Serous fluid: Reactive conditions

Predilections by gender

In general, the incidence is equal between both the sexes; however, effusions associated with certain systemic diseases show some sex predilection in parallel with the general distribution of these diseases in the population. For example, it is noted that effusions associated with systemic lupus erythematosus (SLE) are observed more frequently among women, whereas effusions associated with chronic pancreatitis and rheumatoid effusions are more frequently noted in men.

Predilections of laterality with pleural effusions

Systemic diseases are often associated with bilateral pleural effusions, whereas isolated unilateral effusions occur more frequently with regional pathology. Isolated right-sided pleural effusions commonly occur with subphrenic or intrahepatic abscess formation, amebic liver abscess, Echinococcus infection, cirrhosis, liver transplantation, and Meigs’ syndrome. Isolated left-sided effusions are more frequently noted with esophageal rupture, pancreatic disease, especially pancreatitis, splenic abscess, splenic infarction, diaphragmatic hernia, pericardial disease, or following coronary artery bypass surgery.

Gross examination: type of fluid and possible etiology

Fluid appearances have been classified into many categories by various observers. Of these about eight different appearances have been well described with very good interobserver concordance.^[4] These eight gross appearances comprise: watery (light yellow), serous (yellow), blood-tinged (reddish), bloody (dark red, similar to blood), purulent (pus), milky (white and less thick than pus), turbid (yellow, but viscous or cloudy), and others (brownish, greenish, black, etc.). In daily practice, effusions can be classified into two major categories: non-bloody and bloody effusions.

Special types of effusions

Glucose estimation

Low glucose content in effusion samples is observed more frequently in patients with tuberculosisand rheumatoidarthritis-associated effusion.

Amylase levels

High amylase content is noted more frequently as a result of chronic pancreatitis or its sequelae.

Adenosine deaminase levels

Fluids from patients with tuberculosis show adenosine deaminase levels above 45 IU/L.

Morphology and histochemical stains

Bacteria [Figures 1-3], parasites (e.g., microfilariae), and fungal forms could be visualized by morphologic examination and may be further highlighted using appropriately selected silver stains, periodic acid–Schiff (PAS) stain, or other special stains (e.g., Ziehl–Neelsen stain). As a routine stain, the organisms are highlighted better in Diff-Quik stained preparations [Figure 2 (arrow)].

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Figure 1:

Many apoptotic neutrophils are noted in the pleural effusion sample from a patient with empyema associated with bacterial infection. (Papanicolaou stain, 20×.)

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Figure 2:

In the same patient as Figure 1, the second day pleural effusion sample demonstrated many neutrophils with cocci within the cytoplasm (arrow) better highlighted in Diff-Quik stained preparation. In such patients, bacterial cultures would help to further speciate the bacteria. (Diff-Quik stain, 20×.)

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Figure 3:

Pleural effusion sample from the same patient also demonstrated macrophages (arrow) with intracellular cocci. (DiffQuik stain, 40×.)

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Cultures

Use of appropriate culture media may help detect bacterial as well as fungal organisms and may further help to speciate the organism and its sensitivity to antimicrobial agents.

Immunophenotyping (immunohistochemistry or flow cytometry)

Demonstration of a polyclonal population of atypical lymphocytes noted in effusion samples may further help to confirm the reactive nature of lymphocytes.

Immunohistochemistry

A panel of immunohistochemical stains rather than one single immunostain performed on atypical cells in an effusion sample may be of additional help to distinguish reactive mesothelial cells from metastatic epithelial malignancies. Importance of these stains and their applications with the ‘subtractive coordinate immunoreactivity pattern’ (SCIP) approach is discussed in other reviews.^[13,14] This is one of the more frequently utilized ancillary studies in serous fluid cytology practice.^[10,15-18] Similar studies for microorganisms are also frequently used.

Liver cirrhosis with activity, uremia, and acute pancreatitis

Serous cavity effusions can develop in these conditions and deserve special recognition. In these conditions, reactive mesothelial cells could be present singly, in groups [Figure 4], may form pseudopapillary structures [Figure 5], or may form small gland-like formations. These cells could show extreme degrees of reactive atypia including multinucleation [Figure 6], enlarged nuclei, nuclear membrane irregularities, nuclear hyperchromasia, prominent nucleoli [Figure 7], and mitoses [Figure 8].

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Figure 4:

Peritoneal fluid from a patient with cirrhosis demonstrates a group of cells with vacuolated cytoplasm of mesothelial cells. Unlike neoplastic epithelial cells, they do not show a mucin droplet or deform the shape of the nucleus. Chronic inflammatory cells are also noted adjacent to mesothelial cells. (Papanicolaou stain, 40×.)

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Figure 5:

Peritoneal fluid from a patient with uremia demonstrates pseudopapillary groups with psammomatous calcification. (Papanicolaou stain, 40×.)

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Figure 6:

This pleural effusion sample from a patient with pancreatitis demonstrates multinucleated reactive mesothelial cells. (Diff-Quik stain, 40×.)

