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Postgraduate Education Corner: CHEST IMAGING AND PATHOLOGY FOR CLINICIANS |

An Elderly Woman With Chronic Dyspnea and Endobronchial Lesion FREE TO VIEW

Saleh Alazemi, MD; Adnan Majid, MD, FCCP; Angela I. Ruiz, MD; Diana Litmanovich, MD; David Feller-Kopman, MD, FCCP; Armin Ernst, MD, FCCP
Author and Funding Information

From the Division of Interventional Pulmonology (Drs Alazemi, Majid, and Ernst), the Department of Pathology (Dr Ruiz), and the Department of Radiology (Dr Litmanovich), Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA; and the Division of Pulmonology (Dr Feller-Kopman), Johns Hopkins Hospital, Baltimore, MD.

Correspondence to: Armin Ernst, MD, FCCP, Chief, Interventional Pulmonology, Beth Israel Deaconess Medical Center, Harvard Medical School, One Deaconess Road, Boston, MA 02215; e-mail: aernst@bidmc.harvard.edu


Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;137(2):460-466. doi:10.1378/chest.09-0876
Text Size: A A A
Published online

A 74-year-old woman presented with a 2-year history of worsening dyspnea and nonproductive cough that were aggravated by lying down. Three months prior, she had community-acquired pneumonia, which was treated successfully with antibiotics on an outpatient basis. During that time, she reported a few episodes of blood-tinged sputum that resolved after 2 days. She denied weight loss, loss of appetite, chest pains, fevers, chills, or night sweats. She had no symptoms suggestive of gastroesophageal reflux disease or postnasal drip syndrome. Her past medical history was significant for paroxysmal atrial tachycardia that was well controlled with metoprolol. Review of her family history indicated that her mother died of colon cancer, her father died of bladder cancer, and she had a brother with bone cancer. She is married and a retired registered nurse with a 30-pack-year history of tobacco use that she quit 40 years ago.

Relevant findings on physical examination included oxygen saturation of 100% while breathing room air at rest, absence of cervical masses or lymphadenopathy, and a faint positional stridor over the trachea when she lay down. Her laboratory workup was normal, and her pulmonary function tests revealed normal spirometry and flow-volume loops.

Radiologic Findings

An initial chest radiograph was unremarkable. CT scan of the trachea and chest revealed a 1.7×1.0 cm polypoid lesion within the trachea, attached to the posterior tracheal wall by a stalk approximately 2 cm above the carina with significant narrowing of the tracheal lumen at least by 50% (Fig 1). On the dynamic coughing sequences (in order to achieve higher levels of intrathoracic-extratracheal pressure to elicit airway collapse), the lesion appeared slightly mobile and lay on the dependent portion of the trachea. It had predominantly soft-tissue attenuation with small foci of low attenuation consistent with fat or necrosis. There were no lung parenchymal or pleural abnormalities.

Figure Jump LinkFigure 1. Dynamic airway CT scan without IV contrast during inspiration ( A - C ) and expiration ( D and E ) at the level of the aortic arch, including mediastinal window ( A ), lung window ( B and D ), and virtual bronchoscopy images ( C and E ). A 1.7 × 1.0 cm polypoid lesion is seen in the dependent portion of the trachea. Dynamic expiratory sequences indicate slight mobility of the lesion and airway collapsibility. The lesion has predominantly soft-tissue attenuation with small foci of low attenuation.Grahic Jump Location
Bronchoscopic Findings

Flexible bronchoscopy examination confirmed the CT finding of a polypoid lesion arising with a stalk in the distal trachea (Fig 2). There was no extension into either the left or right mainstem bronchi. There was an additional small island of “tumor” on the right posterior trachea approximately 1 cm distal to the main lesion. The distal airways appeared normal with no additional endobronchial lesions.

Figure Jump LinkFigure 2. Bronchoscopic images of a polypoid yellowish, smooth, and pedunculated lesion in the distal trachea. It appears to arise with a stalk the left posterolateral wall of the trachea.Grahic Jump Location
What is the diagnosis?
Diagnosis: Benign Endobronchial Fibrolipoma

The main tumor was resected en bloc using an electrocautery snare followed by argon plasma coagulation ablation of the base of the tumor and the additional tumor island. Histopathologic evaluation showed that the tumor was composed of broad, bulbous fronds containing fibrous connective tissue, adipose tissue, and mucous glands, and covered by pseudostratified ciliated columnar (Fig 3).

