Keywords
computed tomography - management - positron emission tomography - pulmonary lipoma
Introduction
A lipoma is a benign mesenchymal neoplasm composed of fatty tissue. Lipomas are the
most common form of benign soft tissue tumors in humans and they infrequently occur
in visceral organs, such as the lungs.[1]
[2] Pulmonary lipomas constitute approximately 0.1 to 1.3% of benign bronchial neoplasms.[2]
[3]
[4]
[5] They can occur as an endobronchial (80%) or as extremely uncommon (20%) peripheral
parenchymal lesion.[2]
[3]
[4]
[5]
[6]
[7] From the literature review, less than 10 cases of lung peripheral lipoma have been
reported in literature, none cavitated.[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9] We report a unique case of peripheral pulmonary cavitated lipoma in a 51-year-old
man which revealed during a routine chest X-ray for emphysema evaluation, confirmed
by high-resolution computed tomography (HRCT) and with positron emission tomography
(PET)/CT. We propose our imaging-guided management of this rare lesion.
Case Report
A 51-year-old man was referred to our Hospital Respiratory Clinic for a routine check-up
due to history of emphysema. He was a 20-pack-year smoker and also affected by diabetes
mellitus and hypertension. He was afebrile, normotensive, and normocardic; laboratory
reports, including C-reactive protein, revealed normal blood count, and renal/liver
function tests were also normal. Physical examination was significant only for sibilant
wheezing rhonchus in the lungs and no other relevant abnormalities. Chest radiograph
showed a nodular cavitated opacity in the right lung, close to the hilum ([Fig. 1]). Chest HRCT confirmed centrilobular emphysema in the upper lung lobes and revealed
a 3 cm × 2.6 cm round well-circumscribed nodule in the middle lung lobe without any
fissural contact, with just thickened medial wall and thin lateral margin. The lesion
had fat attenuation (i.e., −130 to −140 HU) and a central inner thin-walled homogeneous
air-density cavitation area, without debris and visible communication with the bronchial
tree ([Fig. 2]). No vessels, necrosis, air bronchogram, or calcification was present within nodule.
Evaluation of the mediastinum revealed no adenopathy, and there were no features of
malignancy. An 18-fluorodeoxyglucose PET/CT scan was subsequently performed and the
nodule did not reveal an abnormal uptake ([Fig. 3]). All imaging features suggested a benign lesion, and patient received a lipoma
diagnosis. He was admitted to a 6-month and then annual low-dose HRCT surveillance
without biopsy or surgical intervention. The nodule remains unchanged after 2 years
of HRCT follow-up.
Fig. 1 Posteroanterior and lateral chest radiograph views show a well-defined rounded middle
lobe cavitating nodular lesion (arrows).
Fig. 2 High resolution CT axial images at (A) lung window and (B) mediastinal window confirm a well-defined, rounded centrally cavitated middle lobe
(medial segment) lesion (arrows), measuring 3 cm × 2.6 cm in the maximum transverse
dimension. (C) Lung nodule attenuation values are of 120 to 140 UH, clearly indicating the presence
of fat. The lesion was highly suggestive of a peripheral cavitated lung lipoma. CT,
computed tomography.
Fig. 3 A 18-F fluorodeoxyglucose positron emission tomography/computed tomography (18-F
FDG PET–CT) examination shows a low grade of FDG uptake in the known middle lobe pulmonary
nodule (SUV, Standardized uptake value max 1.1), confirming a benign lesion (arrows).
CT, computed tomography; SUV, standardized uptake value.
Discussion
Intrapulmonary lipomas are rare fat-containing benign lung lesions. There are different
theories about their intrapulmonary origin. Endobronchial lipomas are usually surrounded
by bronchial epithelium, probably arising from adipose tissue within proximal lobar
or segmental bronchial wall.
The origin of peripherical lipomas can be from peribronchial or subpleural fat tissue.
