Pulmonary Pathology Online
Pathology of Mucoepidermoid Carcinoma of the Lung
carcinoma (MEC) is the most common primary salivary gland-type tumour
of the lung.
It arises from the excretory ducts of the bronchial mucosa.
This rare tumor is more common in adults than in children, and infrequently presents with hemoptysis.
In children and adolescents, primary neoplasms of the tracheobronchial tree and lungs are rare, with most tumors involving the respiratory system being metastatic, small, blue cell tumours of childhood.
Of the primary pulmonary neoplasms, most are malignant with mucoepidermoid carcinoma representing about 10% of these malignant tumors.
Mucoepidermoid tumours of the tracheobronchial tree carry a more favorable prognosis in children than adults.
The tumour can be successfully managed by surgical intervention alone in children and adolescents.
Recurrent pneumonia and persistent cough are the most common presenting findings in children.
These tumours are of low-grade malignant potential but they can become locally invasive, extending into cartilage and surrounding soft tissue.
Mucoepidermoid carcinoma of the tracheobronchial tree, usually located in a segmental bronchus, appears at CT as a smoothly oval or lobulated airway mass.
It adapts to the branching features of the airways.
The tumour usually presents as a polypoid endobronchial mass involving the proximal bronchi. High-grade mucoepidermoid carcinoma of the lung may present as a cavitary lesion.
It is classified into low- and high-grade tumours using criteria derived from similar tumours of the major salivary glands.
Low-grade MEC behaves in a benign fashion with less parenchymal and hilar lymph nodal invasion.
Note : Mucoepidermoid carcinoma of the bronchus can be recognized on histology as well as cytology by the presence of three characteristic cell types: mucus secreting, epidermoid and intermediate.
Histologically, the tumour displays an elaborate tubulocystic epithelial component. It is composed of intermediate, sheets of cells with epidermoid differentiation, and mucus-producing cells containing intra and extracellular mucin, and variable numbers of clear cells, multinucleated giant cells, columnar cells, and oncocytic cells.
Low grade tumour : Marked cellular atypia is absent in the solid or epidermoid component.
High grade tumour: There is marked cellular atypia , prominent mitotic activity, areas of necrosis and hemorrhage. (Differential diagnosis : Poorly differentiated squamous cell carcinoma). PAS and mucicarmine may be useful in identifying scattered mucocytes in poorly differentiated tumours.
In some cases dense lymphoplasmacytic infiltrate with occasional Russell bodies may be present. (Differential diagnosis : low-grade lymphoma )
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