Residual mesenchyme in temporal bones of children

Thyroid hormone receptors control developmental maturation of the middle ear and the size of the ossicular bones

Thyroid hormone is critical for auditory development and has well-known actions in the inner ear. However, less is known of thyroid hormone functions in the middle ear, which contains the ossicles (malleus, incus, stapes) that relay mechanical sound vibrations from the outer ear to the inner ear. During the later stages of middle ear development, prior to the onset of hearing, middle ear cavitation occurs, involving clearance of mesenchyme from the middle ear cavity while the immature cartilaginous ossicles attain appropriate size and ossify. Using in situ hybridization, we detected expression of Thra and Thrb genes encoding thyroid hormone receptors α1 and β (TRα1 and TRβ, respectively) in the immature ossicles, surrounding mesenchyme and tympanic membrane in the mouse. Thra(+/PV) mice that express a dominant-negative TRα1 protein exhibited deafness with elevated auditory thresholds and a range of middle ear abnormalities including chronic persistence of mesenchyme in the middle ear into adulthood, markedly enlarged ossicles, and delayed ossification of the ossicles. Congenitally hypothyroid Tshr(-/-) mice and TR-deficient Thra1(-/-);Thrb(-/-) mice displayed similar abnormalities. These findings demonstrate that middle ear maturation is TR dependent and suggest that the middle ear is a sensitive target for thyroid hormone in development.

A Case of Pneumocephalus and Meningitis as a Complication of Silent Otitis Media

Silent otitis media is a progressive otogenic disease. Intracranial manifestations of this complication are limited; the most common is meningitis. We report a case of meningitis and pneumocephalus as a complication of silent otitis media. To the best of our knowledge, this is the first reported case of pneumocephalus as a complication of silent otitis media.

Histopathologic study of the temporal bones and Eustachian tubes of children with cholesterol granuloma

Six temporal bone-eustachian tube (ET) specimens with cholesterol granuloma (CG), obtained from 6 children 6 months to 15 years of age, were studied histopathologically to obtain further information about the pathogenesis of CG. We observed CG in the mastoid air cells in 5 ears, the mastoid antrum in 1 ear, the aditus ad antrum in 2 ears, and the epitympanum in 1 ear. All 6 cases exhibited a large amount of remaining mesenchyme that was in continuity with the hematopoietic bone marrow in the locations in which CG was present. All cases demonstrated otitis media with effusion and inflammation of the ET. Apparent morphological abnormalities of the ET and its associated structures, including hypoplastic ET cartilage and an abnormal tensor veli palatini muscle, were noted in 3 of the 6 cases. Furthermore, the posterior cartilaginous portion of the ET that includes its narrowest portion was completely filled with effusion in 2 of the 3 cases with the ET anomaly. The findings obtained were compared with data from age-matched control cases. Our results suggest that the source of erythrocytes in the remaining mesenchyme is the hematopoietic bone marrow. The pathogenesis of CG in children is likely promoted by ET dysfunction resulting in failure of ventilation of the middle ear.

Chronic silent otitis media

Otitis media occurs along a continuum. For example, otitis media with effusion characterized by fluid pathology can lead to chronic otitis media plus chronic mastoiditis, characterized by the presence of intractable tissue pathology such as cholesteatoma, cholesterol granuloma or granulation tissue. The literature defines chronic otitis media as having a tympanic membrane perforation and otorrhea. Amongst many other sequelae, which can result from the continuum, an important common one is chronic silent otitis media. This overlooked entity which includes pathology beneath an intact tympanic membrane is commonly seen in our human temporal bone laboratory and in patients. The clinical pathological correlates of this important disease are discussed herein.

Temporal bone histopathological study of Noonan syndrome

Four temporal bone specimens, obtained from three individuals 1--6 years of age with Noonan syndrome (NS), were studied histopathologically. All four specimens were accompanied by similar inner ear abnormalities including the reduced number of spiral ganglion cells, enlarged lateral semicircular canal, and dislocated endolymphatic sac and vestibular aqueduct. The mean population of spiral ganglion cells (15,699 cells) was approximately half of those (32,978 cells) in four age-matched control cases. In addition, they had several middle ear abnormalities including the remaining mesenchyme and dehiscence of the facial canal. To our knowledge, this is the first report to describe the histopathological temporal bone findings in patients with NS. We discuss the implications of the observed abnormalities with regard to clinical issues.

Residual mesenchyme in the middle ear cavity of the newborn with malformation of the kidney

Microscopic sections of 37 temporal bones from 22 foetuses were examined, five with renal agenesis, six with Potter's sequence without renal agenesis and two with mild kidney pathology. Every tenth section containing the stapes were used for measuring the volume of mesenchymal tissue in the middle ear cavity. At 5% significance level, foetuses with serious renal pathology had more mesenchymal tissue in the middle ear cavity than a control group of nine foetuses with no renal or urinary tract abnormality.

