Introduction: Ewing's sarcoma (ES) is an aggressive tumor occuring more frequently in childhood and adolescence, mainly observed during the first three decades of life. Microscopically consists of small round cells, with a high nuclear cytoplasmic index, originating from primitive neuroectodermal cells. Most often such tumor occurs in early childhood or adolescence. [1] Ewing's sarcoma refers to tumors of the bone tissue : the limbs, ribs, and pelvic bone, but also it may occur in soft tissues, which means any localization in the human body. Among extra-skeletal localities, ES rarely occurs in the head and neck (2-3% of all ES) and extremely rare in the nasal cavity or paranasal sinuses [1,2,3]. Diagnosis the primary of ES nasal localization is complex and mainly depends on histopathological research, as visual diagnostic methods (x-ray, CT, MRI) do not identify the type of tumor. MRI examination of tumors of such localization may suggest a malignant nature, so further differential diagnosis should exclude the following: malignant lymphoma, rhabdomyosarcoma, moderately differentiated carcinomas, and ES. These tumors have common radiological features, so they require additional research [4,5]. From abovementioned, the following clinical case of primary Ewing's sarcoma in the nasal cavity in a 14-year-old girl seemed to be interesting . The patient complained on the difficulty of breathing, swelling in the right half of the nose wing. MRI showed a large neopasm of the facial skull on the right (pterygoid and subterranean fossa, right half of the nose, nasopharynx, latticed bone and paranasal sinuses). Histological examination of the samples revealed a solid neoplastic tissue consisting of monomorphic small circular or oval cells with a high nuclear-cytoplasmic index. Some exapnsion of the tumor cells around the vessels was observed, while part of epithelial lining and glandular structures were preserved in the same places. Foci of necrosis and extensive hemorrhages were visualized. The immunohistochemical study with the CD99 antibody showed a total positive membrane reaction with the closure of the stained membranes ( with the presence of membranes ring staining ). The reaction with anti Fli1 revealed total nuclear staining of tumor cells, except for the stromal cells. Thus: as primary Ewing's sarcoma affects the sinus tract very rarely, diagnosis of the tumor in this location is difficult. MRI and other visual methods in these cases are not informative, because a number of tumors have common radiological features, that make the differential diagnosis very difficult. In this regard, the pathomorphological study including immunohistochemical research is the main method of diagnosing ES.

Introduction: Ewing's sarcoma (ES) is an aggressive tumor occuring more frequently in childhood and adolescence, mainly observed during the first three decades of life. Microscopically consists of small round cells, with a high nuclear cytoplasmic index, originating from primitive neuroectodermal cells. Most often such tumor occurs in early childhood or adolescence. [1]