Clinical presentation differs according to the origin. Most peripheral lipomas are
asymptomatic, with the majority being found incidentally on routine radiographs as
solitary opacities, indistinguishable on plain films from malignant neoplasms.[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9] Conversely, endobronchial ones can present with atelectasis, cough, fever, and pneumonia.[10] Risk factors are smoking, obesity, and diabetes mellitus.[1] The main commonest entity considered in the differential diagnosis of intrapulmonary
nodules containing fat is hamartoma ([Table 1]). Pulmonary hamartomas frequently have focal areas of fat (up to 60%) alternating
with solid areas and typically dispersed popcorn calcifications (from 5 to 50%).[2]
[11] Magnetic resonance imaging (MRI) also enables the distinction of different lesion
components, including fat. Fat within a lesion appears hyperintense on T1- and T2-weighted
images and shows decreased signal intensity on fat-saturation techniques. Opposed
phase gradient-echo MRI can show evenly distributed microscopic intralesional fat.[12]
Table 1
Main differential diagnosis of fat-containing lung nodule(s)
|
Fat-containing nodules of the lung
|
Imaging features
|
Specific features
|
|
Pulmonary hamartoma (soft tissue nodule or mass) most common benign lung lesion
|
Well-circumscribed round or ovoid up to 60% have fat, 20–30% have calcification fat
and calcium, in 19%, cavitation not seen heterogeneous enhancement FDG PET variable
avidity
|
Usually incidental and solitary lesion popcorn-like calcifications (multiple clumps
throughout the lesion) endobronchial (3–20%) slow growth
|
|
Lipoma (peripheral lesions exceptionally rare)
|
Well-defined fat attenuation uncommonly calcification(s)
|
Typically solitary endobronchial and obstruction findings
|
|
Pleural or mediastinal lipoma
|
Homogeneous fat attenuation well-defined margins
|
pleural or mediastinal lesion Also fissural lesions
|
|
Myelolipoma (rare lesions)
|
Well-circumscribed fat and hematopoietic components generally as small nodules or
<5 cm
|
Typically pleural-based rare calcifications slow or no growth
|
|
Lipoid pneumonia (oily or lipid components within pneumonia)
|
Low (fat) attenuation GGO areas or consolidation(s) rarely crazy-paving ossific foci
may be present
|
Inflammatory chronic aspiration risk predilection for dependent lung
Lung fibrosis possible
|
|
Metastatic disease: liposarcoma
|
Significant amounts of soft tissue within the fatty mass up to 5 cm lesion(s) FDG
PET usually high uptake
MRI characteristics
|
Usually extrathoracic mass history
Histology needed
|
|
RCC
|
Lipid-rich cells clear cell RCC
|
Renal cancer history
Histology needed
|
Abbreviations: FDG PET, fluorodeoxyglucose positron emission tomography; GGO, ground-glass
opacity; RCC, renal cell carcinoma.
The originality of the described lipoma is that it appears cavitated and features
never described in the medical literature to our knowledge. A cavity is defined in
the Fleischner glossary as “a gas-filled space, seen as a lucency or low-attenuation
area, within pulmonary consolidation, a mass, or a nodule.”[12] Many types of solitary pulmonary nodules may result in cavitation, so its presence
or absence is of limited diagnostic value. In our case, the absence of debris and
thickening of the cavitation wall excludes a suppurative, caseous, or ischemic necrosis.
Conversely, it is possible to think to a nodular encasement of a panlobular emphysema/bulla
area or of a cystic dilation of microscopic bronchial structure.
Conclusion
In conclusion, both CT and MRI can help to identify intranodular fat, and PET/CT may
show a normal physiological uptake; all these are reliable indicator of benign nature,
excluding the use of invasive procedures, such as pulmonary biopsy or surgery. Although
rare, peripheral lung cavitated lipomas should be included in the differential of
fat-containing lung lesions. A suggested image-guided management option includes watchful
waiting (wait and see) with follow-up CT imaging.
