Asymptomatic large intrathoracic lipoma: case report and literature review

Clinical History

We are presenting a case of 24-year-old Caucasian male patient, with a body mass index (BMI) 25 kg/m², who was referred to our institution for further examination, because of a undefined expansile thoracic mass found on a routine chest X-ray examination. The patient did not present with any symptoms.

Imaging Findings

The CXR demonstrated a well-circumscribed homogeneous shadow, which was inseparable from the lateral thoracic wall. Widening of the third intercostal space was also described. Remaining intrathoracic status was found normal.
Contrast-enhanced CT scan was performed, depicting an extensive lipomatous formation sized 124 x 60 x 116 mm, located dorsolaterally on the right side, next to the upper right pulmonary lobe, averaging -107 HU. The mass was for the most part located adjacent to the external contour of the thoracic wall, and partially extending between the intercostal space of the third and fourth rib, which were displaced by the formation. The mass did not demonstrate significant contrast uptake.
The patient underwent fine needle aspiration of the mass, which demonstrated mature adipocytes with no cellular atypia. In consultation with the thoracic surgeon, we have decided not to perform any further invasive procedures. The patient was referred for regular X-ray follow-ups.

Discussion

Lipomas, are well-known neoplasms, classified into two types according to the location, subcutaneous and deep-seated lipomas [1]. They are also considered to be more common in obese patients [2, 3]. Our patient did not fit this criterion, considering his BMI of 25 kg/m2 . The intrathoracic lipomas arise from epipleural fatty tissue, which coincides with our patient. Thoracic lipomas can also be divided into two classes, entirely intrathoracic (the more common type) and the hourglass or transmural type [4]. While the tumour is usually incidentally detected on a CXR, the CT scan is the standard for accurate detection of thoracic lipomas. CT allows a definitive diagnosis by demonstrating a homogeneous fat attenuation mass (-50 to -150 HU). The density may not be entirely uniform because lipomas often contain fibrous stroma [5, 6].
There is always a radiological diagnostic challenge between lipoma and liposarcoma, especially liposarcoma with low-grade malignancy. Definitive diagnosis here can be achieved only by pathohistological examination such as percutaneous biopsy.
There is still no consensus regarding management of asymptomatic lipoma. Some authors suggest radiologic follow up, but other authors recommend surgical excision because the possibility of liposarcoma cannot be excluded [2].
Most patients remain asymptomatic, but since lipomas are able to grow to a significantly large size, they may incite compression symptoms [7, 8]. Pleural lipomas can also cause complications such as intratumoral haemorrhage, and they can invade intercostal spaces and induce rib osteolysis [7, 9]. As for our patient, despite a significant tumour mass he did not have any symptoms, and although he had ribs displacement, the CT scan did not show any signs of rib osteolysis.
Tumours consisting of uniform, mature fat without cytologic atypia are diagnosed histologically as lipomas. Tumours 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 [2, 10]. As reported by Jayle et. al. secondary transformation of lipoma into liposarcoma has never been reported in the literature, that is why excision of the tumour should not be performed to prevent such an evolution [11]. With that in mind, we should consider surgical resection in three cases: in case of inhomogeneous mass, when we cannot exclude the presence of the liposarcoma, when adjoining organs are severely compressed, and if the presence of tumour mass causes symptoms [11].

Differential Diagnosis List

Final Diagnosis

Intrathoracic lipoma

URL:	https://www.eurorad.org/case/13238
DOI:	10.1594/EURORAD/CASE.13238
ISSN:	1563-4086