Pulmonary Neoplasia

Classification

• Although metastatic pulmonary tumours are common in the lung, primary pulmonary tumours are relatively rare in domestic animals (cf. humans)
• However, primary tumours are more common in dogs and cats than in other animals

• Classification of pulmonary tumours can be difficult due to the metaplasia which can occur in both inflammation and in neoplasia
  • Bronchial papilloma
  • Bronchial adenoma/ carcinoma (arising from major airways)
  • Bronchioloalveolar adenoma/ carcinoma (arising from small airways or alveolar parenchyma - either secretory bronchiolar cells or type II epithelial cells)
  • Carcinoid: in humans, these tumours arise from neuroendocrine cells - rare in animals

Primary tumours

Pulmonary carcinoma and emphysema (Image sourced from Bristol Biomed Image Archive with permission)

Adenomatosis (Image sourced from Bristol Biomed Image Archive with permission)

Alveolar cell carcinoma (Image sourced from Bristol Biomed Image Archive with permission)

• Most arise from pulmonary epithelium
• Usually middle aged to old dogs and cats

Bronchogenic carcinoma

• In dogs usually invasive bronchogenic carcinomas mostly arising from hilar region an metastasise via the airways to other parts of the lungs
• Types:
  • Squamous cell - large cells with vesicular nuclei
  • Adenocarcinoma - invasive and destructive, least malignant
  • Adenosquamous carcinoma - both squamous and glandular part in one tumour, common, similar to metastatic
  • Undifferentiated - very rare in animals
• Large, irregular, pale, not well defined border
• Spread through pulmonary lymphatics

Bronchioloalveolar tumours

• Most common in dogs
• Arise from either secretory bronchiolar or alveolar type II epithelial cells, often both types in same tumour
• May be an incidental necropsy finding
• Often occur as solitary nodules at the periphery of the lung, occasionally multiple
• Histologically:
  • Regular alveolar pattern
• May resemble chronic inflammation or rapid metastatic spread of tumour from a primary elsewhere in the body

Carcinoids

• Occasionally occur in animals, mainly in humans
• Originate from neuroendocrine components of major airways
• Microscopically:
  • Large number of small secretory granules

Granular cell tumours

• Also called myoblastomas
• Mesenchymal origin
• Occurs in horses
• Grossly:
  • Multiple discrete of partially confluent nodules
  • Tend to be associated with major bronchi
  • May cause obstruction
• Histologically:
  • Large polyhedral cells aggregation
  • Fibrovascular stroma

Lymphomatoid granulomatosis

• Occurs in dogs
• Histologically:
  • Mixed, atypical lymphoreticular cells infiltrating one or more lung lobes
  • Tend to invade blood vessel walls and airways
  • Fibrous stroma
  • Many mitotic figures

Metastatic tumours

Lung carcinoma in a dog (Image sourced from Bristol Biomed Image Archive with permission)

Metastatic fibrosarcoma in canine lung (Image sourced from Bristol Biomed Image Archive with permission)

Metastatic sweat gland carcinoma in feline lung (Image sourced from Bristol Biomed Image Archive with permission)

• All are malignant by definition
• Relatively common in domestic species
• Examples of common metastatic tumours include :
  • Mammary carcinoma (dog and cat)
  • Haemangiosarcomas
  • Osteosarcomas
  • Uterine adenocarcinoma (cattle)
  • Malignant melanoma (horse)
• Often manifest as multiple nodules scattered throughout the parenchyma - these lesions are often referred to as "cannon-ball" metastases, in all lung lobes
• Histological examination usually shows the metastases to resemble the primary tumour however they may be either better or less well differentiated
• Sometimes the metastasis can be sen only microscopically, grossly the lungs are discoloured and more firm than usual
• Disseminate widely through lymphatics

• In horses
  • cranial mediastinal lymphosarcoma
  • pulmonary granular cell tumour
  • malignant melanoma
  • haemangiosarcoma
  • metastatic adenocarcinoma
  • metastatic carcinoma

A space occupying lesion in the canine lung may produce periosteal thickening of the long bone - Hypertrophic Osteopathy

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