You are in: eMedicine Specialties > Radiology > CHEST Hamartoma, LungArticle Last Updated: Sep 22, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Sarah Al Ghanem, MBBS, Consulting Staff, Department of Medical Imaging, King Fahad National Guard Hospital, Riyadh, Saudi Arabia; Klaus L Irion, MD, PhD, Consulting Staff, The Cardiothoracic Centre Liverpool NHS Trust, The Royal Liverpool University Hospital, UK; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Carolyn M Allen, MB, BCh, MRCP, FRCR, CCST, Consultant Radiologist, Department of Clinical Radiology, North Manchester General Hospital, UK Editors: Kitt Shaffer, MD, PhD, Director of Undergraduate Medical Education, Associate Professor, Department of Radiology, Cambridge Health Alliance; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; W Richard Webb, MD, Chief of Thoracic Imaging, Professor, Department of Radiology, University of California at San Francisco; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Barry H Gross, MD, Professor, Department of Radiology, University of Michigan Medical School; Professor, University of Michigan Cancer Center Author and Editor Disclosure Synonyms and related keywords: lung hamartoma, hamartochondroma, chondromatous hamartoma, Carney's triad, Carney triad, Carney's syndrome, Carney syndrome, pulmonary chondroma, solitary pulmonary nodule, benign lung tumor INTRODUCTIONSection 2 of 12
  BackgroundPulmonary hamartomas, the most common benign tumors of the lung, are the third most common cause of solitary pulmonary nodules. Accounting for 75% of all benign lung tumors, hamartomas are composed of tissues that are normally present in the lung, including fat, epithelial tissue, fibrous tissue, and cartilage. However, they exhibit disorganized growth. Pulmonary hamartomas have little or no malignant potential, and most of them are asymptomatic, but because bronchogenic carcinoma is an important differential diagnosis,1 accurate imaging interpretation and diagnosis are important.2 Peripheral tumors are usually simply observed after the definitive diagnosis; central tumors may be excised. The prognosis is excellent.3, 4, 5, 6 For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Bronchoscopy. PathophysiologyThe exact etiology of pulmonary hamartomas is unknown, although several theories have been postulated, including that these hamartomas result from congenital malformation of a displaced bronchial anlage, hyperplasia of normal lung tissues, a cartilaginous benign neoplasm, or a 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 histologically in 54% of lesions in amalgamated series. Myxomatous connective tissue, smooth muscle, bone, blood vessels, and other mesenchymal elements also may 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, hamartomas seem to be well circumscribed and to usually be slightly lobulated. They may compress the adjacent lung. The peripheral location of pulmonary hamartomas usually renders them asymptomatic. Pulmonary hamartomas grow slowly, and most of them are smaller than 4 cm, although they may reach 10 cm in diameter.7 The tumors are usually solitary, although multiple tumors in the Carney triad have been reported.8 The triad includes pulmonary chondroma, gastric epithelioid leiomyosarcoma (leiomyoblastoma), and functioning, extra-adrenal paraganglioma.9, 10, 11, 12 A partial Carney triad may be seen when pulmonary hamartomas coexist with smooth muscle tumors of the stomach.13 Associations with other developmental anomalies and with benign, gastrointestinal stromal tumors, such as gastrointestinal autonomic nerve tumors,14 also have 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 leiomyosarcomas of the stomach, which are a recognized complication. FrequencyUnited StatesHamartomas represent 6-8% of all solitary pulmonary nodules and 0.25% in autopsy series. In rare cases, they are multiple. InternationalThe international frequency of pulmonary hamartoma may differ from that in the US. Mortality/MorbidityPulmonary hamartomas are not associated per se with any significant morbidity or mortality. Problems may arise, however, when a pulmonary nodule is found in a person who smokes and when the nodule has atypical features. In this context, morbidity and mortality may be related to diagnostic procedures, such as bronchoscopy, percutaneous or endobronchial biopsy, or thoracotomy.15 RaceNo race predilection exists for pulmonary hamartoma. SexHamartomas occur more often in men than in women, with a male-to-female ratio of between 2:1 and 3:1. AgeThe incidence of pulmonary hamartoma peaks in persons aged 50-60 years, but the average patient age at presentation is 45-50 years. Only 6% of these hamartomas are found in persons younger than 30 years. The tumors rarely occur in children. Clinical DetailsPulmonary hamartomas are usually asymptomatic and are typically discovered as an incidental coin lesion on a routine chest radiograph. Occasionally, the tumors may be endobronchial, but they rarely cause hemoptysis or bronchial obstruction with signs and symptoms of coughing, wheezing, expectoration, leukocytosis, and fever.16, 17 The Carney triad may exceptionally present, with malignant hypertension resulting from hormonally active extra-adrenal paragangliomas.10 Pheochromocytomas also have been reported with the Carney variant.18 Preferred ExaminationMost pulmonary hamartomas are discovered incidentally on routine chest radiographs. Chest radiographic findings are rarely diagnostic, and most patients require a computed tomography (CT) scan examination for further evaluation and characterization of the lesion. In some cases, bronchoscopic or percutaneous biopsy may be necessary for a definitive diagnosis. Ultrasonography, magnetic resonance imaging (MRI), and radionuclide studies are useful techniques for investigating the Carney triad. Limitations of TechniquesChest radiography has limited value when calcification or fat cannot be detected in the lesion or when multiple nodules are present. CT scanning is expensive in terms of cost and radiation burden. CT scanning also has limitations in that characteristic calcification and/or fat in the lesion is absent in one third of patients. On CT scans, central endobronchial hamartomas may have features that are indistinguishable from those of a bronchial carcinoid. DIFFERENTIALSSection 3 of 12
