Page 1439 - Small Animal Internal Medicine, 6th Edition

CHAPTER 88 Lymphadenopathy and Splenomegaly 1411

SUBLUMBAR
REGION
VetBooks.ir 2 1
LNS

1 2
1
Dist 8.33cm
2
A Dist 4.86cm

FIG 88.4
Massive mandibular lymphadenopathy in a young feline
leukemia virus–positive cat with idiopathic reactive
lymphadenopathy. The lymphadenopathy resolved with
supportive care.

paying particular attention to the skin, subcutis, and bone.
In dogs and cats with generalized lymphadenopathy, evalu-
ation of other hemolymphatic organs, such as the spleen,
liver, and bone marrow is important.

B SPLENOMEGALY

FIG 88.3 Etiology and Pathogenesis
(A) Ultrasonographic image of massive sublumbar (iliac)
lymphadenopathy in a Great Pyrenees with malignant Splenomegaly is defined as a localized or diffuse splenic
histiocytosis. (B) Cytologic evaluation revealed a enlargement. The term localized splenomegaly (or splenic
pleomorphic population of round cells exhibiting cytophagia mass) refers to a localized palpable enlargement of the
(Diff-Quik stain; ×1000). spleen. Diffuse splenic enlargement occurs as a consequence
of the proliferation of normal cells or infiltration with normal
or abnormal cells. Rarely diffuse splenic enlargement can
syndrome of distinctive lymph node hyperplasia usually occur as a result of vascular changes (e.g., hyperemia, con-
results in massive lymphadenopathy (Fig. 88.4). Rarely met- gestion). Focal splenomegaly is more common in dogs, and
astatic lymph nodes exhibit this degree of enlargement; the diffuse splenomegaly is more common in cats.
main example of massive metastatic lymphadenopathy is the Diffuse splenomegaly is classified into four major catego-
apocrine gland adenocarcinoma metastases to the sublum- ries in terms of its pathogenesis—lymphoreticular hyperpla-
bar lymph nodes. Recognizing that lymph nodes of normal sia, inflammatory (e.g., splenitis), infiltration with abnormal
size may contain metastatic neoplasia is important; this is cells (e.g., lymphoma) or substances (e.g., amyloidosis), and
relatively common in dogs with mast cell tumors, where a congestion (Table 88.3).
node that is normal on palpation may contain large numbers The spleen commonly reacts to bloodborne antigens and
of metastatic mast cells. Dogs with salmon poisoning may RBC destruction with hyperplasia of the MP-AP and lym-
also have marked generalized lymphadenopathy as the pre- phoid components. This hyperplasia has been referred to as
senting feature, preceded by or in conjunction with bloody work hypertrophy because it usually results in varying
diarrhea. Mild to moderate lymph node enlargement (two to degrees of splenic enlargement. Hyperplastic splenomegaly
four times the normal size) occurs mostly in a variety of is relatively common in dogs with ehrlichiosis, leishmaniasis,
reactive and inflammatory lymphadenopathies (e.g., ehrlichi- bacterial endocarditis, systemic lupus erythematosus, or
osis, bartonellosis, anaplasmosis, RMSF, systemic mycoses, chronic bacteremic disorders such as diskospondylitis and
leishmaniasis, immune-mediated diseases, skin diseases) brucellosis, and in cats with mycoplasmosis or immune-
and in leukemias. mediated cytopenias.
As noted, the area draining the enlarged lymph node(s) RBC phagocytosis by the splenic MP system in humans
should always be thoroughly examined (Suami et al., 2013), can lead to hyperplasia of this cell population, resulting in