Most pleural neoplasms are metastatic in origin. Primary tumors of the pleura can be categorized as diffuse or localized. Diffuse malignant mesothelioma is more common, is related to asbestos exposure, and is associated with a poor prognosis. Localized mesothelioma is called localized fibrous tumor of the pleura (LFTP; also known as solitary fibrous tumor of the pleura); this neoplasm is less common, has a controversial histogenesis, and is unrelated to asbestos exposure.
LFTPs exist in benign and malignant forms. Only rarely is the localized fibrous tumor invasive or does it cause local recurrence after resection. The ratio of benign to malignant tumors is 7:1. The diagnosis of LFTP is important because the tumor is potentially resectable for cure despite its typically large size. In many cases, resection can repeatedly be used to treat recurrence, although usually with increasing difficulty. [1, 2, 3, 4]
Usually, LFTP is discovered incidentally on chest radiographs. Findings from computed tomography (CT) scanning and magnetic resonance imaging (MRI) can suggest the diagnosis of LFTP. However, histopathologic examination is needed for a definitive diagnosis. [5, 6, 7] Chest radiographic findings are nonspecific, and the lesion can sometimes be obscured by associated pleural effusion. CT and MRI scans may show characteristic findings that are suggestive of LFTP but that are not always pathognomonic. The pleural origin of large lesions can be difficult to detect, especially on chest radiographs and even on CT and MRI scans.
An example of a benign LFTP is shown in the images below.
In most patients, an LFTP is detected as an incidental finding on a chest radiograph, appearing as a well-circumscribed, homogeneous soft-tissue mass that is related closely to the pleura.
The lesion can arise anywhere along the pleura and can even be seen in the pulmonary fissures or along the mediastinal or diaphragmatic pleura (as in the images below).
The margins with lung parenchyma are well defined in most patients, although in 2% of patients, the lesion is somewhat ill defined, and in another 2% of patients, the lesion is completely obscured by pleural effusion.
The angle with the chest wall or mediastinum is either acute (as seen in the images below) or obtuse. The obtuse angle is seen more often in small lesions, indicating the pleural origin of the lesion.
Large tumors may present as an opaque hemithorax (as demonstrated in the images below).
Pleural effusion may occur in 17% of patients, especially in patients with the malignant variant of LFTP.
Chest radiographic findings are nonspecific; however, a change in the position of the lesion with respiration or gravity is particularly suggestive of a pedunculated LFTP.
The lesion may mimic a mass of parenchymal or mediastinal origin, and large lesions may simulate an elevated diaphragm. (See the images below.)
An LFTP is usually 1.5-25 cm in size. Typically, the lesion appears as a smoothly marginated, soft-tissue–attenuating mass abutting the pleura, with a round or lobulated contour. On contrast-enhanced CT scans, the lesion enhances more than the soft tissue does, because of its rich vascularization. Nonenhancing areas within the mass are correlated with the presence of necrosis, hemorrhage, or degeneration.
Areas of low attenuation can be seen within an LFTP, especially when the lesion is large. Unlike other pleural lesions, the angle between the mass and the pleura is most often acute (although it can be obtuse, especially in small masses). A small, ipsilateral pleural effusion can be seen. Calcification is not common, but it can be seen. The detection of a pedicle or a change in the lesion's position is suggestive of an LFTP.
The lesion displaces the adjacent mediastinum and lung parenchyma, resulting in atelectasis.
The malignant form of LFTP cannot be confidently differentiated from the benign form by imaging. However, malignant lesions are typically larger than 10 cm and are more likely to be associated with central necrosis and a large pleural effusion.
Manifestations of LFTP on CT scans are usually not pathognomonic, although some CT findings are highly suggestive of the diagnosis.
Small lesions may mimic primary lung carcinoma; however, a localized fibrous tumor is not associated with metastases or lymphadenopathy.
Magnetic Resonance Imaging
Spin-echo, T1-weighted MRI scans predominantly demonstrate low to intermediate signal intensity, and T2-weighted images depict low signal intensity. The low intensity is attributed to the presence of fibrous, hypocellular tissue.
Foci of increased signal intensity can be seen on T2-weighted images. These foci correspond to the regions of decreased attenuation on CT scans and represent areas of necrosis, hemorrhage, or degeneration.
Intense enhancement is seen on gadolinium-enhanced T1-weighted images.
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography scans. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see Medscape.
MRI machines can produce multiplanar images, and MRI has superior tissue characterization compared with that of CT scanning; therefore, MRI is helpful in evaluating an LFTP and in defining its pleural origin and extension. After excluding calcifications, the presence of low signal intensity on T1- and T2-weighted images is highly suggestive of the fibrous nature of the lesion. T1- and T2-weighted images appear below.
Ultrasonography plays a limited role in the diagnostic workup of pleural masses.  In some patients, however, ultrasonography may be performed to evaluate a pleural effusion or to guide procedures. The fibrous tumor typically demonstrates homogeneous low echogenicity, as in the image below. Associated pleural effusion appears anechoic.
A case report described the potential use of a fluorodeoxyglucose–positron emission tomography (FDG-PET) scan to evaluate the possibility of malignancy in LFTP. In this report, a high FDG uptake (with a standardized uptake ratio [SUR] of 3.0) was noted in a portion of the mass that exhibited malignant features histopathologically.  The article suggested that FDG-PET can be helpful to determine preoperatively the presence of malignancy in patients with LFTP, whose prognoses are usually difficult to predict. Yan et al report a case in which a PET diagnosis was confirmed by pathology. 
The mass demonstrates hypervascularity with tumoral vessels. Typically, no early venous drainage is seen. The arterial supply is usually derived from the aorta (segmental arteries) and, in some patients, from the internal mammary artery. The angiographic appearance of the LFTP lesion is nonspecific.