Clinical Correlates

Deafness and External Ear Abnormalities

Congenital deafness, usually associated with deaf-mutism, may be caused by abnormal development of the membranous and bony labyrinths or by malformations of the auditory ossicles and eardrum. In the most extreme cases the tympanic cavity and external meatus are absent.

Most forms of congenital deafness are caused by genetic factors, but environmental factors may also interfere with normal development of the internal and middle ear. Rubella virus, affecting the embryo in the seventh or eighth week, may cause severe damage to the organ of Corti. It has also been suggested that poliomyelitis, erythroblastosis fetalis, diabetes, hypothyroidism, and toxoplasmosis can cause congenital deafness.

External ear defects are common; they include minor and severe abnormalities (Fig. 16.11). They are significant from the standpoint of the psychological and emotional trauma they may cause and for the fact they are often associated with other malformations. Thus, they serve as clues to examine infants carefully for other abnormalities. All of the frequently occurring chromosomal syndromes and most of the less common ones have ear anomalies as one of their characteristics.

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