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Figure 7:

Pleural effusion sample from a patient with uremia demonstrates a flat sheet of reactive mesothelial cells with marked variation in cell size, mesothelial cell ‘windows,’ nuclear enlargement, and prominent nucleoli. (Papanicolaou stain, 40×.)

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Figure 8:

Peritoneal fluid sample from a patient with cirrhosis demonstrates occasional mitosis (arrow). (Papanicolaou stain, 20×.)

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• As a general rule, therefore, a diagnosis of malignancy should be made with extreme caution in patients who have a history of effusions noted in association with the abovementioned etiologies.

In these effusions all atypical cells will show similar features and will resemble mesothelial cells. Thus a ‘morphologic continuum’ and not two distinct cell populations is noted in these conditions. Immunophenotyping may further help in distinguishing reactive mesothelial cells from metastatic adenocarcinoma by the SCIP approach.^[13,14]

Pulmonary Embolism and Infarction

Effusions associated with pulmonary infarction may show reactive mesothelial cells that may require them to be distinguished from adenocarcinoma. These effusions may also show increased hemosiderin-laden macrophages [Figure 9], neutrophils, and eosinophils [Figure 10].

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Figure 9:

Pleural effusion from a patient with pulmonary infarction shows macrophages, and some also demonstrate hemosiderin pigment (arrows) in the cytoplasm. (Diff-Quik stain, 40×.)

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Figure 10:

Pleural effusion sample from a patient with pulmonary infarction demonstrates areas with increased eosinophils. This example shows characteristic eosinophilic cytoplasmic granules and bilobed nuclei (arrows). (Diff-Quik stain, 20×.)

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Systemic Lupus Erythematosus^[22-24]

Effusions associated with SLE are noted most frequently in the pleural cavity. Although less frequent, SLE-associated effusions may be noted in pericardial cavities. Effusions associated with SLE show characteristics of an exudate. On cytology, these effusions show predominance of inflammatory cells (neutrophils, rarely eosinophils or lymphocytes). One of the most characteristic features is the presence of LE cells. LE cells are inflammatory cells (usually a neutrophil but could be a macrophage) which contain a homogenous hematoxylin body [Figures 11, 12]. The number of LE cells noted in effusion samples can vary. Although the presence of LE cells is a characteristic feature of SLE, it is not pathognomonic of this condition. Other conditions, including drug-associated change, may also show similar features. It should also be recognized that LE cells may not be present consistently in SLE-associated effusions.

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Figure 11:

LE bodies (arrow) are noted in a neutrophil in this pleural effusion sample obtained from a patient with a history of systemic lupus erythematosus. (Diff-Quik stain, 40×.)

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Figure 12:

LE bodies are seen in both neutrophils (1) as well as a macrophage (2) in pericardial effusion in a patient with a history of systemic lupus erythematosus. (Papanicolaou stain, 40×.)

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Rheumatoid Effusions^[22-31]

Pleural effusion is a relatively uncommon but known complication of rheumatoid arthritis. It may be concurrent, or occur prior to, or after the development of joint manifestations of the disease. Rheumatoid effusions are exudative fluids and, as noted earlier, are more frequently noted in males with rheumatoid arthritis in comparison to females. These fluids have reduced glucose levels. On cytology, these effusions show many degenerated cells, necrotic debris, atypical spindled cells resembling spindled squamous cells, histiocytes, and round multinucleated giant cells [Figure 13] in addition to many lymphoplasmacytic cells. • It has been suggested that the presence of necrosis in an effusion specimen is almost characteristic of a rheumatoid nodule. Spindled cells may show varying degrees of degeneration and are frequently pyknotic. Spindled cells in these effusions may raise the differential diagnosis of squamous cell carcinoma.

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Figure 13:

Pleural effusion from a patient with a history of rheumatoid arthritis, lung nodule, and pleural effusion. The effusion sample shows multinucleated giant cells with many chronic inflammatory cells and degenerating as well necrotic cells in the background characteristic of rheumatoid effusion. (Papanicolaou stain, 40×.)

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Such characteristic features may not always be seen in these effusions. These effusions may only show increased neutrophils, lymphocytes, and mononuclear cells. Mesothelial cells may either be absent or rare.

Other less-common causes of reactive effusions include fistulous-tract-associated effusions, endometriosis, asbestosexposure-associated effusions, and talc-associated effusions. Correlation with history and corroborative cytologic features are helpful to arrive at a correct interpretation.

Case 1

Cytology

Evaluation of samples demonstrated many mature lymphocytes [Figure 14]. Many lymphocytes also demonstrated marked nuclear membrane irregularity [Figure 15]. Extensive review demonstrated only rare reactive mesothelial cells.

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Figure 14:

Many mature lymphocytes are noted in this patient with pleural effusion. (Diff-Quik stain, 40μ.)

