| disease | Bronchial Adenoma |
| alias | Bronchial Adenoma |
Bronchial adenoma is a group of benign tumors originating from the bronchial mucous glands, glandular duct epithelium, or Kulchitsky cells beneath the mucous membrane, but with a tendency to become malignant. It commonly occurs between the ages of 30 and 50, with an average age of 45. The incidence is similar in both men and women.
bubble_chart Pathological Changes
It can be divided into three types:
(1) **Bronchial Carcinoid** (also known as Carcinoid adenoma) accounts for 1–7% of primary lung tumors and 80–90% of bronchial adenomas. It commonly occurs in large bronchi and originates from the Kulchitsky cells in the bronchial wall. About 80% are central-type, with only 1/5 occurring in peripheral bronchi below the subsegmental level. The tumor tends to grow beneath the bronchial mucosa. If it grows into the lumen, it often forms a smooth, vascular polypoid mass that obstructs the lumen, leading to obstructive emphysema, atelectasis, pneumonia, or even lung abscess. If it grows inward and outward through the bronchial wall, it may form a typical dumbbell-shaped mass. Most of these tumors have a complete capsule, with a gray-white or pale-red cut surface and clear boundaries from surrounding lung tissue, making them easy to separate from the lung. They may also break through the capsule and grow invasively. Microscopically, the tumor cells are small, cuboidal or polygonal, uniform in size, and arranged in clusters, cords, or gland-like structures. The cytoplasm is abundant and eosinophilic, containing dark argyrophilic granules corresponding to neurosecretory granules seen under electron microscopy. These granules secrete various bioactive substances, leading to ectopic endocrine symptoms of carcinoid syndrome. The nuclei are round or oval, with clear nuclear membranes and rare mitotic figures. The tumor stroma is rich in capillaries and may show hyalinization, amyloidosis, calcification, or even ossification. About 10% of bronchial carcinoids exhibit atypical growth, with variable cell sizes, irregular arrangements, nuclear pleomorphism, increased mitotic activity, and frequent necrosis. Atypical carcinoids have a 70% rate of local lymph node, liver, or bone metastasis, whereas typical carcinoids have a distant metastasis rate of less than 5%.
(2) **Adenoid Cystic Carcinoma** (formerly called cylindromas) accounts for 10–15% of bronchial adenomas. It arises in the trachea, carina, or large bronchi, growing infiltratively along the bronchial wall and potentially invading surrounding tissues and organs. It rarely forms polypoid growths but may obstruct the bronchial lumen. The cut surface is gray-white. Microscopically, the tumor consists of small, basaloid epithelial cells with scant cytoplasm and dark, regular nuclei, forming solid or lobulated nests and cords. Transparent matrix deposits are present within and around the cell cords. The tumor cells are arranged in interwoven cylindrical or tubular structures containing PAS-positive epithelial mucin. Mitotic figures are more common than in carcinoids. This tumor has the highest malignancy among bronchial adenomas, capable of local invasion and distant metastasis to organs such as the liver and kidneys.(3) **Mucoepidermoid Tumor** originates from the mucous glands of large bronchi and is a rare tumor, accounting for 2–3% of bronchial adenomas. It typically grows as a sessile intrabronchial mass, obstructing the lumen and invading locally. The cut surface shows multiple mucus-filled cystic spaces. Microscopically, the tumor is composed of keratinized cells, mucin-secreting cells, and intermediate or transitional cells. Histologically, it is further divided into: - **Well-differentiated tumors** (more common), which have clear boundaries and grow outward. They consist of cells with small, regular nuclei, abundant cytoplasm, and no mitotic figures. Goblet cells are numerous, and glandular lumen formation is prominent. Transitional and squamous cells are rare. - **Poorly differentiated tumors** (less common), which have indistinct boundaries and grow inward, with local necrosis, large and pleomorphic nuclei, scant cytoplasm, and mitotic activity. Goblet cells and squamous cells are rare, glandular lumen formation is minimal, and transitional cells are abundant. These tumors exhibit local invasion and may undergo malignant transformation.
