Diagnosis of Mediastinal Schwannoma With Endoscopic Ultrasound-Guided Fine Needle Aspiration

Abstract

Introduction: Endoscopic Ultrasound (EUS) is a minimally invasive modality that can be used for the evaluation and diagnosis of most mediastinal lesions. We present here an uncommon use of EUS and fine needle aspiration (FNA) for the diagnosis of a mediastinal Schwannoma. Case: A 66 y/o man with newly diagnosed prostate cancer underwent CT scan of the chest and abdomen for staging which revealed a 2.5 cm mass in the lower mediastinum. Evaluation by linear scanning EUS revealed a 35mm x 29mm, partially cystic heterogeneous mass adjacent to the distal esophagus and FNA was performed. Four passes were made with a 22 gauge needle under doppler guidance. No other lesions were identified and patient tolerated the procedure well. Cytopathology revealed bland spindle cells that stained positive for S-100 but negative for CD117, Actin and Desmin which is consistent with a Schwannoma. Discussion: Schwannomas are the most common neurogenic mediastinal tumors arising from peripheral nerves. They are typically slow-growing, benign and asymptomatic. They are generally found incidentally on imaging. Imaging may reveal calcifications, cysts and hemorrhage. It is important to differentiate Schwannomas from other mediastinal tumors. Resection is the treatment of choice as they could grow over time and also because of low risk of malignant transformation. The esophageal relationship with the surrounding structures makes EUS-FNA an ideal diagnostic tool for mediastinal tumors. The use of doppler allows for avoidance of blood vessels and safe FNA of lesions. EUS-FNA has been shown to be 97% sensitive and 100% specific for malignant mediastinal lesions1; benign lesions can also be accurately diagnosed. Conclusions: To our knowledge, there have been only two previously reported cases utilizing EUS-FNA for the diagnosis of a mediastinal schwannoma2,3. Most mediastinal lesions are easily and safely accessible with EUS-FNA and the modality has high diagnostic accuracy. This approach should be considered before more invasive mediastinoscopy is perfomed for diagnosis.