Ann Thorac Surg 2008;86:261-265. doi:10.1016/j.athoracsur.2008.03.052
© 2008 The Society of Thoracic Surgeons
Original Articles: General Thoracic
Intrathoracic Lipomas: Their Clinicopathological Behaviors Are Not As Straightforward as Expected
Hiroyuki Sakurai, MDa,*,
Masahiro Kaji, MDa,
Kazuto Yamazaki, MDb,
Keiichi Suemasu, MDa
a Department of Thoracic Surgery, Saiseikai Central Hospital, Tokyo, Japan
b Department of Pathology, Saiseikai Central Hospital, Tokyo, Japan
Accepted for publication March 25, 2008.
* Address correspondence to Dr Sakurai, Department of Thoracic Surgery, Saiseikai Central Hospital, 1-4-17, Mita, Minato-ku, Tokyo, 108-0073, Japan (Email: sakuraihm{at}ybb.ne.jp).
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Abstract
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Background: Lipomas are a common type of benign tumor, and may involve numerous sites. They are common in the subcutaneous region of the upper back, neck, and shoulder, but are rarely seen in the thoracic cavity. Intrathoracic lipomas are a type of deep-seated lipoma, unlike subcutaneous lipomas. Due to the rarity of intrathoracic lipomas, little is known about their clinicopathological features.
Methods: We conducted a retrospective review of the clinicopathological records of 10 patients who had undergone surgical resection for intrathoracic lipomas during a 16-year period (1991 to 2006).
Results: There were 9 men and 1 woman with a mean age of 57.9 years. The number of lesions was one in 9 patients and two in 1 patient. Symptoms caused by the tumor were seen in only one patient. Radiographically, the tumors showed well-defined, homogeneous, and fatty density masses/nodules. Intrathoracic lipomas were most frequently seen in the parietal pleura. The resected tumor size ranged from 1.0 to 6.0 cm. Pathologically, three lesions showed an infiltrating type in which mature fat cells were seen between and within muscle or nerve fascicles. One of these three ended in an incomplete resection because the tumor infiltrated the brachial plexus. One patient had a recurrent tumor arising from a resected margin.
Conclusions: Intrathoracic lipomas should be surgically resected if they are detected, because the possibility of liposarcoma or infiltrating development of the tumor cannot be excluded preoperatively. We think that surgical resection of the tumor, rather than conservative management by close observation alone, is a safer treatment.
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Introduction
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Lipomas are common benign tumors that occur mostly in subcutaneous tissue [1, 2], but are rarely seen in the thoracic cavity [2]. It has been sporadically reported that intrathoracic lipomas can arise from the mediastinum, diaphragm, bronchus, lung, or thoracic wall [3–8]. They are classified as deep-seated lipomas, in contrast to subcutaneous lipomas [1]. Although most intrathoracic lipomas are asymptomatic and are ordinarily discovered at a medical examination, symptoms are likely to depend on their site and size [3, 4]. They may occasionally lead to manifestations including coughing, dyspnea, heart disorder, or even death [4, 6, 7]. In other circumstances, deep-seated lipomas, including intrathoracic lipomas, need to be carefully differentiated from the potential of malignancy such as liposarcoma or infiltrating tumor spread, because lipomatous malignancy commonly occurs at sites deeper than the subcutaneous region [1, 2]. However, little is known about the clinicopathological features of intrathoracic lipomas because there have been few reports on scattered cases in the literature. Therefore, we sought to review our surgical experience with intrathoracic lipomas in a single institution, with emphasis on the clinicopathological features, management, and outcome.
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Material and Methods
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Our Institutional Review Board approved this retrospective study and waived the need for patient consent. For the 16-year period from January 1991 through December 2006, there were 2,013 general thoracic procedures under general anesthesia, based on the clinicopathological database at Saiseikai Central Hospital, Tokyo. Of these, 11 patients had undergone surgical treatment for intrathoracic lipomas. We reexamined the clinicopathological findings from these medical records and found that one patient, who was previously diagnosed with diaphragmatic lipoma, actually had retroperitoneal lipoma-like fatty proliferation from a foramen of Bochdalek hernia of the diaphragm on chest computed tomography (CT) review. Consequently, 10 patients with intrathoracic lipoma were considered in this retrospective study. The clinical record of each patient was examined with regard to sex, age, presenting symptom, body-mass index (BMI), medical past history, preoperative workup, location and size of the tumors, mode of operation, and prognosis. A BMI of more than 25 was considered obese. The pathology specimens were reviewed to confirm the diagnosis of lipoma. Follow-up information was obtained from the medical chart or direct patient contact by telephone interviews.