Figure Jump LinkFigure 3. Polypoid mass with broad fronds covered by pseudostratified ciliated columnar epithelium ( A ). The cores of the fronds are composed of adipose tissue admixed with fibrous connective tissue (hematoxylin-eosin, × 10). Fibrous tissue surrounding lobules of mature adipose tissue ( B ) (hematoxylin-eosin, × 20).Grahic Jump Location

The patient had complete resolution of her symptoms following the procedure. Three years later, she had recurrence of a tumor at the same site, for which she underwent another bronchoscopic resection.

Clinical Discussion

Primary tracheal tumors account for <0.1% of all malignant neoplasms and are the least common neoplastic lesions of the airway (Table 1). This is partially due to the higher local mucosal capacity for immunoediting and immunosurveillance in the trachea and subglottic regions compared with the rest of the bronchial tree.1 Eighty percent of tracheal tumors in adults are malignant with squamous cell and adenoid cystic carcinomas being the predominant histologic subtypes.2

Table Graphic Jump Location
Table 1 —Clinical, Radiologic, Bronchoscopic, and Histologic Features of Common Endobronchial Tumors

HPF = high-power field; HPV = human papillomavirus; HU = Hounsfield units; RRP = recurrent respiratory papillomatosis.

Benign tumors of the trachea occur less commonly and are characterized by a slow growth rate and nonspecific symptoms, such as dry cough and wheezing. They are usually misdiagnosed as asthma or chronic bronchitis and elude detection for months or years. In addition, in the absence of hemoptysis, such tumors often grow quietly until they obstruct >75% of the tracheal lumen before stridor, wheezing, cough, and dyspnea on exertion develop. Occasionally, these symptoms might worsen with certain positions, such as recumbency (due to the narrowing of the tracheal lumen in this position). Although an abnormal flow-volume loop pattern was expected in our case, the mobile nature of the lesions may have obscured this finding because these maneuvers are usually done in the sitting position.

Fibrolipomatous tumors account for 4.6% of all benign tumors of the lung3 and only a few cases of endobronchial fibrolipomas have been reported in the English literature. Interestingly, our patient had recurrence of her tumor in the same location 3 years after the initial resection. Although recurrence of benign endobronchial tumors is extremely rare after complete surgical resection,4 the rate of recurrence after endobronchial resection is less well described. Because most of these tumors grow into or through the tracheal wall, complete endobronchial resection is often difficult to achieve, and some patients may need repeated endobronchial interventions.4,5 Endobronchial resection, however, offers a less invasive approach with a lower morbidity when compared with surgical resection and is also associated with excellent symptomatic and local control. Inoperable patients with poor surgical risks, patients with unresectable tumors, and patients with a strictly endoluminal tumor with limited extent into the airways wall (polypoid lesions) are the best candidates for endobronchial therapy.4,5 Nevertheless, this decision should only be made in centers experienced in this field. This particular patient opted for repeat endobronchial resection, when given the option of curative surgical resection.

The need for routine bronchoscopic surveillance after endoscopic resection of a benign airway tumor is debatable. Airway CT scan offer a less invasive surveillance approach; however, it carries a risk of radiation exposure. In our institution, we recommend a more conservative approach with symptom-guided CT scan/bronchoscopy.

Radiologic Discussion

Radiologic examination often helps to characterize endobronchial lesions and limit the list of differential diagnoses, and also provides important information for prebronchoscopic and presurgical planning. Chest radiography is of limited value in this setting because of its low sensitivity (66%).6 Although conventional CT scanning is superior to chest radiography in detecting central airway diseases with a sensitivity greater than 90%,6 multidetector CT scanning with isotropic resolution and slice thickness as thin as 1 mm is the imaging modality of choice for detection and staging of central airway neoplasms.7,8 Multiplaner reformation with three-dimensional reconstruction and virtual bronchoscopy images are new technologies that can provide more anatomically meaningful display of the tumor and better delineate its size, length, location, and relationship to other endobronchial landmarks and adjacent vital mediastinal structures.9,10 In addition, it can accurately define intraluminal and extraluminal extension of tumor, as well as postobstructive complications, such as atelectasis, pneumonia, and mucous plugging.7 Finally, assessment of the lesion density provides important clues to its nature, such as fluid, soft tissue, hemorrhagic, or fat-containing lesion.

