An aneurysmal bone cyst (ABC) is believed to be attributable to intraosseous circulatory disturbance. An ABC is a vascular tumor of the bone caused by bony expansion after partial vascular occlusion and congestion. Most ABCs are found in adolescents (approximately 75% of ABCs are observed in patients under 20 years of age). The most common ABC sites are the long bones of the limbs, the vertebrae, and the cranial bone. Aneurysmal bone cysts in the skull base or ethmoid sinus have been but rarely reported worldwide. The authors report on a patient with a very large ABC in the skull base and the ethmoid sinus; this was successfully managed by a neurosurgeon.

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A malignant tumor of the external auditory canal (EAC) is a rare tumor, with a prevalence of between 1 and 6 people per 1 million population. Common symptoms of the EAC cancer include otorrhea, hearing loss, otalgia, or tinnitus, which are similar to symptoms of otitis media or otitis externa. Therefore, diagnosis may be delayed due to lack of EAC cancer-specific symptoms and the prognosis is also relatively poor despite intensive treatment. The most malignant tumor of the EAC is squamous cell carcinoma (SCC), which usully invades the ear unilaterally. SCC of bilateral EAC is extremely rare. We report here a rare case of bilateral EAC SCC. In this case, unilateral EAC SCC was treated via stereotactic radiosurgery and contralateral EAC SCC developed subsequently. This case implicates that radiosurgery can be a treatment option for EAC SCC but it may have carcinogenic effect. This case also shows that the ear should be examined bilaterally even when unilateral EAC cancer is encountered.