Disclosure
Background: Hamartomas are the third most common cause of a solitary pulmonary nodule and the most common benign tumor of the lung. Hamartomas account for 75% of all benign lung tumors and are composed of tissues that are normally present in the lung, including fat, epithelial tissue, fibrous tissue, and cartilage, but they exhibit disorganized growth. Although most hamartomas are asymptomatic and although they have no malignant potential, bronchogenic carcinoma is an important differential diagnosis, and an accurate imaging interpretation and diagnosis is important. Peripheral tumors are usually simply observed after the definitive diagnosis, while central tumors may be excised. The prognosis is excellent. For excellent patient education resources, visit eMedicine's Procedures Center . Also, see eMedicine's patient education article Bronchoscopy. Pathophysiology: The exact etiology of pulmonary hamartomas is not known, though several theories have been postulated, including congenital malformation of a displaced bronchial anlage, hyperplasia of normal lung tissues, a cartilaginous benign neoplasm, and response to inflammation. The lesions originate in the submucosal fibrous connective tissue of the bronchial wall, and they are composed of cartilaginous nests surrounded by connective tissue and mature fat cells. Fat is a key component, being present in 54% of lesions histologically in amalgamated series. Myxomatous connective tissue, smooth muscle, bone, blood vessels, and other mesenchymal elements may also be seen histologically. The tissues are arranged in a disorganized manner. Malignant transformation is either extremely rare or nonexistent. Sarcomas arising in the wall of cystic mesenchymal hamartomas have been reported in children. However, cystic mesenchymal hamartomas are histologically different from adult pulmonary hamartomas. Unlike carcinoid tumors, more than 90% of hamartomas are peripheral. Only 10% or less are located centrally, and even these are thought to arise pathologically in the connective tissue of small bronchi. On gross examination of pathology specimens, they seem to be well circumscribed and usually slightly lobulated. They may compress the adjacent lung. The peripheral location of pulmonary hamartomas usually renders them asymptomatic. Pulmonary hamartomas grow slowly, and most are smaller than 4 cm, although they may grow to 10 cm in diameter. The tumors are usually solitary, although multiple tumors have been reported in the Carney triad. The triad includes pulmonary chondromas, gastric epithelioid leiomyosarcoma (leiomyoblastoma), and functioning extra-adrenal paraganglioma. A partial type of the Carney triad may be seen when pulmonary hamartomas coexist with smooth muscle tumors of the stomach. Associations with other developmental anomalies and benign gastrointestinal stromal tumors such as gastrointestinal autonomic nerve tumors have also been reported. The Carney triad is usually seen in young women who present with slow-growing lung tumors. Multiple tumors in this setting often represent metastases, occasionally leiomyosarcoma of the stomach, which is a recognized complication. Frequency:
Mortality/Morbidity: Pulmonary hamartomas per se are not associated with any significant morbidity or mortality. However, problems may arise when a pulmonary nodule is discovered in a smoker and when the features of the nodule are atypical. In this context, morbidity and mortality may be related to diagnostic procedures such as bronchoscopy, percutaneous or endobronchial biopsy, or thoracotomy. Race: No racial predilection exists. Sex: Hamartomas occur more often in men, with a male-to-female ratio of 2-3:1. Age: The incidence peaks in those aged 50-60 years, but the average patient age at presentation is 45-50 years. Only 6% are found in those younger than 30 years. The tumors rarely occur in children. Clinical Details: Pulmonary hamartomas are usually asymptomatic and discovered as an incidental coin lesion on a routine chest radiograph. Occasionally, the tumors may be endobronchial, and they rarely cause hemoptysis or bronchial obstruction with signs and symptoms of coughing, wheezing, expectoration, leukocytosis, and fever. The Carney triad may exceptionally present, with malignant hypertension from hormonally active extraadrenal paragangliomas. Pheochromocytomas have also been reported with the Carney variant. Preferred Examination: Most pulmonary hamartomas are discovered incidentally on routine chest radiographs. Chest radiographic findings are rarely diagnostic, and most patients require CT examination for further evaluation and characterization of the lesion. Bronchoscopic or percutaneous biopsy may be necessary for definitive diagnosis in some cases. Ultrasonography, MRI, and radionuclide studies are useful techniques for investigating the Carney triad. Limitations of Techniques: Chest radiography has limited value when calcification or fat cannot be detected within the lesion or when the nodules are multiple. CT is expensive both in terms of cost and radiation burden. CT also has limitations in that characteristic calcification and/or fat within the lesion is absent in one third of patients. On CT scans, central endobronchial hamartomas may have features indistinguishable from those of a bronchial carcinoid.
