Unusual giant pleural lipomas: imaging features
- 1 Radio Diagnosis, All India Institute of Medical Sciences, New Delhi, Delhi, India
- 2 Surgical Oncology, All India Institute of Medical Sciences, New Delhi, Delhi, India
- 3 Pathology, All India Institute of Medical Sciences, New Delhi, Delhi, India
- Correspondence to Dr Sheragaru Hanumanthappa Chandrashekhara; drchandruradioaiims@gmail.com
Abstract
Pleural lipomas are rarely encountered in the thoracic cavity. Sometimes, they infiltrate the intercostal space to have a component on either side of the intercostal space forming a hourglass configuration. They are generally solitary, small and asymptomatic. We present the case of a 49-year-old man with two giant pleural lipomas, both originating from the right parietal pleura, and one of which was passing through the intercostal space giving rise to a hourglass-shaped configuration. When they occur, although benign, considering the evolutionary potential, excision is recommended.
Background
Lipomas are benign tumours of adipose tissue which are often encapsulated by a thin layer of fibrous tissue. Although they can develop in any part of the body, they are often located in the subcutaneous tissue of the upper trunk, head, neck, shoulder and back of the body.1 Though uncommon, intrathoracic lipoma, if present, is usually seen in mediastinal, bronchial and pulmonary locations.2 A pleural lipoma is extremely rare.3 The hourglass-shaped thoracic lipomas are very rarely found.4–6 Most patients are asymptomatic and are incidentally detected on chest radiography or CT.7 Although benign, considering the evolutionary potential, excision is recommended.3
Case report
A 49-year-old non-smoker man presented with a 1-year history of right-sided chest pain and shortness of breath. There was no other significant medical history. A chest radiograph showed a homogenous peripheral longitudinal right thoracic mass, having a broad base towards the pleura (figure 1A). Ultrasound of the same was done, which showed an ill-defined predominantly homogenous hypoechoic mass with no to minimal internal vascularity (figure 1B). CT showed two homogenous fat-containing masses (mean Hounsfield units (HUs) of −113 HU) in the right anterior and lateral chest wall (figure 2A–D). No enhancing soft tissue was seen. No infiltration of adjacent structures was noted. Anterior mass was seen to infiltrate into the first and fourth intercostal spaces causing displacement of the intercostal muscles outwards. Both the intrathoracic and extrathoracic components were giving rise to a dumbbell-shaped configuration, which was better appreciated in the sagittal view. The similar morphology lateral chest wall mass was associated with rib widening and hypertrophy. Our primary impression was a giant pleural lipoma. However, to rule out well-differentiated liposarcoma and solitary fibrous tumour of pleura, a contrast enhanced MRI was done. The MRI confirmed homogenous T1W/T2W hyperintense masses with lobulated margins with few thin internal septations, and no enhancing solid component and homogenous fat suppression on fat-suppressed T1W images (figure 3A,B). Ultrasound-guided biopsy was done which was inconclusive.
Chest radiograph. (A) A large homogenous mass in the right hemithorax with broad base towards chest wall with well defined superior, inferior and medial borders, which was causing remodelling of the right fourth rib (black arrow) and widening of intercostal spaces; no calcification seen within the mass. Ultrasonography sagittal image (B) shows a heterogeneously hypoechoic mass without any calcifications or internal vascularity.
Contrast-enhanced computed tomography(CECT) images. Axial image (A and B) shows a large fatty attenuation (Region of interest (ROI)-mean Hounsfield units (−113 HU)) mass (thick black arrow in (A)) with an extrathoracic component (thin black arrow in (A)) in lateral aspect of right hemithorax. Sagittal image (C) shows another similar mass (thick white arrow) in anterior aspect with extrathoracic component (thin white arrow) forming a hourglass configuration. Coronal image (D) shows a mass causing widening of intercostal space (asterisk) and right fourth rib showing remodelling and a bony exostosis (thin white arrow).
T2 weighted axial MRI images show T2 hyperintense mass (A) having both intrathoracic and extrathoracic components showing homogenous suppression in fat saturated T2 weighted image (B), suggestive of fat signal intensity mass.
Outcome and follow-up
The patient was followed up for 3 months. The patient underwent a video-assisted thoracoscopic surgical excision because of shortness of breath and chest pain and also taking into consideration the evolutionary potential of the tumour. The gross specimen of the chest wall resection showed an encapsulated lesion on the pleural aspect which appeared to involve the underlying fourth rib. Cut surface showed only fat. No solid areas or haemorrhage was seen. Serial sectioning showed features of lipoma. There was no evidence of malignancy (figure 4A–D). Post surgery, the patient is doing well.
Photomicrograph of mass (A) shows mature adipocytes with entrapped skeletal muscle bundles (arrow) (H&E ×200). (B) Thickened fibrous septa and interspersed blood vessels (arrow) (H&E ×200). (C) Infiltration of the bony trabeculae (arrow) (H&E ×400). (D) Invasion around nerve twigs (arrow) (H&E ×200). No evidence of atypia or lipoblasts is identified.
