Facial palsy and Valsalva-induced vertigo in a patient with temporal bone cystic fibrous dysplasia

•Cystic Polyostotic FD can erode middle and inner ear structures.•In an FD patient with Valsalva-induced vertigo, a labyrinthine fistula through cystic degeneration should be considered.•Cystic FD is diagnosed through GNAS1 detection in a cyst wall biopsy.•Differential diagnoses for cystic FD are aneurysmal bone cyst and telangiectatic osteosarcoma.•Treatment of cystic FD consists of surgical removal of as much cyst as possible.