Lung Cancer, Non-Small Cell
Bronchogenic carcinoma - Calcification rare
Findings: On chest radiographs, pulmonary hamartomas characteristically appear as well-defined solitary pulmonary nodules, which may show varying patterns of calcification, including an irregular popcorn, stippled, or curvilinear pattern, or even a combination of all three. Calcification detectable on plain radiography is reported to occur in 10-15% of patients. Popcorn calcification is virtually diagnostic. Most lesions are smaller than 4 cm in diameter; well circumscribed; and, most often, lobulated. They show no lobar predominance. Cavitation is extremely rare. Rarely, bronchial obstruction may occur with a central tumor, which results in obstructive pneumonitis, bronchiectasis, and progressive peripheral lung destruction. Serial chest radiographs may demonstrate slow growth. Rapid growth has rarely been reported. This feature may make the differentiation of a hamartoma from a bronchogenic carcinoma difficult. Degree of Confidence: When calcification or fat is detected within a well-circumscribed peripheral lung tumor, a hamartoma can be diagnosed confidently. However, the characteristic calcification is seen in only approximately 15% of patients, and detection of fat within a nodule is even rarer on plain radiographs. False Positives/Negatives: A central lucency within a hamartoma due to adipose tissue may be misinterpreted as air within a cavity, for which the differential diagnosis is significantly different. When no characteristic calcification or fat is identified within a coin lesion or when multiple lesions are present, the differential diagnosis is extensive (see Differentials). |
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Findings: The fundamental appearances of a hamartoma on CT scans are similar to those on chest radiographs. However, thin sections also allow for more detailed evaluation of the internal architecture and morphology of lesions. In particular, calcium and fat are better visualized with CT than with radiography. The Hounsfield values for fat lie within the range of –50 to –120 HU. Fat is identified in 34-50% of lesions, and calcification, in 15-30%. On high-resolution CT (HRCT), fat attenuation is detectable in 34% of tumors, and fat and calcium, in 19%. The finding of both fat and calcification is a specific combination for hamartomas, particularly in tumors smaller than 2.5 cm in diameter. The presence of calcification increases with increasing tumor size, with only 10% of lesions smaller than 2 cm containing calcification. This rate increases to 75% of lesions larger than 5 cm. CT may also have a role in the diagnosis of the Carney triad. Degree of Confidence: CT is more sensitive than chest radiography in the detection of fat and calcification. Hamartomas may be confidently diagnosed on CT when a sharply marginated, smooth lesion containing calcification and fat is identified. False Positives/Negatives: In one third of hamartomas, no calcium or fat is demonstrable on CT scans. The differential diagnosis is extensive in these cases. Central endobronchial tumors may have features indistinguishable from those of a bronchial carcinoid.
Findings: MRI is not used in the detection or diagnosis of pulmonary hamartomas. However, MRI is the modality of choice for screening and follow-up of suspected cases of the Carney triad in which clinical and biochemical evidence suggests a paraganglioma. Degree of Confidence: MRI is said to be as sensitive as iodine-131 metaiodobenzylguanidine (MIBG) scintigraphy in the diagnosis of paraganglioma, but it may not be useful in differentiating paragangliomas from other neurogenic tumors in the Carney triad. False Positives/Negatives: MRI may not be helpful in differentiating between paraganglioma and other neurogenic tumors.
Findings: Ultrasonography is not used in the detection or diagnosis of pulmonary hamartomas. However, transthoracic ultrasonographic guidance may be used for image-guided percutaneous biopsy of lesions in close contact with the chest wall. Ultrasonography may also be useful in the diagnosis of nonthoracic manifestations of a Carney triad.
Findings: A paraganglioma associated with the Carney triad may be identified with iodine-123 or iodine-131 MIBG scanning. Radionuclide studies have no role in the diagnosis of a lung hamartoma. Degree of Confidence: MIBG radionuclide scanning is a reliable and noninvasive technique in the diagnosis of paragangliomas. False Positives/Negatives: MIBG uptake may occur in other neuroendocrine tumors.
Findings: Angiography has no role in the diagnosis of a lung hamartoma.
Intervention: Pulmonary nodules not demonstrating the typical features of a hamartoma (as outlined above) require further investigation to confirm their benignity and to exclude malignancy. Image-guided percutaneous aspiration or cutting-needle biopsy of an indeterminate lung nodule is usually performed by using fluoroscopic or CT guidance. Ultrasonographic guidance can be used when a peripheral nodules is in contact with the thoracic wall. Pneumothorax and hemoptysis are recognized complications. The incidence of pneumothorax varies and is approximately 10-30%. Hemoptysis is usually a self-limiting complication. Benign lesions are usually hard and difficult to penetrate because the tumor tends to push away from the needle. In these circumstances, fluoroscopy performed perpendicular to the plane of biopsy provides for better control of the needle. In addition to routine cytologic examination, cell-block preparation is extremely important in the diagnosis of benign lesions. Bronchoscopy and bronchial biopsy may be required in the centrally placed lung hamartoma. Thoracotomy may be required in rare cases in which the diagnosis cannot be established by using imaging or percutaneous biopsy. Special Concerns:
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