Depends on the topic of the case report, but many top psychiatry journals should have special submissions for case reports, case series, and brief reports
I'd recommend you Neurocase, which is a peer-reviewed journal specializing in case studies in the neuropsychology, neuropsychiatry and behavioral neurology of adults and children.
You can submit your case reports in BMJ case reports section or BMC Psychiatry journal (of Biomed Central); both of these are Pubmed indexed. if you need any further help/assistance with your article then do let me know.
There many high impact journals that publish interesting or unique case reports, especially those that lead to hypotheses about mechanisms, which can subsequently be tested in proper trials. You do, however, need the written consent of the person whose case is being presented or, should the person be a minor or be decisionally incompetent, the written consent of parent or guardian.