Discussion
According to Keeley, Vana, Williams and Parsons, intrathoracic lipomas are classified into two types: intrathoracic lipoma in which the growth is limited to the thoracic cavity and hourglass thoracic lipoma that passes through the thoracic inlet or intercostal space,8 such as in our case. Pure intrathoracic lipomas are more common. A pleural lipoma is extremely rare. Pleural lipomas can occur in all age groups, with the mean age being 60.1 years and involve both sexes equally.9 They originate from the submesothelial layer of the parietal pleura10 and may extend into subpleural and extrapleural space. Most patients are asymptomatic,11 but the lipomas have the potential to grow to large sizes and subsequently cause compressive symptoms. Bone erosion, cortical thickening and exostosis secondary to extrinsic pressure and irritation have been documented.12 Ultrasound can be done to characterise the nature of the lesion and also look for vascularity. It acts as a complementary imaging tool that can also be used to guide interventional procedures. A definitive diagnosis can be made by CT if it shows a homogenous fatty attenuation mass (−50 to −150 HU), not showing enhancement by contrast injection, displacing adjacent pulmonary parenchyma and vessels, and making obtuse angles with chest wall.13 However, differentiation with well-differentiated liposarcoma might be difficult.14 Infiltration to surrounding structures, inhomogeneous enhancement and attenuation values greater than −50 HU favour malignancy.15 MRI can be done in doubtful cases. Homogenously fatty mass, no or minimal thin (less than 2 mm) septa, no or minimal T2 hyperintense foci, and no or mild linear enhancement favour lipoma over liposarcoma.16 Another close differential is a solitary fibrous tumour of pleura. It is also a rare benign tumour of pleura with homogenous soft-tissue attenuation. Fat forming variants have also been reported.17 MRI plays an important role in differentiating from lipomas. Due to the fibrous contents, the solitary fibrous tumour of pleura shows low to intermediate T1 and T2 signal intensity. A biopsy is the gold standard for the diagnosis of pleural lipoma. But due to various complications such as intertumoral haemorrhage, fat necrosis and chronic inflammation, these biopsies may be often non-diagnostic.13 Considering the evolutionary potential, excision is recommended even for asymptomatic patients, preferably by video-assisted thoracic surgery.3 The outcome of resection is also generally good. The recurrence rate is reported to be less than 5%, which is mostly attributed to incomplete surgical removal.18
Patient’s perspective
I first found out I had a swelling over the right chest wall which was slowly increasing over the last one year. After a while, I started feeling another swelling anterior to the previous one. Initially, it was neither painful nor was causing any symptoms. So, I did not pay much attention to these swellings. But when they started to grow, I got worried. Gradually, it started to be painful and I also started experiencing chest discomfort and difficulty in breathing which was increasing over a while. The first thing that came to mind was what if it is cancer. So after consulting some private physicians, I underwent USG and CT scan. A few of the physicians also raised the suspicion of cancer, which again got me worried. I started thinking it is cancer only and I am going to die within a couple of months—your mind always goes to the worst-case scenario.
The physicians raised suspicion of lipoma versus liposarcoma. So about a week later, I underwent a USG-guided biopsy along with a few other tests. The biopsy was inconclusive. The radiologist told it looks more benign rather than true malignant. However, an MRI needs to be done to rule out any malignancy. I was getting more anxious and did not want to take any chances, and so I consulted the cancer institute at AIIMS New Delhi. Here I again underwent a Contrast-enhanced computed tomography(CECT) scan. The radiologist and surgeon told me that the findings are consistent with that of a lipoma. However, it was an unusual presentation for the same. They have counselled me about the disease and that the slow progression of the tumour favours benignity. The surgical oncology consultant briefed me about everything and explained that because of the way it was growing, causing a mass effect on the right lung, they may require a thoracic surgeon during the operation. Finally, I underwent an elective surgery to excise the tumour. Now I feel a lot better. Now I do not feel as breathless as before. I was briefed that my pathology report showed no evidence of cancer, which made me a lot relived. I thank the AIIMS doctors and staff for all their support and help. I have been advised to be on regular follow-up in the OPD. I will be sticking to the same.
Learning points
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Pleural lipomas are extremely rare benign tumours that are usually asymptomatic. But, in a rare case, the patient can present with chest pain and discomfort.
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CT scan helps in making a diagnosis. MRI can be done in doubtful cases.
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Surgical resection is necessary due to various reasons: first, it is difficult to differentiate between lipoma and well-differentiated liposarcoma; second, biopsy is frequently inconclusive and third, the potential for growth and compressive symptoms.
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Local recurrence after surgery is uncommon.
Footnotes
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Contributors Dr DS: conduct and reporting; Dr MS: pathology reporting; Dr SHC: guarantor; Dr SK: treating physician.
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Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
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Competing interests None declared.
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Provenance and peer review Not commissioned; externally peer reviewed.
- © BMJ Publishing Group Limited 2021. No commercial re-use. See rights and permissions. Published by BMJ.
References
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