Cranial Nerves: Mind Your Head

Tractography analysis results of the trigeminus nerve, which contains fibers responsible for proprioception sensation and motor control in Adolescent Idiopathic Scoliosis

STUDY DESIGN

Cross-sectional Study.

BACKGROUND

It is not yet clear whether the loss of proprioceptive sensation and muscle weakness seen in adolescent idiopathic scoliosis (AIS) is the result of central nervous system dysfunction or secondary to spinal deformity. In our study, in order to find an answer to this question, we examined the microarchitecture of the nervus trigeminus, which is least affected by spinal deformity and contains both proprioceptive sensory and motor fibers.

METHODS

In this single-center, cross-sectional cohort study, 40 Lenke Type 3 (27 female, 13 male) AIS patients and 40 (25 female, 15 male) healthy individuals between the ages of 10-18 years. Tractography of the nervus trigenimus was performed using the "DSI Studio" program. The volumes of the targeted musculus pterygoideus lateralis and musculus pterygoideus medialis were measured using the Insight Segmentation and Registration Tool Kit (ITK -SNAP) program. The data were evaluated using the Statistical Package for the Social Sciences 22.0 program for Windows.

RESULTS

There was no significant difference between the two groups in terms of baseline characteristics (p˃0.05). Left nervus trigeminus fiber number and fiber ratio were significantly higher in the control group compared to the scoliosis group p < 0.05. Right and left lateral pterygoid muscle showed lower volume and volume percentage in the scoliosis group compared to the control group (p < 0.05).

CONCLUSION

According to the study data, proprioceptive sensory and motor control dysfunction in AIS is predicted to develop independently of spinal deformity.

The inferior alveolar nerve and its relationship to the mandibular canal

Previous work on the mandibular canal, mental foramen, and mandibular foramen has focused on humans and some other non-primate mammals (with small sample sizes), but little work has investigated the mandibular canal and inferior alveolar nerve (IAN) across primates. However, it is important to understand the relationship between the IAN and mandibular canal due to the IAN's close relationship to the teeth and mastication, and thus dietary adaptations. While it is assumed that most bony canals within the skull grow around and form to pre-existing nervous structures, this relationship has never been validated for the IAN and mandibular canal. MicroCT scans of 273 individuals (131 females, 134 males, and 8 unknown sex) from 68 primate species and three mammalian outgroups, and diceCT scans of 66 individuals (35 females, 23 males, and 8 unknown sex) from 33 primate species and the same mammalian outgroups were used to create 3D models of the IAN and mandibular canal from which cross-sectional areas were taken at various points on the structures. Using qualitative descriptions, phylogenetic generalized least squares analysis, and phylogenetic ANOVAs, we were able to establish three main conclusions: (1) the mandibular canal is most often not a defined canal within the mandible of primates, (2) when the canal can be identified, the IAN does not comprise most of the space within, and (3) there are significant relationships between the IAN and the corresponding canals, with most showing isometry and the mental foramen/nerve showing negative allometry.