Several radiographic mimics of subarachnoid hemorrhage (SAH) have been reported. The pseudosubarachnoid sign may be seen in patients with marked hypoxic–ischemic injury. Our case was a 12-year-old boy with a known history of autism spectrum disorder. He was submersed in water for 20 minutes, after diving into a river, and brought to our emergency department where resuscitation was performed. He achieved a return of spontaneous circulation 45 minutes after the accident but was in a coma. Brain computed tomography showed severe brain edema and loss of sulci with increased attenuation of the basal cisterns that was compatible with SAH, but was later revealed as the pseudosubarachnoid sign. In this case, the misdiagnosis of SAH had several clinical implications for the management of the patient. This could have clinical implications if a patient with the Glasgow Coma Score greater than 3 were inappropriately treated for SAH. Furthermore, there are possible medical–legal implications regarding child abuse with SAH misdiagnosis.