Diaphragmatic Schwannoma Mimicking Hydatid Cyst Depicted by FDG PET/CT

摘要

Schwannoma is generally a benign, slow-growing, encapsulated tumor originating from the nerve sheath most commonly located in the head and neck regions and extremities. Present study aimed to report FDG PET/CT findings of an extraordinary located schwannoma arising from the right diaphragm. Thoracic CT of a 39-year-old male showed an encapsulated, well-defined round, heterogenous cystic lesion on the right hemithorax which was falsely diagnosed as a hydatid cyst. FDG PET/CT was requested for the metabolic characterization of this mass and revealed mild to moderate hypermetabolism at the solid components of this lesion. Surgical excision was performed and histological examination revealed schwannoma. INTRODUCTION Schwannoma is a benign tumor that originates from the Schwann cells surrounding peripheral and cranial nerves. It has a predilection for the head and neck and ?exor surfaces of the upper and lower extremities (1).Schwannoma most frequently present in patients aged 20 to 50 years, more frequently in men than in women (2). They comprise 5% of all benign soft tissue tumours (3). Schwannoma of the chest wall and diaphragm are rare. Schwannoma is often found incidentally or present with vague, non-speci?c symptoms. This benign tumor is almost invariably slow growing, non-aggressive neoplasm and it is solitary in the vast majority of cases. Of 5% to 18% schwannomas are associated with neuro?bromatosis type I (4), in which case lesions may be multiple and often plexiform. Malignant transformation is very rare. On gross appearance, schwannoma is usually seen as solitary, well circumscribed, encapsulated lesion (5). The definitive diagnosis remains histologic. Histologically, typical schwannomas are composed of intermixed Antoni A components (cellular and arranged in short bundles or interlacing fascicles) and Antoni B areas (less cellular and organized with more myxoid components). The cellular variant (which includes most large retroperitoneal and pelvic schwannomas) has a uniform spindle cell appearance without Antoni A or B areas. Characteristically, all schwannomas show uniform and intense staining for S100 protein (6). It is important for the radiologist to consider the diagnosis of benign schwannoma when presented with a retroperitoneal or pelvic mass, to avoid unnecessary surgery, because these lesions can be managed conservatively (3). In this case report we aimed to report FDG PET/CT findings of an extraordinary located schwannoma arising from the right diaphragm. CASE REPORT A 39-year-old man suffered from cough and sputum was referred to the outpatient clinic of chest medicine. Diagnostic computed tomography (CT) was performed. It showed encapsulated, well-defined, round, heteregenous cystic soft tissue mass that arised from the right diaphragm. The lesion was measured approximately 10 cm in diameter and extended from right dome of the diaphragm to superior pole of the right kidney. Since Turkey is an endemic country for Echinococcus infestation, it was initially misdiagnosed as a hydatid cyst according to its CT pattern. F-18 flourodeoxyglucose (FDG)PET/CT was requested to exclude possible malignancy. (A) Axial, (B) coronal, (C) saggital PET, CT and combined PET/CT images demonstrated mild to moderate FDG uptake [maximum standardized uptake values (SUVmax): 4,1] at the solid components which were located in the peripheral and central zones of this cystic lesion.The total resection was perfomed and histological examination revealed a benign schwannoma.