Background: The microanatomy of the central myelin portion and transitional
zone of several cranial nerves including trigeminal, facial, vestibulocochlear,
glossopharyngeal, and vagus nerves have been clearly demonstrated to provide
information for neurovascular compression syndrome such as trigeminal neuralgia
and hemifacial spasm. However, the study of oculomotor and abducens nerve
is limited.
Materials and methods: Oculomotor and abducens nerves were harvested with
a portion of brainstem and embedded in paraffin. Longitudinal and serial sections
from ten of each cranial nerve were stained and a photomicrograph was taken
to make the following observations and measurements: 1) patterns of central
myelin portion, 2) length of central myelin portion, and 3) depth of central myelin-
peripheral myelin transitional zone.
Results: For oculomotor nerve, the longest central myelin bundle was always
seen on the first nerve bundle and that the length of central myelin decreased
gradually. For abducens nerve, morphological patterns were classified into four
types based on number of nerve rootlets emerging from the brainstem and number
of nerve bundles in each rootlet. Length of central myelin portion was between
0.36–6.10 mm (2.75 ± 0.83 mm) and 0.13–5.01 mm (1.66 ± 1.39 mm) for
oculomotor and abducens nerves, respectively. The oculomotor nerve transitional
zone depth was 0.07–058 mm (0.23 ± 0.07 mm), while for abducens nerve,
depth was 0.05–0.40 mm (0.16 ± 0.07 mm). Positive weak correlations between
central myelin and depth of TZ were found in oculomotor nerve (r +0.310,
p < 0.05) and abducens nerves (r +0.413, p < 0.05).
Conclusions: Detailed microanatomy of the central myelin and transitional zone
might be beneficial for locating the site of compression in neurovascular conflicts
at oculomotor and abducens nerves.