Lung Cancer, Non-Small Cell Lung Cancer, Small Cell Lung, Arteriovenous Malformation Lung, Carcinoid Lung, Metastases Other Problems to Be Considered
RADIOGRAPHSection 4 of 12
FindingsOn chest radiographs, pulmonary hamartomas characteristically appear as well-defined, solitary pulmonary nodules; they may show varying patterns of calcification, including an irregular popcorn, stippled, or curvilinear pattern, or even a combination of all 3 patterns. Calcification that is 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 and well circumscribed; they are usually lobulated. The lesions show no lobar predominance, and cavitation is extremely rare. In unusual cases, bronchial obstruction occurs with a central tumor, causing 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 ConfidenceWhen calcification or fat is detected in a well-circumscribed peripheral lung tumor, a diagnosis of hamartoma can confidently be made. 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/NegativesWhen a central lucency occurs in a hamartoma because of the presence of adipose tissue, the lucency may be misinterpreted as air within a cavity, resulting in a significantly different differential diagnosis. When no characteristic calcification or fat is identified in a coin lesion or when multiple lesions are present, the differential diagnosis is extensive (see Differentials). CT SCANSection 5 of 12
FindingsThe fundamental appearances of hamartomas 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.19, 20, 21 In particular, calcium and fat are better visualized with CT scanning than with radiography.22, 23 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) scans, fat attenuation is detectable in 34% of tumors, and fat and calcium, in 19%. The finding of fat and calcification together is a specific combination for hamartomas, particularly in tumors below 2.5 cm in diameter. The frequency of calcification increases with increasing tumor size; calcification is found in only 10% of lesions smaller than 2 cm, but this rate reaches 75% for lesions larger than 5 cm. CT scanning may also have a role in the diagnosis of the Carney triad. Degree of ConfidenceCT scanning is more sensitive than chest radiography in the detection of fat and calcification. Hamartoma may be confidently diagnosed when a sharply marginated, smooth lesion containing calcification and fat is identified on a CT scan. False Positives/NegativesIn 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 that are indistinguishable from those of a bronchial carcinoid. MRISection 6 of 12
FindingsMRI 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 if clinical and biochemical evidence suggests that a paraganglioma is present. Degree of ConfidenceMRI is said to be as sensitive as iodine-131-meta-iodobenzylguanidine (MIBG) scintigraphy in the diagnosis of paraganglioma, but it may not be useful in differentiating paragangliomas from other neurogenic tumors in the Carney triad.24 False Positives/NegativesMRI may not be helpful in differentiating between paragangliomas and other neurogenic tumors. ULTRASOUNDSection 7 of 12
FindingsUltrasonography is not used in the detection or diagnosis of pulmonary hamartomas. However, transthoracic ultrasonographic guidance may be employed in 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. NUCLEAR MEDICINESection 8 of 12
FindingsA paraganglioma that is 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 ConfidenceMIBG radionuclide scanning is a reliable and noninvasive technique in the diagnosis of paragangliomas. False Positives/NegativesMIBG uptake may occur in other neuroendocrine tumors. ANGIOGRAPHYSection 9 of 12
FindingsAngiography has no role in the diagnosis of a lung hamartoma. INTERVENTIONSection 10 of 12
Pulmonary nodules that do not demonstrate the typical features of a hamartoma (as outlined above) require further investigation to confirm their benignity and to exclude malignancy.25 Image-guided percutaneous aspiration or cutting needle biopsy of an indeterminate lung nodule is usually performed by using fluoroscopic or CT scan guidance.23, 26, 27 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, being 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. Under these circumstances, fluoroscopy performed perpendicular to the plane of biopsy enables better control of the needle. In addition to routine cytologic examination, cell-block preparation is extremely important in the diagnosis of benign lesions. When the lung hamartoma is centrally placed, bronchoscopy and bronchial biopsy may be required. Thoracotomy may be needed in rare cases in which the diagnosis cannot be established by using imaging or percutaneous biopsy.15 Special Concerns
MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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