Sarcoma of histiocytic or splenic stromal origin
Whats your Diagnosis #2The original post with history and clinical findings can be found here
Thin body condition.
The mediastinum was filled and expanded by enlarged tracheobronchial lymph nodes forming two distinct multilobular masses measuring 8 cm x 6 cm x 3 cm and 6 cm x 5 cm x 3 cm. The masses surrounded secondary bronchi and the aorta, and were firmly adhered to the aorta approximately 3 cm from its origin from the left ventricle. The normal lymph node architecture was replaced by a mass of firm yellow tissue with multifocal hemorrhages and small necrotic areas.
The mesenteric lymph nodes were multifocally enlarged and the normal architecture replaced by firm yellow tissue.
The spleen was large with multiple sharply delineated, dark red, swollen areas. On cut section these dark red areas were sharply delineated from the normal splenic parenchyma.
The liver was filled with numerous firm, pale yellow nodules ranging in size from 5 mm diameter to 1.5 cm in diameter. The left kidney had two firm, pale yellow 4 mm nodules in the cortex.
Spleen: The mass is highly cellular, arranged in sheets and whorls with abundant extramedullary hematopoiesis. Neoplastic cells are of two basic types. The first are large polygonal histiocytic cells with distinct cellular borders and a moderate amount of eosinophilic cytoplasm. Nuceli are round to oval and occasionally folded with coarse chromatin. The second population of neoplastic cells is composed of spindyloid cells with small amounts of eosinophilic cytoplasm. Nuclei are elongated with coarse chromatin. There are abundant erythroid and myeloid precursors admixed with the neoplastic cells with large numbers of immature granulocytes and erythrocytes. There is mild anisocytosis and anisokaryosis and 20 mitotic figures in 10 random 400x fields. The neoplasm contains multifocal lymphocytic infiltrates and a few neutrophils.
The first type of cell mentioned is polygonal to round (histiocytic) and looks like the photo below:
The second type of cell looks like a spindle cell (see the two photos below):
The spleen was composed of a mixture of the two cell types with lots of hematopoietic cells. No multi-nucleated giant cells or erythrophagocytosis was seen in any tissue.
The liver had mostly histiocytic cells with some hematopoiesis. The tracheobronchial lymph nodes were almost completely spindle cells with an obvious whorling pattern.
The neoplasm was also found in the lungs , kidneys (interstitium), and bone marrow.
Because of the lack of multinucleated giant cells and erythrophagocytosis we did not call this a histiocytic sarcoma.
The splenic disease in this dog shares many similar clinical and morphologic features to the syndrome of myeloid metaplasia, histiocytosis, and hypersplenism described by Spangler and Kass (Vet Path 36:583-593 1999), as well as the canine hemophagocytic histiocytic sarcoma described by Moore et al. (Vet Path 43: 632-645 2006). In both of these syndromes and in this case the dogs had anemia and
thrombocytopenia and the spleens were diffusely enlarged with prominent extramedullary hematopoiesis and a mixture of spindyloid and histiocytic components. This case differs from the hemophagocytic histiocytic sarcoma by not having notable erythrophagocytosis or multinucleated giant cells.
Spangler and Kass also described cases of fibrohistiocytic nodules (Vet Path 35: 488-498 1998 ), which were microscopically similar to the spleen, lung, liver, and lymph nodes in this dog. However grossly the spleens were described as having focal nodules and were not diffusely enlarged. When severe these fibrohistiocytic nodules were similar to sarcomas called Malignant Fibrous Histiocytosis, and had a predominant spindyloid component. All of these splenic diseases are thought form a continuum from reactive hyperplasia to neoplasia. The origin of the neoplastic cells have been attributed to histiocytic cells or various splenic stromal elements but so far there is no consensus. Recent investigation into immunophenotyping these diseases has provided more information to help characterize these
cells, but these methods are not available for formalin fixed tissues.
Lysozyme: The spindle cells were negative in all tissues. The spleen had some positive lysozyme cells but we did not think this was significantly more than normal, especially witht the abundant hemosiderin in the spleen which is indistinguishable from the lysozyme in cells.