Multifocal micronodular pneumocyte hyperplasia
Multifocal micronodular pneumocyte hyperplasia is a subtype of pneumocytic hyperplasia.
Several synonymous terms have been done for this entity: adenomatoid proliferation of alveolar epithelium, papillary alveolar hamartoma, multifocal alveolar hyperplasia, multinodular pneumocyte hyperplasia.
These multifocal lesions are observed in tuberous sclerosis, and can be associated with lymphangioleiomyomatosis and perivascular epithelioid cell tumour ).
It can be diagnosed through lung biopsy using thoracoscopy.
Microscopy
- Well-demarcated, nodular lesions ranging 2–5 mm in pulmonary parenchyma.
- Type II pneumocytes without nuclear atypia lined thickened alveolar septa and proliferated papillary structures.
- Enlarged cuboidal cells lining mildly thickened alveolar septa.
- Enlarged cuboidal cells have abundant, eosinophilic cytoplasm and large, round nuclei.
- Papillary pattern with irregular margin and lymphocyte infiltration in the stroma.
- No proliferation of immature smooth muscle cells suggestive of lymphangioleiomyomatosis.