[Silent mastoiditis in a 5-month-old infant].

We report the case of a 5-month-old female infant who developed a progressive unilateral retroauricular swelling without further symptoms in the first 5 months of life. The otherwise healthy infant was breast fed and had no history of previous otitis media. The clinical suspicion of silent mastoiditis was confirmed by CT scans and the intraoperative finding of an abscess due to Streptococcus pneumoniae. The onset is unusual, since mastoid pneumatization develops only after birth, and it is presumed that maternal antibodies should protect the infant from serious infections within the first months of life.