Diagnosis and Differential Diagnosis



Minute Meningothelial-like Nodule

Cells form small nests and bundles around a small vein (arrow). A second nest is present separate from the main nodule (arrowhead).

The following images show some minute cellular lesions that may be mistaken for MMNs. Focal cellular scars and small metastases also must be considered.

Differential Diagnosis

Atypical Adenomatous Hyperplasia (AAH)


These lesions, varying up to 7 mm in diameter, are composed of benign or slightly atypical epithelial cells lining slightly thickened alveolar walls. Except for a few lymphocytes, an inflammatory component is absent within the lesion and in the adjacent lung.


Compare the wall thickness and epithelial prominence in the lesion with the same features in the adjacent normal lung (extreme right).

The current hypothesis is that these clonal lesions are precursors of peripheral adenocarcinomas or bronchioloalveolar carcinomas. The presence of AAH does not change the prognosis of an accompanying carcinoma.

Small adenocarcinomas or bronchioloalveolar carcinomas are also included in the differential diagnosis of AAHs.

Above left--AAH: above right--adenocarcinoma in same patient (same magnification)

Compare the epithelial sizes in the two lesions. Nuclei of AAH are small with uniform chromatin and absent mitoses. Cells vary in height from flat to low columnar. Nuclei of the adenocarcinoma are large with clumped chromatin.


Nakata M, Saeki H, Takata I, Segawa Y Mogami H, Mandai K, Eguchi K. Focal ground-glass opacity detected by low-dose helical CT. Chest 2002; 121:1464-1467. Abstract

Chapman A, Kerr K. The association between atypical adenomatous hyperplasia and primary lung cancer. Br J Cancer 2000; 83:632-636. Abstract


Angiomatoid Lesion of Plexogenic Pulmonary Angiopathy

This lesion is composed of small vascular channels surrounded by cellular endothelium. It is connected to a parent artery (arrow), which can be verified by an elastic tissue stain showing 2 elastic layers. An airway would lie nearby. In this case, the surrounding larger spaces (asterisks mark three) are dilation lesions, which are sometimes present with the angiomatoid lesion.

Tumorlet (Minute Carcinoid Tumor)

The proliferating cells here fill an airway (arrow) and proliferate in adjacent air spaces. They do not grow in the interstitium. A stain for chromogranin would be positive.

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