Perigastric solitary fibrous tumor (SFT) diagnosed on fine needle aspiration: A case report and review of literature.

Solitary fibrous tumor (SFT) is a mesenchymal tumor initially described in the pleura. When the tumor is located in the pleura and the classic histologic findings are present, the diagnosis of SFT can be straightforward. However, the cytologic diagnosis of perigastric SFT can be challenging due its rarity with only one cytology case report. Another confounding factor is its potential mimicry with other perigastric/gastric mesenchymal tumors. Herein, we report a case of perigastric SFT diagnosed on cytology in conjunction with immunohistochemical stains. The patient is a 79-year-old woman who presented with an enlarging perigastric mass on computerized tomography scan which was highly concerning for a saccular aneurysm. Endoscopic ultrasound (EUS) revealed a 6.6 cm hypoechoic lesion abutting the stomach. An EUS-guided fine needle aspiration was performed. The smears showed singly scattered to clusters of bland spindle cells with scant cytoplasm dispersed in a bloody background. The cell block showed similar spindle cells focally supported by a collagenized stroma. Immunohistochemical stains performed on the cell block showed the tumor cells were positive for CD34, BCL2, and STAT6 and negative for CD117, DOG1, CD31, ERG-ENDO, AE1/AE3, S-100, desmin, and synaptophysin, supporting the diagnosis of solitary fibrous tumor.