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Results
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The clinical characteristics of the 10 patients are shown in Table 1. The mean age at presentation was 57.9 years. There was no significant history of thoracic trauma except for one patient (patient 2), who had broken his right clavicle 32 years previously. As to symptomatic patients, one (patient 10) presented with chest pain due to pneumothorax, and a lipoma on the chest wall was unexpectedly found during the operation for pneumothorax. The remaining patient (patient 7) had dyspnea due to an intrathoracic lipoma lesion. Regarding two patients with endobronchial lipoma, in one patient the lesion was detected by CT screening and in the other patient the lesion was unexpectedly detected by bronchoscopy as part of a detailed investigation of an abnormal shadow in the chest under mass screening. The BMI was calculated for 9 patients, and 3 were considered obese. The mean maximal diameter of the tumor was 3.3 cm. The intrathoracic locations of the lipoma lesions were most frequently the parietal pleura. The number of lesions was one in 9 patients and two in 1 patient (patient 5). The two lesions in patient 5 were, respectively, located anteriorly and posteriorly on the parietal pleura. Chest roentgenogram and CT scan were performed in all patients, magnetic resonance imaging (MRI) study was performed in 3, and F-18 fluorodeoxyglucose-positron emission tomography (FDG-PET) was performed in 2, as part of the preoperative workup. Chest roentgenogram revealed a well-defined, homogeneous tumor shadow in all patients whose tumor was detected by chest roentgenogram. Chest CT showed a well-circumscribed tumor with a homogeneous fat density, and the attenuation value ranged from –95 to –120 Hounsfield units (HU). Based on the results of radiography, 3 patients had an increase in tumor size during the preoperative follow-up period. On T1- and T2-weighted MRI images, the tumor showed high signal intensity. The FDG-PET scan showed negative FDG-uptake for the tumor. Laboratory findings were unremarkable in all patients. Preoperative bronchoscopic biopsy was performed in 3 patients; 2 had an endobronchial lesion and the other had a parietal lesion. The pathological diagnosis by bronchoscopic biopsy of 2 patients with endobronchial lesions was suspected lipoma, and that of 1 patient with a parietal lesion was normal alveolar cells. Although a CT-guided needle aspiration biopsy was performed in 1 patient, the obtained sample was insufficient to make a diagnosis. The other 7 patients underwent no diagnostic approaches except for radiologic examinations.
Upon gross examination, intrathoracic lipomas were smooth on the surface and exhibited hemispherical and pedunculated forms. Ten lesions were yellowish in color, and the remaining lesion was whitish-lustrous. Two patients with endobronchial lesions had pedunculated appearances, and they were resected at the portion of the stalk by a snare and yttrium-aluminum-garnet laser. Regarding the 9 remaining lesions in the 8 other patients, they were all surgically extirpated.
Pathologically, 1 patient (patient 3) showed myxomatous change (myxolipoma), which was whitish-lustrous in color, and 2 (patients 1 and 2) had infiltrating spread between and within nerve and muscle fascicles (infiltrating lipoma), although tumors were composed of mature fat cells (Figs 1; 2).
Patients did not always develop symptoms just because the lesions showed infiltrating growth. Upon gross examination, infiltrating lipoma cases had hemisphere sessile forms and not pedunculated forms.
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Fig 1. Chest computed tomographic scan and photomicrograph of the infiltrating lipoma (patient 1). (A) The tumor appears as a broad-based and uniform fat density (–100 Hounsfield units) mass of the parietal pleura. (B) Histologically, mature fat cells are seen between and within muscle fascicles (hematoxylin and eosin staining at original magnification x100).
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Fig 2. Sagittal T1-weighted magnetic resonance imaging and photomicrograph (patient 2). (A) The tumor exhibits a high signal intensity, and passes from the mediastinum into the neck (cervicomediastinal lipoma). (B) Histologically, the lesion shows infiltration into skeletal muscle fibers by mature adipocytes (hematoxylin and eosin staining at original magnification x400).