The age of diagnosis for bronchial adenoma is earlier than that of bronchial carcinoma. Symptoms vary depending on the tumor's location, whether there is bronchial obstruction, local infiltration, and distant metastasis. Tumors located at the periphery of the lung are often asymptomatic and usually discovered during X-ray examinations. If the tumor occurs in a larger bronchus, the initial stage [first stage] may present with an irritating dry cough and recurrent bloody sputum. As the tumor grows, localized obstructive lung qi swelling and fixed wheezing may occur. Complete obstruction of the lumen can lead to atelectasis. Secondary infections distal to the obstruction may result in pneumonia, lung abscess, or bronchiectasis. Since adenomas are benign, symptoms may persist for a long time, with some cases taking 5–15 years to be diagnosed. If malignant transformation and metastasis occur, the symptoms resemble those of other metastatic cancers. A few patients with bronchial carcinoid may experience paroxysmal skin flushing, abdominal pain, diarrhea, asthma, and tachycardia, indicative of carcinoid syndrome, or manifestations of ectopic ACTH syndrome such as central obesity, hypertension, edema, lack of strength, hypokalemic alkalosis, and hyperpigmentation.
X-ray findings: The results may be negative if the tumor is extremely small. Bronchial adenomas near the hilum may appear as round or semicircular shadows, while those in the peripheral lung may present as nodular or spherical shadows. These may be accompanied by obstructive lung qi swelling, atelectasis, obstructive pneumonia, or even lung abscess, sometimes obscuring the tumor itself.
Bronchial adenoma tends to occur at a younger age and is often characterized by prolonged bouts of coughing, hemoptysis, and recurrent lung infections. Chest X-rays typically reveal round, dense shadows. Particularly, tomography and CT scans can clearly delineate the tumor's location, shape, size, the extent of bronchial obstruction, and the presence of regional lymph node metastases. Bronchoscopy is one of the key diagnostic methods for this condition, as it not only identifies the tumor's position but also allows for biopsy to provide a pathological diagnosis. The positive biopsy rate via fiberoptic bronchoscopy can reach 66–86%. Due to the tumor's rich vascularity and its surface being covered by intact mucous membrane epithelium, improving diagnostic accuracy requires repeated deep biopsies, though care must be taken to prevent bleeding. Conversely, sputum cytology, bronchial lavage, and brush smear examinations are not helpful in diagnosing this condition.
bubble_chart Treatment Measures
Surgical resection is currently the only curative method for all types of bronchial adenomas. The extent of resection depends on the tumor's location and the condition of the affected distal lung tissue. The principle is to completely remove the tumor, clear suspicious regional lymph nodes, preserve as much normal lung tissue as possible, and avoid pneumonectomy, which can improve survival rates and reduce complications. Endobronchial resection, whether by electrocautery or laser therapy, is only suitable for symptomatic central adenomas in patients with medical contraindications to thoracotomy. The 5-year survival rate after surgical resection reaches 95%, but drops to 57% to 70% if regional lymph node metastasis is present. Due to the variable growth patterns of metastatic pulmonary carcinoids—remaining unchanged or growing slowly over years, or behaving like small cell carcinoma—there is no definitive treatment. However, the tumor's growth rate and histology should be evaluated in individual cases to determine whether chemotherapy or radiotherapy is warranted.
The following diseases should be differentiated from adenomas when identifying lung masses.
(1) Peripheral bronchogenic carcinoma: The age of onset is relatively older compared to adenomas, and the growth is faster. On X-ray, the nodular or round lesions of adenomas have sharper borders than lung cancer, but sometimes differentiation is difficult. When diagnosis is challenging, timely thoracotomy exploration should be performed to avoid missing the opportunity for radical treatment.
(2) Pulmonary subcutaneous node ball: It commonly occurs in the apical-posterior segment of the upper lobes or the dorsal segment of the lower lobes, often surrounded by satellite lesions. The lesions frequently exhibit concentric or dense calcifications.
(3) Pulmonary hamartoma: It appears as a round or lobulated mass shadow with clear edges, containing calcification spots within the lesion, sometimes resembling popcorn.
