the thickness of the pleura did

not appear to correlate with the diag-

nosis. Of the 36 effusions associated

with parietal pleural thickening, 12

showed diffuse, smooth, parietal

pleural thickening in association with

Table

Diagnoses in Patients with 86 Effusions

the pleural effusion (Fig 1) and two

had diffuse, irregular thickening

(Table 4, Fig 2). The remaining 22 ef-

fusions were associated with irregular

or smooth focal pleural thickening.

All effusions were crescentric and uni-

locular. Diffuse, irregular thickening

was seen in the presence of malig-

nancy and asbestos exposure; how-

ever, only two effusions were associ-

ated with this finding (Fig 2). Focal,

irregular, pleural thickening was seen

with malignancy. Twenty-three pleu-

ral exudates did not show parietal

pleural thickening (Table 2). These

included 12 effusions associated with

malignancies, eight parapneumonic

effusions, two of unknown cause, and

one occurring after chest trauma.

Parietal pleural thickening was vis-

ible in all 10 empyemas (Fig 3) but

was present in only 10 (56 )

of 18

parapneumonic exudates (Fig 4). All

five complicated parapneumonic effu-

sions (LDH > 1,000 LU or glucose 4

mm

Malignancy

Positive cyto-

logic

findings

10 2

1 1

Negative cyto-

logic findings 2

3 2 2

Pneumonia 8 3 6 1

Empyema 0 3 6 1

FocaILIP

Dressler syndrome 0

0 1 1

Asbestos exposure 0 0 1 0

Pulmonary

embolus

Trauma 1 0 0 0

Undiagnosed

Total

2 0 0 0

23 13

17 6

ing developed bilateral effusions in

association with congestive heart fail-

ure (Fig 5). CT demonstrated unilat-

eral, diffuse, parietal pleural and ex-

trapleural fat thickening, visceral

pleural thickening, reduction in vol-

ume of the ipsilateral hemithorax, and

collapse of the underlying lung. It

was subsequently determined that

this patient likely had a preexisting

pleural peel resulting from prior em-

pyema. Of the remaining 26 transuda-

tive effusions, 25 were crescentric and

unilocular. One transudative effusion

caused by congestive heart failure

showed unilateral loculation of fluid

in the fissures without pleural thick-

ening. Of the 27 transudates, most


3/6

Table 3

Summary

of CT Findings in 59 Exudates and 27 Transudates

Parietal Extrapleural Visceral

Group Pleural Thickening Fat Thickening

Pleural Thickening

Exudates 36

21 13

Transudates

1 1

1

2.

Figures 1, 2. (1) Contrast-enhanced CT scan of the thorax of a 70-year-old man with Dressier

syndrome who recently underwent open heart surgery. The parietal pleura adjacent to the

left effusion is diffusely thickened. The underlying fat is more than 4 mm thick and is of inter-

mediate attenuation. Results of biopsy and cytologic examination indicated a benign effusion,

consistent with inflammation. (2) Contrast-enhanced CT scan shows a malignant pleural effu-

sion in a 72-year-old woman with a history of breast carcinoma. Irregularly thickened parietal

pleura is adjacent to the effusion, which was proved to be malignant at cytologic examination.

The subpleural fat is thickened and of intermediate attenuation.

Table 4

Characteristics of Parietal Pleural Thickening in

59

Exudates

ns

Diagnosis

Normal

Focal

Smooth

Thickening

Irregular

Diffuse

Smooth

Thickening

Irregular

Malignancy

Positive cytologic finding 10

1 1 1 1

Negative cytologic finding

2 4 3 0 0

Pneumonia 8 5

0 5 0

Empyema

0 6 0 4 0

FocalLIP

0 1

0 0 0

Dress le r syndrome

0 0 0

2 0

s estos exposure

0 0 0 0

1

Pulmonary embolus 0 1 0 0 0

Trauma 1 0 0

0 0

Undiagnosed

Total

2 0 0

0 0

23 18 4 12 2

Volume 92

{149}

umber 3

Radiology {149}5

Note-LIP

= lymphocytic interstitial pneumonia.

additional cases had an extrapleural

fat layer that was less than 2 mm

thick, which was considered normal.

