Page 712 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

690 PART IV Specific Malignancies in the Small Animal Patient

cranial mediastinal LNs, thymus, or both (Fig. 33.2). Hypercalce- originates from T cells, 73–77 similar to the case in humans. In
+
mia is reported to occur in 10% to 40% of dogs with lymphoma dogs, these more commonly represent CD8 cells, whereas in
76
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humans they are typically CD4 cells. A rare form of cutane-
and is most common with the mediastinal form. In a study of 37
VetBooks.ir dogs with lymphoma and hypercalcemia, 16 (43%) had mediasti- ous T-cell lymphoma, characterized by skin involvement with evi-
dence of peripherally circulating large (15–20 μm in diameter)
nal lymphoma. The mediastinal form in dogs is most commonly
67
associated with a T-cell phenotype. 68,69 A single case of mediasti- malignant T cells with folded, grooved nuclei, has been described.
nal γδT-cell lymphoma with large granular lymphocyte morphol- In humans, this is referred to as Sézary syndrome and has been
ogy has been reported. 70 reported in both dogs and cats. 78–80 Nonepitheliotropic cutane-
Cutaneous lymphoma can be solitary or more generalized and ous lymphomas form single or multiple dermal or subcutaneous
is usually classified as epitheliotropic (mycosis fungoides) or non- nodules or plaques; histologically, they spare the epidermis and
epitheliotropic. 71,72 Canine epitheliotropic cutaneous lymphoma papillary dermis and affect the middle and deep portions of the
dermis and subcutis. An inflamed form of nonepitheliotropic
72
cutaneous T-cell lymphoma (NE-CTCL) is more pleocellular and
can be difficult to differentiate from reactive histiocytosis. 71
Atypical Anatomic Forms of Lymphoma
Hepatosplenic lymphoma is a relatively uncommon, distinct pre-
sentation in the dog marked by a lack of significant peripheral
lymphadenopathy in the face of hepatic, splenic, and bone mar-
row infiltration with malignant lymphocytes, usually of T-cell
origin. 81–83 Biologically, this form of lymphoma is extremely
aggressive and poorly responsive to therapy. In humans and dogs,
the tumor usually is composed of γδT cells (i.e., T cells that
express the γδT-cell receptor). 81,82
Intravascular (angiotropic, angioendotheliomatosis) lym-
phoma is a distinct form of lymphoma defined as proliferations of
neoplastic lymphocytes within the lumen and wall of blood vessels
in the absence of a primary extravascular mass or leukemia. It has
been reported several times in the veterinary literature and often
involves the CNS and peripheral nervous system (PNS), includ-
ing the eye. 84–89 The B-cell immunophenotype is most common
in humans; however, in most reported cases in dogs, the origin is
either T cell or null cell (neither B nor T cell), although one case
of a B-cell phenotype has been reported.
• Fig. 33.1 A dog with obvious mandibular lymphadenopathy resulting Pulmonary lymphomatoid granulomatosis (PLG), also termed
from multicentric lymphoma. angiocentric B-cell lymphoma, is a rare neoplasm of the lung and

A B
• Fig. 33.2 (A) Lateral radiographic projection of a dog with mediastinal lymphoma. (B) Ventrodorsal projec-
tion of the same dog.