This case report demonstrates that EUS-FNA can be used as an effective and noninvasive modality for the diagnosis of a mediastinal schwannoma. Transthoracic imaging studies such as CT, magnetic resonance imaging, and positron emission tomography can define the exact location of the lesions and may narrow the differential diagnosis; however histological diagnosis is invariably required to establish the diagnosis of schwannoma. The diagnostic modalities available to obtain tissue for diagnosis in this clinical scenario include mediastinoscopy, CT-guided biopsy, video-assisted thoracotomy, EUS-FNA, and endobronchial ultrasound FNA. Among these, EUS-FNA is the least invasive test. In addition, the availability of Doppler ultrasonography during EUS-FNA also helps to minimize injury to the surrounding vascular structures during FNA of mediastinal lesions.
Although mediastinal schwannoma is not that uncommon, this is only the second case report demonstrating the diagnosis of this lesion by EUS-FNA [6
], suggesting that EUS is not often performed for this indication. By opting to undergo EUS-FNA as the diagnostic modality to obtain tissue from the mediastinal lesion, the patient avoided the complications associated with other more invasive procedures such as mediastinoscopy. In addition, EUS has the additional advantage of being an outpatient procedure. However, EUS is not a preferred technique to investigate the anterior mediastinum as the presence of air in the trachea decreases the resolution and quality of imaging.
There might be a concern for using EUS in this scenario as the amount of tissue obtained by FNA may not be adequate for cytologic interpretation, however most programs like ours have a bedside cytopathologist available who will guide endosonographers to perform enough FNA passes so that an adequate specimen is obtained to make a conclusive diagnosis. Immunostains can also be performed on the aspirate that further help to differentiate schwannoma from other mediastinal tumors. The specimens obtained by EUS-FNA are also not subject to artifacts from crush or cautery injury that are usually seen with samples obtained by other modalities like mediastinoscopy. The later phenomenon can make pathological interpretation difficult.
In conclusion, EUS-FNA should be offered to patients as a viable diagnostic modality for all accessible mediastinal lesions, including schwannoma. Potential complications from other invasive procedures can be avoided by opting to perform EUS for this indication. Studies comparing the efficacy and safety of EUS-FNA with other procedures for this indication such as CT-guided biopsy, mediastinoscopy or video-assisted thoracoscopic surgery are awaited.