JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1820691): Unknown age and gender owl monkey
HISTOPATHOLOGIC DESCRIPTION: Lung: Expanding up to 75% of alveolar septa and peribronchial and perivascular interstitium, are multifocal to coalescing granulomas that compress adjacent alveoli and are composed of a center of large numbers of macrophages containing amphophilic to light brown, granular to specular anisotropic material which is also present extracellularly. Surrounding the core of macrophages are rare multinucleated giant cells (Langhans type), with a rim of lymphocytes, plasma cells, with fewer neutrophils. In less severely affected areas, alveolar lumina are filled with eosinophilic homogenous proteinaceous material (edema) and scattered macrophages. There is multifocal minimal type II pneumocyte hyperplasia.
MORPHOLOGIC DIAGNOSIS: Lung: Pneumonia, granulomatous, multifocal to coalescing, severe with intraalveolar and intrahistiocytic anisotropic foreign material, owl monkey, Aotus trivirgatus, primate.
ETIOLOGIC DIAGNOSIS: Inhalation/aspiration (foreign body) pneumonia
SYNONYMS: Bolus alba, white clay, China clay, Fuller’s earth
- Kaolin is a hydrated aluminum silicate (kaolinite) previously used in many antidiarrheal medications
- When aspirated, it causes interstitial pneumonia and neck and anterior thoracic cavity granulomas
- Initially, the alveolar epithelial and capillary endothelial cells are injured and then serofibrinous exudate fills the alveoli
- In severe cases, hyaline membranes composed of fibrin, serum proteins, and cell debris line the air spaces
- Upon initial contact with the particles, alveolar macrophages release chemotactic factors (IL-8) that recruit activated inflammatory cells; these cells infiltrate alveolar lumina and interstitium, then release injurious (oxidants, cytokines) and fibrogenic mediators (platelet derived growth factor, fibroblast growth factor, IL-1)
- Fibroblasts proliferate and there is increased collagen deposition in the interstitium
- If there are multiple or more severe episodes or chronic exposure, inflammation persists and normal regeneration is inhibited
TYPICAL CLINICAL FINDINGS:
- Acute signs include moist, spastic paroxysmal coughing, increased respiratory rate, wheezing, dyspnea, and in advanced cases, cyanosis
TYPICAL GROSS FINDINGS:
- Multifocal areas of pulmonary consolidation and hyperemia; commonly, lesions are lobar
- Distribution depends on the position of the animal upon inhalation or aspiration of foreign material
- If standing, middle and accessory lobe bronchi of the right or left side affected
- If prostrate, middle, cranial or accessory lobes of the recumbent side affected
- Kaolinite granulomas may be small, cystic, spongy masses or firm, variably sized masses; some may cavitate and contain a creamy, gray, nonodorous material
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- In acute lesions, there is peribronchial to diffuse, intraalveolar dull eosinophilic exudate containing varying numbers of macrophages and neutrophils
- Phagocytized by macrophages and admixed with the exudates are highly birefringent, irregular, needle-shaped crystals
- With any aspiration pneumonia, there can be acute bronchiolitis with various degrees of acute alveolar inflammation and foreign material or lipids
- Chronically, form classic granulomas
- Barium Sulfate: in peracute cases, anisotropic crystals of barium sulfate may be free within airways without any noticeable cellular response; in older lesions, material may be within neutrophils or macrophages surrounded by areas of fibrosis
- Silicosis: microscopically, anisotropic crystals within areas of fibrosis, which appear as dense sclerotic coalescing nodules; associated with osteoporosis and equine bone fragility syndrome
- Siderosis: iron dust is inhaled primarily as hematite or iron oxide and does not incite fibrosis or an inflammatory reaction; hematite and iron oxide appear as red crystals of varying size; they are anisotropic, appear orange with polarized light, and can be demonstrated with iron stains such as Prussian blue
- Asbestosis: asbestos bodies are long beaded rods with rounded ends, which appear yellow due to an iron coating, which can be demonstrated with a Prussian blue stain; incites fibrous scarring of the pleura, around bronchioles and alveolar ducts, and within alveolar septa; discrete nodules, as in silicosis, do not develop
- Anthracosilicosis: macrophages near terminal bronchiolar areas contain black, granular isotropic carbon pigment inter‑mixed with numerous anisotropic crystalline spicules (silicate crystals)
- Lipid pneumonia/mineral oil: most commonly seen in cats where mineral oil is used as a laxative to relieve chronic constipation or in horses after treatment of impaction colic with mineral oil via nasogastric tube
- Asian sand dust (kosa aerosol): causes air pollution in China, Korea and Japan; granulomas that are composed of epithelioid cells, macrophages, multinucleated giant cells, neutrophils and crystal-like transparent particles
- Meconium: Most common in neonatal calves, lungs contain amorphous yellow-orange meconium, keratin, and squamous epithelial cells; obstructs airwaysàhypoxic pulmonary vasoconstrictionàpulmonary hypertension and right-to-left shunting across ductus arteriosus or foramen ovale
- Causes pneumoconiosis (lung disease from inhalation and retention of inorganic dusts) and dense pulmonary scarring or fibrosis in humans (mining or industrial exposure)
- Silicate pneumoconiosis in horses, rarely dogs, is the only clinically important pneumoconiosis in domestic animals and occurs in certain geographical areas containing crystalline forms of free silica in the soil
- Aspiration pneumonia in domestic animals is often of liquids, a common sequela to cleft palate, and has the following characteristics
- Localized or unilateral (right cranial lung lobe most severely affected unless animal in lateral recumbency)
- Extensive necrosis, liquefaction, foul smell, rapid green discoloration
- Plant material may be visible in herbivores
- Inhaled milk is observed in pail-fed or tube-fed calves
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