Only one of the 23 exudates without

parietal pleural thickening was inter-

preted as showing extrapleural fat

thickening; this occurred in a patient

with a parapneumonic effusion. Fat

thickening was associated with a tran-

sudate only in the patient with pari-

etal pleural thickening. The specificity

of this finding was 96 (confidence

interval, 79 -99 ). Increased attenu-

ation of extrapleural fat (intermediate

or the same as that of soft tissue) was

seen in 10 patients with fat thicken-

ing. Most patients had fat of interme-

diate attenuation, and eight had em-

pyemas or parapneumonic effusion

(Figs 3, 4).

Visceral pleural thickening was vis-

ible in 13 patients with exudates (five

with pneumonia, five with empyema,

and three with malignancy) (Fig 4)

and in the patient with a transudative

effusion and pleural thickening (Fig

5). Thickened visceral pleura mea-

sured less than 2 mm in all patients.

The sensitivity of this finding was

22 and the specificity 96 .

Of the 31 effusions in patients with

malignancies, 23 were exudates (Table

6). Eleven showed parietal pleural

thickening. Seven of the 11 had nega-

tive findings at cytologic examination,

and four had positive findings (Fig 2).

There was no difference in the degree

or appearance of pleural thickening

between those patients with positive

and negative cytologic findings

(Tables 2, 4). Of the 12 exudates asso-

ciated with malignancy that did not

show parietal

pleural thickening, 10

had positive cytologic findings (Fig 6).

Of the effusions associated with lung

cancer, none of those associated with

pleural thickening had positive cyto-

logic findings; four of seven effusions

associated with

lymphoma, breast

cancer, or other tumors had pleural

thickening and positive cytologic re-

sults. The malignant mesothelioma

diagnosed with open biopsy showed

diffuse nodular thickening. Extrapleu-

ral fat thickening was visible in three

of the 23 exudative effusions.

DISCUSSION

occurred in patients with a history of

malignancy but were associated with

benign pleural fluid at cytologic ex-

amination or were parapneumonic

effusions in the absence of empyema

(Table 1).

Of the 36 exudates associated with

parietal pleural thickening, 20 showed

extrapleural fat thickening; therefore,

the sensitivity was 36 (confidence

interval, 24 -49 ) (Table 3). Eight of

these exudates were empyemas and

eight were parapneumonic effusions

(Table 5). The extra pleural fat was

2-4

mm thick in nine cases and at

least 4 mm thick in 12 (Table 5); eight

Exudative effusions can have a vari-

ety of causes. They often reflect the

presence of pleural inflammation, in-

fection, or neoplasm, and in such

cases are thought to be due to an in-

creased permeability of abnormal

pleural capillaries and the release of

high-protein fluid into the pleural

space (2,6). In patients with malig-


4/6

Figures 3, 4. (3) Contrast-enhanced CT scan of the thorax of a persistently febrile 48-year-old

woman I month after orthotopic liver transplantation. A pulmonary abscess in the right lower

lobe is in direct communication with the adjacent pleural effusion. The panietal pleura is en-

hanced, and the subpleural fat is thickened and has almost the same attenuation as that of soft

tissue. Enterococci were found at culture of the effusion. (4) CT scan of the thorax of a 29-year-

old man with acquired immunodeficiency syndrome and a partially treated pneumococcal

pneumonia. The posterior parietal pleura is smoothly thickened, and the underlying fat is of

intermediate attenuation. The visceral pleura is also enhanced (arrow). Although the findings

were highly suggestive of empyema, results of multiple cultures of the effusion were negative.

