Pulmonary meningothelial nodules are sometimes large enough to be recognized on CT and are commonly asymptomatic and indolent. They may present as numerous randomly distributed nodules, termed diffuse pulmonary meningotheliomatosis (DPM) 7.
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Terminology
They were originally called pulmonary chemodectomas, but further studies revealed meningothelial cells and an absence of endocrine granules 3,5.
Epidemiology
The reported incidence varies from 0.3-9.5% at autopsy or surgical biopsy and likely reflects the extent of sampling 4. They are absent from foetal and neonatal lung and are therefore acquired 7. DPM is ten times more common in women, with a median age of 60 at presentation (range 30 - 80) 7. The nodules are commonly less than 2mm in diameter and may escape detection by CT.
A review of 44 cases of meningothelial nodules revealed an increased incidence of primary and metastatic lung cancer (mainly adenocarcinoma), pulmonary embolism and infarction, hypoxemic disease, smoking-related ILD, heart disease and hypertension 7.
Diagnosis
If confirmation is required, surgical lung biopsy is the most reliable means of diagnosis. Transbronchial and percutaneous biopsy can be diagnostic or can lead to misdiagnosis due to inadequate sampling.
Diagnosis requires clinical, radiological and pathological correlation, disease stability and exclusion of metastatic meningioma.
Clinical presentation
The condition is commonly an asymptomatic incidental finding however 43% may experience dry cough or dyspnea which may or may not related.
Pathology
Histology demonstrates nests of perivenular and interstitial spindle-to-epithelioid cells with morphologic, ultrastructural and immunohistochemical profiles identical to meningiomas. Intracranial meningiomas and meningothelial nodules can display similar genetic alterations i.e. deletion of the NF2 gene and chromosomal gains of 22q.
Immunohistochemistry
Positive for:
epithelial membrane antigen (EMA)
progesterone receptor
CD56
somatostatin receptor 2a (SSTR2a), a possible therapeutic target
Staining is negative for cytokeratins, melanocytic, muscle, and vascular markers.
Radiographic features
CT
When they are large enough to be detected on CT, they appear as small soft-tissue or lower attenuation nodules, or as tiny rings with central lung attenuation, giving rise to the cheerio (fruit loop) sign. They are usually less than 6 mm diameter, occasionally up to 11 mm.
DPM presents as scattered randomly distributed micronodules with similar appearance.
Differential diagnosis
miliary metastases from intracranial meningioma
miliary metastases from other primaries
miliary infection
multifocal lung adenocarcinoma
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