Sensorineural Hearing Loss Caused by Carbon Monoxide Poisoning―A Case of Unilateral Hearing Loss with an Arachnoid Cyst―

Abstract

　Carbon monoxide (CO) poisoning is one of the rare causes of hearing loss. The affinity of CO for hemoglobin is about 200 times higher than that of oxygen. Therefore, the hypoxemia associated with CO poisoning can potentially cause disorders in various organs and can be fatal. Our patient reported herein was a 52-year-old woman working in an ice cream factory who had never previously been diagnosed as having deafness. Incomplete combustion of an ice cream stirrer at the workplace caused the employees to develop consciousness disturbance. She was taken to an emergency room and was diagnosed as having CO poisoning based on the history of exposure to CO and other history/examinations, etc. She complained of hearing loss in the left ear on the day after she was hospitalized. Various examinations, including the test for auditory brainstem response, revealed that the hearing loss was sensorineural hearing loss and possibly arose from an inner ear disorder. MRI showed an arachnoid cyst on the right side, in front of the medulla oblongata, which seemed to be compressing the vertebral artery and the internal auditory artery. The possibility of this anatomical abnormality leading to inner ear resistance to hypoxia was considered. Previous reports about unilateral hearing loss by CO poisoning have not included the results of anatomical imaging examinations, e.g. CT, MRI, and so on. To understand the mechanism of hearing loss caused by CO poisoning, we wish to emphasize the need for thorough anatomical and physiological studies.