The presence of fat density within an endobronchial tumor, as in our case, is an important clue that can significantly narrow the list of differential diagnoses. These densities typically have an attenuation of around −100 Hounsfield units. Pure endobronchial lipoma appears as a homogeneous mass with attenuation value of fatty tissue. Fat-containing tumors appear as a heterogeneous soft-tissue density with islands of fatty tissue (eg, fibrolipomatous tumors) or with collection of fat alternating with foci of calcification (hamartoma).11

Bronchoscopic Discussion

Bronchoscopy is an integral part of the diagnostic and therapeutic algorithm of any endobronchial tumor. Certain tumors (eg, papillomas and carcinoid tumors) and inflammatory conditions (eg, endobronchial amyloidosis and tracheopathia osteochondroplastica) exhibit a characteristic location/appearance during bronchoscopic examination,12 the discussion of which is beyond the scope of this article (Table 1). Fibromas and fibrolipomatous polyps, as in the current case, usually appear as yellowish pedunculated masses that are often mobile and attached to the tracheal wall by a fibrous stalk.

Initial bronchoscopic examination of patients with endobronchial tumor should provide detailed documentation of the airway anatomy, tumor size and length, residual tracheal lumen, and relationship of the tumor to other endobronchial landmarks, namely the vocal cords, cricoid cartilage, and the main carina. Complete endobronchial examination is mandatory to rule out any synchronous tumors, which have been reported to occur in up to 30% of patients.13

Radial endobronchial ultrasound is an additional valuable tool that allows the bronchoscopist to accurately assess the depth of invasion of endobronchial tumors and it has been shown to be superior to CT scan in this particular setting.1416 This provides important information for proper staging of malignant neoplasm.17 Although the role of endobronchial ultrasound in benign endobronchial tumors is less clearly defined, it may help to better stratify patients for endobronchial vs surgical resection and to choose the right endobronchial intervention based on the depth of tumor penetration.

A variety of endobronchial therapies are available that offer a minimally invasive therapeutic approach for both benign and malignant endobronchial tumors with curative or palliative intents, respectively.18 The choice of the endobronchial therapy is tailored according to the underlying pathology and anatomic location of the tumor, the degree of airway compromise, and the respiratory status of the patient. Centrally located tumors with critical airway obstruction and impending respiratory compromise are best treated with modalities that offer immediate effects, such as mechanical tumor debridement (coring maneuver), laser therapy, and/or electrocautery. Rigid bronchoscopy is superior to flexible bronchoscopy in this setting because it offers secure airways, better view and suctioning capacity, and its larger lumen can accommodate larger tools and devices. The effects of cryotherapy and photodynamic therapy are delayed for several days after the initial application, and are better reserved for stable patients with noncritical airway obstruction by the endobronchial tumors.

Pathologic Discussion

Benign tracheal tumors can arise from all components of the tracheal wall: the respiratory epithelium, such as squamous papilloma/papillomatosis; the submucosal salivary glands, such as pleomorphic adenoma; and the mesenchymal soft tissues, such as fibroma, chondroma, leiomyoma, and hemangiomas.4 Attempts at classifying and summarizing their pathologic features are limited by the low occurrence, represented primarily as case reports/series. Endobronchial lipomas are exceedingly rare and account for 2% to 4% of all benign tracheal tumors.4,5 Grossly, they appear as yellow soft-tissue masses with a greasy cut surface. Microscopically, they are composed of mature adipose tissue often surrounded by a thin capsule and arranged in lobules separated by delicate fibrous septae without cytologic atypia.19 The term fibrolipoma is used to designate a lipoma with an abundance of admixed collagenous fibrous tissue.20 Fibrolipomas have been reported in the pyriform sinus, larynx, hypopharynx, and bronchi.21,22

The differential diagnosis of endobronchial fibrolipoma includes typical lipoma, squamous papilloma, hamartoma with admixed adipose tissue, and less likely, a low-grade liposarcoma. The abundance of fibrous tissue in the stroma and the unusual arborizing architecture in the present case exclude the diagnosis of typical lipoma. Squamous papillomas are exophytic epithelial neoplasms composed of slender fibrovascular cores lined by benign multilayered squamous epithelium; both features were absent in our case.23 Hamartomas can occur in the trachea and are typically composed of a disordered proliferation of mature cartilage (which was not identified in the current case), but may include adipose tissue, bone, and entrapped epithelial structures.19 Liposarcomas have been reported in the trachea and are thought to arise de novo rather than through the malignant transformation of a lipoma.19,24 The lack of cytologic atypia in the current case excludes the diagnosis of liposarcoma. Immunohistochemical stains typically are not contributory in this setting, as the diagnosis is based on histomorphologic features.

