The Journal of Laryngology and Otology August 1999, Vol. 113, pp. 772-774 Radiology in Focus Monostotic fibrous dysplasia of the temporal bone J. XENELLIS, PH.D., A. BIBAS, M.SC, F.R.C.S.I., (OTOL)*, L. SAW, F.R.C.R.f, P. MARAGOUDAKIS, P. NOMICOS, PH.D. Abstract Fibrous dysplasia is a slowly progressive bony disorder where normal bone is replaced by abnormal fibro- osseous tissue. Its monostotic variety in the temporal bone is very rare and such a case is presented here. Computed tomography (CT) may be adequate for the diagnosis and follow-up of these patients. Limited surgery should only be considered in cases of symptomatic disease. Key words: Fibrous dysplasia, monostotic; Temporal bone Introduction Fibrous dysplasia is a slowly progressive, expansile bony dysplasia of unknown aetiology in which normal bone is replaced by abnormal fibro-osseous tissue. It may be monostotic or polystotic. Craniofacial involvement is found in only 10 per cent of cases of the monostotic variety, while monostotic fibrous dysplasia of the temporal bone is very rare (Brown et al, 1995). Case report A 47-year-old man presented with several months history of progressive hearing loss and tinnitus in the left ear. There were no other ear-related symptoms and his medical history was unremarkable. Otoscopy revealed a narrow left external ear canal and through it part of a normal looking tympanic membrane could be seen. Rinne was negative on the left side and Weber lateralized to the left. On clinical examination, a hard non-tender swelling was felt over the left pre- and post-auricular regions. The rest of the examination was normal. Pure tone audiometry demonstrated a 40 dB air-bone gap with a Caarharts notch at 2000 Hz. Impedance audiometry gave a type A tympanogram. A CT scan was obtained (Figure 1) which showed sclerosis and marked focal expansion of the left squamous temporal bone, with a 'ground glass' appear- ance, which is characteristic of fibrous dysplasia. A Tl- weighted magnetic resonance image (MRI) scan with gadolinium DTPA revealed expansion of the squamous temporal bone with loss of normal architecture of the cranial vault and diffuse low signal due to sclerosis. There is an enhancing extradurai component medial to the osseous mass, which indents the temporal lobe. This may represent a fibrous component. The left internal auditory meatus and the right temporal bone were normal (Figure 2). Biopsy of the lesion confirmed fibrous dysplasia of the temporal bone. Discussion Fibrous dysplasia is a relatively uncommon bone disease in which normal bone is replaced by abnormal fibro- connective tissue proliferation. Although its aetiology is FIG. 1 Fibrous dysplasia of the left temporal bone. Axial CT shows focal expansion of the squamous temporal bone and petrous base with sclerosis and a 'ground glass' appearance. Anteriorly the abnormality is limited by the sphenotemporal suture. There is minor bone encroachment on the attic, but not on the labyrinth or internal auditory canal. From the Departments of Otolaryngology - Head and Neck Surgery, Hippokration Hospital University of Athens, Greece, the University Hospital Lewisham* London and the Royal National Throat, Nose and Ear Hospitalt, London, UK. Accepted for publication: 26 April 1999. 772