Pulmonary meningothelial-like nodule

Pulmonary meningothelial-like nodule, abbreviated MLN, is a common benign finding in the lung.

They are also referred to as minute pulmonary meningothelial-like nodules (abbreviated MPMN) and minute pulmonary chemodectoma.

General

• Benign.
• Very common - seen in almost half of well sampled lobectomies.
• May be grouped with pulmonary meningioma in the larger category primary pleuropulmonary meningothelial proliferations.
• Can mimic metastatic deposits.

Associations:

• More common in females (odds ratio 2).
• Seen more frequently in the context of cancer - esp. adenocarcinoma.

Gross

• Tan or yellow nodules - pleural or parenchymal - typically 1-3 mm.

Note:

• Found in all lobes.
• May be seen on imaging if large.

Microscopic

Features:

• Small cell nests - expanding alveolar septa.
  • Whorled appearance/streaming.
  • Composed of bland cells with round/ovoid nuclei without appreciable nucleoli.

DDx:

• Lung tumourlet - associated with airway.^{[citation needed]}
• Poorly differentiated carcinoma.
• Lobular carcinoma.

Images

• MLN (nih.gov).

IHC

Features:

• CD56 +ve (18 of 18 cases).
• EMA +ve (11 of 11 cases).
• Vimentin +ve (10 of 14 cases).
• PR (18 of 18 cases.

Others:

• S-100 -ve.
• NSE -ve.
• Cytokeratin -ve.
• Actin -ve.

See also

• Lung tumourlet.
• Meningioma.