E1907. Extrapleural Solitary Fibrous Tumor, Essentially Anywhere!
  1. Alejandra Bonilla; National Institute of Cancer Diseases
  2. Marco Laura; National Institute of Cancer Diseases
  3. Flores Marycarmen; National Institute of Cancer Diseases
  4. Berenice Mayta; National Institute of Cancer Diseases
  5. Melany Pacheco; National Institute of Cancer Diseases
  6. Marcelo Alcalde; National Institute of Cancer Diseases
  7. Renier Cruz; National Institute of Cancer Diseases
Solitary fibrous tumors (SFTs) are uncommon, distinctive soft tissue neoplasms of pluripotent fibroblastic or myofibroblastic origin that may be benign or malignant (10 to 20%)1,2,3,4 The new OMS classification of soft tissue tumors now classifies most hemangiopericytomas as SFTs.2 Although SFTs were thought to predominantly involve the pleura, it is now established that SFTs can originate in virtually any site of the body, with extrapleural SFTs being even more common than pleural SFTs, in recent reports and recognized to have a wider range of clinical and radiological features. 2,3 Purpose: List the imaging findings of SFTs in the diverse extrapleural localization. Remarc the imaging characteristics and the role of imaging in diagnosis. Pathology-radiology correlation of SFTs in different localizations.

Educational Goals / Teaching Points
1. Solitary fibrous tumor is a highly vascularized defined mass. 2. It commonly occurs in the pleura, but can also occur extrapleural. 3. The larger the size, the higher the risk of malignancy. 4. CT: isodense to muscle with some hypodense areas representing necrotic, myxoid, or cystic changes, and MR: hypointense on T2 due to fibrous content. 5. CT and MRI moderate enhancement due to abundance of blood vessels.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Malignancy rate increases with size (usually >10 cm). However, a size less does not exclude malignancy. 3, 4. The most common extrapleural tumor sites are the orbits and extremities, other less frequent sites are the oral cavity, salivary glands, thyroid, larynx, trachea, spinal cord and intracranial meninges, liver, pancreas, adrenal glands, kidney, female genital tract, prostate, pelvis, spermatic cord, omentum, retroperitoneum, breast and periosteum of the bone. Immunohistochemical: CD34 is the most important marker. Generally, well-defined masses, tend to displace adjacent structures rather than invade them, highly vascularized tumors, infrequent calcifications. CT and MRI findings are generally not pathognomonic for the diagnosis. Larger tumors are isodense to muscle with some hypodense areas representing necrotic, myxoid, or cystic changes. On MRI, in the T2 sequence, hypointense lesions are related to hypercellularity and abundant collagenous stroma. Hyperintense lesions represent necrotic, myxoid, or cystic changes. Lesions show mild to marked heterogeneous contrast enhancement that correlates with hypocellularity or hypervascular areas.

SFTs are ubiquitous mesenchymal neoplasms, found predominantly in pleura and in a wide variety of extrapleural locations. The most commonly extrapleural sites are the head and neck region, abdomen, pelvis, and extremities. Findings on radiographs and CT scans or MRI alone are generally nonspecific for SFTs. MRI features include a well-circumscribed lesion, smooth margins, strong contrast enhancement, and the presence of fibrous contents which are hypodense on T2-weighted MRI imaging. Histologic and immunohistochemical studies are mandatory for the confirmatory diagnosis. Surgical excision is the treatment of choice for localized tumors. There is no established standard systemic therapy for metastatic disease.