Residual mesenchyme persisting into adulthood

Purpose: (1) To detect the presence of residual mesenchyme in temporal bone s of adults and children above 5 years of age; (2) to evaluate its regressi on with increasing age, and; (3) to detect pathologic conditions associated with the presence of unresolved mesenchyme. Materials and Methods: We examined 1,404 human temporal bones of donors fro m 5 to 94 years of age for histopathologic evidence of mesenchyme. The pres ence of stellate (star-shaped) cells with interdigitating processes and lar ge nuclei embedded in a structureless ground substance was labeled as "pure mesenchyme." Temporal bones showing these features and focal areas of fibr osis, fibroblasts, and capillaries were classified as showing "transitional mesenchyme." Selected sections were stained with Gomori's trichrome. Patho logical features indicating otitis media and congenital anomalies of the ea r were also documented. Case histories were reviewed, and any otologic comp laints were noted. Statistical analysis was performed with the Chi-square t est, analysis of variance, regression analysis, and confidence interval. Results: Mesenchyme was found in 2.07% of temporal bones of patients from 5 to 81 years of age. Of these, 92.1% had transitional mesenchyme, whereas 7 .9% had pure mesenchyme. Seventy-six percent of the bones showed mesenchyme in the mastoid air cells. In all 3 bones with pure mesenchyme, it was pres ent in the round window niche. Otitis media was associated with residual me senchyme in 84.2% of the temporal bones. No pattern of regression of mesenc hyme with increasing age was observed in temporal bones from patients over the age of 5 years. Conclusions: Residual mesenchyme can be present in patients older than 5 ye ars of age and can persist into adulthood, especially in the mastoid air ce lls. Persistence of mesenchyme is closely associated with evidence of otiti s media. Copyright (C) 1999 by W.B. Saunders Company.