en علوم پایه پزشکی Basic medical sciences گزارش مورد Case report <h3 style="text-align: justify;"><strong>Background:</strong> Thymic epidermoid cysts are very rare. These masses arise from migration of ectodermal cells into the tissue that does not contain these cells. The imaging findings are non-specific and surgical excision is required to reach definitive diagnosis.</h3> <h3 style="text-align: justify;"><strong>Case description:</strong> We describe an asymptomatic woman in her early 40s with an anterior mediastinal mass detected in the spiral chest CT scan for COVID 19. She underwent thymectomy and the histopathological exam revealed a dermoid cyst in thymus gland.</h3> <h3 style="text-align: justify;"><strong>Conclusion: </strong>The dermoid cysts etiology is unknown and there are many unproven theories. The clinical sign, symptoms and location of the cyst can be variable. Our case was asymptomatic and the cyst was accidently found in the imaging. The initial diagnosis was a thymoma and at the patient&rsquo;s insistence, cystectomy was performed and pathological findings indicated a thymic dermoid cyst.</h3> Dermoid cyst, Histopathology, Mediastinal mass thymus 13 16 http://jcbr.goums.ac.ir/browse.php?a_code=A-10-208-3&slc_lang=en&sid=1 Reza Afghani af_med75@yahoo.com 10031947532846003140 10031947532846003140 Yes School of Medicine, Golestan University of Medical Sciences, Gorgan, Iran Roozbeh Cheraghali 10031947532846003141 10031947532846003141 No School of Medicine, Golestan University of Medical Sciences, Gorgan, Iran Mahshid Mehrjerdian 10031947532846003142 10031947532846003142 No Department of Pathology, School of Medicine, Golestan University of Medical Sciences, Gorgan, Iran Hanieh Raghimi 10031947532846003143 10031947532846003143 No School of Medicine, Golestan University of Medical Sciences, Gorgan, Iran Sina Mohajernoei 10031947532846003144 10031947532846003144 No School of Medicine, Golestan University of Medical Sciences, Gorgan, Iran