Multifocal micronodular pneumocyte hyperplasia

Multifocal micronodular pneumocyte hyperplasia (MMPH) is a subtype of pneumocytic hyperplasia (hyperplasia of pneumocytes lining pulmonary alveoli).^{[1][2][3][4][5]}

Micrograph showing multifocal micronodular pneumocyte hyperplasia. H&E stain.

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,^[6][7] and can be associated with lymphangioleiomyomatosis^[8] and perivascular epithelioid cell tumour (PEComa or clear cell "sugar tumor")).^[9]

It can be diagnosed through lung biopsy using thoracoscopy.^[10]

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.^[11]
• Enlarged cuboidal cells have abundant, eosinophilic cytoplasm and large, round nuclei.^[12]
• Papillary pattern with irregular margin and lymphocyte infiltration in the stroma.^[13]
• No proliferation of immature smooth muscle cells suggestive of lymphangioleiomyomatosis.

See also

• atypical adenomatous hyperplasia
• pneumocytic hyperplasia