Extracanalicular Osteoma of the Mastoid Region of Temporal Bone-A Rare Presentation

Introduction Osteomas of temporal bone are rare, slow growing bone forming tumors (1, 2). The mastoid area of temporal bone is the most common site for extra-canalicular osteoma followed by squamous area and internal auditory canal (1, 2). These tumors are most often found in postpubertal age and occur more commonly in women (1-4). They mostly present as cortical lesion giving rise to cosmetic deformity. When located in mastoid region, they are solitary, sessile or pedunculated and normally present as extra-cranial growth (3). Our patient presented to us as a unique case of mastoid osteoma in a young adult male that was causing headache as patient was myopic and he had problems in wearing glasses. He also wanted to get it operated for cosmetic reasons. Case Report A 19 year old adult male presented to our tertiary care institute with a painless gradually progressive swelling in the left post-auricular area for 6 years (Fig 1). Swelling was gradually increasing in size and now had reached to a size of approx. 3 cm x 3cm. Since swelling was covering whole of the post-auricular region of temporal region, patient used to have headache as he was myopic and had problems while wearing spectacles. Patient wanted this swelling to be removed for cosmetic reasons also. On examination, the swelling was smooth and bony hard in nature; it was attached to the mastoid part of the temporal bone and the skin over the swelling was normal. Detailed ENT examination was done and it was unremarkable. Seventh and eighth cranial nerves were normal on clinical examination. We ordered axial and coronal cuts of high resolution CT scan of temporal bone to know the nature of swelling and its possible intracranial extension and to assess whether the swelling is isolated or multiple. On CT scan, the swelling appeared to arise from cortex of the bone and the swelling had inner fibrous core with outer bony covering (Fig 2). The CT scan findings were characteristic of osteoma. The patient was fully investigated and the posted for removal of post-auricular swelling under general anaesthesia. Skin incision was made and periosteal flap was elevated over the swelling. Tumor was freed all around of the periosteal flap and the tumor was removed enbloc using chisel and hammer. The residual margins were smoothened with the help of drill and the defect was covered with surgicel hemostat. The incision was closed in two layers and pressure dressing applied. The excised specimen was sent for histopathological examination. On microscopy, the tumor sections showed mature lamellar bone surrounded by fibro-collagenous tissues consistent with the findings of compact osteoma. Patient is on regular follow-up for last 4 months now and is asymptomatic till date. Discussion Temporal bone osteomas are slow growing tumors whose exact etiology is still not known (5). Probably, they arise from preosseous connective tissues, most often localized at the suture line (6). A variety of theories inciting Abstract Extracanalicular temporal bone Osteomas are rare slow growing benign bone tumors of lamellar bone.Osteomas are commonly found in fronto-ethmoid region. In the temporal bone, they mostly occur in canalicular portion (EAC), but are very rare in extracanalicular portion of temporal bone. They are mostly asymptomatic and treatment is required mostly for cosmetic reasons. We report here an isolated case of extracanicular osteoma of temporal bone due to its rarity in world literature and unusual site of presentation.