Neonatal mesenchyme temporal bone study: typical receding pattern versus increase in Potter's sequence.

The fate of mesenchyme, which lines the fetal and newborn bony middle ear, is not well understood. The authors wished to test previous observations that a greater amount of mesenchyme was found in Potter's sequence (renal anomalies, pulmonary hypoplasia, and oligohydramnios). Using celloidin-embedded neonatal temporal bones (68 cases, 123 ears), with clinical and autopsy information, middle ear volumes were compared among diagnostic groups using analysis of variance. In 16 ears of Potter's sequence cases the volume of mesenchyme increased in proportion to the size of the middle ear. Conversely, in all other cases the volume of mesenchyme remained constant compared to increasing middle ear size. Both the volume of the bony middle ear and the volume of the air cavity increased at 15 mm3/500 g of body weight (gbw). Mesenchyme percentage decreased by 2%/500 gbw. Middle ear mesenchyme appears to recede rather than reabsorb. However, in Potter's sequence cases the volume of mesenchyme increases, raising issues of a missing renal signal that inhibits mesenchymal growth under normal circumstances.

Chronic ear pathology in a model of neonatal amniotic fluid ear inoculation.

Human histopathologic studies have demonstrated that amniotic fluid cellular contents, keratinized squamous epithelial cells and lanugo hair, induce an intense inflammatory reaction including granulation tissue in the neonatal temporal bone. To investigate this reaction over a prolonged period, an animal model was studied. An aliquot of sterilized autologous hair and keratinized epithelial cells was placed into 14 gerbil bullae; saline was used as a contralateral control. The animals were sacrificed at intervals up to 6 months and the temporal bones were studied by light microscopy. All animals demonstrated nonpurulent inflammatory changes on the experimental side including granulation tissue, osteoneogenesis, tympanosclerosis, and cholesteatoma; the control side demonstrated minimal middle ear changes. We conclude that in this model autologous keratinized tissue provokes a foreign body response similar to the granulation tissue observed in human infants and, further, that over a prolonged period the middle ear demonstrates more severe pathologic consequences.

Meconium contamination of the neonatal middle ear.

The neonatal middle ear and mastoid cavity are frequently contaminated by cells and hair of the amniotic fluid. This amniotic fluid cellular content provokes a foreign body inflammatory reaction that can persist for months. To evaluate whether clinical and postmortem findings might correlate with the amount of amniotic fluid cellular content in the middle ear, we compared temporal bones of nine patients born through meconium-contaminated amniotic fluid with those of 10 patients born through clear amniotic fluid. All patients were examined at less than 17 days postpartum and provided 37 temporal bones for histologic analysis. The volume of contaminant was quantified for each patient. The cases were arranged according to volume of contaminant in the middle ear and compared with clinical information and autopsy findings. Patients with larger volumes of contaminant in the middle ear were born through thick, meconium-stained amniotic fluid (1.9-38 mm3; average 9.3 mm3). Conversely, patients with lesser volumes of contaminant in the middle ear were born through unstained amniotic fluid (none to 3.2 mm3; average 0.9 mm3). We speculate that patients born through thick, meconium-stained amniotic fluid may be at greater risk of sequelae such as otitis media from this foreign body inflammatory reaction in the middle ear and mastoid cavity.

Hair-cell innervation by spiral ganglion cells in adult cats.

A horseradish peroxidase technique was used to trace the peripheral terminations of two types of ganglion cells in adult cats. It was found that large, usually bipolar ganglion cells end on inner hair cells and small, usually pseudomonopolar ganglion cells end on outer hair cells. Thus, a virtually complete segregation of afferent neural inputs from the two types of hair cells was directly confirmed.