Pleural, Peritoneal, and Pericardial Effusions
centrifuged deposit contains a deep layer of red blood cells, dip-
ping the loop only a millimeter or so too deeply into the deposit
may result in smears that have a high proportion of red blood
cells and very few cells from the buffy layer.
Red blood cells are readily recognized in Papanicolaou-stained
smears as neatly round orange-red discoids about 7 pm in
diameter, although many may become distorted into elongated
forms in the process of spreading the cellular sample. Fixation
may cause red blood cells to undergo lysis, leaving residual
empty cell membranes with a slightly cyanophilic staining reac-
tion. Hemoglobin released from these cells may remain as part
of the proteinaceous background of a smear, thereby imparting a
reddish cast to the smeared material, both to the naked eye and
under the microscope. In the toluidine blue-stained wet films,
red blood cells are unstained, having a light straw yellow color.
Apart from these artifacts, normal red blood cells generally
show little morphologic variation. Spherocytic forms have been
described in air-dried preparations of pleural effusion from
patients with hemothorax.9 Heinz bodies, globules of degraded
hemoglobin formed in stagnant collections of blood, may be
seen in Papanicolaou-stained smears, but they are more readily
identified in stained wet films.
Immature red blood cells may be present in serous effusions
when they are present in circulating blood as, for example,
in leukoerythroblastic anemia, chronic myelogenous leukemia,
and myeloproliferative disorders. However, we have found it
virtually impossible to discern these immature forms in smears
prepared by the Papanicolaou method; air-dried Romanowsky-
stained smears are far superior for this purpose.9 Neutrophilic
leukocytes may undergo degenerative changes in which their
nuclei become pyknotic, a change that simulates normoblasts.
Intraerythrocytic crystallization of hemoglobin, a result of
polymerization of the hemoglobin molecules, may occur in
peripheral blood in certain hemoglobinopathies, being more
pronounced in hemoglobin C disease. Zaharopoulos and Wong
described two examples of such crystallization in red blood
cells in pleural effusions from patients who had neither clini-
cal nor other evidence of hemoglobinopathy.27 Under labora-
tory conditions, they produced intraerythrocytic crystallization
of hemoglobin in specimens of hemorrhagic pleural effusion by
subjecting them to agents that induced decreased oxygen con-
centration and osmotic dehydration of the cells. They suggested
that a similar process takes place in effusions accumulated in
confined body spaces such as the pleural cavity.
Intact red blood cells may be phagocytosed by macrophages.
When red blood cells disintegrate, their hemoglobin is converted
into hematoidin or hemosiderin, which, if present in a large
enough amount, imparts a distinctly yellow (xanthochromic)
appearance to the supernatant. In stained wet films, hematoi-
din pigment may occasionally be seen as sheaves of fine, elon-
gated, yellow-brown extracellular crystals, whereas hemosiderin
is seen as dark blue granules in the cytoplasm of macrophages.
In Papanicolaou-stained smears, hematoidin retains the same
appearance, but the staining reaction of hemosiderin is golden
brown to olive green. Hemosiderin gives a positive staining
reaction for iron (Perls test), whereas hematoidin does not.
Key features of red blood cells
• Seen in virtually every specimen;
• Biconcave discoids, frequently lysed;
Fig. 19.37 Neutrophilic leukocytes in pleural effusion. Their cytoplasmic
granularity is barely visible (toluidine blue-stained wet film x HP).
• Shape possibly distorted by processing; and
• May degenerate to produce hematoidin and/or hemo-
Almost every specimen of serous effusion contains neutrophil
leukocytes. Their number varies from just the occasional cell to
highly cellular purulent effusions in which all or almost all of
the cells are neutrophils. Purulent effusions are of a light yellow
turbidity and a creamy consistency; if infected, they may be mal-
odorous. Neutrophils are readily recognized in toluidine blue-
stained wet films, Papanicolaou-stained permanent smears, and
Inflammation, infarction, and rupture of an organ are the
principal causes of serous effusion containing numerous neu-
trophils. Hypertrophied mesothelial cells may also be present
in the early stages of acute inflammation, but as the neutrophils
dominate the picture, the mesothelial cells die and disintegrate.
Even in purulent effusions, a small percent of the cells may be
histiocytes or lymphocytes or both.
In wet films, the cytoplasm remains unstained or weakly stained
(Fig. 19.37). It is finely granular, and the granules may exhibit
Brownian movement. Their nuclei are usually trilobed, although
two-, four-, and five-lobed nuclei are not uncommon. In Papan-
icolaou-stained smears, neutrophils are smaller and their cyto-
plasm exhibits a faintly cyanophilic staining reaction. In these
preparations, as in cell blocks, the cytoplasmic granules are vir-
tually impossible to discern, although a suggestion of cytoplas-
mic granularity may be detected.
Neutrophils in noninfected effusions are generally well pre-
served. In infected purulent fluids, neutrophils degenerate; in
some effusions, virtually every neutrophil is necrotic. Necrotic
neutrophils become transformed into ill-defined, light gray to
gray-blue particles without any visible nuclear material or cyto-
plasmic granularity (Fig. 19.38). The nuclei of necrotic cells may
also condense into round, solitary, deeply cyanophilic masses,
or they may become fragmented.
In stained wet films, neutrophils may contain well-defined,
light yellow, glistening, refractile cytoplasmic granules of lipid.