Gusher syndrome is a rather rare condition complicating surgical interventions on the stapes. It is characterized by profuse effusion of perilymphatic fluid from the vestibule into the lumen of the tympanic cavity during fenestration or removal of the foot plate of the stapes and rapid filling of the volume of the tympanic cavity and the external auditory canal with perilymph. This is due to increased pressure of perilymph fluid in the inner ear cavity in some developmental anomalies. Preoperative diagnosis of gusher syndrome can be difficult when the CT scan does not show any abnormalities in the anatomy of the inner ear canal and inner ear structures. The rarity of this phenomenon greatly complicates the procedure of its study, as well as the development of optimal schemes of therapeutic and diagnostic tactics in a real clinical situation. A clinical case of a combination of congenital isolated middle ear developmental anomaly and gusher syndrome is studied. A patient with suspected otosclerosis underwent stapedoplasty at Saint-Petersburg Research Institute of Ear, Throat, Nose and Speech. During the operation, abundant perilymphorrhea "Gusher" symptom was obtained, as well as thickening of the stapes legs and thin tendon of the stirrup muscle were revealed. The postoperative diagnosis was changed from otosclerosis to congenital isolated anomaly of middle ear development (isolated ankylosis of the stapes), gusher syndrome. The tactics of management of a patient with otosclerosis and isolated middle ear anomaly are similar. CT of temporal bones and virtual CT endoscopy should become the standard of examination of patients before surgical treatment. The use of cartilage and supracartilage is a safe way to stop perilymphorrhea in patients with gusher syndrome.