Solitary Fibrous Tumor

Shital Rajni Shah, MD - Case Coordinator
Donnella S Green, MD - Radiology Discussion
Fabiola Medeiros, MD - Pathology Discussion
Pablo R Ros, MD, MPH - Attending Radiologist
Steven E Seltzer, MD - Attending Radiologist

February 24, 2003

Presentation

Imaging Findings

Pre-biopsy, non-contrast axial CT through the upper pelvis demonstrates a large soft tissue mass displacing the bowel loops. There is one focal area of lower attenuation, perhaps representing fat.

Pre- and post-contrast sagittal MR images of the pelvis show that the lesion is homogeneously slightly hyperintense to muscle. Pre- and post-contrast coronal images demonstrate hyperintensity on T1. This is likely a bladder or prostate lesion.

Differential Diagnosis

Diagnosis

Discussion

The specimen consists of a large (13 cm), well circumscribed, firm mass attached to the posterior serosal bladder wall. The mass does not invade the bladder. The gross appearance suggests a benign lesion. The low-power view of the cells shows a variegated appearance caused by the mixture of hypercellular and hypocellular areas. The cells are bland and spindle with associated characteristic collagen fibers. The sample was strongly positive for CD-34, which supports the diagnosis of solitary fibrous tumor.

Radiology Discussion

The differential diagnosis for bladder filling defects includes:

• Malignant tumors (Primary bladder tumor, metastasis [e.g., prostate, uterus, cervix, colon])
• Benign bladder neoplasms (leiomyoma, fibroepithelial polyp, hemangioma, adenoma, pheochromocytoma)
• Blood clot
• Edema (adjacent to calculi)
• Ureterocele
• Enlarged prostate gland
• Muscular wall hypertrophy
• Post-operative change
• Endometriosis
• Fungus ball

Solitary fibrous tumors are likely of either mesothelial cell origin or fibroblast/primitive mesenchymal cell origin. The most common locations for these tumors are the pleura and mediastinum. Other reported locations include the abdominal cavity, parotid gland, pericardium, ovary, liver, intestine, lung, orbit, upper respiratory tract, bladder and periosteum. The unifying characteristic of solitary fibrous tumors is positive staining for CD-34, resulting from the spindle cells. Cases have been reported in patients from 9 to 86 years of age (average age: 57 years) and appear to be nearly evenly distributed between males and females.

CT is useful for assessment of pelvic sidewall, adjacent viscera, and evaluation of lymphadenopathy; it is limited in differentiating post-operative or post-radiation change vs. tumor. CT staging is 75% accurate.

MR is better than CT for staging and for evaluation of bladder base or dome tumors. T2 sequencing is effective for evaluating the urine-bladder wall interface, while T1 shows the interface between the bladder and perivesical fat. Gadolinium helps assess small tumors.

References

Zotalis G, Hicks DG. Solitary fibrous tumor of the soft tissues. Archives of Hellenic Pathology. 11(3), 1997.

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