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bronchial mucous gland adenoma

Friday 18 January 2013

mucous gland adenoma of the bronchus, mucous gland adenoma of the lung; bronchial cystadenoma; mucous cell adenoma.

A bronchial mucous gland adenoma is a very rare and entirely benign tumour.

The lesion is classed as a benign epithelial tumour of the lung, among the salivary gland-type adenomas.

The bronchial mucous gland adenoma is a benign, usually an exophytic, tumour of the tracheobronchial mucus glands. It is also very rare.

For example, in a major series of 164 patients with benign tracheobronchial tumors, only two had bronchial mucous gland adenomas.

The tumour occurs with equal frequency in men and women and at any age (mean 52), including in children.

It localizes usually in the root or lobar bronchi and in the middle or inferior lobes; more rarely, it may be found in the trachea or in the lung periphery.

Clinical synopsis

Symptoms are a result of bronchial obstruction by the tumour.

The clinical presentation may be mistaken for asthmatic disorders or chronic obstructive pulmonary disease for long periods of time.

Other non-specific observations such as a chronic cough, unilateral wheezing, haemoptysis or pulmonary infections can also contribute to long delays (a mean of 20 months according to Gaissert and Mark) before a correct diagnosis is made.

Exploratory methods vary in efficacy but may also be complementary.

Radiology

The chest X-rays may be normal, show a solitary nodule or a bronchial obstruction with downstream atelectasis.

The CT scans can reveal a well-defined intraluminal mass, typically with an air meniscus sign, suggesting the endobronchial and expansive nature of the tumour.

Endoscopy

Bronchoscopy will find a firm, smooth, shiny and well-defined intraluminal mass that is sometimes pedunculated.

On average, the mass will have a diameter of ∼18 mm (8–68 mm in the series reported by England et al.).

Endoscopic specimens are generally insufficient for confident diagnosis; complete resection is recommended as this allows for thorough histological analyses and is usually curative.

Endoscopic removal has been described, but total surgical resection remains the reference.

Microscopy

Histology studies will find a well-circumscribed (but unencapsulated) proliferation of mucosal glands in the form of an exophytic nodule with no invasion of the cartilage or bronchial wall.

The lesion is composed of variously dilated, sometimes cystic glands filled with mucous.

Tubules and papillae may also be present.

Glands in the tumour are lined with mucous-secreting cells whose form may be columnar, cuboidal or flattened.

  • Their cytoplasm is clear.
  • The lining may show stratified or papillary luminal folds.
  • Nuclei are usually normal.
  • Indications of mitosis are rare.

The stroma is composed of hyaline connective tissue.

The surface respiratory epithelium may comprise the areas of squamous metaplasia.

Immunochemistry

Immunohistochemically, the gland-lining cells are positive for epithelial markers and generally express high molecular weight keratins (cytokeratins 5/6 and keratin 903); they are negative for TTF-1.

Focal positivity for broad-spectrum keratins, actin and S-100 protein indicate a myoepithelial component. Ki67 and other proliferation markers are rarely positive.

Benign glandular tumours of the tracheobronchial tree remain out of the limelight of pulmonary medicine.

They are nonetheless capable of provoking mechanical and symptomatic bronchial obstruction.

This observation gives credence to the necessity of an in-depth lung workup following acute respiratory infections in the upper lung.

Differential diagnosis

There are two primary differential diagnoses that merit investigation:
- low-grade mucoepidermoid carcinoma
- pulmonary mucinous cystadenoma (mucinous cystadenoma of the lung)

- low-grade mucoepidermoid carcinoma

  • The first is the low-grade mucoepidermoid carcinoma with papillary or cystic components.
  • The mucoepidermoid carcinoma is a rare malignant tracheobronchial tumour, although it is encountered more frequently than the bronchial mucous gland adenoma.
  • The careful assessment of squamous and intermediate cells will confirm this diagnostic and careful confirmation of the absence of atypical cells will exclude it.

- pulmonary mucinous cystadenoma (mucinous cystadenoma of the lung)

  • The second differential diagnosis is the "mucinous cystadenoma of the lung".
  • This is another benign lesion histologically similar to the "bronchial mucous gland adenoma".
  • However, it occurs in the peripheral pulmonary parenchyma, not in the tracheobronchial tree.
  • They are often confused, even in the literature, despite differences in clinical presentation and natural history.

References

- Bronchial mucous gland adenoma revealed following acute pneumonia. Couraud S, Isaac S, Guibert B, Souquet PJ. Interact Cardiovasc Thorac Surg. 2012 Mar;14(3):347-9. doi : 10.1093/icvts/ivr104 Epub 2011 Dec 20. PMID: 22186127