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In a case of "cervicomediastinal" lipoma (patient 2), surgical resection was incomplete because of invasive tumor spreading into the brachial plexus, although we tried to extirpate the tumor through a trap-door incision. However, the residual tumor in this patient showed no growth for 5.8 years after the operation. This patient then moved from our hospital to receive treatment for newly detected pancreatic cancer and was lost to follow-up. The other patients underwent a resection without gross residual tumor. Tumor recurrence was detected in one patient (patient 6) (Fig 3); a diaphragmatic lesion showed local recurrence 3.7 years after the initial resection and we performed a repeat excision. In a pathological examination, the tumor showed infiltrating spread into diaphragmatic muscle. This patient (patient 6) shows no recurrence 4 years after the second operation. No recurrence of lipoma has been noted in the other 8 patients. All but one patient have remained healthy.
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Fig 3. Chest computed tomographic scan and photomicrograph of the recurrent diaphragmatic lipoma (patient 6). (A) The tumor grows surrounding the previous resected stapled line. (B) Histologically, the lesion shows infiltration into the diaphragm by mature fat cells (hematoxylin and eosin staining at original magnification x100).
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Comment
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Lipomas, composed of mature fat, are well-known benign neoplasms in general practice, and are ordinarily soft, freely mobile, and well-circumscribed masses/nodules [1]. They are classified into two types according to their location (ie, superficial or subcutaneous and deep-seated lipomas) [1]. The subcutaneous or superficial regions are the most commonly involved sites [1]. Clinically, most lipomas become apparent in patients at 40 to 60 years of age [1, 3, 8], and are thought to be common in obese persons [1]. In the present study, 3 of the patients were considered obese.
Deep-seated lipomas are likely to be less well-defined than subcutaneous lipomas [1], and can occasionally exhibit an infiltrating behavior (infiltrating lipomas) [2, 9, 10]. Regarding the location of intrathoracic lipomas, in our study the tumors were most frequently seen in the direction of the parietal pleura (chest wall), but not in the direction of the visceral pleura. Endobronchial lipomas have been reported to account for only 3.2% of all benign tumors of the tracheobronchial tree [11]. Lipomas arising from the diaphragm are also very rare [6, 8]. Diaphragmatic lipomas are often found on the left side of the diaphragm, mainly in a posterolateral location [8], and our present patient (patient 6) showed similar findings. Regarding the mode of tumor growth of intrathoracic lipomas, the tumors may not only lie entirely within the thoracic cavity but can also extend from the upper mediastinum into the neck (cervicomediastinal lipoma) such as in patient 2, or from the subpleural region through the subcutaneous tissue of the chest wall (transmural lipoma) [4, 9]. Deep-seated lipomas can sometimes show a peculiar histologic pattern of mature fat cells infiltrating muscle or other tissue (ie, infiltrating lipomas) [2, 10]. In our study, 3 patients showed infiltrating lipoma. Although 1 patient showed obvious extension of a cervicomediastinal lipoma into the cervical region through the chest cavity in preoperative radiographic findings, infiltrating growth was not anticipated in the other patients based on diagnostic imaging.
Radiologically, intrathoracic lipomas appear as smooth, rounded nodules/masses [3, 5]. On chest CT findings, they show well-defined homogenous low attenuation with a negative CT number (–50 to –150 HU) [5, 12]. On MRI, they show high signal intensities on both T1- and T2-weighted images [1]. Although radiographs are useful for the diagnosis of a lipoma overall, they cannot be used to invariably differentiate lipomas from well-differentiated liposarcomas. Although thoracic liposarcomas themselves are very rare, there have been some sporadic reports on lipoma-like liposarcoma within the thorax, which had been considered lipoma on preoperative radiologic findings [13, 14]. Other reports have discussed a frequent radiologic diagnostic dilemma between lipoma and liposarcoma, especially well-differentiated liposarcoma [15].
A strategy for the management of asymptomatic intrathoracic lipomas has not been established. Some authors recommend a radiologic follow-up of asymptomatic intrathoracic lipomas [5] and others recommend surgical excision because the possibility of liposarcoma cannot be excluded [6, 8]. Intrathoracic lipomas may cause severe symptoms by subsequently increasing in size, or a possible infiltrating growth may make an operation the more complicated even if they are histologically benign. In addition, it can be difficult to preoperatively differentiate lipomas from liposarcomas, especially well-differentiated liposarcomas (lipoma-like liposarcomas). Some of well-differentiated liposarcomas over time may dedifferentiate or progress histologically to high-grade lesions (dedifferentiated liposarcomas) [1]. Once dedifferentiation occurs, the lesions can usually be considered fully malignant sarcomas [1]. Therefore, we recommend a surgical resection for intrathoracic preoperatively lipoma-like lesions. Consequently, surgical resection of intrathoracic lipomas can be used for both a firm diagnosis and treatment. Conservative follow-up seems to be suitable for patients of high age and in poor general condition. However, we should always keep a potential of progression of the lipoma-like lesions in mind because, by any chance, the lesions can be pathologically considered a well-differentiated liposarcoma and not a simple lipoma.
