In recent years, petrositis and petrous bone abscess subsequent to mastoiditis are rare diseases. Masked mastoiditis is considered to be a “treatment failure” of acute otitis media. The infection in the mastoid can progress into another intratemporal and intracranial complications. We present a 12-year-old boy with petrous bone abscess due to masked mastoiditis. He complained of right otalgia, headache and spiking fever and received antimicrobial treatment for 3 weeks. Then he complained of right abducens nerve and oculomoter nerve paralysis. MRI and CT showed right mastoiditis and abscess formation in the petrous apex and paravertebral space. He received intravenous antimicrobial treatment (ceftriaxone and vancomycine) and surgery (mastoidectomy and ventilation tube insertion). Mastoid cells and antrum were full of inflammatory granulation tissues, causing a considerable block at the level of aditus ad antrum. He recovered and discharged in excellent condition within 2 weeks after the treatment. Masked mastoiditis is a threatening disease that requires clinical awareness. Immediate mastoidectomy must be performed for masked mastoiditis in cases with severe otogenic intratemporal and intracranial complications.
