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.Fibrous dysplasia (FD) is a benign entity in which normal bone is replaced by immature bone and fibrous tissue, caused by mutations in the Gs-α gene. It is not commonly seen in the temporal bone. Patients with temporal bone FD often present with painless swelling or hearing loss, usually secondary to ear canal deformities or ossicular involvement. Different types of FD are known, differentiated by extent of disease, such as monostotic, polyostotic and McCune-Albright syndrome, or by radiological presentation, such as pagetoid, sclerotic and cystic. FD affecting the labyrinth or fallopian canal is rare, with only a few cases reported in literature of each. We present the unique case of a patient with both facial palsy and labyrinthine fistula caused by polyostotic cystic temporal bone FD.Right cortical mastoidectomy revealed spongeous bone, of which a sample was sent for histopathology.

A cystic lesion was encountered, which encroached the lateral semi-circular canal, the facial nerve and posterior dura. Incision caused clear yellowish fluid to leak out. A biopsy was taken from the wall of the cyst. The facial nerve was identified in the middle ear and followed towards the mastoid, where it was not possible to divide the cyst wall from the facial nerve. Part of the cyst wall was removed, resulting in an opening in the cyst of 20 × 8 mm. The dehiscent part of the posterior semi-circular canal could not be identified because of the cover by the cyst wall. Because it was deemed to hazardous for the inner ear to remove this last layer, it was decided perioperatively to apply bone dust and fibrin sealant on the expected site of dehiscence. This was further covered with temporal fascia.

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Mishita
Jornal co-ordinator
Journal of Bone Research and Reports