Diffuse pulmonary meningotheliomatosis (DPM) is a rarely recognized condition manifested by random pulmonary meningothelial nodules (PMNs) scattered throughout the lungs.
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Epidemiology
There is a strong female predilection, with one literature review of surgically proven DPM finding that 92% of cases occurred in females 9. DPM is most commonly detected between the 5th and 7th decades of life, however the reported age range is from 30-80 years. Although most are too small to be detected by CT, the autopsy incidence has been reported as 7.2% and depends on the extent of sampling 11.
Associations
In one study, in 44% of cases, there was concurrent or previous malignancy 9, with a specific association with lung adenocarcinoma and secondary (metastatic) adenocarcinomas. Additionally, there are associations with pulmonary embolism and hypoxemic states 13, 14. Intracranial meningioma is also an association and may be recognized either before or after the DPM diagnosis 14.
Clinical presentation
These nodules are frequently asymptomatic and are usually found incidentally at CT, at autopsy or in surgical specimens resected for unrelated causes. Some patients may have mild clinical symptoms such as dyspnea and dry cough 3.
Pathology
Minute pulmonary meningothelial nodules are acquired and are commonly less than 2 mm in diameter, range 100 µm - 11 mm. They are composed of small nests of mostly perivenular spindle-to-epithelioid cells and are identical to meningothelial cells in morphology, ultrastructure and immunohistochemical profile. Intracranial meningiomas and meningothelial nodules can display similar genetic alterations i.e. deletion of the NF2 gene and chromosomal gains of 22q 14.
Immunohistochemistry
Positive for:
epithelial membrane antigen (EMA)
vimentin
progesterone receptor 9
Negative for:
cytokeratin
actin
S-100 protein
CD34
chromogranin
synaptophysin
Radiographic features
CT chest is the modality of choice to investigate DPM. However, with neuroimaging, intracranial meningioma may co-exist.
CT
They may be seen throughout the lungs as randomly distributed micronodules usually less than 6 mm, but up to 11 mm. The nodules may be ground glass or soft-tissue attenuation and may display relative central lucency, a helpful diagnostic feature 10 giving rise to the cheerio sign.
Treatment and prognosis
DPM is benign and indolent. The nodules demonstrate long-term stability.
History and etymology
Minute pulmonary meningothelial‐like nodules (MPMNs) were first described by Korn et al. in 1960 7.
Differential diagnosis
Metastatic meningioma is rare, approximately 1:1,000, and although lung is the most frequent site, metastases usually present as multiple nodules or masses.
Primary pulmonary meningioma is exceedingly rare and presents as a lung nodule or mass.
The differential diagnosis for the CT appearance includes:
miliary tumor or infection
metastatic adenocarcinoma