© Georg Thieme Verlag KG Stuttgart · New York
Endoscopic ultrasound-guided fine-needle aspiration for the diagnosis of retroperitoneal schwannoma
26 November 2010 (online)
Schwannoma is a rare peripheral nerve sheath tumor that is difficult to diagnose by imaging features alone. Endoscopic ultrasound (EUS)-guided fine-needle aspiration (FNA) with specific immunohistochemical (IHC) staining may be the only tool to obtain a diagnostic sample from such lesions. There are only a few case reports describing EUS-FNA diagnosis of retroperitoneal Schwannoma  . In this report, we describe four cases (three males; mean age: 54.5 ± 16.4 years) with retroperitoneal Schwannoma, in whom the diagnosis was achieved with EUS-FNA and adjunctive IHC staining.
All lesions were well demarcated, and had a rounded contour ([Fig. 1 a]).
Fig. 1 Imaging findings and histopathological features. a Contrast enhanced computed tomography (CT) scan showing well-demarcated low density mass in the retroperitoneal region. b Endoscopic ultrasound image showing a fine needle inserted into the mass (arrow). c Spindle cells on cellblock sections, without any mitosis (hematoxylin and eosin stain, original magnification × 400). d Immunohistochemical S-100 positive staining (magnification × 400).
The mean size of the lesions on EUS was 23.7 ± 3.6 mm. EUS-FNA was successfully performed with a 22-gauge needle in all cases ([Fig. 1 b]), with a sufficient yield for both cytological and cellblock analysis. The median number of needle passes was 2.5 (range 2 – 3). The cellblock analysis revealed bland proliferation of spindle cells with a palisading appearance and wavy fibrillar architecture ([Fig. 1 c]). Further evaluation with IHC revealed negative staining for actin, CD34, CD-117, and strong positive staining for S-100 antibody in all cases ([Fig. 1 d]). Further evaluation of the cellular proliferative activity was studied with Ki-67 staining, and a low proliferation rate (Ki-67 < 5 %) was reported in all cases, supporting the benign nature of the lesions.
We recommended conservative follow-up for our patients rather than surgical resection, because all of the patients were asymptomatic and there were no mitotic figures on FNA, with a low Ki-67 index in all the aspirates. It is worth noting that most reports have stressed on complete surgical resection as the appropriate management of retroperitoneal schwannomas  . Our view is that the morbidity associated with surgical resection is not justified in these benign lesions, and the use of EUS-FNA to establish the diagnosis may help in avoiding unnecessary surgery.
Competing interests: None
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Department of Gastroenterology
Aichi Cancer Center Hospital