Benign endobronchial tumors are rare, and their diagnosis is usually delayed because of their slow growth rate and nonspecific symptoms. Multidetector CT scanning is superior to conventional chest radiography for imaging the central airways. Detailed bronchoscopic examination to characterize and sample the tumor and delineate its exact endobronchial anatomy is mandatory. Finally, the choice of therapeutic intervention should be individualized according to several patient- and tumor-related factors, which should be carefully evaluated by a multidisciplinary team in centers experienced in complex airway disorders.

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Barker E, Haverson K, Stokes CR, Birchall M, Bailey M. The larynx as an immunological organ: immunological architecture in the pig as a large animal model. Clin Exp Immunol. 2006;1431:6-14. [CrossRef] [PubMed]
 
Gelder CM, Hetzel MR. Primary tracheal tumours: a national survey. Thorax. 1993;487:688-692. [CrossRef] [PubMed]
 
Jensen MS, Petersen AH. Bronchial lipoma. Scand J Thorac Cardiovasc Surg. 1970;42:131-134. [CrossRef] [PubMed]
 
Gaissert HA, Grillo HC, Shadmehr MB, et al. Uncommon primary tracheal tumors. Ann Thorac Surg. 2006;821:268-272. [CrossRef] [PubMed]
 
Shah H, Garbe L, Nussbaum E, Dumon JF, Chiodera PL, Cavaliere S. Benign tumors of the tracheobronchial tree. Endoscopic characteristics and role of laser resection. Chest. 1995;1076:1744-1751. [CrossRef] [PubMed]
 
Kwong JS, Adler BD, Padley SP, Müller NL. Diagnosis of diseases of the trachea and main bronchi: chest radiography vs CT. AJR Am J Roentgenol. 1993;1613:519-522. [PubMed]
 
Boiselle PM. Imaging of the large airways. Clin Chest Med. 2008;291:181-193. [CrossRef] [PubMed]
 
Boiselle PM, Ernst A. Recent advances in central airway imaging. Chest. 2002;1215:1651-1660. [CrossRef] [PubMed]
 
Boiselle PM, Reynolds KF, Ernst A. Multiplanar and three-dimensional imaging of the central airways with multidetector CT. AJR Am J Roentgenol. 2002;1792:301-308. [PubMed]
 
Finkelstein SE, Summers RM, Nguyen DM, Stewart JH IV, Tretler JA, Schrump DS. Virtual bronchoscopy for evaluation of malignant tumors of the thorax. J Thorac Cardiovasc Surg. 2002;1235:967-972. [CrossRef] [PubMed]
 
Gaerte SC, Meyer CA, Winer-Muram HT, Tarver RD, Conces DJ Jr. Fat-containing lesions of the chest. Radiographics. 2002;22:S61-S78. [PubMed]
 
Duhamel DR, Harrell JH. Clinical Atlas of Airway Diseases: Bronchoscopy, Radiology, and Pathology. 2005;1st ed. Philadelphia, PA Elsevier Saunders
 
Honings J, van Dijck JA, Verhagen AF, van der Heijden HF, Marres HA. Incidence and treatment of tracheal cancer: a nationwide study in the Netherlands. Ann Surg Oncol. 2007;142:968-976. [CrossRef] [PubMed]
 
Herth F, Becker HD. Endobronchial ultrasound of the airways and the mediastinum. Monaldi Arch Chest Dis. 2000;551:36-44. [PubMed]
 
Herth F, Ernst A, Schulz M, Becker H. Endobronchial ultrasound reliably differentiates between airway infiltration and compression by tumor. Chest. 2003;1232:458-462. [CrossRef] [PubMed]
 
