Page 1318 - Small Animal Internal Medicine, 6th Edition

1290 PART XII Oncology

general rule, FNA of the lungs should not be performed in The clinician should remember that nodular lesions of the
cats or dogs with coagulopathies. In most patients, meta- liver or spleen in dogs with a primary malignancy should
VetBooks.ir static lesions are easily diagnosed using this simple approach. not necessarily be considered metastatic. FNA or biopsies of
such lesions frequently reveal normal hepatocytes (i.e., regen-
If an FNA of the lungs fails to yield a diagnostic sample,
a lung biopsy performed with a biopsy needle (under ultra-
lymphoreticular hyperplasia.
sonographic, fluoroscopic, or CT guidance) or through a erative hepatic nodule) or extramedullary hematopoiesis/
thoracotomy or thoracoscopy should be contemplated. This In addition, an ultrasonographically “normal” liver or
procedure is associated with an extremely low morbidity spleen in a patient with suspected metastases may contain
and should be recommended if owners are considering abundant malignant cells. For example, in dogs with lym-
treatment. phoma and increased ALT activity, FNA of ultrasonographi-
Metastatic lesions in other organs or tissues (e.g., liver, cally normal liver oftentimes yields neoplastic lymphoid
bone) can also be diagnosed on the basis of FNA findings. cells. The authors occasionally find large (i.e., 4-6 cm) meta-
static lesions in the liver of dogs with normal ultrasono-
graphic appearance. Ultrasonographic features of internal
TABLE 78.1 lymph nodes may assist in classifying the lymphadenopathy
as metastatic or reactive; for example, it has been reported
Metastatic Behavior of Some Common Neoplasms in that the resistive index (RI) and pulsatility index (PI) were
Dogs and Cats significantly higher in neoplastic than in reactive medial iliac
and mesenteric lymph nodes (Prieto et al., 2009).
COMMON METASTATIC Primary bone lesions or bone metastases can easily be
NEOPLASM SPECIES SITES aspirated using a hypodermic needle (20- to 22-gauge) that
is inserted blindly or under ultrasonographic guidance; if
HSA D Liver, lungs, omentum,
kidney, eye, CNS this fails to yield cells, a 16- or 18-gauge bone marrow aspira-
OSA D Lungs, bone tion needle can be used. If a cytologic diagnosis cannot be
made, a core (needle) biopsy can be performed.
SCC—oral C, D Lymph nodes, lungs As discussed in Chapter 75, cats and dogs with metastatic
aCA—mammary C, D Lymph nodes, lungs neoplasms can now be treated fairly successfully using con-
aCA—anal sac D Lymph nodes ventional or metronomic chemotherapy. To do this, however,
aCA—prostate D Lymph nodes, bone, lungs it is necessary to know the histologic (or cytologic) tumor
TCC—bladder D Lymph nodes, lungs, bone type. The clinician should always bear in mind that euthana-
MEL—oral D Lymph nodes, lungs sia is a viable option for some owners.
MCT D Lymph nodes, liver, APPROACH TO THE PATIENT WITH A
spleen MEDIASTINAL MASS
MCT C Spleen, liver, bone
marrow Several lesions are found as anterior mediastinal masses
(AMMs) during physical examination or plain thoracic radi-
aCa, Adenocarcinoma; C, cat; CNS, central nervous system; D,
dog; HSA, hemangiosarcoma; MCT, mast cell tumor; MEL, ography (Table 78.2). Some of these lesions are malignant
malignant melanoma; OSA, osteosarcoma; SCC, squamous cell neoplasms; therefore diagnosis and treatment should be
carcinoma; TCC, transitional cell carcinoma. approached aggressively in such animals.

TABLE 78.2

Anterior Mediastinal Masses in Cats and Dogs

LESION CAT DOG COMMENTS
Thymoma Common Common See text
Lymphoma Common Common See text
Thyroid adenocarcinoma Rare Rare
Lipoma Rare Rare Low radiographic density
Branchial cysts Rare Rare Cystic on ultrasound
Thymic hematomas ? Rare Traumatic, rodenticides?
Heart base tumors ? Rare Brachiocephalic breeds
?, Questionable.