대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Solitary fibrous tumor of the pleura

Radiologic Findings

The PA (Fig.1) and lateral (Fig.2) chest radiographs show a mass in the right posterior mediastinum in close contact with the adjacent rib heads and vertebrae. The mass is 8.2 cm in size and shows heterogeneous enhancement on contrast-enhanced CT in the axial (Fig. 4) and coronal (Fig. 5) views. The adjacent rib shows mild hypertrophy. On MRI, the mass had no neural foramen or spinal canal involvement. (T2 fat sat Fig 6,7,8)

Brief Review

The tumor was resected. The tumor was surrounded by serous membrane and attached to the heads of the right 5th, 6th ribs. There was strong adhesion to the parietal pleura and ribs. Bleeding prevented the resection of a small portion of the tumor with fibrotic tissue.

The pathologic diagnosis was solitary fibrous tumor, low risk (total score 2/7: patient age>55 (score 1/1), tumor size (score 1/3), mitosis (score 0), tumor necrosis (score 0))

Solitary fibrous tumour (SFT) is a fibroblastic neoplasm with a characteristic histologic appearance, immunohistochemical profile, and NAB2-STAT6 gene rearrangement.
Most intrathoracic SFTs arise from the visceral pleura, but they may occur at any site, including within the lung parenchyma and pericardium. They rarely occur in the mediastinum.
SFTs are macroscopically well-circumscribed, solid, tan to grey homogeneous masses, frequently pedunculated and often large (>100mm). Cystic necrosis, haemorrhage, and calcification are occasionally present. In 3% of cases, no pleural attachment can be identified, and the tumour is surrounded by lung parenchyma. Tumours are uncommonly found to involve the pericardium.
On histopathology, SFTs have a distinctive morphology, with uniform fibroblastic spindle cells, varying cellularity, a patternless architecture, fibrosis, and branching staghorn vessels. There is a wide histopathological spectrum, ranging from paucicellular lesions with abundant stromal keloidal-type collagen to highly cellular tumours consisting of closely spaced cells with little or no intervening stroma. Myxoid change may be present.
By immunohistochemistry, SFTs are typically positive for CD34 and nuclear STAT6. Expression may be lost in dedifferentiated SFTs.
Most SFTs have low mitotic counts and show little nuclear pleomorphism. The presence of mitotic figures (greater than 10 per high power field), necrosis, infiltrative growth pattern and large size is associated with aggressive (malignant) behavior. Age above 55 years is also a risk factor.

Most SFTs grow slowly and form large masses, which could be asymptomatic or cause variable compression symptoms depending on the tumor size and location. Large SFTs are associated with paraneoplastic syndromes. Secretion of insulin-like growth factor 2 by the neoplastic cells may result in refractory hypoglycemia (Doege-Potter syndrome). More rarely, IGF2 production can produce an acromegaly-like syndrome. Thoracic lesions may be associated with hypertrophic osteoarthropathy.

Local or distant recurrence of SFTs has been documented in about 10–30% of cases with 10–40% of recurrences reported after 5 years from tumor resection. Recurrence after 15 years is rare. Metastases most commonly occur in the lung, but can also be found in the liver, brain and bones.

On MRI, SFTs show hypo to isointense signal on T1-WIs, and variable signal intensity on T2-WIs. The T2 signal variability is linked to the relative amounts of mature fibrous tissue and myxoid or cystic degeneration within the tumor. Tumors with predominance of collagen and fibroblasts have low signal on T2-WIs, while degenerated lesions present high T2 signal. SFTs are highly vascular and usually show intense heterogeneous enhancement after intravenous gadolinium administration. Linear or rounded hypo-enhancing areas can also be seen within the lesions and are attributable to hypovascular collagenous stroma.

The role of PET/CT in the differentiation of benign from malignant SFTs is not well established.

References

 Badawy, M., Nada, A., Crim, J., Kabeel, K., Layfield, L., Shaaban, A., Elsayes, K. M., & Gaballah, A. H. (2022). Solitary fibrous tumors: Clinical and imaging features from head to toe. European Journal of Radiology, 146, [110053]. https://doi.org/10.1016/j.ejrad.2021.110053
 Demicco, E.G., Wagner, M.J., Maki, R.G., Gupta, V., Iofin, I., Lazar, A.J., Wang, W.-L. (2017). Risk assessment in solitary fibrous tumors: Validation and refinement of a risk stratification model Modern Pathology, 30 (10), pp. 1433-1442.
 J.H. Choi, J.Y. Ro (2021). The 2020 WHO classification of tumors of soft tissue: selected changes and new entities Adv. Anat. Pathol., 28 (1), pp. 44-58, 10.1097/PAP.0000000000000284
 Solitary fibrous tumor of the thorax, p284-285 In: Thoracic Tumours. 5th ed. WHO classification of tumours series. 5. WHO Classification of Tumours Editorial Board. International Agency for Research on Cancer, Lyon, France 2021

Keywords