Kurimoto N, Murayama M, Yoshioka S, Nishisaka T, Inai K, Dohi K. Assessment of usefulness of endobronchial ultrasonography in determination of depth of tracheobronchial tumor invasion. Chest. 1999;1156:1500-1506. [CrossRef] [PubMed]
 
Gu P, Zhao YZ, Jiang LY, et al. Endobronchial ultrasound-guided transbronchial needle aspiration for staging of lung cancer: A systematic review and meta-analysis. Eur J Cancer. 2009;458:1389-1396. [CrossRef] [PubMed]
 
Ernst A, Feller-Kopman D, Becker HD, Mehta AC. Central airway obstruction. Am J Respir Crit Care Med. 2004;16912:1278-1297. [CrossRef] [PubMed]
 
Fraire AE. Tumors of hamartomatous, osteochondromatous, lipomatous, neural and vascular origins. Dail and Hammar’s Pulmonary Pathology. 2008;3rd ed New York, NY Springer:462-499
 
Weiss S, Goldblum JR.Weiss SW, Goldblum JR. Benign lipomatous tumors. Enzinger and Weiss’s Soft Tissue Tumors. 2008; Philadelphia, PA Mosby:429-476
 
Jesberg N. Fibrolipoma of the pyriform sinuses: thirty-seven year follow-up. Laryngoscope. 1982;9210 pt 1:1157-1159. [CrossRef] [PubMed]
 
Spinelli P, Pizzetti P, Lo Gullo C, Rocca F, Gobbi A, Ravasi G. Resection of obstructive bronchial fibrolipoma through the flexible fiberoptic bronchoscope. Endoscopy. 1982;142:61-63. [CrossRef] [PubMed]
 
Ewing BM.Wenig BM. Classification of neoplasms of the larynx, hypopharynx and trachea. Atlas of Head and Neck Pathology. 2008;2nd ed Philadelphia, PA Saunders:448-453
 
Van Den Beukel JT, Wagenaar SJ, Vanderschueren R. Liposarcoma of the trachea. Thorax. 1979;346:817-818. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1. Dynamic airway CT scan without IV contrast during inspiration ( A - C ) and expiration ( D and E ) at the level of the aortic arch, including mediastinal window ( A ), lung window ( B and D ), and virtual bronchoscopy images ( C and E ). A 1.7 × 1.0 cm polypoid lesion is seen in the dependent portion of the trachea. Dynamic expiratory sequences indicate slight mobility of the lesion and airway collapsibility. The lesion has predominantly soft-tissue attenuation with small foci of low attenuation.Grahic Jump Location
Figure Jump LinkFigure 2. Bronchoscopic images of a polypoid yellowish, smooth, and pedunculated lesion in the distal trachea. It appears to arise with a stalk the left posterolateral wall of the trachea.Grahic Jump Location
Figure Jump LinkFigure 3. Polypoid mass with broad fronds covered by pseudostratified ciliated columnar epithelium ( A ). The cores of the fronds are composed of adipose tissue admixed with fibrous connective tissue (hematoxylin-eosin, × 10). Fibrous tissue surrounding lobules of mature adipose tissue ( B ) (hematoxylin-eosin, × 20).Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1 —Clinical, Radiologic, Bronchoscopic, and Histologic Features of Common Endobronchial Tumors

HPF = high-power field; HPV = human papillomavirus; HU = Hounsfield units; RRP = recurrent respiratory papillomatosis.

References

Barker E, Haverson K, Stokes CR, Birchall M, Bailey M. The larynx as an immunological organ: immunological architecture in the pig as a large animal model. Clin Exp Immunol. 2006;1431:6-14. [CrossRef] [PubMed]
 
Gelder CM, Hetzel MR. Primary tracheal tumours: a national survey. Thorax. 1993;487:688-692. [CrossRef] [PubMed]
 
Jensen MS, Petersen AH. Bronchial lipoma. Scand J Thorac Cardiovasc Surg. 1970;42:131-134. [CrossRef] [PubMed]
 
Gaissert HA, Grillo HC, Shadmehr MB, et al. Uncommon primary tracheal tumors. Ann Thorac Surg. 2006;821:268-272. [CrossRef] [PubMed]
 
Shah H, Garbe L, Nussbaum E, Dumon JF, Chiodera PL, Cavaliere S. Benign tumors of the tracheobronchial tree. Endoscopic characteristics and role of laser resection. Chest. 1995;1076:1744-1751. [CrossRef] [PubMed]
 