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Figure 15:

Many mature lymphocytes were noted, with marked membrane irregularity, in this pleural effusion sample. (Papanicolaou stain, 20×.)

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Cytology

Cytology reveals predominantly small mature lymphocytes [see Figures 14, 15]. Conditions associated with predominant lymphocytes include congestive heart failure, spontaneous bacterial peritonitis, tuberculosis, cirrhosis, nephritic syndrome, sarcoidosis, and SLE.

In addition to lymphocytes, only rare mesothelial cells are noted. Lack of mesothelial cells in effusion samples with predominant lymphocytes is characteristically noted in patients with tuberculosis. Cytology samples also shows cells with marked nuclear membrane irregularity. Such cells are most frequently an artifact result of centrifugation. Occasional activated lymphocytes and plasma cells may also be noted. In such a scenario, a possibility of chronic lymphocytic leukemia [Figure 16], primary effusion lymphoma, or a T-cell lymphoproliferative process should be excluded before considering a chronic inflammatory condition as a possibility. Ancillary studies such as immunophenotyping of lymphocytes either using flow cytometry or immunohistochemical studies on cell lock preparations could be useful.

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Figure 16:

Many mature lymphocytes are noted in this elderly patient with a history of chronic lymphocytic leukemia. These cells are morphologically indistinguishable from mature lymphocytes noted from other chronic inflammatory conditions. (Diff-Quik stain, 20×.)

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Case 2

Gross appearance and biochemical estimations

A turbid blood-tinged fluid was recovered that demonstrated increased protein content. Lactate dehydrogenase levels were >200 U/L in the effusion sample.

Cytology

The effusion sample demonstrated increased cellularity at lower magnification. This cellularity was a result of many neutrophils [Figure 17], clearly identifiable mesothelial cells, and atypical cell groups. The latter group of cells demonstrated either hobnailing or cells with community borders [Figure 18]. Individual cells demonstrated centrally placed nuclei with conspicuous nucleoli and moderate granular cytoplasm with endoand ectocytoplasm [Figure 19]. In addition, few multinucleated cells [Figure 20] and cells with nuclear hyperchromasia were also identified.

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Figure 17:

Pericardial effusion reveals a cellular sample predominantly composed of neutrophils with admixed reactive mesothelial cells. Rare mesothelial cells show cytoplasmic vacuolation. (Papanicolaou stain, 20×.)

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Figure 18:

Effusion sample from same patient as in Figure 17 also demonstrates a group of cells (arrow) with three-dimensional organizations with community borders. (Papanicolaou stain, 40×.)

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Figure 19:

Effusion sample from the same patient as in Figure 17 also revealed a morphologic continuum, with reactive mesothelial cells demonstrating cells with conspicuous nucleoli, and two-zoned cytoplasm, as would be noted with reactive mesothelial cells. (Papanicolaou stain, 40×.)

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Figure 20:

Effusion sample from the same patient also revealed occasional multinucleated cells with cells with cytoplasm showing cytoplasmic vacuolization. (Diff-Quik stain, 40×.)

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A diagnosis of atypical cells with possibility of metastatic adenocarcinoma was raised.

Immunophenotype

Immunohistochemical stains performed on the cell block were positive for calretinin and were negative for carcinoembryonic antigen, BerEP4, Leu-M1, cytokeratin 7 and 20, and thyroid transcription factor-1, and supported lack of a second population and confirmed the mesothelial nature of these atypical cells.

Diagnosis

Reactive mesothelial cells: favor therapy-associated changes.

Discussion

A new pericardial effusion in a patient with history of resected non-small-cell carcinoma of lung raises a possibility of metastatic carcinoma.

Evaluation of gross and biochemical estimations suggests this to be an exudate rather than a transudate [Table 6]. An exudate is usually associated with either malignancy or inflammatory/infectious etiology. In this context, this feature does not help distinguish the two.

Cytology also reveals a dual cell population with increased neutrophils. In addition, many of the cell groups reveal groups with hobnail appearance as well as occasional groups with community borders. Most of the cells show features associated with mesothelial cells. Table 7 summarizes some of the salient features that distinguish reactive mesothelial cells from metastatic cells. An immunohistochemical staining pattern supports the mesothelial nature of these cells.

Features associated with chemotherapy or radiationtherapy-induced reactive mesothelial cells

With cancer chemotherapy and radiation, there may not be a large effusion but when the effusion samples are evaluated they may present a significant diagnostic challenge for the pathologist. These samples are often cellular, hemorrhagic, and show increased protein concentration. The cellular composition may include highly reactive mesothelial cells with degenerative changes, occasional ‘community’ borders, and cytoplasmic vacuolation. In addition, histiocytes and bizarre cells may also be noted. A clear two-cell population, a cytologic clue to malignancy, is not identified in these samples. In addition, the cells may show features of a radiation therapy effect, including cytomegaly, multinucleation, smudging of chromatin, cytoplasmic vacuolation, and two-toned staining of cytoplasm.