Page 1441 - Small Animal Internal Medicine, 6th Edition

CHAPTER 88 Lymphadenopathy and Splenomegaly 1413

using Gram stain. Most dogs with pyogranulomatous sple- of the vena cava. Splenic vein thrombosis is a common inci-
nitis had leishmaniasis. dental finding in dogs; it is usually associated with the
VetBooks.ir animals. Marked splenomegaly is a common finding in dogs administration of corticosteroids and is typically of no clini-
Infiltrative splenomegalies are also common in small
cal relevance. Ultrasonographic evaluation in these patients
and cats with acute and chronic leukemias, although it is
veins or thrombi.
more common in dogs; in dogs and cats with systemic mas- usually reveals markedly distended splenic, portal, or hepatic
tocytosis; and in dogs with malignant histiocytosis. In addi- A relatively common cause of congestive splenomegaly
tion, diffuse neoplastic infiltration of the spleen commonly in dogs is splenic torsion (DeGroot et al., 2016). Torsion of
occurs in dogs and cats with lymphoma or multiple myeloma. the spleen, by itself or in association with gastric dilation-
Diffuse splenomegaly may be the only physical examination volvulus syndrome, commonly results in marked spleno-
and imaging finding in cats with monoclonal gammopathies; megaly caused by congestion. Splenic torsion can occur
fine-needle aspiration (FNA) of the spleen reveals diffuse independently of gastric dilation-volvulus syndrome. Most
infiltration with plasma cells and is a common presentation affected dogs are large, deep-chested breeds, primarily
for myeloma in this species. Metastatic splenic neoplasms Great Danes, Chows, and German Shepherd Dogs. Clini-
usually result in focal splenomegaly but are rare. cal signs can be acute or chronic. Dogs with acute splenic
Nonneoplastic causes of infiltrative splenomegaly are torsion are usually evaluated because of acute abdominal
uncommon, with the exception of extramedullary hemato- pain and distention, vomiting, depression, and anorexia.
poiesis (EMH), which is more common in dogs than in cats. Dogs with chronic splenic torsion display a wide variety of
Because the spleen retains its fetal hematopoietic potential clinical signs, including anorexia, weight loss, intermittent
during adult life, a variety of stimuli—such as anemia, severe vomiting, abdominal distention, PU-PD, hemoglobinuria,
splenic or extrasplenic inflammation, neoplastic infiltration and abdominal pain. Physical examination usually reveals
of the spleen, bone marrow hypoplasia, and splenic marked splenomegaly, and radiographs typically reveal a
congestion—may cause the spleen to resume its fetal hema- C-shaped spleen. Ultrasonography of the abdomen in these
topoietic function and produce RBCs, white blood cells, and patients may show greatly distended splenic veins. Hema-
platelets. Finding EMH by percutaneous FNA of the spleen tologic abnormalities usually include regenerative anemia,
is the norm in dogs and cats with diffuse or focal spleno- leukocytosis with a regenerative left shift, and leukoeryth-
megaly; the presence of hematopoietic blasts may lead to an roblastosis. Disseminated intravascular coagulation appears
erroneous diagnosis of lymphoma in some of these patients. to be a common complication in dogs with torsion of the
I have also observed splenic EMH in dogs with pyometra, spleen. A high percentage of dogs with splenic torsion have
immune-mediated hemolysis, immune-mediated thrombo- hemoglobinuria, possibly as a consequence of intravascu-
cytopenia, several infectious diseases, and a variety of malig- lar or intrasplenic hemolysis. Dogs with splenic torsion and
nant neoplasms as well as in seemingly healthy dogs. Another hemoglobinuria seen at our clinic occasionally have a posi-
disorder that commonly results in prominent infiltrative tive direct Coombs test result. The treatment of choice for
splenomegaly is the hypereosinophilic syndrome of cats (and dogs with splenic torsion is splenectomy.
some dogs, such as Rottweilers), a disease characterized by Splenic masses are more common than diffuse spleno-
peripheral blood eosinophilia, bone marrow hyperplasia of megaly in dogs, whereas the opposite is true for cats. Most
the eosinophil precursors, and multiple-organ infiltration by splenectomies in dogs are done to remove splenic masses.
mature eosinophils (see Chapter 85). Because splenic masses in cats are extremely uncommon, the
The canine and feline spleens have a great capacity to following discussion pertains primarily to localized spleno-
store blood, and under normal circumstances they store megaly in dogs.
between 10% and 20% of the total blood volume. However, Most oncologists use the rule of two thirds—two thirds of
tranquilizers and barbiturates can cause splenic blood the splenic masses are tumors, two thirds of the tumors are
pooling because of relaxation of the smooth muscle of the malignant, and two thirds of the malignant tumors are hem-
splenic capsule, leading to congestive splenomegaly. The angiosarcomas (HSAs). However, the prevalence of different
blood that has pooled in an enlarged spleen can account for histologic types of splenic masses may vary geographically.
up to 30% of the total blood volume. Anesthetics rarely used Splenic masses can be classified according to their his-
these days, such as halothane, also may result in marked topathologic features and biologic behavior as neoplastic
decreases of 10% to 20% in the packed cell volume and or nonneoplastic. Neoplastic splenic masses can be benign
plasma protein concentration in dogs as a result of the same or malignant and mainly include hemangiomas (HAs)
mechanism. and HSAs, although the former are less common than the
Portal hypertension can lead to congestive splenomegaly; latter. Other neoplastic splenic masses found occasionally
however, such splenic congestion does not appear to be as are leiomyosarcomas, fibrosarcomas, leiomyomas, myeloli-
common in dogs and cats as it is in humans. Causes of portal pomas, metastatic carcinomas or sarcomas, malignant his-
hypertension that may lead to splenomegaly in small animals tiocytic tumors, and occasionally lymphomas. As a general
include right-sided congestive heart failure, obstruction of rule, the larger the splenic mass, the less likely it is to be a
the caudal vena cava as a result of congenital malformations, malignant tumor (Mallinckrodt and Gottfried, 2011). Non-
neoplasia, heartworm disease, and intrahepatic obstruction neoplastic splenic masses include primarily hematomas,