[Marrow-tympanum connections in fetuses and infants]

The connections between hematopoietic bone marrow and the tympanum caused by bony dehiscences in immature middle ear were examined in 58 temporal bones of fetuses and infants. There were no anomalies in any of the cases, and they were divided into two groups: a group with inflammation of middle ear and a group without inflammation. The tympanic cavity was compartmentalized into thirteen portions to investigate the appearance of the connection, and the connections were classified into the mesenchymal type and the direct type dependent on residual mesenchyme in each portion. Marrow-tympanum connections were observed from 20 weeks of gestation until 14 months of age. In most cases the connections were the mesenchymal type. A large amount of mesenchyme remained in the inflammatory group. Some direct-type connections were observed in the non-inflammatory group from 1 month after birth onward and the mesenchyme was completely absorbed in these connections. Both types of the connections were frequently found in the antrum, facial recess and tympanic sinus. These results indicate that a marrow-tympanum connection is usually present in the temporal bone not only anomaly cases but also normal fetuses and infants. In addition, in normal cases without otitis media the connections first appear as mesenchymal type, and progress to direct type due to the absorption of mesenchyme. Presumably marrow-tympanum connections have structural disadvantage to induce osteomyelitis in cases with otitis media. And evoked osteomyelitis may cause complications such as acute mastoiditis and facial paralysis. The results of this study suggest that children under 2 years of age are at higher risk of complications of otitis media owing to marrow-tympanum connections than older children. Further study of the role of mesenchyme in otitis media is needed.