I Table5

Thickness and

Attenuation of Extrapleural Fat in 59 Exudates

I

2mm 2-4mm >4mm

{149}

Interme- Soft Interme- Soft

Interme-

Soft

Diagnosis

Malignancy

Normal Fat diate Tissue Fat diate Tissue Fat diate Tissue

Posit ive cytologic

finding 2

Negat ive cytolog ic

finding 6 1 0 0 0 0 0 1 1 0

Pneumonia 6 2

1 1 0 1

2 3 2 0

Empyema 2 4

FocalLIP

Dressler syndrome 0 0 0 0 1 0 0 0 1 0

sbestos exposure 1 0 0 0 0 0 0 0 0 0 I

Pulmonary embolus 1 0 0 0 0 0 0 0 0 0 :

Trauma 2

Undiagnosed

Total

I 0 0 0 0 0

0 0 0 0

30 4 3 1 5 2 2 6 5 1

Note.-Fat = same attenuation as that of chest wall fat, intermediate = attenuation between that of

fat and soft

tissue

soft

tissue =

same attenuation as that of soft tissue. LIP

=

lympho cyti c in terstitial

pneumonia.

806 {149}

adiology September 994

nancy, exudates can also reflect the

presence of lymphatic obstruction or

lung disease rather than a pleural ab-

normality (6). Furthermore, it is theo-

rized that some exudates may result

from fluid released directly into the

pleural space by a damaged lung, as

with pneumonia, pulmonary embo-

lism, and lung transplantation (6).

Transudative effusions are not asso-

ciated with pleural disease and are

considered to be the result of systemic

abnormalities that cause an imbalance

in the hydrostatic and osmotic forces

leading to the formation of pleural

fluid. This results in an outpouring of

low-protein fluid from the pleural

capillaries and, occasionally, the pa-

renchymal interstitium into the pleu-

ral space (6). Common causes of a

transudative effusion include conges-

tive heart failure, cirrhosis, and ne-

phrotic syndrome.

Differentiating an exudate from a

transudate can be important in clini-

cal management, particularly in pa-

tients with infection and malignancy.

For example, the presence of a transu-

dative effusion in association with

pneumonia does not warrant further

evaluation or treatment; an exudative

parapneumonic effusion may not re-

quire

chest-tube drainage if simple.

However, if the exudate becomes

complicated, chest-tube therapy is

indicated because it is likely that em-

pyema will occur. In a patient with an

underlying malignancy, an exudative

effusion in the absence of infection is

strongly suggestive of pleural metas-

tases or recurrence despite negative

cytologic findings. Often these effu-

sions necessitate drainage and sclero-

therapy when symptomatic or recur-

rent. In a patient with neoplasms, the

presence of a transudate excludes ma-

lignant involvement of the pleura,

although they can be seen in the early

stages of mediastinal involvement

with lymphatic obstruction (7).

Exudates and transudates differ in

many ways, but according to gener-

ally accepted criteria proposed by

Light (2), exudative effusions are con-

sidered to be those with a pleural

fluid total protein/serum total protein

ratio of more than 0.5, a pleural fluid

LDH/serum LDH ratio of more than

0.6, or an absolute pleural fluid LDH

of more than two-thirds of the normal

value of serum LDH. A pleural fluid-

specific gravity exceeding 1.016 or a

pleural fluid protein exceeding 3 g/dL

are other criteria used to diagnose

exudate, but these have a somewhat

lower specificity (8). Although the

classification of a pleural effusion as

an exudate or transudate is usually

based on results of thoracentesis, it is

also important to know the accuracy

of imaging studies in assessing pleural

fluid, as they are commonly obtained

in this setting and are often used to

guide interventional procedures.

Sonography can be useful for de-

tecting pleural fluid characteristics

compatible with an exudative effu-

sion. Yang et al (9) found that all effu-

sions with septation, complex non-

septation, or homogeneous echogeni-

city at sonography were exudative.

Anechoic effusions, however, could

be either transudative or exudative.

The sensitivity of sonography in their

study was 66 , with a specificity of

100 and a positive predictive value

of 100 In our study, parietal pleural

thickening was shown at contrast-

enhanced CT in 61 of exudates, and

this finding had a specificity of 96

and a positive predictive value of 97 .