Development of the middle ear in neonatal chinchillas. I. Birth to 14 days

Measures of middle-ear function in humans show large differences among neonates, infants, and adults. In contrast, hearing sensitivity is essentially mature at birth. Hypotheses that have been proposed to explain the developmental changes in middle-ear function include: (i) contaminating effects of the immature neonatal ear-canal wall and (ii) persistent fetal tissue in the ear canal, tympanic membrane (TM), and middle-ear space. To better understand the relationships between middle-ear function, hearing sensitivity and the structure of the middle ear, 30 chinchillas, aged 1-14 days, were studied. Middle-ear function was assessed by multifrequency tympanometry with probe tones ranging from 226 to 2,000 Hz. Hearing sensitivity was measured by auditory brainstem response using clicks and 1, 2, 4, and 8 kHz tone bursts. Structural characteristics were analyzed from temporal bone histologic preparations. At all frequencies, the acoustic admittance of the neonatal car is very low and tympanometric patterns are complex and irregular, compared to adult animals. The admittance is essentially constant from 1 to 14 days, indicating that developmental changes occur over a much wider age span than that investigated here. Hearing sensitivity of the chinchilla appears to be mature at birth. Histologic analysis indicated that there were no age-related changes in TM thickness, TM diameter, distance from TM to promontory, and stapes footplate diameter. There were small increases in bone thickness, middle-ear area, mastoid bulla area, and in the perimeters of the middle ear and mastoid bulla. There were no significant amounts of loose mesenchyme or other fetal tissue in the middle-ear space.

Residual mesenchyme persisting into adulthood

PURPOSE

(1) To detect the presence of residual mesenchyme in temporal bones of adults and children above 5 years of age; (2) to evaluate its regression 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 from 5 to 94 years of age for histopathologic evidence of mesenchyme. The presence of stellate (star-shaped) cells with interdigitating processes and large nuclei embedded in a structureless ground substance was labeled as "pure mesenchyme." Temporal bones showing these features and focal areas of fibrosis, fibroblasts, and capillaries were classified as showing "transitional mesenchyme." Selected sections were stained with Gomori's trichrome. Pathological features indicating otitis media and congenital anomalies of the ear were also documented. Case histories were reviewed, and any otologic complaints were noted. Statistical analysis was performed with the Chi-square test, 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 present in the round window niche. Otitis media was associated with residual mesenchyme in 84.2% of the temporal bones. No pattern of regression of mesenchyme 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 years of age and can persist into adulthood, especially in the mastoid air cells. Persistence of mesenchyme is closely associated with evidence of otitis media.

Tympanoplasty: prudent considerations of silent otitis media and interactions of middle ear and inner ear

Otitis media is a common problem, often with simple, minimally invasive solutions; however, a small subset of patients progress to chronic disease despite provision of standard therapies. The flexible approach to tympanoplasty is a prudent consideration for patients with chronic otitis media, especially children. This article discusses the findings and implications of silent otitis media, interactions of the middle ear and inner ear, and obstructive sites in the middle ear cleft. Tympanoplasty by the flexible approach is described in the context of these findings.

Human temporal bone study on the postnatal ossification process of auditory ossicles

OBJECTIVE

In infancy the head of the malleus and body of the incus normally contain bone marrow, which is gradually replaced by bone and converted into vascular channels with age. This study was carried out to clarify the age at which ossification of the ossicles is complete and to examine factors influencing the ossification process.

STUDY DESIGN

Human temporal bone sections from 32 infants and children with or without congenital anomalies, aged 1 day to 9 years, who were born at term were studied.

METHODS

The percentage bone marrow area occupying the head of the malleus and body of the incus was calculated in three horizontal temporal bone sections for each case, using computer-aided digital processing of images.

RESULTS

Bone marrow was observed in both the malleus and incus in children until 25 months of age, while after the age of 25 months no bone marrow tissue was present in either of the ossicles. It appeared that the bone marrow space disappeared somewhat earlier in the malleus than in the incus. The bone marrow space around the otic capsule disappeared much earlier than that within the ossicles. The age at completion of ossification was correlated with neither the presence of congenital anomalies nor the presence of residual mesenchyme in the middle ear.

CONCLUSIONS

Ossification of the ossicles seems to occur steadily throughout fetal life and after birth during development of the middle ear. Although the clinical significance of postnatal residual bone marrow within the ossicles is not known, it possibly plays a role as a blood-forming organ in early infancy.