PA (Fig. 1A) and lateral (Fig. 1B) chest radiographs reveal the presence of a 2.5 cm (long axis) by 1.5 cm (transverse axis) lentiform-shaped opacity in the axillary portion of the left thorax. The lesion has a well-defined medial border but an incompletely visualized lateral border, tapered superior and inferior borders, and is better defined on the frontal as opposed to the lateral exam. This constellation of features supports the lesion being pleural or chest-wall-based. Note the absence of adjacent rib destruction. Single view chest radiograph from one-year earlier (Fig. 2) also reveals the presence of this lesion. The absence of change in size, shape or morphology over the past year supports the non-aggressive nature of this lesion. Selected chest CT axial (Fig. 3A-C) and coronal (Fig. 4A-D) (frontal radiograph equivalent) images (mediastinal windows) confirm the presence of this lesion and its relationship to the pleura. Compare the attenuation of this particular lesion’s matrix with that of the subcutaneous tissues. The matrix is lipomatous or fatty in nature. Note the absence of chest wall extension or rib destruction (Images and case write-up provided by Samer Hijaz, MD, VCU Medical Center, Richmond, Virginia).
Differential Diagnosis Solitary Pleural Lesion
Loculated Pleural Effusion
Organized empyema
Focal Metastasis / Pleural Implant (e.g., adenocarcinoma, sarcoma, lymphoma)
Hematoma
Lipoma / Liposarcoma
Mesothelioma
Mesothelial Cyst
Neurogenic Tumor (e.g., Schwannoma and Neurofibroma)
Discussion
The classic radiologic description of a pleural-based mass is that of an opacity with an incomplete border and tapered superior and inferior borders. The tapered superior and inferior borders are valuable signs for confirming an intrathoracic but extrapulmonary location.
The distinction of loculated pleural fluid from a pleural tumor may be problematic. The most practical approach is to review serial exams. Because localized collections of pleural fluid may change rapidly, they are frequently referred to as “vanishing tumors”. This lesion did not change in size, shape or morphology over a prolonged period of time. The fatty matrix of the lesion on CT confirms the benign lipomatous nature of this particular lesion.
Pleural Lipomas are benign soft-tissue neoplasms that originate from the submesothelial layers of parietal pleura and extend into the subpleural, pleural, or extrapleural space. These fatty tumors may demonstrate slow growth over long periods of time but are non-aggressive. Pleural Lipomas can occasionally arise from the diaphragm and or chest wall. Pleural lipomas are usually encapsulated with smooth but sharply delineated margins. These lesions tend to conform to the adjacent muscle, bone, and fascial planes and range 1-10 cm.
Clinical Findings
Most pleural lipomas remain asymptomatic until incidental detection at radiography. Some lesions may be associated with non-productive cough, back pain, exertional dyspnea, or a sensation of heaviness in the chest.
Imaging Findings
Chest Radiography (Fig. 1A; 1B; Fig. 2)
- Lentiform / ovoid / elliptical lesion
- Tapered superior and inferior borders
- Incomplete border sign
- Homogenous opacity
- Non-aggressive
- Slow or no perceptible growth on serial studies
CT / MRI
Similar features to those outlined above (Fig. 3A-C; Fig. 4A-D)
Attenuation coefficients confirm the fatty nature of the lesion (-100HU) on CT (
Fig. 3A-C; Fig. 4A-D)
Signal intensity confirms fatty nature of lesion / suppresses on fat-suppressed pulse sequence (MRI)
Caveats
Lipomatous lesions larger than 10 cm in size or those containing soft-tissue elements and not a purely fatty matrix raise the specter of possible Liposarcoma.
Biopsy and or excision should be considered in these latter cases.
Suggested Readings
- Gaerte SC, Meyer CA, Winer-Muram HT, Tarver RD, Conces DJ., Jr Fat-Containing Lesions of the Chest. RadioGraphics 2002; 22 Spec No (61-78).
- Parker MS, Chasen MH, Paul N: Radiologic Signs in Thoracic Imaging: Case-Based Review and Self-Assessment Module. AJR Am J Roentgenol 2009; 192(Suppl 3):S34–S48, 2009
- Politis J, Funahashi A, Gehlsen JA, et al. Intrathoracic Lipomas: Report of Three Cases and Review of the Literature with Emphasis on Endobronchial Lipoma. J Thorac Cardiovasc Surg 1979; 77: 550-556.