Waite et al (1) have reported that

CT

shows pleural thickening and en-

hancement in almost all patients with

empyema or parapneumonic effusion.

In their study, 24 of 25 empyemas

demonstrated pleural thickening and

enhancement at CT; however, some

patients underwent thoracostomy

tube insertion before undergoing CT.


5/6

Table 6

Characteristics of 31 Pleural Effusions Associated with Malignancy

Diagnosis

No. of

Exudates

No. of

Transudates

No. with

Thickened

P anie tal P leu ra

No. with No

Thickening of

Parietal Pleura

Lymphoma

Positive cytologic findings 4 0

2 2

Negative cytologic findings 3 3 2 4

Breast cance r

Positive cytologic findings 5 0 1 4

Negative cytologic findings I 3 0

4

Lung cancer

Positive cytologic findings 3 0 0 3

Negative cytologic findings 4 0 4 0

Other

Positive cytologic findings 2 0

1 1

Negative cytologic findings

Total

1

2 1 2

23 8 2

Note-Other = esophageal cancer, hepatocellular cancer, Kaposi sa rcoma , mali gna nt meso the lioma,

ovarian

cancer.

Volume 192

{149}

umber

3

Radiology {149}

07

5.

6

Figures

5, 6. (5) Contrast-enhanced CT scan of a fibrothorax with superimposed congestive heart failure in a 53-year-old man. The thorax

shows right-sided volume loss with an ipsilateral shift of the mediastinum. The right lung is collapsed, and the parietal and visceral (straight

arrows) pleura are diffusely thickened. The subpleural fat (curved arrow) is thicker than that in the left side. (6) CT scan shows a malignant

pleural effusion in a 77-year-old man with adenocarcinoma of the left lung. The adjacent pleura is normal. The associated pleural effusion was

exudative, and findings at cytologic examination were positive. The thin line with the same attenuation as soft tissue lying between the poste-

nor ribs is normal intercostal musculature (arrow).

In our study, CT was sensitive in de-

tecting pleural thickening in empy-

ema; all 10 empyemas showed pleural

thickening. Conversely, pleural thick-

ening was seen in 56% of the unin-

fected exudative (culture-negative)

parapneumonic effusions. Included in

this group with pleural thickening,

however, are all of the complicated

parapneumonic effusions (ii = 5),

which were treated with chest-tube

drainage. Twenty-eight percent of

parapneumonic effusions were tran-

sudates and

did not show pleural

thickening. The thickness of the pan-

sions. Of the 23 exudative effusions

associated with neoplasms, 11 (48%)

showed pleural thickening (Table 2).

Surprisingly, only four (28%) of 14

malignant effusions showed pleural

thickening. In the study by Waite et al

(1), 73% of malignant effusions did

not show pleural thickening, and of

the five with thickening, three had

prior sclerotherapy or infection. Ir-

regular pleural thickening was seen

only in association with malignancy

or asbestos exposure (Table 4); the

presence of nodular pleural thicken-

ing has previously been reported as

having a sensitivity of 51% and a

specificity of 94% for the diagnosis of

a malignant pleural process (10).

Thickening and increased attenua-

tion of extrapleural fat is another

finding that is suggestive of pleural

inflammation or infection and has

been reported in patients with empy-

etal pleura or the shape of the effu- ema, malignancy, and asbestos expo-

sion was not helpful in distinguishing sure (1,5,11). Eight of 10 empyemas in

empyemas from uninfected parapneu- our study demonstrated extrapleural

monic effusions because all were cres- fat thickening, with three showing

centric and unilocular (Table 2). abnormally increased fat attenuation

Pleural thickening was less fre- (Fig 3). The two cases that did not

quent when associated with malig- have extrapleural fat thickening had

nancy, and if these cases are ex- fungal empyemas. A prior study (11)

