Clinical Examination of Farm Animals - CYF MEDICAL DISTRIBUTION

CHAPTER 3
Clinical Examination of the
Lymphatic System
Lymphatic system
The lymphatic system consists of the carcase lymph
nodes, the network of lymph vessels which connect
them and the lymphatic parts of the spleen. Many of
the nodes are readily palpable in the healthy animal.
Others can be palpated only when enlarged. Details
of the location of the individual nodes and their ease
of palpation are given below. The lymph vessels are
normally palpable only if they are enlarged. Some
vessels may be seen and palpated as they run subcutaneously
towards the regional lymph nodes.
Clinical examination of the
lymphatic system
Grossly enlarged lymph nodes may have been seen
during observation of the patient before it is handled.
Further observation and palpation is possible when
the animal is restrained. The lymph nodes can be examined
as a separate system or checked during the
examination of the skin when the clinician’s hands
run over the whole body surface. Each paired node
should be compared for size and consistency with
the contralateral node.
Lymph node enlargement
This may occur for two main reasons.
(1) Enlargement of one or more lymph nodes may occur
in cases of infection of the lymphatic system. This
can occur in a number of diseases including
bovine tuberculosis, actinobacillosis and a number
of other bacterial infections. It can also occur
in both forms of bovine leucosis – enzootic bovine
leucosis (EBL) and sporadic bovine leucosis. EBL is
an uncommon but notifiable disease in the UK.
Infection is widespread in some other countries.
Any animal over 2 years of age with enlargement
of the carcase lymph nodes and in which bovine
leucosis is suspected is blood tested for serological
evidence of EBL. Positive cases of EBL are
slaughtered.
Cases of sporadic bovine leucosis may be examined
further to determine which carcase and palpable
visceral lymph nodes are involved. Gross
lymph node enlargement may be seen, for example,
in the prescapular lymph nodes. In most
cases some enlargement is present in other
lymph nodes. Ulceration of affected lymph
nodes may occur. Areas of tumour tissue may be
seen in the skin and in the thymus. Internal lymphoid
tumours may be found in many locations
including the heart base, the mediastinum and
wherever lymph nodes are present. Affected
lymph nodes are usually non-painful to the
touch but may interfere with many body functions.
Heart base and thymic tumours may
obstruct venous return. Mediastinal tumours
may compress the oesophagus causing bloat or
dysphagia.
(2) Lymph node enlargement in response to local infection
or inflammation in the region of the body drained
by the lymph node involved. In these circumstances
the lymph node is acting as a sentinel of
local disease. The enlarged node may be warm
and inflamed, and sensitive to the touch. On finding
an enlarged lymph node the clinician should
examine the area draining into the affected node
for evidence of any pathological problem. As
with tumour infiltration, the enlarged lymph
nodes may affect the function of adjacent organs.
Location of the carcase lymph nodes
Many of the nodes are paired and should be compared
for size and consistency. Lymph nodes are
normally firmer than adjacent muscle and other soft
tissues (Fig. 3.1).
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