Discussion

Osteomas of the temporal bone are infrequent, slow-growing, benign tumours that are commonly observed in the external ear canal. However, middle-ear osteomas, usually asymptomatic and incidentally detected, are an extremely rare entity. Osteomas of the temporal bone occur predominantly in males and younger patients, as in our case.^{Reference Molher, Pujol, Zounon, Darrouzet and Bonnard1} Although the aetiology of osteomas still remains unclear, genetic factors, embryological developmental disorders and chronic inflammation have also been proposed to play a role in osteoma formation.^{Reference Abouzayd and Seghir2} Middle-ear osteomas usually occur in patients with no previous history of ear surgery or trauma, with normal otoscopy findings, and are incidentally diagnosed in patients without any symptoms.^{Reference Silver, Orobello, Mangal and Pensak3} Osteomas of the middle ear present symptoms according to their involvement site when they reach a certain size. Curtis et al. reported a case of middle-ear osteoma that caused House–Brackmann grade IV facial nerve dysfunction that improved to House–Brackmann facial nerve dysfunction grade II after surgery.^{Reference Curtis, Bance, Carter and Hong4} Conductive or mixed hearing loss is the most frequently presented symptom of middle-ear osteomas.^{Reference Molher, Pujol, Zounon, Darrouzet and Bonnard1,Reference Yuan, Chen, Jiang and Zhang5}

In most cases, osteoma diagnosis is established according to high-resolution CT findings. Histopathological confirmation is possible by examining the specimen intra-operatively in symptomatic cases. The classic histopathological view of osteomas contains few osteocytes or lacunae and includes an excess of fibrovascular channels covered by lamellar bone tissue.^{Reference Yoon, Yoon and Lee6} Temporal bone high-resolution CT is the preferred radio-diagnostic modality in the diagnosis of middle-ear osteomas.^{Reference Silver, Orobello, Mangal and Pensak3} Moreover, high-resolution CT is very helpful in detecting the localisation and boundaries of tumours and identifying whether or not there is ossicle or facial nerve involvement. Surgical approach and ossiculoplasty techniques may be planned pre-operatively according to high-resolution CT findings.^{Reference Curtis, Bance, Carter and Hong4}

Because middle-ear osteomas exhibit an extremely low growth rate, surgery is not recommended in asymptomatic cases. Follow-up with otoscopic examination and temporal bone high-resolution CT scans is recommended in asymptomatic patients.^{Reference Silver, Orobello, Mangal and Pensak3} Surgery is indicated when findings associated with middle-ear osteoma become symptomatic. On the other hand, Yoon et al. advocated that surgical treatment of the asymptomatic middle-ear osteomas incidentally detected on CT scans should be performed due to potential complications later in life, including facial nerve paralysis, sensorineural hearing loss and vertigo.^{Reference Yoon, Yoon and Lee6}

So far, to the best of the author's knowledge, only two cases of middle-ear osteoma involving the stapes have been reported. Yuan et al. reported a case of middle-ear osteoma originating from the stapes that caused conductive hearing loss. They reported that the air–bone gap improved after ossiculoplasty using titanium prosthesis following the removal of the osteoma with stapes.^{Reference Yuan, Chen, Jiang and Zhang5} Vérillaud et al. reported a conductive hearing loss due to middle-ear osteoma involving the stapes and incus that improved post-operatively.^{Reference Vérillaud, Guilleré, Williams, El Bakkouri and Ayache7} In this study, it was fortunate that the osteoma that was only limiting stapes mobility had originated from the promontory and was not invading the stapes or other middle-ear structures. Therefore, the meticulous removal of the osteoma arising from promontory without performing ossiculoplasty was sufficient in the treatment of conductive hearing loss in this case.