Minute Pulmonary Meningothelial-Like Nodules--So-called Chemodectoma

Definition: These lesions are common, often multiple, incidental findings that are more frequent in women than men (5:1). Smaller than 3 mm in diameter, they consist of nests or bundles of spindled cells that widen alveolar walls. They are located around small veins and radiate into the surrounding alveolar walls in a stellate fashion. Nests are separated by scant fibrous tissue and capillaries. They have been found in all lobes.

Differentiation: Abnormal cell proliferations usually show differentiation reminicent of some normal cell. With H&E stains, these nodules were initially believed to be composed of chemoreceptor cells, but ultrastructural examination surprisingly show similarities to meninogothelial cells, and immunohistochemical stains support the similarity.

Clinical significance: The lesions are usually found in adult lungs with some abnormality. They have no known clinical significance.

Differential diagnosis: Other similar-appearing lesions include tumorlets, which are associated with small airways; plexiform lesions, which are associated with arteries; and metastatic tumor, which is composed of malignant-appearing cells.

Meningothelial-like nodule: Whorls and nests of spindled cells surround a small vein (arrow) and extend into, and widen, the adjacent alveolar walls. Cells are uniform with moderate amounts of pink cytoplasm and ovoid nuclei. Mitoses are absent. Fibrous tissue separates the nests and surrounds the nodule. Note the nest in the widened alveolar wall at the lower right (arrowhead).



Gaffey M, Mills S, Askin F. Minute pulmonary meningothelial-like nodules. A clinicopathologic study of so-called minute pulmonary chemodectoma. Am J Surg Pathol 1988; 12:167-175.


Table of Contents































This lesion was an incidental postmortem finding. Nests of cells are present under the airway epithelium at the upper left.

At higher magnification, the cells have uniform, ovoid nuclei and a moderate amount of cytoplasm. Mitoses are absent.

Tumorlets: Tumorlets are nodular proliferations of neuroendocrine cells that are normally present in the airways. In the neonate, neuroendocrine (Kulchitsky) cells are present frequently as single cells or clusters in the epithelium. They become less frequent with age. In certain lung diseases--cystic fibrosis, asthma, COPD, eosinophilic granuloma, and primary pulmonary hypertension--these cells sometimes become hyperplastic for unknown reasons. Tumorlets are nodular proliferations up to 4 mm in diameter in the airway wall. (Larger tumors are called carcinoids.) Tumorlets are common incidental findings in lungs scarred by chronic bronchitis or bronchiectasis [1,2], but they may also be found in otherwise normal lungs [1]. Often multiple, and usually peripheral, they are characterized by small nests of cells having neurosecretory granules. They lack mitoses and cellular atypia. Typically, they have a hyalinized, fibroelastic stroma [1]. Lymph node metastases have been noted in 4 or 5 cases. One case that was associated with Cushing's syndrome had tumor that metastasized widely [3]. In 36 cases, females predominated, 28 to 8, and the average age was 70 [1].

Authors of a recent report have proposed that in patients with innumerable tumorlets, they are the cause, rather than the result, of an obstructive/restrictive lung disease. The seven patients that were described had complaints of chronic cough and dyspnea. Chest radiographs showed diffuse reticulonodular opacities [4,5].


1. Churg A, Warnock M. Pulmonary tumorlet. A form of peripheral carcinoid. Cancer 1976; 37:1469-1477.

2. Pelosi G, Zancanaro C, Sbabo L, Bresaola E, Martignoni G, Bontempini L. Development of innumerable neuroendocrine tumorlets in pulmonary lobe scarred by intralobar sequestration. Immunohistochemical and ultrastructural study of an unusual case. Arch Pathol Lab Med 1992; 116:1167-1174.

3. D'Agati V, Perzin K. Carcinoid tumorlets of the lung with metastasis to a peribronchial lymph node. Report of a case and review of the literature. Cancer 1985; 55:2472-2476.

4. Miller M, Mark G, Kanarek D. Multiple peripheral pulmonary carcinoids and tumorlets of carcinoid type, with restrictive and obstructive lung disease. Am J Med 1978; 65:373-378.

5. Aguayo S, Miller Y, Waldron J Jr, Bogin R, Sunday M, Staton G Jr, Beam W, et al. Idiopathic diffuse hyperplasia of pulmonary neuroendocrine cells and airways disease. N Engl J Med 1992; 327:1285-1288.


Table of Contents




























Cartilaginous Hamartoma

These circumscribed, benign tumors are composed of cartilage, loose connective tissue, and fat. They are related to airways and have multiple invaginations of non-neoplastic respiratory epithelium (arrow). See Case 7.



Table of Contents