September 2017



Slide A:

Signalment (JPC #2237659):  A 6½-year-old Bernese mountain dog

HISTORY:  Unknown

HISTOPATHOLOGIC DESCRIPTION:  Lung:  Effacing approximately 95% of the pulmonary architecture and abutting the moderately thickened pleura is a poorly demarcated, infiltrative, densely cellular neoplasm composed of round to spindle cells (histiocytes) arranged haphazardly in short streams and variably sized sheets separating the pre-existing pulmonary fibrovascular matrix.  Neoplastic cells have variably distinct cell borders, moderate to abundant eosinophilic granular and often microvacuolated to foamy cytoplasm, irregularly round to reniform nuclei with finely stippled chromatin and 1-3 variably distinct nucleoli.  Anisocytosis and anisokaryosis are marked.  Mitotic rate is regionally variable with up to 5 per high power field in the most mitotically active areas and with occasional bizarre mitotic figures.  Within the neoplasm, there are numerous neoplastic multinucleated giant cells containing up to 30 nuclei which occasionally exhibit nuclear molding.  There is multifocal scattered phagocytosis of leukocytes and erythrocytes by neoplastic cells; many degenerate neutrophils, lymphocytes, and plasma cells; mixed areas of lytic and coagulative necrosis; multifocal invasion of vessels by neoplastic cells; rare single cell necrosis; and few ectactic lymphatics.  Multifocally the pleura is lined by reactive mesothelium and expanded up to 500 microns thick by fibrous connective tissue (fibrosis) and fewer inflammatory cells.

MORPHOLOGIC DIAGNOSIS:  Lung:  Histiocytic sarcoma, Bernese mountain dog, canine.

CONDITION:  Disseminated histiocytic sarcoma

Slide B:

Signalment:  13-year-old, female, domestic long hair, feline

HISTORY:  The cat had a 5-day history of increased respiration, with 3-4 days of rapid shallow breathing and 2 weeks of weight loss. The owners had noticed a recent change in the cat"s vocalization. Thoracic radiographs revealed a diffuse bronchointerstitial pattern throughout the lungs. There was no response to treatment with bronchodilators or glucocorticoids.

HISTOPATHOLOGIC DESCRIPTION:  Lung:  Throughout the section of lung, large numbers of alveoli and alveolar ducts contain densely packed, round to slightly spindle-shaped cells with variably distinct cell borders that completely fill the alveolar and ductal lumens. The cells form dense rounded clusters within alveoli and are often arranged in a lightly streaming pattern. The infiltrating cells have a histiocytic appearance, characterized by a moderate amount of lightly eosinophilic to pale basophilic cytoplasm, which is sometimes lightly vacuolated, and cell nuclei that are round to oval, often eccentrically placed and slightly indented, and which contain variably condensed basophilic chromatin. Mitotic figures are rare (<1 per 400x field). Some alveoli also contain individual or small central clusters of macrophages with abundant, highly vacuolated, foamy cytoplasm and small condensed nuclei. Many alveoli are segmentally lined by prominent, cuboidal epithelial cells (type II pneumocyte hyperplasia). The smooth muscle within alveolar septa is markedly thickened in many areas (smooth muscle hyperplasia). Peribronchiolar and peribronchial lymphocytes are prominent, and clusters of densely packed lymphocytes with lesser numbers of plasma cells are also scattered throughout the section. Many alveoli contain abundant eosinophilic proteinaceous fluid (edema). In some areas the normal alveolar architecture is replaced by thin interlacing bands of collagenous tissue (interstitial fibrosis), with moderate numbers of lymphocytes and plasma cells and multifocal areas of mild hemorrhage. Alveolar septa are lost in many areas resulting in enlarged, confluent air spaces (emphysema).

MORPHOLOGIC DIAGNOSIS:  Lung:  Alveolar and bronchiolar histiocytosis, proliferative, severe, diffuse with smooth muscle hyperplasia, type II pneumocyte hyperplasia and moderate lymphoplasmacytic and histiocytic inflammation

CONDITION:  Pulmonary Langerhans cell histiocytosis








Histiocytic proliferative disorders:



Cell of origin





Langerhans cell

Canine cutaneous histiocytoma; Feline PCLH

E-cadherin, CD1a, CD11a/CD11c/CD18, MHC II

Thy-1, CD4

Interstitial dendritic cell

Canine reactive histiocytoses

Thy-1, CD4, CD1a, CD11c/CD18, MHC II


Interstitial dendritic cell

HS complex, FPH

CD1a, CD11c/CD18, MHC II

Thy-1, CD4,


Macrophage (splenic red pulp)

Hemophagocytic HS (dogs and cats)


CD1a, CD11c



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