A Case of Mediastinal Vagal Schwannoma Diagnosed by EUS-FNA

Abstract

Purpose: Schwannomas, also known as neurilemmomas, are peripheral nerve sheath tumors that arise from any nerve in the body although they most commonly occur in the soft tissues of the head and neck, as well as extremities. Schwannomas originating from the vagus nerve are extremely rare, accounting for only 2% of all mediastinal neurogenic tumors. Typically vagal schwannomas are asymptomatic but at times present with hoarseness, chest pain, or cough. We present a case of a paraesophageal vagal nerve schwannoma that was diagnosed incidentally during workup of a patient with abdominal pain. Case Report: A 36-year-old male presented with right upper quadrant abdominal pain. Initial labs and abdominal ultrasound were non diagnostic. EGD showed mild gastritis and a bulge at the GE junction. Radial EUS revealed a 3.7 cm × 2.5 cm hypoechoic paraesophageal mass best seen from the GE junction. Linear EUS with FNA showed spindle cells mixed in fascicles in a loose stroma. The spindle cells were strongly positive for S-100 protein and negative for CD34, DOG-1, desmin, smooth muscle actin and CD 117c (C-kit). These findings were consistent with a schwannoma. CT scan of abdomen showed no other masses or lymph nodes. On laparoscopy it was found to be stemming from the right vagus nerve. A segment of the vagus nerve with the mass was resected in its entirety. Histopathological evaluation confirmed the diagnosis and showed no invasive component and no mitotic activity. Discussion: Although there have been case reports describing schwannomas it is often not considered in the differential diagnosis of mediastinal masses. They are often misdiagnosed as GISTs or leiomyoma. They lack specific features on Ultrasound, CT and MRI and hence we depend on pathology to make the diagnoses. With FNA capabilities EUS has emerged as an excellent tool to make the diagnosis. Some authors on EUS have identified a marginal halo in schwannomas. They also suggest that its echogenecity is much lower than the normal surrounding muscle layers. The marginal halo corresponds to a lymphoid cuff that is often present in this tumor (1). These findings if present and if validated by more cases may be useful to differentiate schwannomas from GISTs or leiomyomas. Although they are very rare, schwannomas of the vagus nerve should be included in the differential diagnosis of mediastinal masses, together with other neurogenic tumors, lymphomas, cystic lesions and esophageal tumors.