In the present study 5 of 8 patients, except for 2 patients with endobronchial lipoma, underwent video-assisted thoracoscopic surgery (VATS) procedure. Based on our institutional experience, we suppose that pedunculated lipomas are the most appropriate indication of VATS procedure because of the absence of infiltrating growth in a pedunculated type. Because a hemisphere type of thoracic lipoma can be infiltrating, surgeons should not be wedded to the VATS approach if tumors cannot be extirpated easily.
The pathological differentiation between lipoma and liposarcoma, especially the well-differentiated type, is sometimes confusing. They must be discreetly differentiated because most liposarcomas arise from deep-seated regions. Traditionally, the identification of lipoblasts has been principal for diagnosing liposarcoma [1, 2]. Tumors that comprised uniform, mature fat without cytologic atypia are diagnosed histologically as lipomas. Tumors that consist predominantly of mature fat with a variable number of atypical spindled cells (usually accompanied with collagenization), and lipoblasts are diagnosed as well-differentiated liposarcomas [1, 2]. In some cases these atypical spindle cells are numerous, whereas in other cases the cells are so rare as to require extensive sampling of the tissue. A varying number of monovacuolated or multivacuolated lipoblasts may be found. Criteria that have proved useful for identifying diagnostic "lipoblasts" include the following [1]: (1) a hyperchromatic indented or sharply scalloped nucleus; (2) lipid-rich droplets in the cytoplasm; and (3) an appropriate histologic background. The mere presence of lipoblasts does not make a diagnosis of liposarcoma because lipoblast-like cells can be seen in a variety of conditions such as lipoma with fat necrosis, fat with atrophic change, and foreign body reaction. In the present study, we thoroughly re-reviewed the pathological findings of the tumor specimens. Cytogenetic studies have been reported to be useful for distinguishing lipomas from malignant lesions [1, 2, 7]. Characteristic tumor-specific chromosomal abnormalities are seen in ordinary lipomas, which may show translocations involving 12q13-15, interstitial deletions of 13q, and rearrangements involving 6p21-23 [1, 7].
The outcome after resection of lipomas is usually good. However, they may recur locally and the rate of recurrence after an excision has been reported to be less than 5% [1]. Additionally, deep-seated lipomas seem to have a greater tendency to recur due to the difficulty of complete surgical removal [1]. We had one patient (patient 6) with a recurrent tumor that grew adjacent to the initial resected stapled line based on a probable incomplete surgical resection. In this patient, the initial preoperative radiographs showed no invasive growth but the tumor partially adhered to the diaphragm during the operation. The tumor was then resected by stapling in the adherent diaphragm. Unfortunately, tumor of the diaphragm would have led to a pathological incomplete resection because the tumor led to local recurrence about 3 years after resection. In a surgical extirpation of deep-seated lipomas, a tumor that adheres to surrounding tissues should, if possible, be resected extensively with adequate surgical margins. On the other hand, when lipomas infiltrate major nerve systems such as the brachial plexus, their extirpation with combined resection can no longer be performed due to excessive damage. In a patient (patient 2) with infiltration into the brachial plexus the operation ended in incomplete resection, but the residual tumor remained stable in size after the operation. Wurlitzer and colleagues [9] reported several cases in which the tumor stopped growing after incomplete tumor removal. Surgical resection might be performed incompletely rather than cause a serious functional disorder due to complete extirpative procedures. If the residual tumor remains stable in size during postoperative course, the lesion may be treated by watchful observation. Inversely, if the incompletely resected lesion becomes progressive later, we may select radiotherapy although the usefulness of radiotherapy for lipoma has not yet been reported.
In conclusion, when an intrathoracic lipoma is suspected in a medical examination, we should consider the potential of liposarcoma or infiltrating growth of the tumor. Regarding the management of an intrathoracic lipoma, surgical resection, if possible, would be recommended from diagnostic and therapeutic perspectives.
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Abstract
Introduction
