British Journal of Radiology (2004) 77, 60-62
© 2004 British Institute of Radiology
doi: 10.1259/bjr/94129286
Peripheral intrapulmonary lipoma: a rare lung neoplasm
J Wood, MRCP, FRCR
1 and
R G Henderson, BSc, FRCP, FRCR
2
1 Radiology Department, James Cook University Hospital, Marton Road, Middlesbrough TS4 3BW and 2 Radiology Department, Darlington Memorial Hospital, Darlington DL3 6HX, UK
Correspondence: Dr R G Henderson
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Abstract
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Lipomas are common benign tumours, but intrathoracic lipomas are rare and peripheral lung lipomas exceptionally rare. Seven cases—all in men—have been described in the world literature, diagnosed after thoracotomy and excision. We report a case of a peripheral intrapulmonary lipoma in a woman presenting as an opacity on a routine chest radiograph. The CT characteristics and the finding of the same lesion on reviewing a barium enema film from 12 years earlier allowed a confident diagnosis, avoiding the need for surgical excision. This is the first reported case of peripheral lung lipoma in a woman and highlights the value of reviewing previous radiographs.
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Introduction
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Lipoma is one of the most frequently encountered benign neoplasms, but intrathoracic lipomas are rare. The vast majority are located centrally within the lung, arising from proximal lobar or segmental bronchi. Only seven cases of peripheral intrapulmonary lipoma have been reported. These are thought to originate from fatty tissue in the wall of peripheral, subsegmental bronchi [1]. Despite their entirely benign nature, in all the cases previously reported the lipomas were surgically removed. In this case, review of a previous unrelated radiological investigation averted the need for any invasive diagnostic or therapeutic intervention.
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Case report
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A 54-year-old woman was referred with a history of right arm paraesthesia, subsequently attributed to cervical spondylosis. Initial investigations included a chest radiograph, which showed a 15 mm diameter well-defined pulmonary nodule in the left lower zone (Figure 1
). She had no relevant symptoms or past medical history, although she had smoked 20 cigarettes a day for 40 years. Clinical examination showed no relevant abnormality. Tumour markers and routine blood tests were all normal.
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Figure 1. (a,b) Posteroanterior chest radiograph demonstrates a well-defined 15 mm nodule in the left lower lobe at the left costophrenic angle (arrowhead).
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The left basal lesion was further assessed with CT. This demonstrated a 13 mm diameter well-defined, homogeneous, rounded lesion in the periphery of the posterior segment of the left lower lobe showing no calcification (Figure 2, window level -600 HU/window width 1000 HU). There were no features of malignancy, and the density of the lesion was that of fat (approximately -100 HU).
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Figure 2. CT of the thorax (10 mm slice thickness, lung windows: window level -600 HU/window width 1000 HU) in the same patient showing a well circumscribed, rounded lesion in the lateral basal segment of the left lower lobe. The density is that of fat.
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It was felt that the lesion was likely to be benign. Subsequent review of a barium enema from 12 years previously (which was otherwise normal) brought to light a film that included the left lung base. This confirmed the presence of the left lower lobe opacity, which had not been noted at the time (Figure 3). The fortuitous discovery of the left lung lesion on the earlier barium enema with no change after 12 years confirmed the benign nature of the lesion. It was concluded that this was almost certainly a peripheral intrapulmonary lipoma, and no further investigation was required.
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Figure 3. Barium enema film of the same patient 12 years earlier confirming the presence of the lung lesion (arrowhead).
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Discussion
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The vast majority of bronchial lipomas arise centrally from fatty tissue in the wall of proximal lobar or segmental bronchi. As few as seven cases of peripheral intrapulmonary lipoma feature in the medical literature over a 90 year period [2–8], the first case reported as early as 1911, the most recent from Japan in 1989 [8]. These benign, peripheral intrapulmonary lipomas usually present as a solitary opacity on chest radiograph, indistinguishable on plain films from malignant neoplasms. They are thought to arise from fatty tissue in the walls of peripheral bronchi at subsegmental level, and pathological analysis of resected lipomatous lesions, central and peripheral, has consistently demonstrated mature fatty tissue [9]. Proximal endobronchial lipomas arising from lobar bronchi are invariably enveloped by bronchial epithelium, peripheral lipomas are more often surrounded by thin connective tissue and normal lung parenchyma. The fat content within the wall of bronchi diminishes with progressive branching of the respiratory tree, hence the greater rarity of lipomas peripherally.
The seven previously reported cases were all adult males (age range 44–71 years). The significance of this gender predilection with such small reported numbers is uncertain, although Suzuki et al [10] postulated for smoking a "strong relation to the occurrence of the tumour". The rarity of these tumours makes substantiation of this theory impossible. The cases previously reported have shown no predilection for one side. The size of the peripheral tumours has varied from 1 cm to 7 cm in maximum diameter. Although the majority of intrapulmonary lipomas are, as here, incidental findings, larger more central tumours may cause symptoms due to local mass effect and compression of adjacent structures.
In their report of the most recent previous case of peripheral intrapulmonary lipoma in 1989, Hirata et al [8] concluded "the treatment of peripheral lipoma is limited to surgical procedure". Although their patient had thoracic CT, the images are not included in their paper, and the description suggests the CT findings were equivocal, and "provided no evidence to exclude malignancy". Indeed all seven reported cases underwent thoracotomy to establish the diagnosis as malignancy could not be confidently excluded. Transbronchial biopsy is not appropriate for such peripheral lesions, although percutaneous biopsy might be. Three subjects underwent lobectomy [4–6], and a further three had an enucleation procedure [3, 7, 8] in an attempt to preserve maximal residual lung function and achieve tumour excision. More advanced CT and MRI techniques allowing confident detection of fat tissue mean that Hirata's assertion is no longer correct. Furthermore in our case, review of previous images demonstrated the tumour was present and unchanged 12 years earlier. This made malignancy very unlikely and avoided the need for any intervention.
The differential diagnosis of a fat-containing peripheral lung mass includes, in addition to lipoma, fibrolipomatous hamartoma [11] and liposarcoma [12, 13]. These tumours however contain other soft tissue elements or calcium in addition to fat and the reported cases of liposarcoma have been very aggressive. The long period between the earlier examination demonstrating the lesion and the current presentation in this case allowed confident exclusion of malignant disease. We have thus elegantly demonstrated the truth of the maxim "the most useful radiological investigation is the old films".
Received for publication October 7, 2002.
Revision received March 14, 2003.
Accepted for publication April 24, 2003.
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References
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Abstract
Introduction
