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© 2001 American Society for Clinical Oncology
Unusual Presentations of Thoracic TumorsCase 3. Parenchymal Lipoma of the LungSaint-Louis University Hospital, Paris, France A 60-year-old woman was diagnosed with right palpable breast cancer in December 1994. The tumor contained estrogen and progesterone receptors. Metastases were found in only two of seven axillary lymph nodes. Complete remission was achieved in April 1995 after tumor excision and radiation therapy. The patient received adjuvant tamoxifen. In February 1997, a left mastectomy was performed for lobular carcinoma. No bone, liver, or lung involvement was found. In December 1999, follow-up chest radiographs disclosed a unique, 1.5-cm, dense, rounded lesion with regular margins located in the right superior lobe of the lung (Fig 1, arrowhead). The diagnosis of lung metastasis was advocated. A lung window computed tomography (CT) scan showed the lesion to be unique, well-defined, and peripheral, without any calcification (Fig 2, arrowhead). Contrast-enhanced CT scan showed the lesion to be homogeneous and hypodense (Fig 3). The lesion demonstrated a homogeneous fatty density of -82 Hounsfield units, slightly similar to the fatty density of thymus (Fig 4). A subsequent CT-guided biopsy of the lesion was performed. Histologic study showed lobules of fatty tissue under the bronchial epithelium without other components (Fig 5).
Although lipomas are the most common benign neoplasms most frequently found in soft tissues, those occurring in viscera are rare, as is the case of intrapulmonary lipoma.1 The frequency of intrapulmonary lipomas is not well established because the majority of the cases occur as isolated case reports and because most of them are considered to be hamartomas.2 In a review of 3,502 pulmonary tumors, 65 were benign and only three cases were lipomas.1 In another review of 32 rare pulmonary tumors, Sekine et al2 found 12 benign tumors with only three cases of lipomas. Intrapulmonary lipomas are divided into endobronchial and peripheral parenchymal lipomas. The endobronchial lipomas are more common, found in 80% of cases.3 They are believed to originate from submucosal bronchial fat that is present when cartilage and bronchial glands exist, but they decrease with progressive branching of bronchi and disappear when the bronchus is less than 1 mm in diameter. This explains the rarity of peripheral parenchymal lipomas.4-6 Peripheral lipomas are more frequent in men, with a peak incidence between the fifth and sixth decades and a predilection for the right side and the upper lobe of the lung.3,6 Endobronchial lipomas are more often found in the left main-stem bronchus.2 Although intrapulmonary lipomas are benign lesions, they are clinically significant because they may cause difficulty in diagnosis by mimicking malignant tumor, as in our case. Parenchymal lipomas are asymptomatic because they are peripheral and are found incidentally on routine radiographs. Endobronchial lipomas, on the other hand, may cause pulmonary damage due to atelectasis and secondary suppuration necessitating lobectomy or pneumonectomy.3 Although a radiographic appearance may be mistaken for a primary or secondary malignant lesion, CT may play a role in the diagnosis whenever a defined, homogenous, fatty, dense lesion (between -50 and -150 Hounsfield units) is seen. However, the definitive diagnosis requires tissue examination, which can be obtained either by bronchoscopy or transthoracic biopsy, as in our case.7 The differential diagnosis includes all benign intrapulmonary lesions, especially fatty tumors, such as thymolipomas, angiolipomas, teratomas, and lipochondroadenomatous hamartomas, in which CT is useful in demonstrating the presence of islands of soft tissue density together with fat.7 Treatment of parenchymal lipoma is limited to surgical procedures with maximum preservation of residual lung function.6 However, surgical treatment is currently not necessary, since the diagnosis has been made easier during the last few years with the advent of new radiologic methods, such as CT.7 REFERENCES 1. Politis J, Funahashi A, Gehlsen JA, et al: Intrathoracic lipomas: Report of three cases and review of the literature with emphasis on endobronchial lipoma. J Thorac Cardiovasc Surg 77: 550-556, 1979[Abstract] 2. Sekine I, Kodama T, Yokose T, et al: Rare pulmonary tumors: A review of 32 cases. Oncology 55: 431-434, 1998[Medline] 3. Plachta A, Hershey H: Lipoma of the lung. Am Rev Respir Dis 86: 912-916, 1962[Medline] 4. Satub EW, Barker WL, Langston HT: Intrathoracic fatty tumors. Chest 47: 308-313, 1965 5. Bango A, Colubi L, Molinos L, et al: Endobronchial lipomas. Respiration 60: 297-301, 1993[Medline] 6. Hirata T, Reshad K, Itoi K, et al: Lipomas of the peripheral lung: A case report and review of the literature. J Thorac Cardiovasc Surg 37: 385-387, 1989 7. Vassallo M, Rana Z, Allen S: A large transmural thoracic lipoma easily mistaken for pulmonary malignancy. Br J Clin Pract 50: 285-286, 1996[Medline]
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Copyright © 2001 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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