Kwong JS, Adler BD, Padley SP, Müller NL. Diagnosis of diseases of the trachea and main bronchi: chest radiography vs CT. AJR Am J Roentgenol. 1993;1613:519-522. [PubMed]
 
Boiselle PM. Imaging of the large airways. Clin Chest Med. 2008;291:181-193. [CrossRef] [PubMed]
 
Boiselle PM, Ernst A. Recent advances in central airway imaging. Chest. 2002;1215:1651-1660. [CrossRef] [PubMed]
 
Boiselle PM, Reynolds KF, Ernst A. Multiplanar and three-dimensional imaging of the central airways with multidetector CT. AJR Am J Roentgenol. 2002;1792:301-308. [PubMed]
 
Finkelstein SE, Summers RM, Nguyen DM, Stewart JH IV, Tretler JA, Schrump DS. Virtual bronchoscopy for evaluation of malignant tumors of the thorax. J Thorac Cardiovasc Surg. 2002;1235:967-972. [CrossRef] [PubMed]
 
Gaerte SC, Meyer CA, Winer-Muram HT, Tarver RD, Conces DJ Jr. Fat-containing lesions of the chest. Radiographics. 2002;22:S61-S78. [PubMed]
 
Duhamel DR, Harrell JH. Clinical Atlas of Airway Diseases: Bronchoscopy, Radiology, and Pathology. 2005;1st ed. Philadelphia, PA Elsevier Saunders
 
Honings J, van Dijck JA, Verhagen AF, van der Heijden HF, Marres HA. Incidence and treatment of tracheal cancer: a nationwide study in the Netherlands. Ann Surg Oncol. 2007;142:968-976. [CrossRef] [PubMed]
 
Herth F, Becker HD. Endobronchial ultrasound of the airways and the mediastinum. Monaldi Arch Chest Dis. 2000;551:36-44. [PubMed]
 
Herth F, Ernst A, Schulz M, Becker H. Endobronchial ultrasound reliably differentiates between airway infiltration and compression by tumor. Chest. 2003;1232:458-462. [CrossRef] [PubMed]
 
Kurimoto N, Murayama M, Yoshioka S, Nishisaka T, Inai K, Dohi K. Assessment of usefulness of endobronchial ultrasonography in determination of depth of tracheobronchial tumor invasion. Chest. 1999;1156:1500-1506. [CrossRef] [PubMed]
 
Gu P, Zhao YZ, Jiang LY, et al. Endobronchial ultrasound-guided transbronchial needle aspiration for staging of lung cancer: A systematic review and meta-analysis. Eur J Cancer. 2009;458:1389-1396. [CrossRef] [PubMed]
 
Ernst A, Feller-Kopman D, Becker HD, Mehta AC. Central airway obstruction. Am J Respir Crit Care Med. 2004;16912:1278-1297. [CrossRef] [PubMed]
 
Fraire AE. Tumors of hamartomatous, osteochondromatous, lipomatous, neural and vascular origins. Dail and Hammar’s Pulmonary Pathology. 2008;3rd ed New York, NY Springer:462-499
 
Weiss S, Goldblum JR.Weiss SW, Goldblum JR. Benign lipomatous tumors. Enzinger and Weiss’s Soft Tissue Tumors. 2008; Philadelphia, PA Mosby:429-476
 
Jesberg N. Fibrolipoma of the pyriform sinuses: thirty-seven year follow-up. Laryngoscope. 1982;9210 pt 1:1157-1159. [CrossRef] [PubMed]
 
Spinelli P, Pizzetti P, Lo Gullo C, Rocca F, Gobbi A, Ravasi G. Resection of obstructive bronchial fibrolipoma through the flexible fiberoptic bronchoscope. Endoscopy. 1982;142:61-63. [CrossRef] [PubMed]
 
Ewing BM.Wenig BM. Classification of neoplasms of the larynx, hypopharynx and trachea. Atlas of Head and Neck Pathology. 2008;2nd ed Philadelphia, PA Saunders:448-453
 
Van Den Beukel JT, Wagenaar SJ, Vanderschueren R. Liposarcoma of the trachea. Thorax. 1979;346:817-818. [CrossRef] [PubMed]
 
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