cluded, the sensitivity of parietal has demonstrated increased attenua-

pleural thickening in diagnosing an tion of extrapleural fat in a larger per-

exudate increases to 69%. Of 31 effu- centage of empyemas than was seen

sions in patients with neoplasm, eight in our study. However, pleural drain-

(26%) were transudates and were not age tubes had been placed in 11 of the

associated with pleural thickening; 13 patients. Waite et al (1) found an

none of these were malignant effu- increase in attenuation of extrapleural


6/6

808 {149}adiology

September 1994

fat in 11 of 18 (61 ) empyemas with-

out prior tube insertion (1). The some-

what lower frequency of increased fat

attenuation we report may reflect dif-

ferences in the duration of empyema

in our cases. Extrapleural fat thicken-

ing was

also common in those pa-

tients

with pleural thickening associ-

ated with parapneumonic effusions

(Table 5, Fig 4). Only one of the 23

exudates without associated parietal

pleural thickening was interpreted as

showing extrapleural fat thickening.

Increased attenuation of extrapleural

fat,

presumably representing edema

or inflammation, was present in

10

patients with fat thickening; eight

had empyema or parapneumonic ef-

fusion. Four of eight effusions associ-

ated with a fat thickness of less than

2 mm showed increased attenuation;

this finding may indicate inflamma-

tion in the absence of thickening or

could reflect a volume-averaging phe-

nomenon.

CT

can

play an important role in

the diagnosis of exudative and tran-

sudative effusions. Pleural thickening

associated with a pleural effusion in a

patient with pneumonia indicates the

presence of an exudate, and thoracen-

tesis is warranted. If pleural thicken-

ing is absent, the presence of an em-

pyema or a complicated parapneu-

monic effusion necessitating chest-

tube drainage is highly unlikely. In

patients with malignancy, the pres-

ence of

pleural thickening indicates

the presence of an exudate; the ab-

sence of parietal pleural thickening

does not exclude the presence of an

exudate or malignant effusion and

thoracentesis should be performed

for diagnosis. The degree of pleural

thickening is not helpful for predict-

ing the diagnosis, although the pres-

ence of extrapleural fat thickening is

suggestive of an empyema or a para-

pneumonic effusion. Irregular pleural

thickening is suggestive of a neo-

plasm.

{149}

References

1. Waite RJ, Carbonneau RJ, Balikian JP,

Umali CB, Pezzella AT, Nash G. Parietal

pleural changes in empyema: appearances

a t CT. Radio logy 1990; 175:145-150.

2. Light RW. Pleural diseases. Philadelphia,

Pa: Lea & Febiger, 1990; 39-73.

3. Romero 5, Candela A, Martin C, Hernan-

dez L, Tnigo C, GilJ.

Evaluation of differ-

ent criteria for the separation of pleural

transudates from exudates. Chest 1993;

2:399-404.

4. Light RW. Parapneumonic effusions and

empyema. Clin Chest Med 1985; 6:55-62.

5.

Im JG, Webb WR, Rosen A, Gamsu G.

Costal pleura: appearances at high-resolu-

tion CT. Radiology 1989; 171:125-131.

6. Broaddus VC, Light RW. What is the ori-

gin of pleural transudates and exudates

(editorial)? Chest 1992; 102:658-659.

7. Sahn SA. Malignant pleural effusions.

Clin Chest Med 1985; 6:113-125.

8. Jay SJ. Diagnostic procedures for pleural

disease. Clin Chest Med 1985; 6:33-48.

9. Yang PC, Luh KT, Chang DB, Wu HD, Yu

CJ, Kuo SH. Value of sonography in de-

termining the nature of pleural effusion:

analysis of 320 cases. AJR 1992; 159:29-33.

10. Leung AN, Muller NL, Miller RR. CT in

differential diagnosis of diffuse pleural dis-

ease. AJR

1990; 154:487-492.

11. Takasugi JE, Godwin JD, Teefey SA. The

extrapleural fat in empyema: CT appear-

ance. BrJ Radiol 1991; 64:580-583.

diagnostico con ct del derrame

Documents