Alveolar soft-part sarcoma in paranasal sinuses

Abstract

Objective To investigate clinicopathological features, immune phenotype, diagnosis and differential diagnosis of alveolar soft-part sarcoma (ASPS) in paranasal sinuses. Methods Retrospective study of clinical manifestations, histopathological features and immunohistochemical features was conducted in one case of ASPS in paranasal sinuses.  Results A 28-year-old female presented with bulging forehead for 2 months. MRI revealed a well-circumscribed lesion in left frontal and ethmoid sinuses extending to anterior skull base that showed slightly hyperintense signal on T₁WI and hypointense signal on T₂WI without obvious enhancement after contrast administration. The patient subsequently underwent endoscopic open surgery on left ethmoid and bilateral frontal sinuses and performed partial resection of the lesion. Three months after the initial surgery, the patient received reoperation for total removal of residual lesion and reconstructive surgery of anterior skull base. Adjuvant chemotherapy and radiotherapy were not administered. Histologically, the tumor was composed of epithelioid cells arranged in organoid nests and/or alveolar structures varying in size and shape, which were separated by connective tissue richly containing sinusoidal vascular channels. The tumor cells were generally large-sized, round, oval or polygonal with abundant eosinophilic granular or translucent vacuolated cytoplasm. The nuclei showed round or oval shape containing centrally placed and obvious nucleoli. The presence a lot of mono- or multi-nuclear giant cells served as another striking feature. Mitotic activities were rare. Reticular fiber staining indicated that reticular fibers surrounded the nest of tumor cells, and diastase-resistant periodic acid-Schiff (PAS)-positive crystalline inclusions were identified within the cytoplasm of tumor cells. Immunohistochemically, the tumor cells were reactive for TFE3, while were negative for glial fibrillary acidic protein (GFAP), melanophore markers [HMB45, Melan-A and S-100 protein (S-100)], and epithelial markers [cytokeratin (CK) and epithelial membrane antigen (EMA)]. Ki-67 labeling index was low (2%). The patient remained well without recurrence 15 months after the second surgery.  Conclusions ASPS is a rare malignant tumor that tends to occur in adolescents. The tumor is predominantly located in deep soft tissues, such as legs and buttocks. ASPS of paranasal sinus and/or extending to skull base is extremely rare. The accurate diagnosis of ASPS mainly depends on histological and immunohistochemical features, and should be considered in differential diagnosis including the similar morphological pattern of primary or metastatic neoplasms. ASPS is characterized by ASPL-TFE3 gene fusions, and TFE3 protein is a specific marker for ASPS which displays nuclear labeling with TFE3 by immunohistochemistry.

DOI: 10.3969/j.issn.1672-6731.2015.07.012