CPD ACCREDITED ARTICLE
CPD ACCREDITED ARTICLE
5. Chylus Effusion / Chyle
Chylus effusions occur due to leakage of lymphatic
fluid into body cavities due to physical or functional
obstructions to lymphatic ducts or to trauma (rare).
These effusions therefore have characteristics similar
to lymphatic fluid in the lymph ducts draining the GIT.
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They are milky and white, TP >25 g/L, NCC < 10
000 cells/ µL.
The dominant cell population is small lymphocytes,
but cytology may vary if the chylus fluid causes
irritation of and inflammation is present.
Lipids are absorbed from the GIT as chylomicrons into
the intestinal lymphatic vessels, and enter the blood
via the thoracic duct. Chylus effusions are therefore
high in triglycerides. If a chylus effusion is suspected,
triglyceride concentrations should be measured in
the fluid. If TGL > 1.13 mmol/L then the effusion is
confirmed as chyle.
Chylus effusions may occur in both the peritoneal and
pleural cavities, depending on where the disruption to
the lymphatics has occurred.
6. Bile Peritoneum
Caused by a rupture in the biliary system due to gall
bladder disease, choleliths or cholangitis. Starts off
as a low protein transudate, but as bile is extremely
irritant to the peritoneum, the protein and cellularity
increase and the process becomes exudative.
The fluid may have a greenish or orange tinge. Bilirubin
concentrations in the fluid are >2x bilirubin in serum.
Bilirubin crystals may be seen on cytology.
7. Neoplastic Effusion
Neoplasia may cause:
• obstruction to lymphatics resulting in a chylus
effusion
• obstruction to blood vessels resulting in a high-
protein transudate
• invasion of blood vessels resulting in a haemorrhagic
effusion
• inflammation resulting in an exudate
A neoplastic effusion is identified as such when
malignant cells are seen in the effusion. (Figure 4) The
most common tumours associated with effusions are
lymphoma and carcinomas.
A cytological diagnosis of neoplasia in an effusion
(excluding mesothelioma) has a high specificity and
high positive predictive value. Sensitivity is however
low, and a negative diagnosis does not rule out
neoplasia.
8. Pericardial Effusions
In dogs, the most common causes are neoplasia
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Figure 4: Peritoneal effusion from a dog with high numbers
of neoplastic epithelial cells, originating from metastasis of a
mammary adenocarcinoma.(x500, Diff-Quick)
(haemangiosarcoma) and idiopathic. Rarely, a
pericardial effusion may be caused by left atrial
rupture, coagulopathy or bacteria. Cytology usually
reveals a haemorrhagic effusion with highly reactive,
atypical looking mesothelial cells. Sensitivity for
identifying HAS is very low. Around 75% of pericardial
effusions in cats are caused by chronic heart failure
(i.e. will have cellularity and protein concentration
consistent with high protein transudate). However,
periocardiocentesis is performed extremely rarely in
cats.
References
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eclinpath.com/cytology/effusions-2/
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