Close apposition and exposure of non-myelinated axons in traumatic neuromas of the human lingual nerve

High-contrast high-resolution imaging of posttraumatic mandibular nerve by 3DAC-PROPELLER magnetic resonance imaging: correlation with the severity of sensory disturbance

OBJECTIVE

Magnetic resonance neurography reveals abnormal morphologies of regenerated nerves and overgrown connective tissue in injured trigeminal nerves, suggesting neuroma formation. We hypothesized that such deformities and scar formation contribute to pain symptoms.

STUDY DESIGN

High-contrast high-resolution magnetic resonance imaging was utilized to evaluate the inferior alveolar nerve and lingual nerve following traumatic injury in 19 patients. The relationship between the morphologic classification and severity of the sensory disorder was assessed.

RESULTS

In all cases, 3-dimensional anisotropy contrast periodically rotated overlapping parallel lines with enhanced reconstruction (3DAC-PROPELLER) successfully revealed the inner structures within the lesion. The isolated type represented the normal course of the nerve isolated from scar-like tissue (8 cases), whereas the deformity type included the deformed nerve either within scar-like tissue or by itself, unassociated with surrounding scar-like tissue (9 cases). In the remaining 2 cases, the nerve tissue and scar-like tissue were incorporated. Patients with the deformity type exhibited significantly more severe pain symptoms compared with patients with the isolated type.

CONCLUSIONS

Overgrown connective tissue does not necessarily block regenerating nerves and itself may not cause pain. The morphologic findings on the 3DAC-PROPELLER were relevant to the severity of pain symptoms.

Nav1.7 sodium channel expression in human lingual nerve neuromas

OBJECTIVE

Peripheral branches of the trigeminal nerve are often damaged during the removal of lower third molar teeth, and a small proportion of patients who sustain an injury develop persistent chronic pain. The cause of the pain is not clear and there are no satisfactory methods of treatment. The aim of the present study was to examine the expression of the sodium channel subtype Na(v)1.7 in damaged human lingual nerves, and to identify any association between Na(v)1.7 expression and reported symptoms of dysaesthesia.

METHODS

Eleven neuromas-in-continuity (NICs) and 11 nerve-end neuromas (NENs) were studied, and were all obtained at the time of surgical repair of the damaged lingual nerve. Specimens were categorised as being obtained from patients with symptoms or without symptoms, according to the degree of pain, tingling or discomfort that had been experienced. The tissue was prepared and processed for indirect immunofluorescence, and image analysis was used to quantify the percentage area of PGP 9.5-labelled tissue that also contained Na(v)1.7.

RESULTS

The results demonstrated that sodium channel Na(v)1.7 was expressed in human lingual nerve neuromas. There was no direct relationship between the level of expression of Na(v)1.7 and the patients' symptoms of dysaesthesia. However, in NICs there was found to be an inverse correlation between Na(v)1.7 and macrophage expression, and in symptomatic NICs a direct correlation was found between Na(v)1.7 expression and axonal apposition.

CONCLUSIONS

These data suggest that Na(v)1.7 expression alone does not play a primary role in initiating the painful symptoms of dysaesthesia. The development of neuropathic pain may involve complex interactions including changes in ultrastructure and ion channel density.

Inflammatory cell accumulation in traumatic neuromas of the human lingual nerve

OBJECTIVE

To quantify the accumulation of inflammatory cells in traumatic neuromas of the human lingual nerve, and to establish any correlation with the patients' reported symptoms of dysaesthesia.

DESIGN

Using fluorescence immunohistochemistry, the extent of any chronic inflammatory infiltrate was quantified in human lingual neuroma specimens removed from 24 patients at the time of microsurgical nerve repair. A pan-leucocyte marker (CD45) and a specific macrophage marker (CD68) were used, and comparisons made between neuromas-in-continuity (NICs) and nerve-end neuromas (NENs) in patients with or without symptoms of dysaesthesia.

RESULTS

CD68 and CD45 labelling was significantly associated with areas of viable nerve tissue in neuromas and the CD68 labelling was significantly higher in NICs than NENs. CD68 labelling density tended to decrease with increasing time after the initial nerve injury, but this correlation was only significant for labelling associated with viable nerve tissue in NENs. No significant difference was found between the level of CD68 or CD45 labelling in patients with or without symptoms of dysaesthesia.

CONCLUSION

This study has demonstrated the presence of inflammatory cells within traumatic neuromas of the human lingual nerve. These cells were found to be closely associated with regions of viable nerve tissue, but there was no correlation with the patients' clinical symptoms.