HIGH-RESOLUTION MR IMAGING OF THE AUDITORY PATHWAY

Early myelination patterns in the central auditory pathway of the higher brain: MRI evaluation study

OBJECTIVE

The purpose of this study was to use magnetic resonance imaging (MRI) to investigate the early myelination patterns of the central auditory pathway and then compare the data with past histological research. We observe the MRI signal intensity of the central auditory pathway and clarify the time course difference between MRI and previous histological research studies.

METHODS

A total of 192 infants ranging in age from -4 to 224 corrected postnatal weeks were included in the study. Images were obtained using a 1.5 T MR unit. We chose three sites (medial geniculate body, auditory radiation, and splenium of the corpus callosum) of the central auditory pathway for analysis. Three cross sections were obtained perpendicular to the long axis of the brain and used to analyze the signal changes of the T1- and T2-weighted MRI by employing a region-of-interest (ROI) methodology that was corrected for postnatal age.

RESULTS

At 10 corrected postnatal weeks, the medial geniculate body showed myelinated intensity changes on T2-weighted images. Auditory radiation showed myelinated intensity changes at 19 corrected postnatal weeks on the T1-weighted images and at 24 corrected postnatal weeks on the T2-weighted images. The splenium of the corpus callosum showed myelinated intensity changes at 16 corrected postnatal weeks on T1-weighted images and at 24 corrected postnatal weeks on T2-weighted images.

CONCLUSIONS

As compared to the histological literature, the MRI documented signal intensity changes caused by myelination occurred approximately 3 weeks later for the medial geniculate body, 7-24 weeks later for the auditory radiation and 7-15 weeks later for the splenium of the corpus callosum. Since myelination is a process that occurs gradually, substantial changes of the myelin sheath makeup, a loss of water and the addition of lipids are more required in order to be detectable by MRI than myelin staining of histological study.

Early myelination patterns in the brainstem auditory nuclei and pathway: MRI evaluation study

OBJECTIVE

The purpose of this study is to investigate the early myelination patterns of brainstem auditory nuclei and pathway on magnetic resonance imaging compared with past histological research. We aimed to identify the time course difference in myelination of the brainstem auditory nuclei and pathway between magnetic resonance imaging and histological research results.

METHODS

Subjects were 192 infants ranging in age from -4 to 224 corrected postnatal weeks. Images were obtained using a 1.5 T magnetic resonance unit. In four sites (cochlear nucleus, superior olivary nucleus, lateral lemniscus, inferior colliculus) of the brainstem auditory nuclei and pathway on four cross-sections obtained perpendicular to the long axis of the brainstem, signal changes of T1- and T2-weighted magnetic resonance images were analyzed using a region-of-interest methodology according to corrected postnatal age.

RESULTS

The cochlear nucleus and superior olivary nucleus showed myelinated intensity change from -3 to 13 corrected postnatal weeks on T2-weighted images. The lateral lemniscus showed myelinated intensity change from -3 to 8 corrected postnatal weeks on T1-weighted images and from -1 to 13 corrected postnatal weeks on T2-weighted images. The inferior colliculus showed myelinated intensity change from -2 to 39 corrected postnatal weeks on T2-weighted images.

CONCLUSIONS

Magnetic resonance imaging revealed the signal intensity change by myelination 11-18 weeks later than those reported in the histological literature. This time lag suggests that apart from histological research, the necessity for the milestones of auditory pathway maturation using MRI is suggested to evaluate the development of brainstem auditory pathway using MRI. This result suggests that myelination does not take place suddenly but happens gradually, so definite myelination, namely the complete change of myelin sheath ingredients, loss of water, and gain of lipids, is needed to be detected by magnetic resonance imaging.

Intrafamilial variability of the deafness and goiter phenotype in Pendred syndrome caused by a T416P mutation in the SLC26A4 gene

Pendred syndrome (PS) is the most common cause of syndromic deafness, accounting for more than 5% of all autosomal-recessive hearing loss cases. It is characterized by bilateral sensorineural hearing loss and by goiter with or without hypothyroidism. Mutations in the SLC26A4 gene cause both classical PS and deafness associated with an enlarged vestibular aqueduct without goiter. To investigate a possible genotype-phenotype correlation in PS, we performed a detailed clinical and genetic study in three adult German sibs with typical PS caused by a common homozygous SLC26A4 mutation, T416P. An audiological long-term follow-up of 23 yr showed that the mutation T416P is associated with a distinct type of hearing loss in each of the three sibs: moderate-to-profound progressive deafness, profound nonprogressive deafness, and a milder but more rapidly progressing form. We show that these phenotypic differences are not caused by either different degrees of inner ear malformations or sequence variations in the GJB2/connexin 26 gene. Because the thyroid phenotype was also highly variable within the family, with thyroid sizes ranging from normal to large goiters requiring thyroidectomy, this study leads to the conclusion that other environmental and/or genetic factors have an impact on the PS phenotype.

Hybrid phased array for improved internal auditory canal imaging at 3.0-T MR

PURPOSE

To develop and evaluate a hybrid phased array for internal auditory canal (IAC) imaging at 3.0 T.

MATERIALS AND METHODS

A hybrid phased array was designed and built as two circular surface receive-only coils combined with a volume transmit-receive birdcage head coil for simultaneous image acquisition. Phantom and volunteer images were obtained to assess the coil performance.

RESULTS

The phantom data show that significant signal-to-noise ratio (SNR) improvement was achieved in the region corresponding to the inner ear, i.e., by a factor of 2.5 compared to the standard head coil data. Volunteer IAC image quality was deemed superior as compared to images acquired at 3.0 T using a standard head coil.

CONCLUSION

This hybrid array combined with three-dimensional fast spin-echo (FSE) acquisition resulted in improved high spatial resolution IAC imaging.