olitary fibrous tumor (SFT) was first described as a primary spindle cell tumor of the pleura in 1931 and has been subsequently reported in extra-pleural sites. 1-4 Orbit is an uncommon location for SFT, where diagnosis is challenging and requires immunohistochemical analy- sis along with clinical, radiological and pathological evaluation. Besides, the nomenclature of specialized fibroblastic tumors of the orbit has changed recently. CD34 immunopositive fibroblastic neoplasms, which were previously classified as separate entities, are now comprised as SFT. 5 In this case report, we present a case of an orbital SFT treated with com- plete surgical excision. Turkiye Klinikleri J Ophthalmol 2017;26(3):219-22 219 An Uncommon Orbital Neoplasm: Solitary Fibrous Tumor: Case Report ABSTRACT The purpose of this case report is to present an intraconally located orbital solitary fi- brous tumor, an uncommon fibroblastic tumor of the orbit which has diagnostic challenges. A 33 years old female patient presented with three years of slowly progressive mass and proptosis of the left eye. Magnetic resonance imaging demonstrated a well-defined, strongly enhancing intraconal orbital mass. Histopathological and immunohistochemical analysis following en - bloc removal of the lesion revealed a mesenchymal tumor showing strong positivity for CD34 and Vimentin. The diagnosis was solitary fibrous tumor. Although uncommon, solitary fibrous tumor should be kept in mind in the differential diagnosis of a well-defined orbital mass associated with slowly progres- sive proptosis. Keywords: Exophthalmos; solitary fibrous tumors; antigens, CD34; immunohistochemistry; orbital neoplasms ÖZET Bu makalede, yavaş ilerleyici propitozisin az rastlanan bir sebebi olan intrakonal yerleşimli bir orbital soliter fibröz tümör (SFT) olgusunu sunmayı amaçladık. Otuz üç yaşında kadın hasta, sol gözünde 3 yıldır yavaş büyüyen kitle ve proptozis şikayeti ile başvurdu. Magnetik rezonans gö- rüntülemede, iyi sınırlı, yoğun kontrast tutan intrakonal kitle tespit edildi. Kitle lateral orbitotomi yoluyla bütünüyle eksize edildi. Çıkarılan 31x31x35 mm boyutlarındaki kitle, immunohistokimyasal analizi de içeren histopatolojik inceleme sonucunda, güçlü CD-34 ve Vimentin pozitifliği gösteren mezenkimal tümör olarak tanımlandı. Bu bulgular ışığında olguya benign orbital SFT tanısı ko- nuldu. Yavaş ilerleyici proptozise sebep olan iyi sınırlı orbital kitlelerin ayırıcı tanısında SFT akılda tutulmalıdır. Anahtar Kelimeler: Ekzoftalmus; soliter fibröz tümörler; antijenler, CD34; immünohistokimya; orbita neoplazileri Okan TOYGAR, a Levent AKÇAY, b Özge YABAŞ KIZILOĞLU, a Baha TOYGAR, a Özlem YAPICIER, c Mustafa Kemal DEMİR d Departments of a Ophthalmology, c Pathology, d Radiology, Bahçeşehir University Faculty of Medicine, b Clinic of Ophthalmology, Dünyagöz Research Hospital, İstanbul Geliş Tarihi/Received: 23.10.2015 Kabul Tarihi/Accepted: 23.01.2016 Yazışma Adresi/Correspondence: Özge YABAŞ KIZILOĞLU Medical Park Göztepe Hospital, Clinic of Ophthalmology, İstanbul, TÜRKİYE/TURKEY ozgeyabas@hotmail.com This case report has been presented as a poster at the 48 th Meeting of the Turkish Ophthalmology Society, 5-9 November 2014, Antalya. Copyright © 2017 by Türkiye Klinikleri OLGU SUNUMU DOI: 10.5336/ophthal.2015-46936